Abstract:
A system for stand-off, continuous, real-time, non-invasive, non-radiological, eye-safe, non-consumable characterization of an object is disclosed that comprises in combination a pulsed laser emitter for directing energy at the surface of an object, wherein the ultrasonic wave is generated within the object to be characterized, and a remote means of measuring the vibrational excitation in the object, whereby the object is remotely characterized.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 60/677,751, filed on May 4, 2005, the entity of which is expressly incorporated by reference herein in its entirety. 
     
    
     FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
       [0002]    The U.S. Government has provided funding for the background research for this invention through an award by the Department of Defense 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates in general to the field of safety, security and process control. More particularly, the present invention relates to a method and apparatus for detecting potential harmful objects in a closed container, measuring critical-to-quality parameters in a container&#39;s contents for process control and identifying defects in the container itself. 
         [0005]    2. Discussion of the Related Art 
         [0006]    As is known to those skilled in the art, the detection of potential harmful materials in a closed container continues to be a problem. This is particularly true where X-Ray radiation cannot be employed for safety or health reason, lack of sensitivity or specificity. Other techniques such as contact-based ultrasound, optical spectroscopy, gas chromatography, mass spectroscopy, bio-assay etc. also lack the ability to perform stand-off, non-invasive, continuous, real-time, non-consumable inspection of closed containers that include plastic, glass, ferrous and non-ferrous metals. 
         [0007]    Below several publications are referenced within parentheses. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for at least the purposes of indicating the background of the present invention and illustrating the state of the art. Various authors have reported schemes for interferometer, e.g., Kamshilin et al. introduces an interferometric technique for linear detection of small ultrasonic out-of-plane vibrations of a rough surface. (Kamshilin et al.) This technique is based on the polarization self-modulation (PSM) effect in the photorefractive crystals under an applied AC field that excludes the field screening. The performance of the PSM interferometer was experimentally demonstrated in photorefractive sillenite crystals (Bi 12 TiO 20 ) by Kamshilin et al. The performance of the PSM interferometer was experimentally demonstrated in photorefractive GaP crystals by (Kobozev et al.) 
         [0008]    The below-referenced U.S. patents disclose embodiments that were at least in-part satisfactory for the purposes for which they were intended. The disclosures of all the below-referenced prior United States patents are hereby expressly incorporated by reference into this present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art:
       U.S. Pat. No. 4,455,268 discloses a “Control System for Processing Composite Materials”,   U.S. Pat. No. 4,758,803 discloses a “Marginal Oscillator for Acoustic Monitoring of Curing of Plastics”,   U.S. Pat. No. 4,862,384 discloses a “Method of Using Dynamic Viscosity Using Acoustic Transducer”,   U.S. Pat. No. 5,505,090 discloses a “Method and Apparatus for Non-Destructive Inspection of Composite Materials and Semi-Monocoque Structures”,   U.S. Pat. No. 5,533,339 discloses a “Method and Apparatus for Non-Destructive Measurement of Elastic Properties of Composite Materials”, and   U.S. Pat. No. 6,029,520 discloses an “Ultrasonic Monitoring of Resin in a Press for the Production of Particle Board and Similar Materials.”       
 
         [0015]    However, what is needed is a cost-effective, accurate way to make measurements of things, e.g., containers, and fulfill one or more of the following inspection conditions: portable, stand-off, non-invasive, continuous, real-time, non-radiological, and non-consumable. 
       SUMMARY AND OBJECTS OF THE INVENTION 
       [0016]    By way of summary, the present invention is directed to an inspection system with a sensor. This system has the capability for stand-off, non-invasive, continuous, real-time, non-radiological, non-consumable, eye-safe inspection of closed containers made of a wide of materials that include ferrous metals, non-ferrous metals, glass, plastics and organic material. Each function is described more fully below: 
         [0017]    Stand-off means the sensor preferably operates in close proximity (millimeters) or at a long distance (kilometers) with certain adjustments to the basic design. Here the sensor preferably uses laser-based ultrasound generation and detection which has been shown to be a viable stand-off detection technology. 
         [0018]    Non-invasive means the sensor preferably determines material properties of the contents of a container closed to material flow. Here the sensor preferably uses laser-based ultrasound generation and detection which has been shown to be a viable non-invasive detection technology. 
         [0019]    Continuous means the sensor preferably takes many consecutive measurements without intervention. Here the sensor has a repetition rate between 1 and 10 Hz and can collect data continually from the sample as long as the sensor is aimed at the container. 
         [0020]    Real-time means the results preferably are available within seconds or fractions of seconds. Here the sensor preferably has a repetition rate between 1 and 10 Hz and can collect data continually from the sample as long as the sensor is aimed at the container. 
         [0021]    Non-radiological means the sensor preferably does not require the use of materials that undergo radioactive decay to produce an energy source for the sensor. Here the sensor preferably uses laser radiation at 1.5 um which is considered by the literature as the “eye-safe” region of the electromagnetic spectrum. 
         [0022]    Non-consumable means the sensor preferably does not require chemical or biological ingredients that are consumed by the activity of sensing. Here the entire sensor preferably consists of hardware and software, as described in the parts lists and associated figures, that does not require use of any disposable test kits, ingredients, or other consumable media. 
         [0023]    Eye-safe means the sensor preferably does not emit radiation that is destructive to the human eye. Here the sensor preferably uses laser radiation at 1.5 um which is considered by the literature as the “eye-safe” region of the electromagnetic spectrum. 
         [0024]    Another aspect of the invention is to provide an apparatus that is ruggedized and reliable, thereby decreasing down time and operating costs. 
         [0025]    Still another aspect of the invention is to provide an apparatus that has one or more of the characteristics discussed above but which is relatively simple to manufacture, assemble, and use using a minimum of equipment, time and resources. In one such a manufacturing process, subsystems would be purchased from other manufacturers and final assembly and integration of these subsystems would be done at a central location. 
         [0026]    Another aspect of the invention is to provide a non-invasive process sensor to monitor the phase transition of the cross linking process that occurs in manufacture of polymer products. Yet another aspect of the invention is to perform a stand-off, non-invasive inspection of returnable beverage kegs for frozen beverage or non-nominal material contents. 
         [0027]    Still another aspect of the invention is to perform stand-off, non-invasive level inspection of beverage cans and bottles without the use of radiological materials. 
         [0028]    Yet another aspect of the invention is to perform stand-off, non-invasive inspection of drums, pipes, warheads, bombs, and other closed containers for chemical and/or biological weapons. Note: Closed containers for chemical and/or biological weapons are generally made of either ferrous, non-ferrous, polymer or glass containers. 
         [0029]    Another aspect of the invention is to detect defects during the creation of laminate materials. 
         [0030]    Still another aspect of the invention is to detect contraband in tires of vehicles moving through border inspection stations. Another aspect of the invention is to verify contents in containers shipped into the US borders. Still another aspect of the invention is to identify flow characteristics in pipelines which is currently being done by contact-based ultrasound sensors (GE for example). Another aspect of the invention is to identify defects in pipelines. 
         [0031]    Yet another aspect is to provide quality assurance of canned and bottled food products using a continuous, real-time, noninvasive sensor. Another aspect of the invention is to detect a small amount of biological material, e.g., a few drops of biological material (dairy fat, blood) in a closed container of water. 
         [0032]    Still another aspect of the invention is to measure mixtures of materials inside a closed container. 
         [0033]    Another aspect of the invention is to provide a method that can be used to satisfy the above aspects of the invention. Still another aspect of the invention is to provide a method that is predictable and reproducible, thereby decreasing variance and operating costs. 
         [0034]    Another aspect of the invention is to provide a method that has one or more of the characteristics discussed above but which is which is relatively simple to setup and operate using relatively low skilled workers. 
         [0035]    These, and other aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical mechanisms provided with the present invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings accompanying and forming a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which  FIGS. 1-7  illustrate various aspects of the present invention. Specifically, 
           [0037]      FIG. 1  shows one embodiment of the present invention with a transmitted material wave and reflected material wave as they probe the material properties of the contents of the container; 
           [0038]      FIG. 2  shows one embodiment of the present invention with a transmitted material wave and reflected material wave probing the material properties a contaminant of the contents of the container; 
           [0039]      FIG. 3  shows one embodiment of the present invention with a transmitted material wave and reflected material wave as they probe the material defect in the container; 
           [0040]      FIG. 4  shows one embodiment of the present invention with a transmitted material wave being detected on the opposite side of the container; 
           [0041]      FIG. 5  shows one embodiment of a hand-held, mobile package of the present invention; 
           [0042]      FIG. 6  shows a schematic of one system configuration of the present invention; and 
           [0043]      FIG. 7  shows a schematic of one optical subsystem of the present invention. 
       
    
    
       [0044]    In describing the preferred embodiment of the invention that is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose. For example, the word connected or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
       DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0045]    The present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
       1. System Overview 
       [0046]    In one embodiment, the inventive system of the present invention includes an optical device that may be mounted on an optical “breadboard.” The breadboard may be mounted on a rail to enable the distance between a sensor of the system and a target container to be varied in a controllable way. 
         [0047]    In another embodiment the inventive system of the present invention includes all optics, electronics, and software in a single hand-held unit, see e.g.,  FIG. 5 . 
         [0048]    The preferred optical device includes an excitation laser that will be a Q-switched Nd:Yag laser pumped with a laser diode. The entire laser will be preferably housed in a TO-3 case; have a Wavelength: 1.550 μm, Pulse Energy: 100 μJ, Pulse Width: 2 ns, Peak Power: 50 Kw, Repetition Rate: SS to 10 Hz and the supplied driver is designed to work from a 3V battery. The excitation beam is preferably launched through an optional pattern generator and is directed collinear with probe and detection beams to minimize angle and distance-dependant focusing effects. A filter is preferably inserted to prevent excitation beam energy from reaching the detector. The high impulse energy and low continuous power make this embodiment ideal for mobile applications 
         [0049]    A probe laser preferably consists of a CW Laser Diode (1550 nm, 130 mW). The probe laser beam preferably is launched through an optional pattern generator into a beam splitter. The beam splitter directs a first part of the beam towards the target (probe or transmitted material wave beam) and a second part of the beam toward a photorefractive crystal of CdTe or similar (reference beam). Two-wave mixing takes place in the photorefractive crystal and the resulting signal is detected by a high-speed differential detector consisting of a polarizing beam splitter and two photodiodes. 
         [0050]    As mentioned, in one embodiment a high peak power Q-switched solid-state laser is used for the excitation source. However, this traditional approach involves high-energy optical pulse irradiation that may lead to surface damage, especially in carbon or glass fiber composites. Therefore, in another embodiment, the simple projection system is substituted with a pattern-based projection system. This enables excitation without damage but requires coded temporal signals. Arrays of patterns generated by semiconductor laser sources may also produce very broadband acoustic signals, both temporally and spatially. 
         [0051]    In one preferred embodiment, the probe laser is a low-cost near infrared laser diode ( 1550  nm 130 mW). The optical arrangement may also have a provision for holographic pattern generation to allow for decoding of encoded excitation laser signals. 
         [0052]    The use of laser diodes in the region of 1550 nm allows the entire system to be eye safe. The system could be created at other wavelengths of light using optical component appropriate for the selected wavelength of light. Of course, the system could be replaced by other radiation sources such as microwaves. 
         [0053]    Semiconductor crystals are known to possess a high mobility of charge carriers resulting in fast formation of the space-charge field. Others including Delaye 1995, Ing et. al. 1996, Campagne et. al. 2001, Iida et. al. 2003, Blouin et. al. 1994, Golovan et. al. 2004, Kobozev et. al. 2001 and Kuroda et. al. 1990 have also demonstrated photorefractive-based interferometers based on semiconductor crystals. The GaP crystal is a representative of a wide-band gap semiconductor, and exhibits the photorefractive effect in red and near-infrared regions of the optical spectrum. In particular, two-wave mixing at red light (wavelength of 633 nm) was first observed in the GaP crystal by Kuroda et al. It was shown that the response time of the space-charge-field formation in the GaP crystal is about 5 ms at a light intensity of 100 mW cm −2 . Linear sensing of speckle-pattern displacements using the PSM effect was demonstrated in a GaP crystal at the same wavelength. For practical implementation, the material has to show some potential in the near infrared because of the availability of low-cost laser diodes in this spectral region. This has been demonstrated by Kobozev et al. who has reported observations of fast response time of space-charge-field formation obtained in the photorefractive GaP crystal in the near infrared (1=807 nm). By using the PSM interferometer for the detection of small out-of-plane vibrations, Kobozev et al. found that a response time of a few milliseconds can be achieved with commercially available laser diodes. 
         [0054]    Kobozev et al. carried out experiments with a GaP crystal cut in the form of a parallelepiped with edges parallel to the [110], [001] and [110] crystallographic axes. The dimensions of the sample were 3.97, 5.8 and 6.52 mm, respectively. To apply external voltage, silver electrodes were evaporated on the (110) faces of the crystal. The light beams propagated at small angles to the [110] crystallographic axis. The semi-insulating GaP single crystal (point symmetry group 43 m) was grown at Sumitomo Metal Mining Co., Japan. 
         [0055]    Kobozev et al. pointed out that the above-described laser diode had a complicated beam intensity profile, which was far from the Gaussian distribution. Nevertheless, this did not limit the performance of the PSM interferometer. Despite large losses of the scattered light, the high intensity of the reference beam provides a fast response. 
         [0056]    Shcherbin et al. and others (Bardeleben et. al., Jarasiunas et. al.) have shown a CdTe crystal, which exhibits the largest electro-optic constant among all known semiconductors, to be suitable for photorefractive applications in the near infrared. 
         [0057]    The data-acquisition system of the present inventions preferably includes a signal processor. The stimulus and response signals are managed with a combination of analog and digital strategies. The focus is in digital technologies, which may be reconfigured for different applications, without too much confusion. 
         [0058]    Amplification is preferably done with an off the shelf pulser/receiver that has noise referred to the input of about 100 μV (pk-pk). This is within the dynamic range of 16 bit A/D converters (65536 counts from 0 to 5 Vdc gives a resolution of 76 μV). In this case, signal conditioning consists of impedance conversion/matching and band-pass filtering with no gain required. If 12 bit converters are used, then some gain will be required, as 4096 counts from 0 to 5 Vdc gives a resolution of 1.2 mV. As such, it is desirable to have computer control of the gain. 
         [0059]    The three factors affecting A/D conversion are: sample rate, dynamic range, and memory depth. For sample rate, a “digital radio” is used to maximum gain flexibility. In other words, a sensor connected directly to an A/D converter. To sample components up to 10 MHz, not less than 20 M samples/second (preferably more) are used. The limiting factor is on the anti-aliasing filter provided. Actual bandwidth may be end at the knee of the filter skirt when the bottom of the skirt reaches the noise floor at 10 MHz. A 96 dB/8 νa  low pass filter provides us a 5 MHz bandwidth. 
         [0060]    For dynamic range, off the shelf converters may be used having typical binary outputs with either 12 or 16 bit resolution. In some instances, 20 or even 24 bit converters may be used. Preferably, if the signal levels and attenuation characteristics are known, then dynamic range becomes less important. On the other hand, if sample thickness and ultrasound attenuation vary greatly, dynamic range is needed to accommodate it. Further, this is less important if a computer controls preamp gain. 
         [0061]    For memory depth, there is need to accommodate several megabytes of sample depth particularly in the design of a commercial system. An adaptive system that first seeks the return signal and then dynamically windows the process to minimize sample depth is desired. 
         [0062]    Digital Signal Processing (DSP) done in real-time DSP at 20 Msamp/sec. Is processor sensitive. However, samples may be captured at that rate and then analyzed off-line at a much slower rate. And, since the repetition rate may be arbitrarily slow, off-line processing may be accomplished at this slower pace. This avoids the need to have DSP specific hardware for computation. In one embodiment, data may be captured from the digital oscilloscope, and stored to a PC. The system may then apply signal processing algorithms to the data. 
       2. Detailed Description of Preferred Embodiments 
       [0063]    The inventive system  1  is generally constructed in accordance with what is shown in  FIGS. 1-7 . It may be employed in variety of environments including airports, military bases, manufacturing sites, transportation centers, construction sites, and border patrol checkpoints. The construction of units typically employing the various components of this invention is well known to those skilled in the art and therefore a detailed description thereof is not necessary to fully understand the present invention 
         [0064]    Specific embodiments of the present invention will now be further described by the following, non-limiting examples which will serve to illustrate various features of significance. The examples are intended merely to facilitate an understanding of ways in which the present invention may be practiced and to further enable those of skill in the art to practice the present invention. Accordingly, the examples should not be construed as limiting the scope of the present invention. 
         [0065]    As shown in  FIGS. 1-4 , one embodiment of the invention preferably contains several components. The system  1  has a laser source  1   a  connected to excitation optics  2 . The system creates various waves which are directed to container vessel  3  and vessel surface  4 . The waves including incident excitation wave  5 , transmitted material wave  7 , reflected material wave, incident probe wave  11 , and reflected probe wave  12  are all preferable emitted from probe laser  14 . The waves of the laser  1   a  are primarily directed at the vessel bulk  6  and are used to make a determination of the container contents  9 . Collection optics  13  preferably work in conjunction with probe optics  15 . The data acquisition systems  16  collect the information received by the reflected material wave  10 . The inventive system  1  preferably also has control electronics  17 , digital signal processing systems  18 , a microprocessor  19  and a database system  20 . A display  21  may also be provided. The object of interest  23  is probed by the various waves of the system  1  to determine the content of the container vessel  3 . The below graphs and tables show the results of some of the tests using one embodiment of the present invention. 

 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Material 
                 Speed of Sound (mm/us) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Polyethylene 
                 2.286 
               
               
                   
                 Steel 
                 5.6 
               
               
                   
                 SAE 20 Oil 
                 1.626 
               
               
                   
                 Glycerine 
                 1.753 
               
               
                   
                 Water 
                 1.473 
               
               
                   
                 Air 
                 0.356 
               
               
                   
                 Oxygen 
                 0.33 
               
               
                   
                   
               
               
                   
                 The above shows the speed of sound for various materials (longitudinal mode propagation). The transition time for a wideband ultrasound pulse can easily be measured and along with the physical dimension of the container a speed of sound may be calculated. The speed of sound varies significantly, even in water, as the chemical composition is varied. If the geometry is known then the speed of sound becomes an easy way to differentiate two materials. 
               
             
          
         
       
       
      
      
      
      
      
     
         [0000]                                                          TABLE 2                       Time-of-       Measured               Flight   Container   Speed of       Container   Contents   (usec)   Diameter (mm)   Sound (mm/usec.)                                Steel   Corn Syrup   35.5   66   1.859       Aluminum   Corn Syrup   34.2   66   1.930       Plastic   Corn Syrup   39.7   75.7   1.902       Steel   Kerosene   52.3   66   1.262       Aluminum   Kerosene   49.5   66   1.333       Plastic   Kerosene   58.6   75.7   1.292       Steel   Water   46.9   66   1.407       Aluminum   Water   45.8   66   1.441       Plastic   Water   53.7   75.7   1.410               Measured Speed of sound using laser-based ultrasound on a number of different containers and contents.            
In one preferred embodiment, the analysis of the signal of the system  1  is preferably based on the following:
 
         [0066]    Timing of the return pulse is used to calculate speed of sound of the material in the container. Spectral analysis is used to determine the frequency and attenuation response of the container and contents. This technique is used to identify various constituents or ingredients in the preparation of food products. Vx in the liquid form preferably has a speed of sound similar to water and the molecular makeup of the material is likely to result in a frequency-dependent spectra that is different than water. 
         [0067]    Fluctuation Enhanced Analysis [Kish, Mendel] is preferably used to investigate the non-Gaussian noise characteristics of the signals that may translate into useful information. Smulko and Kish have identified a methodology that suggests the stochastic component of a chemical sensor signal contains valuable information that can be visualized not only by spectral analysis but also by methods of higher-order statistics (HOS). The analysis of HOS enables the extraction of non-conventional features that lead to significant improvements in selectivity and sensitivity. We pay particular attention to the bispectrum that characterizes the non-Gaussian component and detects non stationary in analyzed noise. As Smulko&#39;s results suggest that the bispectrum can be applied for material recognition, this will be tried also. 
         [0068]    Ultrasound data for each measurement was acquired as multiple time series, which were then phase locked and averaged in software to provide a clear signal, well above the noise floor. The third order cumulant of the processed time series was obtained by the expression: 
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         [0000]    This was done over the range k=(−128 . . . 128), l=(−128 . . . 128) times a scale factor, with n running over the range (0 . . . 6500), producing the two-dimensional plots given below. A second order Fourier Transform was then performed on each cumulant to obtain the bispectrum, by the expression: 
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         [0000]    Each bispectrum is plotted in gray scale pixel values, as the sum of the sine and cosine Fourier components. 
         [0069]    Another example of the preferred embodiment is shown in  FIG. 6  which shows an example system configuration. Here the device under test or object ( 71 ) is, for example, a 55 gal. Drum or container. Beam steering optics ( 72 ) is, for example, a telephoto lens. An excitation beam combiner ( 73 ) is preferably a beam splitter. A probe beam combiner ( 74 ) is, for example, a beam splitter. A preferred adaptive interferometer ( 75 ) is a photorefractive crystal, mirror, and polarizer. A detector assembly ( 76 ) is, for example, a beam splitter differential photo-detector combination. An excitation laser assembly ( 77 ) includes preferably a Q-switched YAG laser while a probe laser assembly ( 78 ) includes, for example, a diode laser. 
         [0070]    A preferred excitation beam driver ( 79 ) is a current controller pulsing circuit. A probe laser driver ( 80 ) is, for example, a constant current supply with diode feedback. Drive electronics for adaptive interferometer ( 81 ) preferably include a bias supply for photorefractive crystal. Detector electronics ( 82 ), for example, include a differential operational amplifier. 
         [0071]    Preferably, a microprocessor assembly ( 83 ) is a PC  104  minicomputer module and power management ( 84 ) includes a power supply battery charging module. Thermal management ( 85 ) includes, for example, a thermoelectric cooler and controller. User interface ( 86 ) is, for example, a LCD touch screen module. Communications interface ( 87 ) is, for example, a Wi-Fi interface module, Ethernet interface module, USB interface module, ZigBee interface module. Optical Subsystem ( 88 ) (see, e.g.,  FIG. 7 ). Business intelligence subsystem ( 89 ) is, for example, an application server, data base server, application software and database software and data to provide list parameters for contents of shipping containers and software integration to software manifests of shipping container contents. 
         [0072]    Another preferred embodiment of the optical subsystem is shown at  FIG. 7 . In this example, the container or device under test ( 201 ) is, for example, a May 55, 1965 gal. drum. A telephoto lens ( 202 ) is also provided. The excitation laser ( 203 ), in an example 1 is a diode-pumped solid state laser housed in TO-3 case having a wavelength: 1.54 μm, Pulse Energy: 100 μJ, Pulse Width: 2 ns, Peak Power: 50 Kw, Repetition Rate: SS to 10 Hz. In an example 2, a diode pumped solid-state laser is provided having a Wavelength: 1.54 μm, Pulse Energy: 4 mJ, Pulse Width: 7 ns, Repetition Rate: SS to 10 Hz. 
         [0073]    The probe laser ( 204 ), for example, is a fabry Perot laser cavity having a single transverse mode of 130 mW in wavelength range 1550 nm. InGaAs MQW. In another example, a single transverse mode of 44 mW is provided in wavelength range 1550 nm. InGaAsP/InP SQW. 
         [0074]    The non-polarizing beam splitter ( 205 ), in an example 1, has a BK7 grade A optical glass having a Dimension Tolerance ±0.2 mm, Flatness 1/4 @ 632.8 nm per 25 mm, Surface Quality 60/40 scratches and dig, 50/50±5%, for random polarization, T=(Ts+Tp)/2, R=(Rs+Rp)/2, Beam Deviation &lt;3 arc minutes, 20 mm. In an example 2, it has a Narrow Band: BK7 grade A optical glass, Broadband: SF5 optical glass, Dimension Tolerance ±0.2 mm, Flatness 1/4 @ 632.8 nm per 25 mm, Surface Quality 60/40 scratches and dig, Transmittance 45%±5%, Absorption &lt;10%, Beam Deviation &lt;3 arc minutes. 
         [0075]    The polarizing beam splitter ( 206 ) is preferably a Narrow Band: BK7 grade A optical glass, Broadband: SF5 optical glass with a Dimension Tolerance ±0.2 mm, Extinction Ratio&gt;100:1, Flatness 1/4 @ 632.8 nm per 25 mm, Surface Quality 60/40 scratches and dig, Principal Transmittance Tp&gt;95% and Ts&lt;1%, Principal Reflectance Rs&gt;99% and Rp&lt;5%, Beam Deviation &lt;3 arc minutes. The polarizer ( 207 ) is preferably a linear NIR polarizer nominal 50% at 1550. Alternatively, the polarizer is a linear polarizer having an extinction ratio better than 10,000:1, High transmission, Wide acceptance angle, and Low wavefront distortion. 
         [0076]    The retardation plate ( 208 ) preferably has dimensions 5 mm×5 mm, Material: Crystal Quartz, Substrate: BK-7, 2 mm thick, Bonding: Cement, Wavelength: 1550 nm, Coating: AR&lt;0.5%. In an example 2, the plate is a Crystal quartz, having Dimension Tolerance +0.0, −0.2 mm, Wavefront Distortion &lt;1/8@632.8, Retardation Tolerance &lt;1/500, Parallelism &lt;1 arc second, Clear aperture &gt;80%, Surface Quality 20/10 scratches &amp; dig, Coating R&lt;0.2% on both surfaces at central wavelength. 
         [0077]    The photorefractive crystal ( 209 ), in example 1, is a CdTe, Ge crystal germanium-doped to give a dark conductivity of 10 −9  Ωcm −1  with dimensions 4 mm×5 mm×10 mm cut along [112], [111], and [110] directions respectively having faces parallel to [110] polished, faces parallel to [111] silvered. In an example 2, a CdTe:V, crystal vanadium-doped is provided with dimensions 3 mm×3 mm×5 mm cut along [112], [111], and [110] directions respectively having the faces parallel to [110] polished, faces parallel to [111] silvered. In an example 3, a GaAs crystal with no doping with dimensions 5 mm×5 mm×5 mm cut along [001], [110], and [110] directions respectively is provided that also has the faces parallel to [110] polished. 
         [0078]    The mirror ( 210 ), in example 1, is preferably BK7, Pyrex or UV Fused Silica, and has a Dimension Tolerance: +0.0, −0.2 mm, Thickness Tolerance: ±0.2 mm, Clear Aperture: &gt;80%, Flatness: 1/10 @ 633 nm, Parallelism: &lt;1 arc minute, Surface Quality: 20/10 (S/D), Bevel (Chamfer): 0.15˜0.35 mm×45° face width×45°±15°, Coating Surface (S1): AOI=0°, R&gt;99.8%, AOI=45°, R&gt;99.5% (Rs&gt;99.9%, Rp&gt;99.2%. In example 2, the material is BK7 Grade A Optical Glass, and the Dimension Tolerance is +0.0, −0.2 mm, Thickness Tolerance is ±0.2 mm, Clear Aperture is &gt;80%, Parallelism is &lt;1 arc minute, Surface Quality is 60/40 (S/D), and Bevel (Chamfer) is 0.15˜0.35 mm×45° face width×45°±15°). 
         [0079]    The photodiode ( 211 ), in an example 1, is InGaAs Photodiode with a 15 MHz Bandwidth and a 1200-2600 nm, Ø1 mm Active Area. In an example 2, it is an InGaAs Photodiode with a 1 GHz Bandwidth, and a 1000-1600 nm, 75 um Active Area. 
         [0080]    Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and scope of the underlying inventive concept. 
         [0081]    Moreover, the individual components need not be formed in the disclosed shapes, or assembled in the disclosed configuration, but could be provided in virtually any shape, and assembled in virtually any configuration. Further, although the components are described herein as physically separate modules, it will be manifest that these may be integrated into the apparatus with which it is associated. Furthermore, all the disclosed features of each disclosed embodiment can be combined with, or substituted for, the disclosed features of every other disclosed embodiment except where such features are mutually exclusive. 
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