CN102944310B - Spectral resolution adjustable interference imaging spectrometer - Google Patents

Abstract

The invention relates to a spectral resolution adjustable interference imaging spectrometer which comprises a front telescopic system, a polarizer, two identical Wollaston prisms, an analyzer, an imaging mirror and a plane array detector which are sequentially arranged in a same optical path. Crystal optical axes of a left wedge plate of a first Wollaston prism and a right wedge of a second Wollaston prism are parallel to incident planes of the prisms and perpendicular to a principal optical axis of the optical path, and crystal optical axes of a right wedge plate of the first Wollaston prism and a left wedge of the second Wollaston prism are perpendicular to the crystal optical axis of the left wedge plate of the first Wollaston prism, the crystal optical axis of the right wedge of the second Wollaston prism and the principal optic axis of the optical path. The interference imaging spectrometer is adjustable in spectral resolution, and the adjusting range of the spectral resolution is wide. By means of the interference imaging spectrometer, as for different detection objects, only useful spectroscopic data are acquired so that requirements for multiple-target and multitask spectrum image detection can be met, occupancy of memory space and communication bandwidth can be substantially reduced, data processing time can be effectively reduced, signal to noise ratios of systems are increased, and overall performances of the instrument can be optimized.

Description

The inteference imaging spectrometer that a kind of spectral resolution is adjustable

Technical field

The present invention relates to a kind of inteference imaging spectrometer, the adjustable inteference imaging spectrometer of a kind of especially spectral resolution.

Background technology

Imaging spectral technology is a kind of advanced optical detector technology that can simultaneously obtain every bit spectral information on target image and image growing up the eighties in 20th century, its data of obtaining are called as " data cube " ［ Sellar R G, Boreman G D2005Opt.Eng.44013602. ］.The instrument of realizing this function is imaging spectrometer.Obtain the difference of principle according to spectrum, imaging spectrometer generally can be divided into four kinds of color dispersion-types, interfere type (Fourier transform type), optical filter type, calculating computed tomography type.Wherein adopting maximum is color dispersion-type and interfere type.Color dispersion-type adopts prism or grating to obtain target optical spectrum as dispersion element, maturation, steady performance possess skills, but structure relative complex, realize high spatial resolution and spectral resolution and all need little entrance slit, limit luminous flux and signal to noise ratio (S/N ratio) [Sellar R G, Boreman G D2005Appl.Opt.441614.], be unfavorable for the detection of low light level target.Interfere type utilizes the Fourier transform spectral characteristic of two-beam interference to realize obtaining of spectroscopic data, has the advantages such as luminous flux is large, wavelength accuracy is high, spectrographic detection wide ranges.Early structure mostly is Michaelson, and under same spectra resolution, luminous flux is about 190 times [Bell R J1972Introductory Fourier TransformSpectroscopy (New York:Academic Press) .] of grating type.But when its work, need precision, stable index glass to scan, therefore cannot carry out real-time detection to target optical spectrum information, applied environment and condition are also extremely restricted.For addressing this problem, develop static inteference imaging spectrometer, become main flow [Barducci A, the Guzzi D of interference type imaging spectrometer, Lastri C, Marcoionni P, Nardino V, Pippi I2010Opt.Express1811622.], [Li J, Zhu JP, Wu HY2010Opt.Lett.353784.] [Hou is X.2011Opt.Commun.2841127. for LiJ, ZhuJP].

Static inteference imaging spectrometer is divided into again reflection-type (as Sagnac inteference imaging spectrometer) and birefringence mode according to the difference of its light channel structure and beam splitter.The former mainly adopts semi-transparent semi-reflecting beam splitter, plane mirror to realize the two-beam interference of incident light.The latter adopts birefringece crystal beam splitter that incident light is divided into the orthogonal two bunch polarized lights of direction of vibration, then makes two-beam have identical direction of vibration and interfere by analyzer.Develop at present with Wollaston prism [Smith WH, Hammer PD1996Appl.Opt., 352902.], [Fox DJ, Velde HT, Preza C, O ' Sullivan JA, Smith WH, Woolsey TA2006Appl.Opt.453009.] and Savart polariscope [Hou X.2011Opt.Commun.2841127. for Li J, ZhuJP] the beam splitter birefringence inteference imaging spectrometer that is core.Bring into play significant role in fields such as earth resources generaI investigation, disaster alarm and monitoring, environmental pollution monitoring, weather forecast, deep space explorations.

Regrettably,, once above-mentioned two kinds of quiescent imaging spectrometer systems are definite, the parameters such as its spectral resolution, spectral range just can not change.In order to meet the demand of different task, must possess high spectral resolution and wide spectral range ［ Chen B, Wang MR, Liu ZQ, Yang JJ2007Opt.Lett.321518. ］, this will cause instrument signal to noise ratio to decline, and spectral image data amount is increased sharply.And the decline of signal to noise ratio (S/N ratio) can affect Image Acquisition quality, the increase of data volume can take more storage space and wider communication channel, has also extended the data acquisition and processing (DAP) time, and these problems show particularly outstandingly in Aero-Space remote sensing.

Taking the contained Sagnac spatial modulation of China's Chang'e I type inteference imaging spectrometer as example, owing to being subject to the restriction of storage space and communication bandwidth on star, its spectral resolution is 325.25cm ^-1corresponding spectrum channel number is 32, and for the contradiction between balance required by task spectral resolution and data volume, the interference fringe data that CCD collects can only be transmitted half, therefore capacity usage ratio has also reduced 50%[Xue B2006Ph.D.Dissertation (Xi ' an:Xi ' an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences) (in Chinese), Xue Bin 2006 doctorate papers (Xi'an: Xian Inst. of Optics and Precision Mechanics, Chinese Academy of Sciences) ］.Become the Main Bottleneck of restriction Imaging Spectral Remote Sensing Instrument Development.

2007, once someone proposed over-rotation Savart polariscope and regulates horizontal shear capacity to realize the method for spectrometer resolution adjustment, but the method range of adjustment is very narrow, and can reduce prism clear aperature [simple little China after rotation, open the pure people, Sun Yao, Wu Lei .2007 Acta Optica, 27643.], be unfavorable for practical application.

Summary of the invention

The object of the present invention is to provide a kind of simple and compact for structure, luminous flux is large, stability is high, technique realizes simple and can realize target two dimensional image and the detection of one dimension spectral information, also there is the adjustable unique advantage of spectral resolution simultaneously, in meeting multitask needs, can reduce unnecessary data storage space and number of communications are passed to taking of bandwidth, shorten data processing time, improve system signal noise ratio, thereby make instrument overall performance reach the optimum adjustable inteference imaging spectrometer of spectral resolution.

For achieving the above object, the technical solution used in the present invention is: comprise the preposition telescopic system that is successively set in same light path, the polarizer, two identical and first and second Wollaston prism WP that spacing is adjustable ₁and WP ₂, analyzer, imaging lens and planar array detector, wherein a Wollaston prism WP ₁left wedge and the 2nd Wollaston prism WP ₂the optical axis of crystal of right wedge is parallel to the prism plane of incidence, and vertical with light path primary optical axis, a Wollaston prism WP ₁right wedge and the 2nd Wollaston prism WP ₂the optical axis of crystal of left wedge with a Wollaston prism WP ₁left wedge, the 2nd Wollaston prism WP ₂the optical axis of crystal of right wedge and light path primary optical axis are all vertical.

For color dispersion-type and static interference type imaging spectrometer spectral resolution fix, the problem such as system effectiveness is not in full use, it is the imaginary light source of two infinite points by target light source lateral shear that the present invention utilizes two identical Wollaston prisms, and there is certain horizontal shear capacity between two light sources, be imaged on focal plane and interfere by imaging lens again, thereby obtain target optical spectrum, view data, real-time, the high spectral resolution (adjustable) of realize target are surveyed.

This instrument system have coaxial light path, simple and compact for structure, without index glass scanning mechanism, luminous flux is large, stability is high, technique realizes simple and can obtain the detecting function of target two dimensional image and one dimension spectral information, also has the unique advantage that spectral resolution is adjustable and range of adjustment is wider simultaneously.For the different detections of a target, utilize this technology, only obtain useful spectroscopic data, can meet the needs of multiple goal, the detection of multitask spectrum picture, can significantly reduce again taking storage space and communication bandwidth, effectively shorten data processing time, improve system signal noise ratio, thereby make instrument overall performance reach optimum.

Brief description of the drawings

Fig. 1 is structural representation of the present invention, and its beam splitter is by two identical first and second Wollaston prism WP ₁(31), WP ₂(32) composition.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

Referring to Fig. 1, the present invention includes the preposition telescopic system 1 that is successively set in same light path, the polarizer 2, two first and second Wollaston prism WP identical and that spacing is adjustable ₁31 and WP ₂32, analyzer 4, imaging lens 5 and planar array detector 6, wherein a Wollaston prism WP ₁31 left wedges and the 2nd Wollaston prism WP ₂the optical axis of crystal of 32 right wedges is parallel to the prism plane of incidence, and vertical with light path primary optical axis, a Wollaston prism WP ₁31 right wedges and the 2nd Wollaston prism WP ₂the optical axis of crystal of 32 left wedges with a Wollaston prism WP ₁31 left wedges, the 2nd Wollaston prism WP ₂the optical axis of crystal of 32 right wedges and light path primary optical axis are all vertical.

By regulating WP ₁31 and WP ₂32 interval can change the spectral resolution of spectrometer.

Work of the present invention is as follows: the light that target is sent becomes directional light after preposition telescopic system 1 is collected, collimated, and becomes a branch of linearly polarized light after the polarizer 2, and this bunch polarized light is through first and second Wollaston prism WP ₁31 and WP ₂after 32, be divided into two bundles and there is certain horizontal shear capacity, the direction of propagation is parallel, amplitude equates, the orthogonal linearly polarized light of direction of vibration, again by analyzer 4, two bunch polarized lights have had identical direction of vibration, are finally imaged mirror 5 and converge to and on focal plane, form target image and interference fringe, and received by planar array detector 6.The interference image receiving, by the operation such as reconstruct, demodulation, can obtain complete two dimensional image and one dimension spectroscopic data about target.

Need difference to be, British scholar Harvey and Fletcher-Holmes[Harvey AR, Fletcher-Holmes DW2004Opt.Express125368.] the gazing type birefringence inteference imaging spectrometer of two Wollaston prisms of a kind of employing also once proposed, utilize first Wollaston prism to make beam splitter, second Wollaston prism moves up and down and realizes the function of similar Michelson index glass, this from the present invention, have essence different.

The interference fringe that the present invention is obtained is carried out Fourier transform and can be obtained target optical spectrum data, its resolution can be expressed as [Zhang G Z1988Principle of Fourier Transform spectroscopy (Guangzhou:Zhongshan University Press) (in Chinese) Zhang Guangzhao, fourier transform spectroscopy principle (Guangzhou: publishing house of Zhongshan University)]:

$\mathrm{\Δ\σ}=\frac{1}{{\mathrm{OPD}}_M}---\left(1\right)$

The wave number that in formula, Δ σ is spectral resolution represents mode, and its unit is cm ^-1, OPD _mthe maximum optical path difference that can reach for interferometer.Optical path difference OPD can be expressed as

$\mathrm{OPD}=d\sin i=d\frac{x}{f}---\left(2\right)$

In formula, d is WP ₁and WP ₂the separately spacing of two bundle directional lights, i.e. horizontal shear capacity, i is angle of incidence of light, and f is imaging lens focal length, and x is the coordinate perpendicular with interference fringe, is positioned at center, imaging lens focal plane its zero point.

As can be seen from the above equation, the spectral resolution of inteference imaging spectrometer is by beam splitter horizontal shear capacity d, imaging lens focal distance f, jointly determine perpendicular to CCD pixel number and the pixel dimension of interference fringe direction (being commonly referred to as spectrum dimension).Once inteference imaging spectrometer device in the past completes process and assemble, its beam splitter shearing displacement, imaging lens focal length and ccd detector parameter just can not change, and are therefore difficult to realize the adjusting of spectral resolution.And the spectral resolution that the present invention proposes is adjustable, its key is just the adjustable of beam splitter horizontal shear capacity.

Adopt Ray-tracing Method to derive the optical path difference in crystal, thereby the expression that can obtain spectral resolution is

${\mathrm{\φ\σ}}_{\mathrm{SZBIS}}=\frac{1}{(\frac{t\tan {\mathrm{\θ}}_{2\mathrm{oe}}+g{\tan \mathrm{\φ}}_{2\mathrm{oe}}}{1-\tan \mathrm{\θ}\tan {\mathrm{\θ}}_{2\mathrm{oe}}}+\frac{t\tan {\mathrm{\θ}}_{2\mathrm{eo}}+g{\tan \mathrm{\φ}}_{2\mathrm{eo}}}{1+\tan \mathrm{\θ}\tan {\mathrm{\θ}}_{2\mathrm{eo}}})\sin i}$

$=\frac{f}{(\frac{t\tan {\mathrm{\θ}}_{2\mathrm{oe}}+g\tan {\mathrm{\φ}}_{2\mathrm{oe}}}{1-\tan \mathrm{\θ}\tan {\mathrm{\θ}}_{2\mathrm{oe}}}+\frac{t\tan {\mathrm{\θ}}_{2\mathrm{eo}}+g{\tan \mathrm{\φ}}_{2\mathrm{eo}}}{1+\tan \mathrm{\θ}\tan {\mathrm{\θ}}_{2\mathrm{eo}}})x}---\left(3\right)$

In formula, t is the thickness of beam splitter monolithic Wollaston prism, and g is two Wollaston prism pitch, and θ is prism structure angle, and i is light maximum incident angle, and f is imaging lens focal length, and x is half length of CCD light-sensitive surface spectrum dimension.θ _2oe, θ _2eobe respectively oe light and eo light at WP ₁incident angle on right interface, φ _2oeand φ _2eofor they aerial refraction angles.

Can be found out by above analysis, the adjusting that realizes spectral resolution by changing airspace g is feasible.Here the lower limit that should be noted that spectral resolution range of adjustment is that airspace g gets zero, and its upper limit is subject to the restriction of CCD spectrum dimension pixel number, must meet sampling thheorem ［ Sellar R G, Rafert J B1994 Opt.Eng.333087. ］:

${\mathrm{\Δ\σ}}_{\mathrm{SZBIS}}\≥\frac{4}{N\·{\mathrm{\λ}}_{\min }}---\left(4\right)$

In formula, N is CCD spectrum dimension pixel number, λ _minsurvey wavelength for spectrometer is minimum.Accordingly, the requirement that just can survey for different target, the structural parameters of design beam splitter, make its spectral resolution adjustable extent can meet the needs of multitask.

The inteference imaging spectrometer that the present invention proposes it is advantageous that and adopted brand-new beam splitter structure compared with sweeping type inteference imaging spectrometer with other birefringence inteference imaging spectrometers or window, realized spectral resolution regulatory function.Can regulate easily and effectively spectral resolution, in meeting multitask needs, can reduce unnecessary data storage space and number of communications are passed to taking of bandwidth, shorten data processing time, improve system signal noise ratio, thereby make instrument overall performance reach optimum.Secondly, the principle of work of this system has determined that it does not need the index glass in similar Michelson interferometer to push away spectrum, the view data of sweeping to obtain target, and therefore vibration resistance is strong, has good Aero-Space and field environment adaptability.The 3rd, this system is without slit, and luminous flux is high, with respect to spatial modulation type spectrometer, adopts window to sweep type data acquisition, cancels the setting of slit, has visual field, 2D space.In addition, whole system is simple and compact for structure, and design, processing, modulation conveniently, are very beneficial for the promotion and application of novel imaging spectral polarimeter.

In addition, the present invention does not have index glass scanning mechanism, coaxial light path, simple and compact for structure, luminous flux is large, stability is high, technique realizes real-time detection function simple and energy realize target two dimensional image and one dimension spectral information, also have the adjustable unique advantage of spectral resolution, the spectrally resolved ability of instrument is adjustable continuously in wide region simultaneously.A large amount of practical experience and theoretical researches show, different observed objects, and different application occasion is very different to the requirement of the spectrally resolved ability of remote sensor.For different application, utilize spectral resolution regulation technology, only obtain useful spectroscopic data, can meet mission requirements, can reduce again the taking of storage space and communication bandwidth, shorten data processing time, thereby make instrument overall performance reach optimum.

Claims (1)

1. the adjustable inteference imaging spectrometer of spectral resolution, is characterized in that: comprise the preposition telescopic system (1) that is successively set in same light path, the polarizer (2), two identical and first and second Wollaston prism WP that spacing is adjustable ₁and WP (31) ₂(32), analyzer (4), imaging lens (5) and planar array detector (6), wherein a Wollaston prism WP ₁(31) left wedge and the 2nd Wollaston prism WP ₂(32) optical axis of crystal of right wedge is parallel to the prism plane of incidence, and vertical with light path primary optical axis, a Wollaston prism WP ₁(31) right wedge and the 2nd Wollaston prism WP ₂(32) optical axis of crystal of left wedge with a Wollaston prism WP ₁(31) left wedge, the 2nd Wollaston prism WP ₂(32) optical axis of crystal of right wedge and light path primary optical axis are all vertical.