WO1999022219A1

WO1999022219A1 - Fluid cavity particle measuring system and methods

Info

Publication number: WO1999022219A1
Application number: PCT/US1998/022711
Authority: WO
Inventors: Dennis J. Knowlton; Larry Fabiny
Original assignee: Particle Measuring Systems, Inc.
Priority date: 1997-10-28
Filing date: 1998-10-27
Publication date: 1999-05-06
Also published as: WO1999022219A8

Abstract

A system detecting particulates within a liquid flow includes a solid state laser exciting a resonant cavity. It contains a liquid cavity flowing liquid through the beam. Optical elements transmit the beam through the liquid cavity such that laser scatter is indicative of particulates within the flow. The system can include a frequency enhancing crystal such that the beam also includes higher frequency lasing. One of the elements is preferably a reflector at one end of the resonator, so that fewer elements and reflections are present within the cavity. The flow is generated by a nozzle jet or by an inviscid flow jet. Certain optical elements can be made into Brewster windows. The resonant cavity can be responsive to an external laser. It has at least one resonator optical element for reflecting the light energy within the resonant cavity and a feedback system maintains its resonance locked to the external laser.

Description

Fluid Cavity Particle Measuring System and Methods

Related Applications

This application is a continuation-in-part of commonly owned and co-pending U.S. Application No.08/891,361, and of U.S. Provisional Application No. 60/063,424, each of which is expressly incorporated herein by reference.

Background of the Invention

Particle detection systems are known. Typical systems utilize laser energy to illuminate a particle flow within a sample volume and a detector to measure scattered laser energy indicative of particle size and passage through the flow. Such systems can, for example, be used to measure particle size and to count particles passing through the sample volume.

Certain particle detection systems utilize intracavity laser power to illuminate the sample volume to increase the sensitivity of detecting particles passing through the sample volume. By way of example, U.S. Patent No. 5,726,753 describes one such system; and U.S. Patent No. 5,642,193 describes another laser-based particle counter.

U.S. Patent Nos. 5,726,753 and 5,642,193 provide useful background to the invention and are thus incorporated herein by reference.

It is desirable in certain circumstances to detect particles within a liquid flow, as opposed to a fluid (e.g., air) flow; and improvements to the above systems are thus desirable to efficiently couple laser energy through a flow within a liquid sample volume. One object of the invention thus provides a laser-based particle detection system which includes an intracavity liquid flow. Another objects of the invention is to provide systems and methods for detecting particles within a liquid intercavity flow with improved efficiency and with fluid-compatible frequencies. Yet another object of the invention is to provide improvements to fluid particle measuring systems. Other objects of the invention will become apparent in the description that follows.

Summary of the Invention

In one aspect, the invention provides a particle detection system for detecting particulates within a liquid flow. A solid state laser generates a lasing beam within a resonant cavity, and a liquid cavity generates a liquid flow through the beam. The liquid cavity has a housing and one or more optical elements coupled with the housing to contain the liquid within the liquid cavity. The optical elements transmit the beam through the liquid cavity such that the beam and the flow interact to scatter light indicative of particulates within the flow. One or more detectors are used to detect the scattered light.

In another aspect, one of the optical elements includes a frequency enhancing crystal such that the beam also includes higher frequency lasing within the resonant cavity. By way of example, the crystal can be a frequency doubling crystal. Therefore, if for example the solid state laser is a YAG laser operating at approximately 1064nm, the higher frequency lasing would be 532nm light.

Preferably, the detectors are responsive to scattered light from the higher frequency lasing, as these higher frequencies are usually better suited for transmission through fluids such as water.

In another aspect, the system includes a processor coupled to the detectors for processing detector signals to determine one of particle size, count and frequency within the flow.

To provide more efficient resonance, at least one of the elements is preferably constructed and arranged to operate as a reflector at one end of the resonator. In this manner, fewer elements and reflections are present within the cavity, increasing the energy and efficiency of the interaction between the flow and the lasing beam. In one aspect, the flow is generated by a nozzle jet; and in another aspect the flow is generated by an inviscid flow jet.

To further increase efficiency within the resonant cavity, one or more of the optical elements are made into Brewster windows which reduce reflections within the resonant cavity.

In still another aspect, the invention provides a particle detection system which includes a resonant cavity that is responsive to an external laser to constructively interfere light energy in the form of a lasing beam within the resonant cavity. The resonant cavity has at least one resonator optical element for reflecting the light energy within the resonant cavity. A fluid cavity generates a fluid flow through the lasing beam and has a housing and one or more optical elements coupled with the housing to contain fluid within the fluid cavity. The optical elements transmit the lasing beam through the fluid cavity such that the lasing beam and the flow interact to scatter light indicative of particulates within the flow. As above, or more detectors detect the scattered light for subsequent processing.

The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.

Brief Description of the Drawings

A more complete understanding of the invention may be obtained by reference to the drawings, in which:

FIG. 1 is a schematic diagram of a generalized particle detection system;

FIG. 2 is a sectional view of an inviscid flow particle detection system; FIG.3 illustrates a fluid cavity particle detection system constructed according to the invention;

FIGs. 4-4C illustrate alternative fluid cavity particle detection systems constructed according to the invention;

FIG. 5 shows a cross-sectional view of a frequency enhanced fluid cavity particle detection system constructed according to the invention; and

FIGs. 6 and 6A illustrate alternative feedback-controlled particle detection systems constructed according to the invention.

Detailed Description of the Drawings

By way of background, FIG. 1 depicts a simplified schematic for a generalized prior art particle detection system 10. Sample fluid 12 contains particles 14 and flows in the direction indicated by arrow 16. Sample fluid 12 is typically a fluid or a gas. Sample fluid 12 may be contained within a conduit (not shown) or may be a stream of fluid as shown in FIG. 1 and may be circular, square or otherwise in cross-sectional shape. Laser 18 produces a beam of light 20 that is shaped by beam shaping optics 22. The resulting beam 24 intersects sample fluid 12 and is incident upon particles 14. Scattered light 26 is caused by the scattering of beam 24 off of particles 14. Scattered light 26 is collected by collection optics 28 and imaged on detector 30. Beam 24 is absorbed in light dump 32 such that beam 24 does not reflect back into sample fluid 12. Detector 30 produces an output signal over path 34 that is indicative of particles 14. Processor 36 processes the output signal received over path 34 to produce an output representative of the size and/ or number of particles 14 in sample fluid 12. There are various and multiple known alternatives for each of the basic elements shown in FIG. 1. For example, collection optics 28, shown in alignment with beam 24 in FIG. 1, could instead be positioned to collect light scattered on a different axis. Various different types of detectors 30 are known as are different types of processors 36. All of these various approaches are known to those skilled in the particle detection art and do not form part of the present invention.

Intersection region 38 is the area of intersection between sample fluid 12 and beam 24. Sample region 40 is the area within intersection region 38 from which scattered light 26 is imaged upon detector 30. There are multiple considerations including, but not limited to, measurement resolution and measurement sensitivity that determine the size of intersection region 38 and sample region 40. For example, a highly sensitive measurement (one capable of detecting relatively small particles) requires a tightly focused light beam 24 within the sample fluid 12. There is a direct relationship between the size of the light beam 24 and the sensitivity of the particle detection measurement since, for a given laser, a more focused beam provides more power per unit area than a less focused beam. A very narrow light beam, however, typically means that only a portion of the sample fluid 12 passes through the intersection region (an in situ measurement). A disadvantage of in situ measurements is that not all particles are illuminated with light of the same intensity. Beam 24 has a gaussian intensity distribution; thus a particle illuminated by an "edge" of beam 24 is illuminated with a lower intensity light than a particle illuminated in the center of beam 24. A further limitation is that scattered light 26 must be scattered by particles 14 moving with a relatively uniform velocity. Processor 36 operates with the assumption that all of scattered light 26 is scattered by particles 14 moving with relatively uniform velocity. Existing particle detection systems employ sample fluid streams characterized by laminar, developed flow where a fluid velocity profile exists orthogonal to the flow direction. Thus even within the intersection region 38 there is, in existing systems, only a small portion of sample fluid 12 that is moving with relatively uniform velocity and is illuminated with a relatively uniform intensity of light. Sample region 40 is typically defined in existing particle detection systems such that only scattered light 26 from particles 14 moving with relatively uniform velocity and illuminated with relatively uniform light intensity is imaged on detector 30. This requirement further reduces the resolution of the detection system and increases the sample time. The size of sample region 40 is defined by sample fluid 12, beam 24, collecting optics 28, and detector 30, as known by those skilled in the particle detection art.

FIG. 2 depicts an inviscid flow particle detection system 50. System 50 includes deceleration chamber 52, collection chamber 54, detection system 56 and illumination source 58 (e.g., a laser 18, FIG.1). Deceleration chamber 52 includes an inlet 60 through which a sample fluid flows from a process line (not shown) through chamber wall 62 to an interior 64 of deceleration chamber 52. In the bottom of deceleration chamber 52 is inviscid flow nozzle 66 having aperture 68 formed therein. Sample fluid flows into inlet 60, through deceleration chamber 52 and into collection chamber 54 through inviscid flow nozzle 66 as inviscid fluid flow jet 70. The velocity of the sample fluid through deceleration chamber 52 is significantly less than the velocity of the fluid in inviscid flow jet 70. By way of example, the velocity through deceleration chamber 52 is approximately 1/40 that of the velocity of inviscid fluid jet 70. Inviscid fluid nozzle 66 and particularly aperture 68 are discussed in more detail within U.S. Application No. 08/891,361.

Illumination source 58 produces beam 72 which passes through wall 74 of collection chamber 54 by way of illumination entrance window 76. Beam 72 intersects inviscid flow jet 70 at intersection region 78 and exits collection chamber 54 through illumination exit window 80. Light scattered by particles in the sample fluid at intersection region 78 passes through detection window 82 and is imaged by collector optics 84 on detector 86. Detector 86 produces signals over path 88 to processor 90. Processor 90 produces an output of particle size and/ or number. Detection system 56 including collector optics 84, detector 86 and processor 90 are shown schematically in FIG. 3. Those skilled in the art of particle detection systems recognize that there are various known approaches satisfying the requirements of detection system 56.

Collection chamber 54 includes light stops 92 each of which includes an aperture 94. Light stops 92 block light scattered by the interfaces 96 and 98 between the interior 100 of collection chamber 54 and illumination entrance window 76 and illumination exit window 80, respectively. Beam 72 is absorbed by light dump 102 to reduce reflections back into collection chamber 54 or to detection system 56. The sample fluid exits collection chamber 54 through outlets 104 to a process line (not shown). Collection chamber 54 is full of sample fluid. Detection system 56 is operable to distinguish between a particle in inviscid flow jet 70 (moving at a relatively high velocity) and a particle outside of inviscid flow jet 70 (moving at a relatively low velocity). Those skilled in the art also recognize that additional outlets 104 may be used.

FIG. 3 illustrates a fluid cavity particle measuring system 200 constructed according to the invention. System 200 includes an optical pumping source (e.g., a laser diode) 202 which pumps a solid state active medium (e.g., a Nd.YAG crystal) 204 within a laser cavity 206 to create a lasing beam 208. The source 202 emits light energy 210 (e.g., a GaAlAs semiconductor laser emitting at 808nm laser energy) which is collected and focused by optics 212 into the medium 204, thereby pumping the medium 204. Through laser transition caused by pump excitation, the medium 204 generates lasing energy which constructively interferes between optical elements 211a, 211b to form the beam 208. One preferred wavelength of the lasing beam 208 is 1064nm; though those skilled in the art should appreciate that other solid state wavelengths can be obtained. Preferably, surfaces SI, S2 of the cavity 206 are highly reflective at the lasing wavelength; and optical element 211a is made transmissive to light energy 210 to provide for efficient pumping into the cavity 206.

A fluid cavity 220 extends through the cavity 206 such that the lasing beam 208 passes through the cavity 220. The cavity 220 is filled with fluid 222, e.g., a process chemistry generated by a process line (not shown), which enters the cavity 220 along direction 221 through an inlet 220a. A flow 224 is created within the fluid 222 by a flow generator 226. The flow generator can for example be a jet nozzel, known in the art, or an inviscid flow jet such as described in connection with FIG. 2. Fluid 222 leaves the cavity 220 through an outlet 228, illustrated by arrow 229. The lasing beam 208 passes through the fluid cavity 220 and through a pair of opposing optical elements 230a, 230b, which thus seal to the cavity housing 232 to keep the fluid 222 contained within the cavity 220. As described in FIG. 2, particulates within the flow 224 generate scattering 225 due to the interaction between the beam 208 and particles within the flow 224; and at least a portion 225a of the scattered light energy 225 is imaged onto the detector(s) 234 by collection optics 236. A processor 238 couples to the detector(s) 234 via signal line 239 to process detector signals in a manner which determines particle size, count and/ or frequency within the flow 224.

As illustrated in FIG.3, collection optics 236 is made integrally with the housing 232 so as to increase the transmission of scattered light energy reaching the detector 234.

However, those skilled in the art should appreciate that this is not required; and that an optical collection arrangement such as shown in FIG. 2 or FIG.4 can be used instead.

The optical elements 230a, 230b are preferably Brewster windows, known in the art, which operate to minimize reflection of the beam 208 through the cavity 220. The Brewster windows have a Brewster angle (not shown) that are functionally dependent upon the index of refraction of the fluid 222 and the lasing cavity 206 (typically the lasing cavity 206 outside of the fluid cavity 220 is in air, with an index of approximately 1.0).

In the description below, like elements are designated with like reference numerals except that annotation apostrophe(s) indicate variation.

The construction and arrangement of the fluid cavity 220 within the lasing cavity 206 can occur in several ways. FIG. 4, for example, illustrates one fluid cavity 220' which is made integrally with one of the lasing cavity's reflectors 211b'. Cavity 220' nevertheless operates as above; and scattered light 225 is collected by optics 236' and detector(s) 234'. FIG. 4 illustrates a variation from FIG. 3 in that scattered light 225 passes through a window 248 prior to collection by the collection optics 236' and detector(s) 234'. It should be noted that only a few components are shown in FIG.4, for purposes of illustration, and that other components exist to make the system of FIG.4 functional, e.g,. such as a processor 238. The same is true of FIGs.4A and 4B described below.

FIG.4A illustrates another variation of the invention where the active medium 204' is made integrally with the fluid cavity 220". In FIG.4B, both of the elements 230a, 230b of FIG. 3 are functionally replaced by the active medium 204' and one of the resonator elements 211b". In this later configuration, increased lasing intensity is achieved through the flow 224 - thereby increasing the particle detection sensitivity in the scattered radiation - since there are fewer optical interfaces and reflections as compared to the FIG. 4 configuration. The fluid cavity 220'" thus provides improved throughput.

FIG. 4C illustrates a preferred particle detection system 201 of the invention, where the lasing cavity 206' includes a frequency enhancing crystal 250 to generate higher frequency lasing energy within the fluid cavity 220. System 201 operates similar to system 200, FIG. 3, except that the lasing beam 208' now includes constructive wave interference of the higher frequency lasing energy, e.g., 532nm. By way of example, the crystal 250 can be a frequency doubling crystal, known in the art, which generates green light at 532nm. In such a case, surfaces SI, S2 are coated to be highly reflective at both the fundamental lasing frequency, e.g., 1064nm, and the higher frequency lasing energy. In addition, collection optics 236" and detector(s) 234" are designed to detect scattered energy 225' at the higher lasing frequency. By way of example, optics 236" are transmissive to 532nm light energy; and detector(s) 234" detects 532nm light energy so that particle size, count and/ or frequency are attainable through processor 238'.

Those skilled in the art should appreciate that the frequency enhancing crystal can also be made integrally with the fluid cavity. By way of example, in FIG. 3, the optical element 230a can represent a frequency doubling crystal to generate the higher frequency lasing within the cavity 206. In such a configuration, reflections are reduced since lasing occurs through fewer optical interfaces, as compared to FIG.4C. As above, however, the optics 236 and detector 234 are arranged to collect scattered light 225 at the higher lasing frequency. The cavity configurations of FIGs. 4A-4B can also be modified to incorporate a frequency enhancing crystal, either as a separate element (as in FIG.4C) or as an element that is integral with the fluid cavity.

The term "fluid" as used herein preferably refers to a "liquid", though particles within fluids such as aerosols are also measurable in accord -with the invention. The prior art does not adequately address coupling of laser energy into a liquid cavity to improve particle detection. By way of example, when the fluid is water, frequency enhancing crystals are useful in that shorter wavelengths such as 532nm are more transmissive through water as the "fluid" 222 within cavity 220. Longer wavelengths - e.g., 1064nm - are highly attenuated within liquids such as water, thereby reducing signal at the detector and the sensitivity to particulate detection. Those skilled in the art should appreciate that other "liquids" exhibit their own absorption spectra; and laser wavelengths and frequency enhancing crystals should be chosen accordingly to match the transmission band of such liquids. Similarly, the angle of the Brewster's window should be set to the appropriate index of refraction for the given process liquid or fluid relative to the index within the laser cavity.

The flow generator 226 of FIGs.3-4C is either a nozzle jet or an inviscid flow jet described in U.S. Application No. 08/891,361. Nozzle jets are known in the art, and particularly within the art of flow cytometry and hydrodynamic focusing.

FIG. 5 illustrates one preferred embodiment of the invention in an enhanced frequency fluid cavity particle detection system 300 utilizing an inviscid flow jet 301. A pump source 302 such as a diode laser provides active pumping to an active medium 304 within a lasing cavity 306. Light 308 from the source 302 is captured and focussed into the active medium 304 by optics 309; and resulting laser transitions within the solid state element 304 cause emissions that constructively interfere in resonance between resonator optical elements 310a, 310b. A lasing beam 312 is thus generated within the cavity 306. Emissions from the active medium 304 are for example at 1064nm such as from a Nd.YAG crystal.

The inviscid flow jet 301 extends through the cavity 306 and includes optically transmissive elements 314, 316 to pass the lasing beam 312 through the interior 301a of the jet 301. One element 314 is a frequency enhancing crystal such as a frequency doubling crystal known in the art. The other element 316 is preferably a Brewster's window; though a planar window is alternatively acceptable. The elements 314, 316 are made integrally with the housing 318 of the inviscid flow jet 301 so that fluid 320 within the interior 301a is contained.

The frequency enhancing element 314 creates a higher lasing frequency within the cavity 306 so that the lasing beam 312 includes both emissions from the active medium 304 and frequency enhanced lasing from the crystal 314. By way of example, the lasing beam 312 can include constructive interferences between the resonator elements 310a, 310b of both 1064nm and 532nm light.

The inviscid flow jet 301 contains fluid 320 such as semiconductor solutions, chemicals and acids generated from a process (not shown) coupled to the jet 301. Fluid 320 enters the jet 301 through an inlet 322 into the jet's deceleration chamber 301b. The fluid 320 then passes through flow nozzle 324 (and particularly aperture 326) to generate high velocity inviscid flow 328. It is the interaction between the lasing beam 312 and the inviscid flow 328 which provides high particle detectivity by collection of scattered light 330 resulting from that interaction. The scattered light 330 is transmitted through a window 332 (preferably a Brewster's window to minimize reflections therethrough) and collected by collection optics 334 for focusing onto the detector(s) 336. In the preferred embodiment of the invention, the window 332, optics 334 and detector 336 are sensitive or transmissive to scattered light energy 330a from frequency enhanced radiation, e.g., "green light", and not to the primary lasing frequency, e.g., 1064nm. A processor 338 coupled to the detector(s) 336 processes detector signals to determine particle size, count and/ or frequency within the inviscid flow 328.

Fluid from the interior 301a exits the jet 301 through outlets 340 in direction 342.

FIG. 6 illustrates an external fluid cavity particle detection system 400 constructed according to the invention. A solid state laser such as a YAG laser 402 generates a beam 404 which is directed to the system 400. The beam 404 enters the system 400 through optical window 406. The window 406 and the optical element 412 form a resonant cavity 408 within the system 400. The system 400 includes a frequency enhancing crystal 410 (e.g., a frequency doubling crystal) within the resonator 408 formed by the optical elements 406 and 412. The resonant cavity 408 produces a lasing beam 414 formed of both the beam 404 frequency and the enhanced frequency from the crystal 410. Elements 406, 412 are preferably coated to ensure high reflectance for both frequencies within the cavity 408.

In order to achieve resonance within the system 400, a frequency detector 416 monitors the frequency of the beam 404, such as by reflection off of the window 406 (as shown). This detected frequency is coupled to a system controller 418 which in turn "tunes" the resonance within the cavity 408 by movement of one or more optical elements 420 within the cavity 408. By way of example, the controller 418 can drive a motor 422 which moves the element 420 in a manner consistent with continued resonance within the cavity 408 in synch with the frequency of beam 404.

A fluid cavity 430 within the system 400 operates as above to couple a fluid flow 432 through the beam 414 to generate scattered light 415 indicative of particles within the flow 432. Fluid 434 is injected into the cavity 430 via inlet 436; and fluid 434 exits the cavity 430 through outlet 438. A jet 440 (e.g., a nozzle jet or an inviscid flow jet, described above) operates to generate the flow 432. As above, a portion 415a of scattered light 415 is collected through window 441 by collection optics 442 and detector(s) and processor 444 for particle detect purposes. As noted above, liquid can be the process fluid within fluid cavity 430. Furthermore, system 400 has usefulness without the frequency enhancing crystal 410. More specifically, FIG. 6A illustrates an alternative system 500 constructed according to the invention. A laser 502 drives a ring cavity 504, known in the art, utilizing for example four ring elements 514a, 514b, 514c, 514d which permit resonance of beam 510 therebetween; and a fluid cavity 506 is arranged within the cavity 504 such that a fluid jet 508 intesects the beam 510. The ring cavity 504 is preferably unidirectional, as shown, so that energy 512 which leaves the cavity 504 does not re-enter the laser 502. As above, the frequency of laser 502 is monitored such as by reflection off of element 514 into the frequency detector 516.

Laser 502 can be one of several known lasers, such as a Nd:YAG laser providing 1064nm light, a frequency doubled YAG laser providing 532nm light, or other lasers. Specifically, laser 502 is chosen such that its output beam 502a matches the desired transmission within fluid or liquid 520 in fluid cavity 506. Typically, fluid cavity 506 is coupled to known processes (not shown) that utilize liquids, aerosols, water or other fluid; and thus laser wavelength 502a can be chosen a priori simply by selecting the appropriate off-the-shelf laser.

Fluid cavity 506 includes windows 524 which pass the beam 510 through the cavity 506. Preferably, windows 524 are matched to the fluid 520 and laser 502 wavelength to provide enhanced transmission of beam 510 therethrough. Windows 524 can thus include Brewster angles matched to respective indices of the fluid 520 and the cavity 504.

Energy 502b reflected from element 514a is measured for its frequency content by frequency detector 516, which communicates frequency information to motor controller 530. As above, this feedback of laser frequency is used to modulate or control one or more elements 514 within the cavity 504 so as to maintain resonance between elements 514a-d. As illustrated, for example, motor controller 530 drives motor 532 coupled to element 514d to provide this feedback control function.

Fluid cavity 506 operates as described above. A jet (e.g., a nozzle jet or inviscid flow jet) 540 generates a fluid jet 508 which passes through the beam 510. Scattered light 550 results from the interaction between the beam 510 and the flow 508; and at least a portion 550a of the scattered light 550 is collected by collection optics 552 through window 554 (shown integrally with cavity 506) for imaging onto detector and processor 556. Analysis of detector signals generated by the scattered light 550a is used to provide particle size, count and/ or frequency within the flow 508. For purposes of illustration, jet 540 is shown unconnected to external processes, as those skilled in the art should realize.

Useful background for the invention of FIGs. 6 and 6A may be found with reference to the following articles and patents, each of which are expressly incorporated herein by reference: Hansch et al., Laser Frequency Stabilization by Polarization Spectroscopy of a Reflecting Reference Cavity, Optics Communication, Vol. 35, no. 3, pp.441-444 (1980); U.S. Patent No. 5,097,476; U.S. Patent No. 5,642,375; U.S. Patent No. 5,437,840; and U.S. Patent No. 5,432,610.

The invention thus attains the objects set forth above, among those apparent from preceding description. Since certain changes may be made in the above systems and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense.

In view of the foregoing, what is claimed is:

Claims

1. A particle detection system for detecting particulates within a liquid flow, comprising:

a solid state laser for generating a lasing beam within a resonant cavity;

a liquid cavity for generating a liquid flow through the beam, the liquid cavity having a housing and one or more optical elements coupled with the housing for containing liquid within the liquid cavity, the optical elements transmitting the beam through the liquid cavity such that the beam and the flow interact to scatter light indicative of particulates within the flow; and

one or more detectors for detecting the scattered light.

2. A system according to claim 1, wherein the one of the optical elements comprises a frequency enhancing crystal wherein the beam comprises higher frequency lasing within the resonant cavity.

3. A system according to claim 2, wherein the crystal comprises a frequency doubling crystal.

4. A system according to claim 2, wherein the solid state laser comprises a YAG laser operating at approximately 1064nm, and wherein the frequency enhancing crystal comprises a frequency doubling crystal such that the higher frequency lasing comprises 532nm light.

5. The system of claim 2, wherein the detectors comprise means for detecting scattered light from the higher frequency lasing.

6. The system of claim 1, further comprising a processor coupled to the detectors for processing detector signals to determine one of particle size, count and frequency within the flow.

7. The system of claim 1, wherein at least one of the elements is constructed and arranged to operate as a reflector at one end of the resonator.

8. The system of claim 1, wherein the fluid cavity further comprises a nozzle jet for generating the flow.

9. The system of claim 1, wherein the fluid cavity further comprises an inviscid flow jet for generating the flow.

10. The system of claim 1, wherein at least one of the optical elements comprises a Brewster window for reducing reflections within the resonant cavity.

11. The system of claim 1, wherein the fluid cavity further comprises an optical collection element integrally coupled with housing, the detectors receiving the scattered light through the optical collection element.

12. The system of claim 11, wherein the optical collection element comprises optical power for imaging the scattered light onto the detector.

13. The system of claim 11, further comprising collection optics between the collection element and the detectors for imaging the scattered light onto the detector.

14. The system of claim 1, further comprising a frequency enhancing crystal arranged within the beam such that the beam comprises higher frequency lasing within the resonant cavity.

15. A particle detection system for detecting particulates within a fluid flow, comprising:

a resonant cavity, responsive to an external laser to constructively interfere light energy in the form of a lasing beam within the resonant cavity, the resonant cavity having at least one resonator optical element for reflecting the light energy within the resonant cavity;

a fluid cavity for generating a fluid flow through the lasing beam, the liquid cavity having a housing and one or more optical elements coupled with the housing for containing fluid within the fluid cavity, the optical elements transmitting the lasing beam through the fluid cavity such that the lasing beam and the flow interact to scatter light indicative of particulates within the flow; and

one or more detectors for detecting the scattered light.

16. A system according to claim 15, further comprising a laser, coupled to the resonant cavity, for providing the light energy for the resonant cavity.

17. A system according to claim 16, further comprising a frequency detector, for determining the frequency of the light energy, and a motor controller, responsive to signals produced by the frequency detector and representative of the frequency, for moving the optical resonator element to maintain resonance of the light energy within the resonant cavity as a function of the frequency.

18. A system according to claim 15, further comprising a frequency enhancing crystal arranged within the lasing beam such that the beam comprises higher frequency lasing within the resonant cavity.

19. A system according to claim 15, further comprising (a) optics for imaging the scattered light onto the detectors and (b) a processor for determining particle size, count and/ or frequency from signals generated by the detectors.

20. A system according to claim 15, further comprising one of a nozzle jet for generating the flow.

21. A system according to claim 15, further comprising one of an inviscid flow jet for generating the flow.