CA2546612A1 - Ultraviolet, infrared, and near-infrared lidar system and method - Google Patents

Abstract

Pushbroom and flash lidar operations outside the visible spectrum, most preferably in near-IR but also in IR and UV, are enabled by inserting - ahead of a generally conventional lidar receiver front end - a device that receives light scattered from objects and in response forms corresponding light of a different wavelength from the scattered light. Detailed implementations using arrays of discrete COTS components - most preferably PIN diodes and VCSELs, with intervening semicustom amplifiers - are discussed, as is use of a known monolithic converter. Differential and ratioing multispectral measurements, particularly including UV data, are enabled through either spatial-sharing (e.g. plural-slit) or time-sharing.

Description

Ultraviolet, infrared, and near-infrared lidar system and method Wholly incorporated by reference herein is the present in-ventors' coowned U. S, provisional patent application 60/440,303, whose priority benefit is hereby asserted.
1~E?~ATED D~CUMENTS
Closely related documents are other, coowned U. S. utility-pat-ent documents - also incorporated by reference in their entirety.
Those docume~ats are: H~~~2:er et ~,1., patents 6,~00,39~ (a~.~dical z5 scale) aa~d a,~6'~,1~~ (ocean scale) r and serial 09/1~~,~~9 (aide raa~~e of scales) ~ ~cLean et ~.1. , serial 09/390,~E (sh~.llo~~ angle) ~lec~sler et al. , serial ~.0/~5~i, 91'7 (plural slit) ~ and Crriffis ~t al., serial 7.0/426,907 (without strew tube). ~ther patents and publications of interest are introduced belong.
FIELD OF THE INVENTION:
This invention relates generally to systems and methods for automatically detecting light reflected or scattered from an object, and determining distance to the object. Also found, in preferred applications of the invention, are other properties of the detected object - such as for e~~ample reflectance, velocitla, and three-dia~~a~,v~.onal rel~.ta.~nships ~.oaag ~alural det~et~g' o~aj~ets .
~~C~~'C~~U1~3D
a.) Threr~-~.ia~ensional im~.ging Some systems and methods for accomplishing these goals are con-ventional in the field of so-called "lidar", or "la.c~ht detection and ranging" - analogous to the better-known "radar" that uses the ra-clio portions of the electromagnetic spectrum. Because most lidar systems use pulsed lasers as excitation, the acronym "lidar" is sometimes said to instead represent "laser illumination detection and ranging".
In a lidar system, a sharp pulse of light is projected toward an object, or field of objects, that is of interest. The object or objects reflect - for turbid media a more descriptive term is "scatter" - a portion of this excitation radiation back toward the 2o system, where the return radiation is time resolved.
As in radar, round-trip propagation times for the radiation form a measure of the distances, or ranges, from the apparatus to the respective objects. radar, ho~~~v~r, simply due to the much lon-eer ~~av~l~ne~ths it employs, cannot pro-~id~ the resolaation avs.ilable ~ceith li~~~ .
Nigh-resolution lidar ims.eine provides fully three-dimensioaas.l images of far higher resolution, on one hand, s.nd ths.t also have distinct advantages in comparison to common two-dimensional imagine (e. c~. photographs) on the other hand,. As compared with such ordi-2o nary two-dimensional images, some of the advantages provided by the addita.onal range information are the ability to remove clutter, to accurately discriminate decoys from objects of real interest, and to provide adda.tional criteria for detection and classification.
Fligh-resolution three-dimensional imaging may provide volumet-ric pixel sizes of approximately 0.75 mrad by 0.75 mrad by 7.5 cm.
Such imaging ree,~uires high bandwidth (~ GHz) lidar receivers with small instants.neous fields of vi~~~ (IF~V) and many pixels in the te~o-dia~.a~asional ia~~.e~ine~ directions .
~e~y to th~s~ oapabilitias is ~ff~otiv~ and v~r~r f~.~a~ time-res-~o olutio~. of the r~tur~a o~atioal sie~aals - ordinarily b~~ a str~~.~~.
tubs, altho~.gh modernly ~~~r~r fast ~l~otr~nics can be su~astit~at~d in relatively less-d~r~~a~.in.g a~aa~alios.tiosas. Such a~apl~.o~.tions ;~aaatiou-larly inolue~.~ a~.~asur~~nts at the scale of ocean volumes , in ~,~hioh t~~aoral resolution xa~ay be in meters rather than o~ntia~.~t~rs .
s5 Finer ~~orZg, especis.lly including lsboratory-scs.le measurement or ultimately medical ranging with resolution finer than a millime-ter, appears to exceed current-day speed and resolution capabilities of electronics and accordingly calls for a streak tube. To use such a device for three-dimensional imaging, the laser pulses must be visible or shorter-wavelena~th light - so that the optical return pulse 21 (Fig. 1) from the object or objects a.s likewise visible or ultraviolet light 22. (While visible lidar excitation is hazardous because it damages the retina, shorter-wavelength excitation too is hazardous due to damage to the lens of the eye.) In either event, the optical return is made to take the form of a substantially one-dimensional image (i. e. slit-shaped, extending in and out of the so plane of Fig. 1), or is reformatted 23 as such an image.
In response to that unidimensional optical input 22, in the form of visible or 'CJy light, a photocathode screen 24 of the streak tube 1~ forms a one-dimensional electronic image 25, c~ra.ich is re-fined by electron-imaging components 26 sc,~ithi~a the stre~.~~ tube. (It ~~ill be une~erstood that sore very special strea~~.-tube photocs.thodes have bee~a developed, to handle E~~.velenerths other than visible ~ ho~~-ever, these s.re not at a.11 commercial materials, and the use of some such photocathode technologies introduces synchronization problems and other drawbacks.) 2o Depending on any image reformatting that may be performed upstream of the streak tube 18, position along these unidimensional optical and electronic images 22, 25 may either represent location along a simple thin image slice of the object field, or represent position in a very complex composite, positionally encoded version of a two-dimensional scene. This will be explained shortly.
~1'ithin the streak tube, a very rapidly varying electrical de-flection voltage 2~, applied across deflection electrodes 27, s~~eeps 2~ the one-dir~.exasions.l electronic image 25 e~uuie~~ly do~~n a ~akaos~alaor-coat~d. su.rfac~ ~1, forma.~a.s~ a, te~o-dia~.~aa~sion~.l ~i~;i~al~ ia~a~c~e ova tae 3Q ~ahos~ahor scb~ega. The sc~eep dir~ctioaa 2~ t~aen ~.epbesents tia~.e - and ~.ccordi~.gly d.istaxa.cea to each ~aa.c~~scatterine~ ~bject - c~r~aile tYae car-t~a.~agona.l c~.rectio~a on t~~e scree~a (again, e~~tendinc~ in a.nd out of the plane of Fag. 1) . re~abesents Sao. ition alone the inaaut o~atgc~,l a.a~ag~e, ~~hether s, simple ia~.~.ge .lice or axa encoded. scene.
The patents mentioned above introduce considerable detail as to behavior and use of a streak tube. They also may represent the highest development of a form of lidar imaging familiarly xnown as "pushbroom" - because data are accumulated a little at a time, in thin strips transverse to a direction of motion.
Relative motion between the apparatus and the object field is provided, as for instance by operating the apparatus in an aircraft that makes regular advance over a volume of seawater, while laser-beam pulses are projected toward the water. The pulsed laser beam is formed into the shape of a thin fan - the thin dimension of the fan-shaped beam being oriented along the "track" (elirection) of this zo relative motion.
In some laboratory-scale systems it is more convenient to instead scan an object or object field past a stationary lidar transceiver. Hence in either instance the broadly diverging ~~ide diae~ex~sion of the fan beam, often called the "cross-trace" dimension, z5 is at right angles to the ~lgreetion of motion: this is the above-mentioneC. case of direct ph~rsical corre«pon~.ence beteaee~a the unidi-mensiona.l optical or electronic image and a. real slice of an object image. The ~leekler patent mentioned above, h.o~aever, shoes that t~~o or more such one-dimensional images can be processed simultaneously 20 - yielding a corresponding number of time-resolved pulse returns.
Each laser pulse thus generates at the receiver, after time-resolution of the return pulse, at least one two-dimensional snap-shot data set representing range (time) vs. azimuth (cross-track detail) for the instantaneous relative position of the system and 2~ object field. Successive pulses, projected and captured during the continuing relative motion, provide many further data frames to com-plete a third dimension of the volumetric image.
The resulting three-~lia~.ensional ix~age c~.n be visus.li~ec~ sim~aly day da.reetly observing t~Ze strea~~-tube p~aoslaYaor sc~:e~n, or by c~.~atur 3o iaag the scre~~a ~.spla~ ~~it~a a C~~ oz other camera at the frame rate (~ne frame ~aer i~aiti~~t~.~ag laser pulse) f~r later viec~ixa.c~. ~n~t~aea:
o~atio~a is to analyse the c~.pture~. data, ~ in ~. c~mputer, by any of x~yriad a~a~alication-s.~apro~ariate alc~orith~as .
35 ~.lternative to pushbroom imaging is so-called "flash'° lidar, represented by patents Re. 33,~6a and 5,412,3?2 of Knight and ~lfano respectively. Here the excitation pulse is ideally formed into a substantially rectangular beam to illuminate the entire object or object field at once.
The resulting backscatter pulse, correspondingly, is all time resolved concurrently - typically requiring, at least for a streak-s tube, temporary mapping of the two-dimensional return into a one-di-mensional (i. e. line) image that the tube can sweep. Such mapping, in the cited patents, is performed by a custom fiber-optic prism., This sort of mapping may be done in a very great variety of ways. For example successive raster-equivalent optical-image slices ~o can be placed end-to-end along the input photocathode, or individual pixels can be subjected to a completely arbitrary reassignment to positions along the cathode. P,ny me.pping intermediate between these extremes is also possible.
t'~fter time-resolution if ~,esired the data can be remapped to 15 recover a multiplicity of original two-dimensional image-data frames - each now having its family of ranged variants. If preferred the full three-dimensional data set can be unfolded in some other way for analysis as desired.
b) The wavelength limitation .
Streak-tube imaging lidar is thus a proven technology, demon-strated in both pushbroom and flash configurations.l~z Unfortunate-1y, however, it is heretofore usable only in the visible-ultraviolet portion of the electromagnetic spectrum, whereas several important applications favor operation in longer-wavelength spectral regions.
critical group ~f applications relates to so-called, °°e~e safe°° ~:equirea~eaats fo:~ a~an~ operating envi,rona~esats. The ra.ua~an eke 3o is e~t:~ea~el~P sensati~e t~ risible rac.is.tion. Severe retinal daas~s.ge can occur if soa~.eone is e~~p~se~, t~ radis,tion transmitted by a con-ventional streak-tube lidar system.
In the near-infrared (3~IR), by comparison, there is far less human sensitivity and likewise less risk. maximum permissible expo-5 sure for NIR radiation at a wavelength of 1.54 ~,m is typically three orders of magnitude greater than at 532 nn. The main reason is that the lens of the eye does not focus NIR radiation onto the retina.

Consequently, in applications where humans might be exposed to the transmitted light, it is desirable to operate the lidar at the longer wavelength. In addition, radiation at 1.54 dun is invisible to the human eye, yielding the advantage of inconspicuous operation s - which is desirable in many applications.
Limitation to the visible/W is in a sense somewhat artificial, arising as it does merely from lack of a commercial streak tube with a photocathode sensitive to nonvisible raeliation - even though NIR-sensitive photocathode materials exist.3 The vendor neither pro-1o duces streak tubes nor will provide the photocathode materials to streak-tube vendors. No streak-tube vendor is currently offering high-quantum-efficiency NIR streak tubes.
The near-infrared, ho~~ever ~ is far from the oa~ly spectral r~-15 e~~.on in ~;~hic~a. lid~.r operation would tae vet ac~1-~antac~~o~a.s . The a~aore-re~.ot~ infrareC~. portion of the ~lectrom~.ga~etic spectrum (3 to 1~ pda~.) overl~.ps strong absorption fes.turess of ms,ny molecules . As a result ~~avelengths in this region are particularly attractive for monitor-ing gaseous contaminant concentrations such as those encountered in 2o atmospheric pollution or industrial process control.
C~~ lasers operating at 9 to 11 Eun can produce high power and have been deployed in space for a number of applications. As will appear from a later section of this document, the present invenstion is well suited for use with C~~-laser-based imaging lidar systems.
25 Moreover, in other fields of optical measurement and analysis it is possible to make differential or ratio measurements - for example, differenti~.l ~bso~tion spectroscop~°, and other analogous ~alural- or r~ultispectr~.l iaw~stac~~.tions . F~eretofore this h~.s not ~a~en ~aractical in t~a~ lid~.r fi.elc~., e~~n go.r s~.~~.~ur~.~xats com~aaria~c~
30 ~.a~c~ c~~at:~asta~a~; m~~.~~ar~~ntw a~ ~a~tcf~~~a tkae ~ris~.bh a~ac~
ultra~~.ol~t.
c) ~ther technology not heretofore associated ~~ith lid~.r 35 United Mates Patent 5,3~~,01.6 of harry Coldren is representa-five of advanced sophistication in a field previously related only to optical communications, optical switching and the like. To the best of the knowledge of the present inventors, that field has never previously been connected with lidar operations or any other form of three-dimensional imaging.
Tabulated below is other related Work of Costello et a1.3 and s Francis et al.,' as Well as related commercial product literature.e~9 These materials too are essentially representative of modern advan-ces in optical switching and communications, unconnected with lidar.
so d) Conclusion As can now be seen, the related art fails to resolve the pre-viously described problems of lidar unavailability for operation outside the visible ~c~avelene~th region. The efforts outlined above, .t5 althoue~h ~araisee~ortYay, leave room for considerable refinement.
SL1~5~5~ ~F T~I~ 1~ISCL~S:
The present invention offers just such refinement. The inven-tion has major facets or aspects, some of which can be used inde-pendently - although, to optimize enjoyment of their advantages, certain of these aspects or facets are best practiced (and most-preferably practiced) in conjunction together.
In preferred. embodiments of its first major independent facet or aspect, the invention is apparatus for detecting objects a.nd de-terminine~ their distance, to form a t~~o-~lia~.ransional or three-da.men-sioxaal ire c~~ . The a.~aparatus ixxchades some mans f~r r~c~i~ring light 3Q : catt~.r~c~ fr~m the objects a~as~ in r~.~~a~~as~ f~i~ac~ a c~rr~sp~rading light of a d.gff~r~nt c~a~r~lexagth from. t~a~ scattered. light. Fcar ~aur~-p~s~s of ~areadt~a and generality ixi discussing the i~a.~reaation, t~.~s~
a~.ea,ns ~~ill be called sia~~aly the "~:~ceivixag-and-foraging re~eaga.s" .
In less-formal portions of this documnt, the receiving-and-forx~ing x~ea.ns ~~ill instead be called. a. "~9avelene~tla converter" (al-though the term "converter" may be semantically imprecise, as dis-cussed later in this document). ~Tereinafter this phrase will be abbreviated "7~.C", using the lower-case Greek letter ~, (lambda) that is the trada.tional symbol for wavelength.
The first aspect of the invention also includes some means for time-resolving the corresponding light to determine respective dis-s tances of the objects. Again for generality and breadth these means will be called the "resolving means".
The foregoing may represent a description or definition of the first aspect or facet of the invention in its broadest or most gen-1o eral form. Even as couched in these broad terms, however, it can be seen that this facet of the invention importantly advances the art.
In particular, inserting the receiving-and-forming means i.n ad-vanee of the time-resolving a~.eans can provide to the latter (e. ee. a streaks tube) - even if the scattered. light is not visible light -25 su~astantially the same visible optie~.l sigaaal that ~~o~ald be okataine~.
kay receivine~ visible scattered light ~.rectly from the objects. The receiving-and-forming means thereby enable the e~sternal portions of the overall system to operate in almost any wavelength rec~ion~ and can free the system from. wavelene~th limitations of the time-resolv-2o ing means. In this way the heretofore-intractable problems dis-cussed above are substantially eliminated.
Although the first major aspect of the invention thus signifi-cantly advances the art, nevertheless to optimize enjoyment of its 25 benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the apparatus is further for use in determining reflec-taa2.c~ of tla~ obj ect~; ~ and. the rec~ivinc~-and-formia~g r~~an. include sox~.~ a~.~a~as f~r ~~as~aring ~,ne~ rccor~sli~ag gr.a~,r-1~~~-el gnfor.tio~a i~a the 3o rec~i~rc-ad aa~e~ fo~,c~. lig~at.
~a.oth~r ~a~,sic pb~feb~aac~ is t~.~.t the b~c~i~riaag-and-f~ba~.ng x~ea~as inclu~.e a fibst, opt~intex~.~di~.te stage th~.t receives the scattered. light and in r~aponse fo~:ms a corresponding intermediate sie~n~.l. ~~ccordingly the receiving'-and-fo.i.nc~ me~.ns ~.lso include a 35 second, intermedioptical stage that receives the intermediate signal and in response forms the corresponding light.

By the coined phrase "optointermediate stage" is here meant a subsystem that receives optical signals (the lidar return beam, in particular) and generates a corresponding signal in some intermedi-ate domain -- which may be electronic (in the present day, possibly s the only practical such domain), or optical, or quantum-based, or a signal formed a.n yet some other medium. The phrase "intermediopti-cal stage" analogously describes a converse subsystem that receives and operates on that intermediate sigx~.al to generate the correspond-ing optical output.
so If this basic preference of employing two stages that communi-cate through a common intermediate signal is observed, then two al-ternative subpreferences arise: preferably the intermediate signal includes either an optical signal or a,n electronic signal. ~ther s~ubpreferences are that the time-resolving means include a strea,~~-Z.s camera c~.e-~icea aaad that the system furthar inclue~,e a lie~ht source, a.nc~ some means for projecting ~aulses of lie~ht from the source toc~a.rd the objects for sca~tt~ring back to~~a.rd the rcceivinc~-and-forming' means.
If the system complies ~~ith the latter subpreference (inclusion 20 of a source, with projecting means), then two alternative preferen-ces are that the streak-camera device be incorporated into a repeti-tively pulsed pushbroom system, or into a flash lidar system. In the pushbroom case it is still further preferred that the system al-so include an aircraft or other vehicle transporting the receiving-2~ and-forming means, and the streak lidar device as well, relative to the objects. (An alternative preference is the converse - i. e., that the apparat~zs be stationary and the scene made to move. In prinei~al~ the pushbroom mode simply involve: relative motion bete~een the tc~o. ) ~aother prefere~ac~ is that the streaw-eam.~ra e~wic~ i~a-3o clud~ a multislit strew,: tube.
~'~.l.~;o ice. t~.e es.s~ of the basic te~sz-stagy pr~feb~nc~, it is faar-th~r preferred t~a~?t the iaatermediate signal include an electronic signal, the first stage iaaclu~.e an optoelectronie stage, and the second sts.ge include an electrooptical stae~e. In this event it is 35 a1:~0 preferred that the optoelectronic stage include light-sensitive semiconductor devices - and these devices in turn include photodi-odes, e. a. PIN ("F-intrinsic°') diodes, or alternatively avalanche photodiodes.
If this a.s so, then yet another nested preference is that the electrooptical stage include vertical-cavity surface-emitting la-y sers, or light-emitting diodes, connected to receive the electronic signal from the PIN diodes. An alternative is that the electroopti-cal stage include edge-emitting lasers, or quantum-dot lasers, or microelectromechanical systems - any of these devices being connec-ted to receive the electronic signal from the PIN or other diodes.
zo Although. these output-stage preferences have been presented as nes-ted subpreferences to the use of PIN or avalanche diodes, they are also preferred even if the input stage uses some other kind of pho-tosensitive ~.evi.ce .
~notFaer basic preference is that the apparatus further inclu~.e 15 utila.~a.tion means re.~pon~sa.ve to the time-resolving anea.nw. "L~tili~~
tion ~.eans~' are any x~e~,ns that utiliGe the resulting out~a~at infor~r~.a tion frown the time:-resolving means .
Preferably the utili~atgon means a.re one or more of:
20 ~ interpretive means for characterising the objects based on the time-resolved light;
~ a monitor that displays an image of the objects for viewing lay a person at the apparatus;
a monitor at a base station for reviewing the objects or rela-ted ds.ta received from the resolving by means by telemetry;
a data-proeessg~ag de-ice for ~.nal~~a.ne~ the objects or images of 3o tb.~a~.;
o autoan~tgcall~n o~aera.tec~ igaterpreti~e ~.o~lule~s that d~termi~a~
~~laetla.er particular cond~.tions are met;
o announcement-broadcastine~ means or other automatic physical apparatus connected to operate in response to the time-resolv-ing means;

~ means for enabling or denying access to secure facilities through operation of doors and gates, or access to computer systems or to financial services including but not limited to credit or banking; and ~ means for determination of hostile conclitions, and resulting security measures including but not limited to automatically deployed area-sealing bulkheads.
to Another basic preference is that the receiving-and-form~.ng means include discrete arrays of light-sensing and light-producing components respectively. In this event it is further preferred that the reeeivine~ and form;.ng means also include a discrete array of circuitry for controlling the formia~~; aneans in response to the re-CG3.'~llng EE~.G~.n~ .
An alternative to these last-recited preferences i8 that the receiving and forming means include at les.st one monolithic hybrid of light-sensing and light-producing components. here it is corre-spondingly preferred that the monolithic hybrid further include cir-2o cuitry for controlling the forming means in response to the receiv-ing means.
In preferred embodiments of its second major independent facet or aspect, the invention is a method for detecting and ranging ob-jects. The method includes the step of receiving light scattered from the objects.
The meth.~d also includes the step of, in resporase to the scs.t-ter~e~ lic~,kat, f~~inc,~ a co.rr~s~aoa~d~.aac~ lic~~at of ~. different c~avelength 3o from t~a~ scattered l~.c~ht. In additio~a tae method. ia~clud~s the stew of ta.m~-rtes~le~a.a~g t~.~ corr~sp~aa~.n.e~ lic~~.t t~ ~.~teine res~a~cti:~e da.stanc~s ~f the objects .
the foregoinc,~ ~.y re~aresent s. e~escription or definition of the second aspect or fs.cet of the invention in its broadest or most gen-oral form. Even as couched in these broad terms, hocsever, it can be seen that this facet of the invention importantly advances the art.

In particular this second, method facet of the invention close-ly parallels the first, apparatus aspect discussed above. It con-fers the same advantages over prior art, essentially transcending the wavelength limitations of current commercial streak tubes and s thereby enabling lidar measurements to be made in the eye-safe near-infrared, for applications involving the likelihood of bystanders;
or in the infrared or ultraviolet for the various other applications mentioned earlier.
Although the second major aspect of the invention thus signifi-Io cantly advances the art, nevertheless to optimize enjoyment of its benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the method is further for use in determining reflects.nce of the objectsg and, the receiving and forming steps both preserve at 15 least some gray-level (i. e. relative intensity) information in the scattered light. lost of the preferences introduced above with regard to the first aspect of the invention are equally applicable to the second aspect now under discussion.
Another basic preference (also applying to the first two facets 20 of the invention) is that the receiving step receive return light in plural wavelength bands, and the forming step form the corresponding light in substantially one common band. If this plural-band prefer-ence is observed, it is further preferred that the bands include at least one W wavelength; and then a still further nested preference 25 is that they include at least one NIR wavelength. (These choices e~h7.bl.t dlstl.nCt abilities of the invention; in practice, spectral regions s.re chosen base. on physics to e~tra.ct unique object data.) Two other alternative basic p:~eference.s are that the ~:eceivinc~
step inclu~.e :deceiving the pl~.~:al sr~avelenc~th bands at (L) plursl 3o slits;~ .respecti~el~PO ~f s, plu:~e.l-slit streak caa~.erao and (~) plural tia~es~ respectively. Iza the fiast of these cs,ses it is further pre-ferred that the method also inclu~.e the step of, before the receiv-ing step, transmitting light in said plural wavelength bands, sub-stantially simultaneously, toward the objects. In the second of the 35 just-stated two cases it is instead further preferred that the re-ceiving step include transmitting the plural wavelength bands at plural times, respectively.
1~

Yet another basic preference a.s that the method also include the step of deriving plural signals from the received light in the plural wavelength bands, respectively. Accordingly the method pref-erably also includes the step of finding differences or ratios be-tween signals received i.n the plural wavelength bands.
In preferred embodiments of its third major facet or aspect, the invention is apparatus for detecting objects and determining .2o their distance and reflectance, to form a two-dimensional or three-dimensional image; the apparatus includes a light source; and means for projectine~ pulses of light from the source toward the objects for scattering kaac~.~ toe~ard the receiving'-and.-forming means;
a5 means for receivine~ light scattered frost the objects a.nd in response f~ing ~. corresponding light of a. differerat c~avelene~th from the scattered light, preserving gray-level informs.tion in the received and corresponding light; and means, including a st~ceak camera, for time-resolving the cor-2o responding light to determine respective distances and reflectances of the objects;
wherein the receiving-and-forming means include:
a first, optoelectronic stage, including an array of light-sensitive PIN diodes, that receives the scattered light and in re-25 sponse forms a corresponding electronic signal;
a second, electrooptical stage, including an array of vertical-cavity surface-emitting lasers Connected t~ receive the electroraic signal from the ~Iii~' diodes, that receives the electronic sis~a~al and in response forms the corr~s~aoa~e~inc~ ligYat; aged so a~a electr~a~ic circuit array c~~anc~ctia~g t~2e electr~~aic signal from the first stae~c~ t~ the sec~~ad. stage, a~ad modifying the siggaal to o~aer~te th.e secoaa~t stage.
The foregoing may represent a description or definition of the 35 thiro~ s.spect or facet of the invention in a broad a.nd general form.
Even as couched in these bros.d terms, however, it can be seen that this facet of the invention importantly advances the art.

In particular, though not wholly independent of the first aspect presented earlier, this facet of the invention aggregates several preferences that may be particularly synergistic. Without in the least denigrating the individual aspects and preferences dis-cussed above, the aggregated system of the third aspect is believed to be especially advantageous in short-term manufacturabality and overall practicality.
Although the third major aspect of the invention thus sagnifi-lo cantly advances the art, nevertheless to optimize enjoyment of its benefits preferably the invention is practiced in conjunction with certain additional features or characteristics. In particular, preferably the streak lida,r device is incorporated into a repeti-tively pulsed pushbroom system. In this case it is further prefera-ble to include in the apparatus an aircraft or other vehicle trans-porting the receiving-and-forming means and the streak lidar device relative to the objects - and also to include utilization means responsive to the time-resolving means.
It is to be understood that the foregoing enumerations of pref-erences for the three aspects of the invention are intended to be representative, not exhaustive. Accordingly many preferred forms of the invention set forth in the following detailed description or claims are within the scope of the present invention though not introduced above.
All of the foregoing operational principles and advantages of the inv~:ntion wall be x~aore full appreciated upon consadera.taon of the foll~wang detaaled descraptaonD ~r,~ith refc~r~eracc to tlae appended ~.ra~,~angs ~ of wYaick~:
HRIEF DESCRIPTI~1~1' ~~ THE DRAWaI~'Gs Fig. 1 as a block daagram of a streak tube an operation, shown together with a CCD camera and an output-data connection - symbo-lining processing and utilization means - that all together form a streak-tube imaging lidar ("STIL") camera;
Fig. 2 is a schematic diagram of a multipixel wavelength con-verter ( "7~C" ) ;
s Fig. 3 is a typical light-output vs. drive-current ("L-I'°) characteristic of a VCSEL;
Fig. 4 is a single-channel ?~C;
Fig. 5 is a ~,C block diagram used for the purpose of estimating the conversion efficiency of the system shown in Fig. 4;
Io Fig. 6 is an optical-bench layout used to validate the perfor-mance of the ~,C ;
Fig. 7 is ~. group of oscilloscope tr~.ces corresponding to vari-ous sie~,xxaals in the ~C;
Fig. S is ~, plot of the receiver and fCSEL output-~~aveforan s5 pulse widths as a function of the drive pulse s~a~ic~th (the sy~~ls representing the data points collected during the experiment, and the solid lines representing least-selua.res-err~r linear fits to the data) ;
Fig. 9 is a lida:x~ image of pulse return from mirror 1 (Fig. 6), 2o with time on the vertical axis - increasing upward;
Fig. 10 is a like image of pulse return from mirror 2;
Fig. 11 is an oscilloscope screen capture shoring the laser drive pulse (top) with the corresponding pulse returns from mirror 1 (left pulse, below) and mirror 2 (right);
25 Fig. 12 is a like oscilloscope screen capture showing the noise created by the signal generator - producing the second, smaller pulse seer i~a the lid~.r iar~~gr~ry, the kaottom li~ae being pbalse rr~turra fbom mirror 1, and the central line that from. mirror ~;
Fig. 1~ is a c~iag:~a~c~° ~per~ ~aigd~l~ schematic, sho~~i~ag one ~f 3o ma~a~ prospective uses of preferred em~a~diments ~f the in~exatio~ -partgC~alarly inehadixae~ an aircraft containi~ag and txanslati~ag the spparat~as in the so-celled "pushbioom'° pulsed, mode, over objects t~
be imaged in eye-safe mode;
Fig. 14 is a like diagram for the so-called "flash'° mode;
35 Fig. 15 is a spectral-response curve for InGaAs;
Fig. 16 is a diagram of a multichannel test setup for imaging box in front of a wall;

Fig. 17 is a multichannel streak image of the Fig. 16 wall alone, i. e. without the box, and showing multiple returns from a twelve-pixel prototype system;
Fig. 18 is a like image captured with the box present, and two feet from the wall (higher reflectivity of the cardboard is indi-cated here by increased brightness of the return pulses);
Fig. 19 is a like image with the box four feet from the wall;
Fig. 20 is an image very generally like Fig. 18 but with a translucent object (window screen) in front of the wall, substituted 1o for the box - and with the background electronically subtracted;
Fig. 21 is a mesh plot of streak return from a screen in front of a wall - showing both the strong return from the solid wall and the ~~ca~~er signal from the screen Fic~. 22 is a graph of predicted ~C sigxaal-to-noi8e ratio for z5 t~~o different types of detectors, nsmely ~-intr~.a~sic ~iior~es s.a~d sval~.a~che photodio~3es o Fig. 23 is a grsph sho~~a.ng predicted signs.l-to-noise ratio for an overall STIL receiver according to the invention, iracorporating the performance of the ~.C (here D is the receiver collection aper-2Q tore diameter, Tr~C is the receiver transmission efficiency, and. ~ is the atmospheric attenuation coefficient;
Fig. 24 is a conceptual block diagram showing the AC used in a time-sharing plural-wavelength-band lidar system;
Fig. 25 a.s a like diagram for a spatial-sharing (plural-slit) 25 plural-wavelength-band lidar system that uses filters to separate wavebands~ and Fief. 26 is a li~~e dis,gram of another spatial-sharing system t~aat isastQ~d uses a e~iffraction e~r~.tanc~.
3~
1'~~T~Ig,Fg2 I~~B~~IFTI~A'~' OF 1$I~ F~~°FR~d~ :~~b~IaI~RTT~
35 In preferred. embodiments, the invention provide, a lo~~-cost al-ternative to visible-light lidar. 1~1IR radiation pulses can be pro-jected toward objects, and the returned NIR pulses 8 (Fig. 2) con verted, at the receiver, into pulses 22' at a visible wavelength.
This visible radiation 22' is then clirected into a streak tube 18, effectively emulating the visible light 22 (Fig. 1) entering a s streak-tube system conventionally. The remainder of the operation is closely analogous to generally conventional operation of the streak tube, excepting only possible effects of positional quanti-~ation along the slit direction - and the result is a streak-tube lidar receiver operable for NIR applications.
.to In principle a number of techniques could be used to accomplish the wavelength conversion. It is possible t~ use nonlinear optical techniques such as Raman scattering, stimulated Raman scattering, and harmonic frequency generation to achieve ~aav~l~sac~th conversion.
~~,ch of these t~chnie~aa~s, ho~acv~r, r~a~zir~~s rel~.tively oom~al~~~ op-ts tical schemes; and g~~n~rally the oonv~rsioa~ ~ffioi~nc~i is, strone~ly dependent on the intensity of the light ~.t the converter.
Such dependence is usually a prohibitive condition at a lidar receiver, where the return signs.ls are ordinarily small (on the order of pioo~~s.tts). In addition, it is difficult to obtain large 2o wavelength translations, particularly in the direction of increasing energy per output photon.
In some instances it is possible to provide optical gain at the receiver to improve the efficiency of the wavelength conversion, Such techniques, however, greatly increase the complexity arid cost 25 of the receiver . 4 It is possible to instead accomplish a I~,ind of wavelength "con-v~rsioa~" electronically. ~~r~ t~a~ term ~oaw~rsion is s~m.~~;:~kaat more figurative than in, for ~~~ampl~, nonlinear optical t~ohniqu~~ - for 3o the pr~~~~2t t~ohaaiarda,~ dogs neat o~aa~ag~ ~~a~r~l~~a.s~tl~a. of particular lig~at to anot~.~b c~~.~~hn.gt~ c~f ~i.r tuall~ the sa~.~ light .
Rather, iaa ~ar~f~rr~~? ~d~.s~.a~ats particular light 8 of one ~~av~hnc~t~a c~ra.ves an int~~.~diat~ opto~l~otroo~atical sta~g~ 1~-17 (Fig. 2) that g~n~r~.t~s oorr~s~aondino' light 22' of another E~~,v~-35 length. This approach uses c~.~t~etors 7.3 ~ a~ceplifi~rs 1~, 3 a, s.nd emitters 1~ already developed for other applications - particularly ~ptical telecommunication or optical switching.

These established technologies, mentioned in subsection c) of the "BACKGROUND" section in this document, include development and marketing of discrete components4~'-~ - as well as monolithic (com-mon-epitaxy) systems introduced in the Coldren patent. They appear s to have never before been associated with lidar or other three-di-mensional measurements.
Nevertheless they are well suited to developing an electronic wavelength "converter" (herein abbreviated "7,,C" as noted earlier).
We have built and demonstrated just such a converter, integrated 1o into a high-bandwidth, high-quantum-efficiency streak-tube lidar receiver. The bandwidth of the system excluding the converter is into the terahert~ range, or over 1 GIi~ considering the response limitations of the converter itself.
25 Fear-infrared. light ~ from the object field a,etu~tes the 2~,C, ~~hich respox~ds by passing visible lig~h.t ~~' to the strea,~~-tube 3~
(1) the visible line image ~2 ° of the backsca.ttered light is fors~e~., as in the conventional system, on a slit in front of the streak-tube photocathode ~~. (pig. 1), bringing about a corresponding line image 20 25 of photoelectrons within the tube that is accelerated toward the anode end 31 where the phosphor lies.
(2) The photoelectrons a are eleetrostatically deflected ~9 across or down the phosphor, at right angles to the linear dimen-sion, forming a two-dimensional image on the phosphor - which re-25 sponds by generating a visible image that is very nearly identical geometrically. These electronic and visible images have spatial (line-image axis) and temporal (deflection/sweep axis) dimensions.
pinally (~) a CCD came~:a 1~ ea~atur~s ~~ the visi&ale t~ao-dimen-sieanal ia~ac~~ fo~r.~d, or a hua~a.~a op~.r2~toa c~.irectly view's the ~ahowphor 3o scree~a. Typically, the third e~ia~e~asgon. is c~.~at~ared as desexibed carlieb - i . a . , either ia~ ~ausT~~:~~a~ g~.o~d.e (b~% repetiti~ elf pul.
gang the laser, awhile ~aro~iding~ :~ela~Ci~e motion gaetc~eexa the sce~ae ~.~.d the sensor platform's ~) or in flash. r~oc~e (by prepping a full t~~~-da.a~.en-sional scene into a. composite line image, and tire-resolvine~ that 35 composite image) .
Thus the far-reaching objective of this invention is to provide a compact, imaging lidar receiver that operates in the near-IR re-1~

gion of the spectrum and provides high-resolution three-climensional imagery. The receiver combines a patented streak-tube imaging lidar ("STIL") receiver from Arete Associates, of Sherman Oaks, Califor-nia, with a complementary receiver front end that accomplishes the figurative conversion of near-infrared (NIR) light to a visible wavelength.
The result is a lidar receiver that can operate at wavelengths outside the range of the streak-tube photocathode sensitivity, yet provide imagery that is similar to that currently available with the to visible-wavelength STIL systems.
a) An electronic ~.C
Conventioaaa.lly tae bae~~,scattered laser return is focused through a slit on the stre~.~~-tube facaplate prior to ia~e~~.ne~ ova the photocathode ~~.. Flacing the ~C at thi. position and converting near-infrared light S to visible ~2' enables the streal~ tube 1~ to be used for NIR applications.
2o A linear array (Fig. 2) of high-bandwidth photodetectors 13 (eaa. PIN InGaAs) is placed at the image plane, i. e. slit entrance to the streak tube 1S.
For each photodetector element the photodetector current is amplified and converted to a voltage signal by a transimpedance am-ts plifier 14. The output of the amplifier drives a vertical cavity surface-em:i.tting laser (~TCSEL) 16 that emits in the visible region of the spectrum. The VCSEL radiation ~~' is incident on the photo-c~?thode of the stre~.~~ tube, a.~a~. t~.e operation of the streaks tubs is as d~scrgb~d ~.~a the ea.rli~r "~'~C~~~F.~~D'° section. of t~ais ~.c~cume~.t -3o ia~ . u~.zsectio~a e' ~ ) '° ~f that s~cti~aa .
~th~b aoc~i~.~a~ts of t~ai~ i~a~~aati~n allots in~a~at ~peration at other c~avelengths, mex~el~r ~a~~ r.e~ala.ceme~at of tae IaaCa~s modules caith ~.etectors 13 sensitive to the ~~avelene~ths of ia~terest - for ~~~amgah InSb or FbSe for t~~o to four microns, or I~gCdTe for five to fifteen 35 microns. Also for L7~' opera.tion, Si detectors are appropriate.
At the output (streak-tube input) end of the ~,C subsystem, for economy the output generators 16 can be LEDs rather than VCSELs.

Such a substitution is expected to inflict no more than a loss a.n sharpness due to optical crosstalk at the output, and at most some degradation of temporal response (i. e., a.t is possible that there will be no temporal degradation at all).
b) Component Selection InGaAs photodetectors 13 used for telecommunications provide 1o high quantum efficiencies and sufficient bandwidth to serve in this application. The technology is quite mature, and large arrays of detectors are commercially available.
It is possible to obtain arrays of receivers, ~_rhich include the det~etor 13 aaad individually addressable transia~pedance amplifiers 25 5.~ . Therefore provision of this compo~aent is not lims.ting.
The one-diar~ensions.l photodio~.e s.sray is in~aut to ~.n ~.rray of transimpeds.nce amplifiers (Tlt~s) 1~ that drives an array of amplifi-ers 15 (Figs. ~. through 6). The signal is then transmitted t~ the vertical cavity surface emitting l~.ser (VCSEL) array 16 and captured 2o by a conventional streak-tube/CCD camera, 1S, 1~ (Figs. 5., 2 and ~).
Vertical-cavity surface-emitting lasers (VCSELs) have been se-lected for the output stage because of their bandwidth and because they are inherently fabricated in array formats. VCSELs are unique, in comparison to other diode lasers, in that they emit from the 25 surface of the structure rather than from the edge. Consequently, they are by nature grown in arrays, and microlens optical arrays 17 can be integrated directly onto the devices - facilitating collima-tion of the output . ~ li~.e atta.cha~.~nt ~aroces.~ ~s be available for light-emattins~ dioe~es .
c) component a.ssea~al~n Comple'~ electric~.l eonta.cts required to su~aport a. large array of VCSELs can be formed through so-called "flip-chip bump bonding".
This is detailed ee. er. by A~sor Technology, Inc. (at www.amkor.com/
enablingtechnologies/FlipChip/index.cfm) generally as follows.

It is a method of electrically connecting a die to a package carrier. The package carrier, either substrate or leadframe, then provides the connection from the die to the exterior of the package.
In "standard" packaging, interconnection between a die and a s carrier is made using wire. The die a.s attached to the carrier, face-up; next a wire is bonded first to the die, then looped and bonded to the carrier. Wires are typically 1 to 5 mm in length, and 25 to 35 pm a.n diameter .
In flip-chip packaging, the interconnection between the die and ro carrier is instead made through a conductive so-called "bump" that is formed directly on the die surface. The bumped die is then inver-ted ("flipped over", in packaging parlance) and placed face-down, ~~itb~, the bumps connecting to the carrier directly. ~ burl is ty~ai-cally 70 to 1~0 ~ t~.ll, a~ac~ 10~ to 3.25 dam in diameter.
z5 The flip-chip connectioxa is gea~~rally formed ~~ith one of tE~o attachirbg media: solC~.er or conductive ~.c~re~~iv~. By far the a~.ore common material is the solder, in either eutectic (~3Vin, ?7u fib) or high-lead (~7~ Pb, 3~ Sn) compositions~ and solder interconnect is used in the initial flip-chip products that :or has brought to 2o market .
The solder-bumped die is attached to a substrate by a solder-reflow process, very similar to the ball-grid array (BGA) process in which solder balls are attached to a package exterior. After the die is soldered, the remaining voids between the die and the sub-25 strate - surrounding the solder bumps - are filled with a special-ly engineered epoxy called "underfill°'.
That ma.teris.l is particularly designed to control stress in the solder joints caused by tae diff~r.~nce in thera,~al ~~~aansion bete~eea~
tYae silicoz~ die and tLh.~ carrier . ~n.ce cu:~~c~ , the ux~derfill akasorbs so that st~:~ss, .r~d~aca.sag t~a~ stbai~. oar tka~ sold,~r ~aumps and.
tka~re~a~n c~r.eatl~ inc:~~asinc~ the life of t~.~ finis~a~d. ~aac~ag~.
The chip-attachment a~ac~ underfill st~~xs are th.~ elemea~ts ~f flip-chap in.t~rconnection. Beyond. this, as the z'ior presentation eoncluc~es, the remaine~er of pae~sage construction surround.ing~ the dig ss cs,n take many forms ~.nd can generally utilise existing x~.nuf~,eturinc~
processes and package formats.

d) Leveraging technologies Analogous features between lidar operation and free-space com-munication allow technical developments a.n the latter potentially large market to benefit the far smaller but important lidar remote-sensing market. VCSELs form a key element of today's free-space communications thrust.
Physical characteristics of VCSELs are well suited to solving the ~,C/STIL problem. First, individual VCSEL structures are small so (about 3 to 10 Etm) although they typically have a high beam diver-gence unless the output is coupled into a m:icrolens.
addition of a lens array 1? (Fig. ~) results in a structure with pitch bet~~een 200 and 250 Vim. ~ VCSEL arrsy ~~it'h X00-~. pitch can be c~uplec~ into the strea2: tube throue~h a. three-to-one fiber taper (also at 17) , providing t~c~o launelre~. fifty-si~~ cross-trace.
pi.~~els on a st~.n~.s.r~.-sire (1~ . ~ ) CCD chip - assuming a stres.~,~-tube magnification of 0 . ? , ~~hich i s common .
Secondly, VCSEL emission wavelengths can be tailored to match the response peak of the streak-tube photocathode. VCSEL output 2o wavelengths between 500 and S50 nm are easily achievable - with AlGaAs/GaAs or InGaAs/GaAs materials and standard molecular-beam epitaxy techniques. Arrays of up to a thousand elements have been manufactured', and several companies offer commercially available custom arrays~~ 9.
Design considerations and drive circuitry for VCSEL,~
~'roa~ a ~alot of typical ~BCSEL o°aat~a~at p~c,~er as a function of iaa-.~o peat cu~:re~at, it is seen tF2at ~CSELs ~aa~re a ~.~.wt~.nct lacing t~ar~.~~~a~1~.
(l~ic~. ~) th~.t m~.:~t b~ ~~~rcc~m~ to obtain sae~aaificant lgg~~t s~~.t-~a~at. In oaxr ~',,C, e~~a.en ~, ~'CSEL spa~aald be ~.aiescent a bias-curr~xat circuit 51 (fig. ~) sup~alies the ~'CSEL ~aath electbic~.l current 5~
held just belong that threshold..
then the lidar return striates the associated receiver elnt 13, drive electronics 14 provide an amplified photocurrent 65 which a.s added to the quiescent-state current 64. The sum, i. e. the VCSEL total drive current, then exceeds the threshold 41 (Fig. 3).
The light/current relationship 42 is very linear from the turn-on point and up toward the region of saturation 43 - accordingly s providing nearly linear response to intensity of the lidar return.
This characteristic is important where contrast or intensity infor-mation in the lidar imagery may provide significant cliscrimination capabilities. Particularly good examples are polarimetric lidar applications, in which maintaining contrast information is critical.
~ur prototype incorporates VCSEL drive circuitry 14 (Fig. 4) that provides ample bandwidth and gain to allow operation of a sin-gle-pixel la.dar system. The eleCtroniCS required to drive the VCSEL
elements a,re quite simple.
bye have built one configuration (Fic~. ~) a~ad confirr~eed that it 25 achieves desired operation for t~,~elve pi~~els e,rhen linearly replica-ted. In a, production confic~arata.on this becomes in essence oxz,e unit of ~. custom large-scale integrated circuit ths.t provides throue~hput for the two 'hundred fifty-six channels . ZTnli~e near-IR strea3~-tube photocathode anaterial, this technology' is readily available.
f) Estimate of converter efficiency A theoretical analysis (see below) of the converter efficiency for a particular form of our apparatus provides a foundation for use of the invention more generally. Conceptually, a minimum operatio-nal value is roughly 0.~~ ju.~t to conserve the energy of the input photons .
7Lga~a~'~s ~ahotodi~des h~~°e an e~st.r~el~~ ~aic~h e~aaaratua~
efficie~acy ia~
3o co~.~,,~~!ris~xa c~ra.t~a a str~a~~-tube r~a~aotocatgao~.~. T~a.~ref~re ~a.ois~ c~aar~c-teristics at the iaa.~aut end 2~ of our 2~~ are ixa oar favor o and aa7,~rr e~~.i~a that can be ~.~x~alied before the neeJly c~e~aerate~. visible lig~at 22~° reac~aes the photocathode 2a, ~~ithout adding significant noise, is adv~.ntageous.
The invention does involve some tradeoffs. inn advisable pro-duction configuration will have two hundred fifty-six channels, in a device of suitable size to couple with a streak tube; this config-uration places many operational amplifiers 14, 15 in a small space.
Accordingly power consumption and physical space must be bal-anced against the gain-bandwidth product. The solution here is a simple configuration that provides arbitrary but significant gain, and that is readily reduced to an integrated-circuit implementation.
We have modeled ?,.C performance as described above. For purpo-ses of such modeling, commercially available components were consid-Io eyed: an InGaAs PIN photodiode 13 (Fig. 5), a transimpedance ampli-fier 14 and transconductance amplifier 15, and finally a VCSEL 16 emitting 2~' at 630 nm. The ?,.C device is capable of high gain.
Ee~uatioa~ 1 sho~,~s that the number of photons emitted per incoming photon is high. (Fic~. 5 identifies the variables in thi:~ equation.) _ ~ l~T~~" = 4~a5 (1) The high conversion efficiency more than compensates for the inherent energy deficit in the transition from NII~ to visible ~~ave-lengths. The large transin~.pedance resistance dominates the conver-sion efficiency.
2o While conversion efficiency is an important factor, signal-to-noise ratio (SNR) is also critical. A model has been developed to compute the SNR of the wavelength converter.
Noise sources include background radiation (F_b), dark current (ID), detector shot noise, and the respective amplifier noise terms for the transimpedance and transconductance amplifiers For practical purposes, E~u~.tion ~ appro~;~ir~tes the SNP for a.
receiver ~c,~it~a ~aa.~.d~~idt~a ~.
,~'1~~ = P~~ (~~
.~o Gic~akie:~t~-ba.~a,~.~~ic~t~a o~,a~batioxa of tae ~,~ is imperative if tree system i. to be used in lidar systems ~~ith resolution res~aaireme~at.~
on the order of ~5 cm or less . using Ec~aation ~ , the Sh~3R at tla~
output of the ~ has been computed and plotted (Fig. 22) s.s a func-tion of bandwidth for an InGaAs FIN and avalanche photodiodes (APD), s5 and incident energy on the photodetector of 4 fJ. In the case of the APD, Equation 2 was modified to reflect the gain of the device as well as the excess noise.
The laser pulse width was varied inversely to the bandwidth of the a,C. For comparison, the lower detectable laser energy for typi cal STIL receivers is approximately 1 fJ/pixel. Thus, use of InGaAs APD's in the ?,.C will allow SNR performance at 1.5 Etm nearly identi-cal to that of STIL receivers operating at 532 nm.
Results of the simulation suggest that the a,C will provide .to adequate SNR to be used in conjunction with the streak tube. The PIN photodiode is adequate for all but the most demanding applica-tions, and the D can be used to achieve improved S1~'R at high band-~~idths or under lo~~-return-energy conditions.
The domi.ns.nt noise factor ia~ the 26,~ is the tr~,nsix~pc~dance am.-plifier. afote that the a~lifier considered here is a cor~mercia.l, off-the-shelf (~~C~TS") item whose design can be iat~rove~.. The high transimpedance resistance and the inherent noise in the amplifier can be traded off to some extent.
simulation of the 2vC incorporated into a STIL receiver c~as 2o completed and the results plotted (Fig. 23). In this case, the peak power transmitted was held constant and the laser pulse Width was varied t~ determine the effect on SNR. This simulation establishes that the invention can meet demanding range-resolution requirements for detection and identification.
The simulation assumes a transmitter at 1.5 pm and PIN photodi-odev as the detectors in the ~. ~3arious other simulation parame-ters are tabulated (Fig. 23, in ~~hich ~ is the recei~°er collection.
a.~ae:~tur~ diam~tcb ~ ~r~~ tae recei~~-er transa~ssio~a ~ff~.ciency, aa~~. ~
t~a~ a~aos~ah~ric a.ttex~uatio~a c~efficiea2t) - taut it is g~~aorta~?t to .~o n~te that tae ~aan~.c~i~.t~a ~f tae 2~ cfa~s ~a~:i~d iaa~~rs~ly c~rit~a t~a~ la-seL pulse ~~ic~th, and the strea2~ rate ~f the electron beam ix~ the tube ~~as maintained at tla~:~e CCD pixels per laser pulse. The date.
shown are parametri~ed by the TIC, noise factor; reducing the po~~e.r spectral density of the Tai yields significant dividends.
s5 The simulation predicts that reducing the TIC noise power spec tral density by a factor of ten will increase the SNR by approxi mately a factor of three. Again the simulation indicates that opti-mization of the TIA is a key component of future work on the 7~.C.
g) Single-element ~,C prototype preparation and operation To characterize and understand the key performance issues for the ?~,C, we built and operated a single-pixel prototype, for one pix-e1 in the receiver focal plane. A ~,C with a large number of pixels 2o is instead a highly specialized ensemble of integrated circuitry, most-preferably packaged as a hybrid multichip module.
The ~iCSEh in our prototype is a Honeywell SV'36~~-~~1 discrete elem~nt. TecYanic~sl specifs.cations of interest for thg~s ~'CSF~ are:
~a7~ nni. output, ~ ~' threshold voltae~e ~,nd ~ r~'~ thresb.old current.
Tt cs.aa be driven above threshold in ~~hort-pulse lOE9-duty-cycle ax~oc~.e froa~n ~ to 5.0~ ac~.~, leadine~ to a 0.01. to 1 a~~~ pea~~. output ~ao~~er range. The receiver module is an In~a~s PIE from Fermionics x~odel num'kaer FRL 15.00. The ~TCSEh drive circuitry used (Fig. 4) is dis-cussed in subsection e) above.
2o The prototype took the form of an optical-bench setup using primarily C~TS components, including a 1.55 ~tm laser cliode 9 (Fig.
6) to generate excitation pulses 6, a signal generator 11 and cliode driver 1~ for powering those laser pulses, and our high-bandwidth ?vC

10. The test investigated the capabilities and limitations of the ~,C, and also used that module in conjunction with a streak tube 1S
and carc~era 19 to demonstrate relative range measurements.
The optical bench setup (Fig. 6) i. assemblee~. so that a laser pulse ~a travelixag from the ~.. a~ pam. laser da..ode ~ throug~ga, a beam s~alitter a .reflects from oage of t~~~ ;~alan~ a~irr~rs 1, ~ ~.~uaated ~aa 3o the ~a~xac~,. ~'~ po~:ti~aa of t~ac i~'IR ;reflected ~.~tura~ la.ght ~:, re~.-rected by the splitter ~, is incident on the input detect~r 1~ of the ~,C 10. The resulting ~CS~~ out~aut is projected throu.c~h a short fiber-optic coupler 5.7 onto the facepl~.te of the stres.~s tube 1~~ .

h) Bandwidth Our first determination, using the apparatus, was the bandwidth of the 7,,C itself. In this measurement the width of the pulse C3 (Fig. 7) from the signal-generator 12 was varied from 16 to 2.6 nsec while observing the relative pulse shapes of the output current waveform Cl from the receiver 13, 14 and the current drive waveform C2 into the VCSEL 16, using a digital oscilloscope (not shown).
That set of three oscilloscope traces was recorded with the .to signal-generator pulse width set to 2.6 nsec. The three waveforms have a sim:i.lar shape, and evidence no significant temporal disper-sion as the signal passes through the various stages of the 2,C.
The pulse generator is not capable of prodtacine~ pulses shorter than 2 . ~ a~sec, beat these obse~.tions nevertheless de~.onstr~,te di-25 r~:ctl~r that the invention achieved a band~,ridth of 400 t~~ very easil~,r - and, by visual interpolation of the screen ~~aveforms, also accomplished a. bandwidth extension into the giga~hert~ regime.
~aeasurements of the same wsvc~form pulse widths taken durine~r this demonstration, over the above-stated range of signal-generator 2o pulse widths, were tabulated and plotted.
The pulse widths 71 (Fig, 3) at the receiver 13, 14, and also the pulse widths 72 at the VCSEL output - i. e., both of the ?~,G
test points - linearly tracle the width of the drive pulse, indi-cating that the bandwidth of the converter is not a limiting factor.
25 Thus the ~C is an excellent match to the already demonstrated high temporal resolution of the streak-tutae lidar receiver.
g) Relative range ~~e~suae~.er,t ~~~.t~a. the ixafrabed s~.~raal co~.e~rerted t~ v~.si~ale la.g~at, t~a.e o~at~a~xt c~as next Cased to actvaally create strea2~-tu'~ae lic~am a.a~.ae~e. Our a~a-paratus rela.ably seed. reproducibly measured, relative ravages e: tab-lished by m~.nipulation of the mirrors 1, 2 on the test bench.
Using the same expc ria~reaatal arrange ment discussed above (Fig.
6), a set of streale-tube images was captured and record~d by the CCD
camera at the back of the streak tube. During the first demonstra-~7 tion, light from a single laser shot was allowed to reflect 4 from a near ml.rror 1 (Fig. 6) and pass through the ?~,C and on to the streak-tube/CCD system.
During the second capture, mirror 1 was removed and the light s was instead reflected at a far mirror 2 (positioned AL = 71 cm behind the near mirror 1). The resulting lidar images include a bright flash 81 (Fig. 9) corresponding to reflection from mirror 1, and another such flash 83 (Fig. 10) corresponding to that from mirror 2.
The flash 81 from the near mirror 1 is much closer to the ori so c,~in of time coordinates (the bottom of the image) than the flash 83 from the far mirror ~. This relationship makes clear that the sys tem is able to detect a range difference from the two signals.
The same information is revealed by displaying both pulse re-turns 81, 83 (Figs. 9 and 10) from the near s,nd gar mirrors 1 and! ~
s5 together in an oscilloscope-screen trace (Fig. 11). The time dif-ference bet~~een the t~~o pulses is measuree~ at ~.7 nsec, precisely the time it ts.~~es light to tr~a~rel the ~ ~1L =1~.~ cm round-trip dif-ferential for the 71-cm mirror separation.
since the VCSEL is operated at its threshold limit, and ~~ith ao the signal generator working close to its operating limitations, any undesirable ringing in the drive circuitry causes the VCSEIa current to rise, only instantaneously, above the threshold - releasing a small pulse of light. This small pulse is detectable by the streak-tube camera and appears in the lidar images as a smaller, dimmer a5 pulse 82, 84 (Figs. 9 and 10).
The same is seen also in the screen capture, with the 'scope set to offsc t the x~.ain traces 81 ~ 83 (Fig. 12) vertically - anc~
also to shift one of those: traces to rou.c~hl~ align t~pora.ll~ (hori-~oa~tall~p) c~it~. the other . Tae txace 83 c~.~x~ to reflection at ~eair.~.~or 30 ~ e~n~s set c~ith its ~'C~EL thrcss~.~l~. l~s~rel 8~ a~a.st at t~a~
~scill~sce~ga~
h~:~i~~a~tal ce~.terli~ae. Tae sp~ari~~as ~aulses a~a~aear as smaller s~.al-1~c~ peak's P2, 8~ trailg~,g the ~arim.~.~ pulses 81, 83 res~aecti~~-el~.
Fninor trimming refinemea~ts to the 2~C suppress the re. onances respon-Bible for this undesired effect.

j) Conceptual notes on the twelve-pixel implementation and testing A multichannel ~,C that we built and tested consists of the original single-channel circuit replicated twelve times. The sin-s gle-element InGaAs photodetector has been replaced with a twelve-channel InGaAs photocliode array (Fermionics P/N FD80DA-12).
The array has a 250 Eun pitch between detector, elements; other-wise the element size, spectral response and sensitivity are all identical to the original InGaAs diode. Care was taken during the 1o board layout to ensure line lengths were kept uniform from channel to channel to avoid a potential phase mismatch due to signal-propa-gation delays.
The same type of Thor Labs telecoas~mungcata.on ~'CSELs was used in the multichannel as in the sis~c~le-chana~el ~,C. This presented an ob-.t5 st~.cl~ to ~ulation of a, very nearly proe~~act~.on-st~sle version of a, r~ultichannel prototype, s.s the la.re~e size of the "T~" c~.ns housing the VCSELs limited minamur~ spacing between 'i3"CSELs to 0.200 inch.
This meant that even though there was only 250 spacine~ be-t~reen elements in the TnGaAs detector, there was a significant dead 2o space between ~TCSEL emitter elements. The 0.2-inch spacing also limited the number of channels visible on the streak tube to eight.
People skilled in this field, however, will understand that the difference in spacing is in the main only cosmetic, provided that interchannel cross.talk at the ~TCSEL output is fully assessed at some 25 other stage of the development. Moreover, the wide spacing between ~iCSEL beams also had a positive implication, offering an opportunity to klatch parallel perforr~nces of the multiple individual ~CBELs in isola.tio~a .
bhp m~alticha~a~.~l wait ~a~.s tasted u.sixag a double. ~3~.:~~G las~.r .~o ~~ith aa~ 8 ns pulse g~n~r~!ti~.g appa~~sitel~r 1.8~ ~3 of a~rerage p~c~e~.
at 2~ 5~2 ate. anc~ 7..20 ~~ at 2~ ~.~~~ . P~.ls~ b~p~t~.ti~n ~re~a.~xac~ LJas 20O Ez .
'Ila~ r~spo~asivity 232 (Fic~. 3.5) of the InGa~'~s sensors to 105~~ nay iv about 3 db reduced from responsivity 2~2 at 7.500 nay. The re-3s sponse (off-scale, 2~1.) of the InGaAs detectors to ~, 5~2 nm visible light is about 8.5 d~ lower still. In addition, the 7v,C board phys-ically blocked the visible light from reaching the streak tube, so images were from the ~, 1064 nm light only.
The beam from a source laser 309 (Fig. 16) was projected through a Fresnel lens (not shown) to produce a fan beam 303 paral-lei to the focal plane of the detector array 13 (Fig. 2) in the ?~C
(Fig. 16). The a,C collection optics consist of a 12.0 mm f/1.3 lens 311 positioned approximately 1 cm in front of the array element.
The 12.5 mm FOV of the lens roughly approximates the horizontal expansion of the fan beam 303.
~ur lidar test objects included a wall 241, at a distance 312 of about 5 m (sixteen feet) from the a,C, and also a cardboard box 242 at an adjustable distance 313 in front of the wall. Resulting streak images (Fig. 17) of the e;~all alone clearly s~aoe,~ the indivic~.-ual channels of the ~~avelength converter.
~s a~oted, earlier, even thoaae~h the spacing of the detector elements i$ 250 , the physical dimensions of the V'CS~h "T~" cans cause the optical emitters to be separated lay about 0.2 inch per channel. This separation on the streak faceplate results in the return being segregated into distinct rows, and the dimensions of 2o the streak faceplate limit viewing to only eight channels.
With the cardboard box 242 (Fig. 16) positioned at a distance 313 of roughly 0.6 m (two feet) in front of the wall (roughly 3.4 m or fourteen feet from the wavelength converter), resulting lidar im-ages (Fig. 13) immeda.ately show very different responses. Clearly the system is indicating a closer object across part of the cross-track field. In our test images (Figs. 17 through 19), range is pre.~ented. from bottom to top: i. e. loader ix~ tl~~esc ir~.ages is closer to the s ou.r c~ .
In additio~a t~ vertical clispl~c~,ent, tae images cobr~ctl~ in-~o dicat~ ~ l~aig~a~r reflectivit~r ~f °he ca~°c~oars~. ~ubf~c~
2~2 (fig'. 16) relati~~e to tka.at of t~a~ c,~a.ll 2~.1.. This ~aggher reflecti~~-it~ is pls.in fxor~ the gseat~r ~aright~.ew.~ (~°i.c~s . 1~ and 19) of the betua:.n p~als~s .
~~'ith the cardboa.rd, boy" moved for~~a.rd. to about 1.3 m (four feet) from the ~~a.ll and thus closer to the lidar unit (roughly 4 x~ or twelve feet from the 2~C) , the resulting images (Fig. 19) clearly follow the shift of the box. A significant increase a.n intensity of the return from the now-closer cardboard box is actually sending the current drivers into saturation and inducing a ringing in the out-put. This ringing results in a greater pulse length (height) for this return.
Tn another test we substituted a translucent object (window s screen) for the box, in the imaging path between the lidar unit and the wall. This allowed us to capture returns from the partial re-flection by the screen (fainter, lower pulses, Fig. 20) while still seeing the wall behind it. These accomplishments are shown more ex-plicitly by a mesh plot (Fig. 21) of streak return from the screen so in front of the wall, as well as the wall itself.
T~ceelve-pia~el system design s5 ~leetronics subsystem - The t~~elve-pi"~el ~,C ahoul~. tae ~auilt ~asinc~ coa~r~.ercially available ~CSFL anew detector ~.rrays . In fact the array dimension of twelve is based upon. coacerc~.s.l availability.
The primary corc~ercial application for ~C~FL arrays is in short-hsul communications. These already existing structures can 2o abbreviate development time and reduce the cost of testing the in-termediate design.
It is recommended to use an InGaAs detector array that is com-mercially available. Custom electronics, but well within the state of the art, are to be designed - including the transimpedance and 25 transconductance amplifiers.
The circuit design discussed earlier (Fag. 4) can be replicated to drive the twelve ~'CSFLs. To assure high bandwidth, all compo-xa~nts are best m~d~ wurfac~-a~ouxat type: , ~Jith strict attention to tra~asmi, lion-line l~aagt~as ~.nc~ control of ,tray ca.~aacitanc~ a~ac~.
3o i~a~.u.ct~.~a.c~ .
F~~IC~~ cibc~a~.t ~.~al~tion, a~~.ilable as softc~~.r~ from. Cade~ace ~es~.c~n ~yst~.s, I~a.c. of ~a~a Nose, California, i. a rec~m~.end~~. c~e-ign support tool garior to boa.re~ fabr.ic~.tion. ~~~ fousad that its ~a.s~
minimi~~:d errors in lsyout and. operation.
Optical subsystem - The optics must focus backscattered radi-ation onto the detector array and deliver the output of the STCSEL

array to a streak-tube receiver. Optics to deliver the backscat-tered light are ideally in the form of a simple telescopic lens sys-tem that has high throughput near 1.5 ptm.
Because the twelve-element array will be quite short (3 mm) and have few pixels, it is possible to butt-couple (i. e. abut) VCSEL
outputs directly to the fiber taper input of the streak-tube recei-ver. The pixel pitch of the VCSELs should be adequate to minimize channel crosstalk after that coupling is achieved efficiently.
An alternative approach is to use a fiber-coupled VCSEZ array so and abut the fibers directly to the streak-tube input. The freedom to move each fiber independently will enable complete elimination of crosstalk.
~a~.e i~.eal laser for this sg~stem is an ~d:'~~G~ unit coupled to an optical pa.rametric oscillator to provide out~aut at 1.5 Vim. ~n opti-2~ cal pulse dicer is recoa~enc~.ec~ to enable tailori~ag of pulse c~icslths in the range from 1 nsec up to the normal laser pulse ~~i~.th of ~.~
nsec.
suitable streak-tube lidar receiver is a.FTamamatsu C~1S7 sys-tem coupled to a DSO 160 CCD camera. ~~ie have used such a. system 2o in multiple STIIa programs and find that it provides a solid founda-tion on which to build experience with the ?v.C.
Data acquisition - A useful data-acquisition system for this purpose is based on a commercially available frame grabber and a PC
25 configured to capture and store the images. To minimize peripheral development time and cost it is advisable to obtain access to a sui-tile soft~~~are library .
L~oa.ato~ me~sur~meaats ~ ,subsystem test - Each ind~.~idu~.l ~o piyyel ~s the arr~.~ spa~~al~. bQ i~ac~epe~.d.eaat.l.~r tested f~r f~aa~ct.a.o~aalit~a a,scertaia~~.a~g tkae sensgti~it~ and ~a~nd~~ie~.t~~a oaf eac~a cha~anel ~xsia~~i tests sir~.lar to those described a~ao-~e for the single-pg~vel ,a~,~st~..
the 2~C should then be cou~aled to the strea.w tube, and aligent and calibration cor~.~aleted.
35 Calibration should include measuring the uniforanity of the various channels so that these variations can be taken out of sub-sequent lidar images. In addition, the dynamic range of the system should be assessed using a calibrated set of neutral-density fil-ters. Our prototype efforts included both these components.
Twelve-pixel imaging-lidar lab measurements - Several tests should be run to characterize the performance of the a.C in a STIh system. Initial tests ideally should involve simple flat-field images using objects of varying contrast spaced apart from each other in range. Such testing is important to quantify the contrast and range measurement capabilities.
zo A second test should determine the range resolution of the sys-tem. In this test the two objects should be moved closer and closer together until the respective returns from the two can no longer be discriminated.. This procedure should be rapea.ted for a variety of laser pulse ~~ic~ths a.nd~ strea.~~-camera settings .
The resolution ~~ith ~~~aicra the distarace bet~~e~:n t~~o ~aa.rtially tranarb~issive objects can be measuree~ should. also be c~.eter~a.az.ed. Or-dinary ~,~indo~a screen serves ad~.rably as test objects in this test.
finally, larger scale (more than twelve-pixel) imagery should be generated by simultaneously scanning the transmitted beam and the 2o receiver field of view with a large mirror to allow full three-dimensional imagery to be collected when the pushbroom sensor is stationary.
The tests discussed above will provide a design team with ex-perience and knowledge of the parts of the system that are sensitive ~5 to component tolerances and the like. It is particularly essential to take this opportunity to identify the most qualified and cost-effective a~.~aa.lable vendors for the much more difficult stage of c~ev~lopa~ent that follo~c~s .
30 1) 'Ic~o-~a~a~,dred.-fifth-. i~u-~,ai~,~~l s~rst~~. ~sie~aa specification. to guide a de.~ign effort - design of a t~~o-hundred,-fifty-si~~-pi~~el system is . ig~aifieantly more eole~> thaw that of a t~~elve-pixel ~;ystem. ~~'itT~a the expertise developed in tine 35~ dozen-pixel prototype, ~a design team can proceed much more confi-dently and with fewer detours.

This effort should encompass design of a ~.C with imaging capa-bilities that can meet real-world objectives. The accompanying table contains lidar system specifications to drive such a design effort.
parameter ~walue comment 7~,C receiver band-1.5 GHa width ?v,C crosstallc <-3~ dB channel to channel 1 7s,C power < 1 ~ W
o consumption transmitted wave- 1..54 mm length VC~~h ~:rnissior~ 640-X50 nx~

~cr~3~l~nC~th angular ~5~ a~ra.c~. '~ . 5 cat at 3~~ a~ standoff cross-~.~. olution (I~~~>tr~c~~

R~~ 64 mrad cr~~s-tra~~

range resolution, variable ~R goo m ~a~~.~um 7.5 cm minimum range extent, RE 100 x OR

absolute range t2 4R defined as the required mea-precision surement accuracy of the distance from the sensor to the first return of a single shot pul~a~ :~ep~t3.tl~8b~~o H2 ma~~3.IILUI~t f3::~qtl~nC~

t2pG:C~tgff~.~' -~.~ t~ m~5 '~~ '4.-~' ~'~.'~ I I
t~R.e: G

~~tect~b a.rra~r - '~h~ detcet~r ax~:a~rr ~~~.11 tae a tc~~-~xuaadr~d-3~ fifth-sg~-~le~.e~a.t ~Ih~' In~~ s de-ice . Three ~aossible ~~~a.~,ear~ of ~aac~a arrays are ~~no~~ga to us: tensors LTnlixs~t~~., Hamar~atsu, and ~~T.
It is advisable to collaborate e~it'h v~rl.e~.~rs to e~etes~aa.~ae th.~
best possible configuration for they ~ and final~.~e the design. The array is advisably flip-chip bonded, as outlined earlier, to pre-serve the bandwidth of the detector and minimize the physical extent of the connection.
It is also advisable to bump-bond the array to a submount as-sembly that will support both the VCSEL and the detector array. A
s set of transmission lines should interconnect the detector array and the amplifier array.
Transimpedance amplifier array - Here too it is recommended to work closely with IC design and process specialists to identify so the best process for the custom chip or chips to achieve the re-quired combination of a low noise transimpedance amplifier, adequate bandwidth, a suitable gain stage, and output buffering to drive the VCSEL array. The desigra from Cf?TS components used on a circuit card should then be coaavertea~ into deva.ce,~ that are readily fabricated in 15 IC form c~itk~ the process chosen.
As noted above, a ~S~ICE~ a~o~.el shoule~, be r~evelo~aed in adva~a.ce to shod that the design, ~rhera implemer~ted in this fashion, provides the performance required. It is preferable to consider the system aspects of the design including packac~ring and thermal modeling. A
2o final system layout for fabrication at a foundry should be reserved for a later stage of development, but the two-hundred-fifty-six-pixel effort will confirm that the work is on track and provide a clear path to the foundry later.
2~ VCSEL array - VCSEL arrays are currently being produced in a large number of various formats. The VCSEL array will be two hun-Bred fifty-six elements ~~ith a device pitch of ~~50 dam.
~°o~ar coarcial vendors arm amo~ag ~~~ao~c~n entities capable of ~aroducing the ~'CSEL Arran% that is nec~ssa~~r: Ho~.e~~ell, Emcore, I~I~i 30 ~~a.ot~aaic~ ~.~.c~ ~~T . Z~.1 ~aa~re significagat expertise i~a c~el~.~r~ri~a.c~
cost~~. Fr'CSEL ~.rx~a~rs .
It is als~ ad~~.sable, ho~~e~er, t~ coxa.side.r colla&aor~.tioa~ in ac~-c~.itio~a, or ia~ste2~d, ~~ith university-~aasee~ academic sgaecialists ir.
this a.re~.. Such coventurers are li~~.ely to provide e~reater flexibil-~5 ity in accommodating the special ree~uire~.nents of the ~,COSTIL ap-proach without overregard for the high production volumes that drive more-conventional commercial applications.

The invention is not limited to using VCSELs. The emitters may instead comprise edge-emitting lasers, or quantum diodes or dots, or MEMS devices.
Cross~-track sampling - Our use of discrete detectors, in front of the slit of the streak tube, in effect samples the image plane of the receiver - as compared with conventional STIL apparatus and op-eration, in which the cross-track image at the photocathode is sub-stantially continuous. One must assure that the sampling has ample so resolution to reconstruct the images desired in the lidar receiver.
This effect is not overly complex, and a closely analogous phe-nomenon conventionally occurs anyway at the output end of the streak tube. There a multiple-discrete-element CCD array, used to capture the out~aut range-azimuth image that appears on the pho.p~.or, neces-.t5 ~sari.ly impoaes a ~anti~.ia~g or discr~ti~iaac~ effect.
secondary effect of the discrete detectors i~~ are c~ff~ctive reduction in the fill factor of the receiver. This ~aroblcan significantly degrade the performance of the system with respect to the adore-traditional mode of operation. Such a limitation can be 20 overcome through the use of a microlens array that can be attached or integrated directly onto the detector array. Such a practice is common in CCD and CMOS imaging devices as well as in detector arrays designed for communications and spectroscopic applications.
m) Representative systems F~er~ly by c~~.y of exale, one ~f a~yriae~. uses may ixav~lve axa aircbaft 101 (~ic~. ~.~) , ser~rixag ~.s part of the in~~xative ~,ppara.t~x, 3o th~.t translate. 3.0~ the STIL s~ste..~ 1~~ in the . o-called "~.a~xs~:~oc~m.°~
haul. ~d mode ~~~r ~r ~.~~~t t~ object: i~a ~ scene 3.~~ to b~ i~--~g~c~.
~~ile ia~ r~otio~a 1.~JQ ~ tkae s~nst~. fogs both the ~.o~~nc~ar~?- or sid~c~a.rc~-traaasmitte~. near-infrared ~aulses 1~~ axae~ the reflected or T~a,c~~-scattered aaear-infra~re~. pulses S ~~ritYain a thin-fan-.~ha~aed beg envelope 10~.

(It will be understood that the return pulses actually are scattered a.n essentially all directions. The receiver optics, how-ever, confine the collection geometry to the fan shape 102.) The aircraft 101 may, further as an example, be searching for a vehicle 109 that has gone off the road a.n snowy and foggy mountains 105. A person 107 in the mountains may be looking 106 directly at the aircraft and into the transmitted STIL beam pulses, but is not injured by the beam because a.t is near-IR rather than visible.
The interpretive portions 91-94 of the apparatus may also in-to elude a monitor 99 that displays an image 9S of the scene 105 for viewing lay a person 97 within the aircraft - even though the scene 105 itself might be entirely invisible to direct human view, ob-scured by fog or clouds (not shogun) . fielding r~.y instead, or in addition, be at a base station (not sho~3n) that receives the results of the data-p.rocessine~ system by telemetry 95.
lrae primary ~.ata processine~ 91, 92 aciwanta.geously produces an image 9S for such vie~s~ing - preferably a, volume-ec~ua.va.lent series of two-dimensional images a.s taught in the pushbroom art, including the earlier-mentioned previous patent documents of Aret~ Associates.
2o In addition the system preferably includes automatically operated interpretive modules 94 that determine whether particular conditions are met (here for example the image-enhanced detection of the vehicle sought), and operate automatic physical apparatus 95, 96 in response.
For example, in some preferred embodiments detection of the desired object (vehicle 109) actuates a broadcast announcement 96.
These interpretive and a.ut~r~a.tically responsive modules 91-96, 99, ho~9ever, are only e~~~alary of a~.ny different forms of ~~la.at away lie called. "utili~atio~a a~~s.ns" t~a~t cea~xzpris~ ~!~atom~tic ~e~ui~ax~~a~t act~a-,~o ~.t~d ~~la~xa ~a~rt~.c~alar optics.lly a~~tecte~. c~a~e~it~.ma~s arm mgt.
~th~rs iaacl~.c~e ~nabl~.ne~ or denying access t~ sec~a.re f~.cilities threauc~Y~ o~aera.tio~a of do~rs and gates, ~r access t~ c~mput~r syst~s or to financis.l services such. as cr~e~,it or ~aan~~ing. Detera~,ina.tioa~
of hostile conditions, and resulting security measures such as auto-s.~ ma.tica.lly deployed area-sealing bulkheads, is also ~~ithin the scope of the invention - as for instance in the case of safety screening at airports, stadiums, meeting halls, prisons, laboratories, office buildings and many other sensitive facilities.
Because the NIR beam is eye-safe, the entire system can be operated at close range to people and in fact can be used harmlessly to image people, including their faces, as well as other parts of living bodies e_. er. for medical evaluations, as also taught in the earlier patent documents mentioned above. The elements of the envi-ronment 105, 107-109 and of automatically operated response 94-96 that are shown shall be regarded as illustrations of all such other 2o kinds of scenes for imaging, and the corresponding appropriate responses, respectively.
The invention is not limited to pushbroom operation, but rather can be e~oda.ec~ i~a ~ flash systems . It will be understood, ho~~-25 ever, that the pushbroom mode makes the a~.ost - in terms of resolu-tion or im~.ge sharpne;~s - of comparatively modest resources.
In particular, relatively fired avs.ilable ims.ging length and area are available at any streak-tube photocathode and phosphor screen, respectively. It follo~rs ths.t if an entire scene is re-2o mapped into a single slit image for streaking, then necessarily only a far tinier sampling of each part (e. er. raster line) of the scene can be taken.
In a flash system what is projected 203 (Fig. 14) and returned 20~ can be a single rectangular-cross-section beam 202, rather than 25 a succession of fan beams 102 (Fig. 13). The aircraft 101 may hov-er, rather than necessarily moving forward at some pace related to frame s.cgui. ition, and may be ~. lighter-than-air craft if desired.
~s in the push~arooae~ system, ho~~ever, the e~~avelene~ths of traaas-sz~.tted aa~d rec~avered p~als~s 203, 203 (Fig. 1~.) abe ~aot ia~ the vis-.~o ible pabt of the s~xectrur~o for xa~ ap~alicati~aas tYae~ a~.~ in t~a~
a~~ar-IR, beat ~.s n~ted ~a~.lier t~a~~r c~.~a Fay a.~. the i~a~raree~ ~b paltry,_ violet a ~s appropri~.t~ to the agpla,catioa~ . X11 t~a~ ill~astr~tioa~s iga this ~.ocur~.~nt are expressly to be seen a. representative of all such.
different ~~avelength e~oe~a.r~.ents .
35 Following the ~ 1.0 ice. a flash system is a mapper 212 that re-arranges elerc~ents (e. fir. pixels) of the image captured by the ~ 10.
The mapper 212 may take the form of a fiber-optic prism that is 3~

sliced, as described in the earlier-mentioned Knight or Alfano pat-ents, t~ place successive raster lines of the image 22' end-to-end and thereby form a single common slit-shaped image 213.
For purposes of the present invention, in purest principle the mapping may instead be accomplished within the a,C, by rerouting electrical connections at some point between the individual detec-tors 13 and the individual VCSELs (or other emitters) 16. Such an arrangement poses a major challenge to maintaining minimum reactan-ces throughout the system - and especially uniform reactances as zo between the multiple channels.
Feople skilled in this field Will recognise that such an effort is at odds with the advantageous properties of flip-chip bump-bonding, and perhsps even more ~aa.th the cos~on-ep~.taprinciples of the Coldren p~.tent . Ine~enuity in geomet:eical ~.rraa~e~ements , ho~~ever , any overcome thQSe obstacles.
~°ollo~~ing the strea.~~ tube 1E, the flash-a~.ov~e output image ~1~
x~~?y be regarded as garbled due to the ma~pper 212 and therefore re-quiring use of a remapper 215 to restore ordinary irc~.ge properties of adjacency. This remapping can be accomplished in various ~aay.
2o The most straightforward is ordinarily a computerised resorting of piacels in the output image 214, to unscramble the effects of the mapper 212.
2s n) Alternate wavelength applications ~s noted earlier, the applicability of the inventi~n is not at all lima.ted to the gaear-infra~:edl. fine ir~ortar~t area eaf use is the .ore-remote infrared, ~.lso ~, relatively difficult regi~~. for ~.e~el-~o ~p~~nt ~f stbe~.~s-tube pea.~t~cathodes ~aec~us~ c~f the eureka lo~~e:~
~a~aotoa~
e~a.erg~~ were t~a,~.~a in tae ne~.r-I~..
Tae infrared. ~a~rti~n of t~.e elects~magnetic s~aectrua~, (3 tm 12 overl~.ps strung ~bwearption features of any molecule. . ~'~s ~.
result ~aavelene~tths in this ree~ion are particularly attr~.ctive for s~ monitoring gaseous conta~.nant concentrations such as those encoun-tered in atmospheric pollution or industrial process control.

CO~ lasers operating at 9 to 11 Etm can produce large amounts of power and have been deployed in space for a number of applications.
The wavelength converter ("?.,C") is well suited for use with C02-la-ser-based imaging lidar systems.
Even though photon energy in the ultraviolet is ample for de-velopment of streak-tube photocathode materials - and in fact such materials do exist - nevertheless the W too e~ffers fertile ground for applications of the present invention. Here the particular ap-peal of the present invention lies in the potential for imaging re-so turns from wholly different spectral regions within a single, comm~n streak tube; and if desired even at the same time.
For example two lasers 409x, 409b (Fig. ~4) producing respec-tive pulse. 4~3a., 403b in different ~~sveba,nds - or if preferred ~.
single laser capable of e~.ssion in differexat bands - can. be ~pera~-tec~1 in a.lterna.tion. The returns ~0~ from. a.n object field ~gl are ~lir~cted to ~ single, coa~m~n 2s,C 1.0 , ~~hich rela~r.~ th..~ ~ptical sigana.ls~
to a stres,~~ tube 13, camera. 19 and interpretive stages 34 just as before. This type of operation yields a time-shared system.
Here the converter 5.0 may have sufficiently uniform response in 2o the two wavebands t~ enable operation of the camera system 13, 19, 34 for processing of both sets of returns 4~8. To enhance such ca-pability the ?~.C, the streak tube 1~, or the back-end stage 19 - or combinations of these - can be synchronously adjusted in sensitiv-ity, electronically.
2s An alternative, acceptable in some applications involving rela-tively stationary object fields, is t~ collect a complete image or large portion of a,n ia,c~e in orae of the ~~avebanc~s based on pulses ~3a. from o~ae laser a~9a o a.ra.~. then change over to collection of a com.~aarable image ox' ~asaxtion i~a the other c~avebaa~~, ~aasee~ on pulses so ~~3b fr~~, the other laser ~.~9be In this ca.~e ~,ret a~aot~aes alte~.n.a five is ~;~aiftia~g X1.1 ~~ tc,~o cab a~~re convebters 1~, ~1~ a.~ato posi~.i~ga in front of the .streaks take 1~ - or, i~ prQf~r~°ed~ retainine~ a siragle converter 10 in position awhile . ~aap~aing optical Filters (xaot sho~~-n) in front of that single converter 10.
35 ~~'taere time .leering is not acceptable or desirable, a spatially_ shared system can be used instead. For this case the system advan-tageously uses a single laser 5~9 (Fag. ~5) that can emit pulses 503 4~

containing light in plural bands, or in particular plural spectral lines.
Here the return 508 from the object field 541 a.s likewise in plural optical bands, or at least lines. The streak tube 518 in s this case advantageously has a plural-slit photocathode as described in the previously mentioned Gleckler patent document. Here e. a.
one wavelength filter 501 is inserted in front of only just one part of the ?~.C - while a second, different-wavelength filter 502 lies in front of another part.
Z0 For instance if just two wavebands or lines are in use, the two filters 501, 502 can be respectively inserted in front of the two ends of the converter array 10, which correspondingly feed optical signals into the t~~o slits. If preferred, the t~~o ends (or more g~~:nera.lly plural parts) of a single stre~.~s-tube slit can be driven 15 in this clay and the lidar ia~ges separately isaterpreted do~~nstre~..
let another option is to use t~~o different ~.~ sections (not .~ho~~ra) , with diffe rent ~~avelwngth sensitivities, in lieu of a single converter 10 - and generally without optical filters. ~ more-spe-cific and more sophisticated implementation that better conserves 20 optical-signal power uses a diffraction grating 503 (Fig. 26) in-stead of filters, to separate the wavebands of interest.
These plural separated wavelength bands 7~,,, ?~, . . . advanta-geously proceed to respective separate detector stages 513-1, 513-2, . . . which are the front-end stages of respective separate wave-25 length converters 10-1, 10-2, . . . . These in turn respectively provide optical signals 522°-1, 522'-2, . . . to plural slits (Slit 1, Slit 2, . . .) at the photocathode 52Q° of the streaks tube 518.
~s c~i.ll no~~ be appreci~,tee~., many a~ba.~~-a.nc~-a~~tc~a options a.re ~aossi~al.e ~,~ith res~a~ct t~ t~a~ s~a~cific c~m~a~xae~ats anc~. modalities s~aoc~ in the 3o plural-c~a~r~~.x~d c~nfa.gu.~:~.tion~ (~°igs. 2~ t~aro~ac~Ya 2~a) ~.isc~as~ec~ ~aer~.
Hy capturing ia~.~.g~s in a single stres.~~ tube concurrently, u.sg~ag any of the systems under discussion (fiefs. 2~ th~.ouch 2S) , the i~a-vention enables the interpretive parts 3~ of the system to develop s5 difference signals, or ratio signal., as bet~~een the plural spectr~.l regions. In this way the invention becomes a system capable of, for example, differential-intensity, or clifferential-absorbance, lidar _rectroscopy as between, e. a., the far-IR and the W - or other such combinations of spectral regions.
s o) Claiming notes In accompanying apparatus claims generally the term "such" a.s used (instead of "said" or "the") a.n the bodies of the claims, when reciting elements of the claimed invention, for referring back to 1o features which are introduced in preamble as part of the context or environment of the claimed invention. The purpose of this conven-tion is to aid in more particularly and emphatically pointing out which features are ele~nts of the claimed invention, and which are parts of its c~nte~~t - and therekay to more distinctly claim tYae 15 i.n~~nt~.~n .
The foregoing disclosure is intended t~ be merely exemplary, and not to limit the scope of the invention - which is to be 2o determined by reference to the appended claims.
p) References:
25 1. Gleckler, Anthony D., and A. Gelbart, "Three-dimensional imag-ing polarimetry," Laser radar technology and applications VI, Pro-ceedine~s of PIE Vol. ~3'?'7, ~erosense (Florida X001) C-~lbart, usher, "Fl~wh la.dar ba. ed on a~ulti~ale-slit stbea~~ tubs ir~ac~ia~e~ lida,r", 7Lase.r Radar T~ch~aology aa~c~ L'~~a~alicatao~a,s VII, Fr~-so cea~.a.~.~s of ~FI~ ~'ol. Q'~~~, ~~r~sen.se (~°lobida ~00~) Costell~, ~e~x3~ae~G~a G~. , ~fi'"~-~'3:1'c.-'' '~~'. G'''~~2i, Gad' ~.
I2:~s~ris, R~ss G'~. h~.
R~a~, and R~b~rt ~ . gneiss , "" Transferred elect:~n bah~t~ca.t~a~ade ~~i~~
greater than 20~ ~a.~.ntum ~fficiea~cy beyond 3 ~.cron", ~T~a.oto'~tectors and P~~~er deters II at 3'77-~~, editors ~~.thleen Rlursy and ~ennetYa s5 ~.ufa~ann (San Diego July ~-3~, 3~~5) 4. Calmes, Lonnie K., James T. Murray, William L. Austin, and Richard C. Powell, "Solid-State Raman Image Amplification," Proceed-ings of SPIE Vol. 3382 (1998) 5. Bowker, Kent, and Stephen C. Lubard, "Displaced-beam confocal-reflection streak lidar apparatus with strip-shaped photocathode, for imaging very small volumes and objects therein", United States Patent 6,400,396 (2002) 6. MeLean, J. W., and J. T. Murray, "Streak tube lidar allows surveillance,'° Laser Focus World at 171-76 (January 1998) 7. Francis, D., H. L. Chen, W. Yuen, G. Li, and C. Chang Hasnain, "Monolithic 2D-VCSEL array with >2W CW and >5W pulsed output power,"
Electronics Letters Vol. 34, 2132 (7.998) 8. Fuji~~ero~ online product literature http://~-~~'a.fuji~ero~.co.jp /eng~/product/vcsel/overvie~ca.hta~l (January 2003) z5 9. Hone~asvell onli~ae ~arod.°~.ct literature http:
//content.hoaaey~~ell . coax/vc.~el/ca~aabilities/~.onolithic . stm (Ja,nua.ry 2003)

Claims (38)

1. Apparatus for detecting objects and determining their distance, to form a two-dimensional or three-dimensional image; said apparatus comprising:

means for receiving light scattered from such objects and in response forming a corresponding light of a different wavelength from the scattered light; and means for time-resolving the corresponding light to determine respective distances of such objects.

2. The apparatus of claim 1, further for use in determining re-flectance of the objects; and wherein the receiving-and-forming means comprise:

means for measuring and recording gray-level information in the received and formed light.

3. The apparatus of claim 1, wherein the receiving-and-forming means comprise:

a first, optointermediate stage that receives the scattered light and in response forms a corresponding intermediate signal; and a second, intermedioptical stage that receives the intermediate signal and in response forms the corresponding light.

4. The apparatus of claim 3, wherein:
the intermediate signal comprises an optical signal.

5. The apparatus of claim 3, wherein:
the time-resolving means comprise a streak lidar device.

6. The apparatus of claim 3, further comprising:
a light source; and means for projecting pulses of light from the source toward such objects for scattering back toward the receiving-and-forming means.

7. The apparatus of claim 5, wherein:
the streak lidar device is incorporated into a repetitively pulsed pushbroom system.

8. The apparatus of claim 7, further comprising:
an aircraft or other vehicle transporting the receiving-and-forming means and the streaks lidar device relative to such objects.

9. The apparatus of claim 5, wherein:
the streak lidar device comprises a multislit streak tube.

10. The apparatus of claim 3, wherein:
the time-resolving means comprise a flash lidar system.

11. The apparatus of claim 3, wherein:
the intermediate signal comprises an electronic signal;
the first stage comprises an optoelectronic stage; and the second. stage comprises an electrooptical stage.

12. The apparatus of claim 10, wherein:
the optoelectronic stage comprises light-sensitive semiconduc-for device.

13. The apparatus of claim 11, wherein:
the semiconductor devices comprise PIN diodes.

14. The apparatus of claim 11, wherein:
the semiconductor devices comprise avalanche photodiodes.

15. The apparatus of claim 12, wherein:
the electrooptical stage comprises vertical-cavity surface-emitting lasers connected to receive the electronic signal from the PIN diodes.

16. The apparatus of claim 12, wherein:
the electrooptical stage comprises devices selected from the group consisting of:
edge-emitting lasers, quantum diodes, quantum-dot lasers, and microelectromechanical systems;
said devices being connected to receive the electronic signal from the PIN diodes.

17. The apparatus of claim 10, wherein:
the electrooptical stage comprises vertical-cavity surface-emitting lasers.

18. The apparatus of claim 10, wherein:
the electrooptical stage comprises light-emitting diodes.

19. The apparatus of claim 1, further comprising:
utilization means responsive to the time-resolving means.

20. The apparatus of claim 19, wherein the utilization means are selected from the group consisting of:
interpretive means for characterizing such objects based on the time-resolved light;
a monitor that displays an image of such objects for viewing by a person at the apparatus;
a monitor at a base station for reviewing, such objects or rela-ted data received from the resolving by means by telemetry;
a data-processing device for analyzing such objects or images of them;
automatically operated interpretive modules that determine whether particular conditions are met;
announcement-broadcasting means or other automatic physical apparatus connected to operate in response to the time-resolving means;
means for enabling or denying access to secure facilities through operation of doors and gates, or access to computer systems or to financial services including but not limited to credit or banking;
means for determination of hostile conditions, and resulting security measures including but not limited to automatically de-ployed area-sealing bulkheads

21. The apparatus of claim 1, wherein:
the receiving and forming means comprise discrete arrays of light-sensing and light-producing components respectively.

22. The apparatus of claim 21, wherein:
the receiving and forming means further comprise a discrete ar-ray of circuitry for controlling the forming means in response to the receiving means.

23. The apparatus of claim 1, wherein:
the receiving and forming means comprise at least one monolith-ic hybrid of light-sensing and light-producing components.

24. The apparatus of claim 23, wherein:
the monolithic hybrid further comprises circuitry for control-ling the forming means in response to the receiving means.

25. A method for detecting and ranging objects, said method com-prising the steps of:
receiving light scattered from the objects;
in response to the scattered light, forming a corresponding light of a different wavelength from the scattered light; and time-resolving the corresponding light to determine respective distances of such objects.

26. The method of claim 25, further for use in determining reflec-tance of the objects; and wherein:
the receiving step preserves at least some gray-level informa-tion in the scattered light; and the forming step also preserves at least some of the gray-level information.

27. The method of claim 25; wherein:
the receiving step receives the scattered light in plural wave-length bands; and the forming step forms the corresponding light in substantially a single, common wavelength band.

28. The method of claim 27, wherein:
the plural wavelength bands include at least one ultraviolet wavelength.

29. The method of claim 28, wherein:
the plural wavelength bands include at least one near-infrared wavelength.

30. The method of claim 27, wherein:
the receiving step includes receiving the plural wavelength bands at plural slits, respectively, of a plural-slit streak camera.

31. The method of claim 30, further comprising the step of:
before the receiving step, transmitting light in said plural wavelength bands, substantially simultaneously, toward the objects.

32. The method of claim 27, wherein:
the receiving step includes receiving the plural wavelength bands at plural times, respectively.

33. The method of claim 32, further comprising the step of:
before the receiving step, transmitting light in said plural wavelength bands, at respective plural times, toward the objects.

34. The method of claim 27, further comprising the steps of:
deriving plural signals from the received light in the plural wavelength bands, respectively; and finding differences or ratios between signals received in the plural wavelength bands.

35. Apparatus for detecting objects and determining their distance and reflectance, to form a two-dimensional or three-dimensional image; said apparatus comprising:
a light source; and means for projecting pulses of light from the source toward such objects for scattering back toward the receiving-and-forming means;
means for receiving light scattered from such objects and in response forming a corresponding light of a different wavelength from the scattered light, preserving gray-level information in said received and corresponding light; and means, comprising a streak camera, for time-resolving the corresponding light to determine respective distances and reflectan-ces of such objects;
wherein the receiving-and-forming means comprises:
a first, optoelectronic stage, comprising an array of light-sensitive PIN diodes, that receives the scattered light and in re-sponse forms a corresponding electronic signal;
a second, electrooptical stage, comprising an array of verti-cal-cavity surface-emitting lasers connected to receive the elec-tronic signal from the PIN diodes, that receives the electronic signal and in response forms the corresponding light; and an electronic circuit array connecting the electronic signal from the first stage to the second stage, and modifying the signal to operate the second stage.

36. The apparatus of claim 35, wherein:
the streak lidar device is incorporated into a repetitively pulsed pushbroom system.

37. The apparatus of claim 36, further comprising:
an aircraft or other vehicle transporting the receiving-and-forming means and the streak lidar device relative to such objects.

38. The apparatus of claim 37, further comprising:
utilization means responsive to the time-resolving means.