1. Field of the Invention
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 potentially harmful objects in a closed container, measuring critical-to-quality parameters in a container's contents for process control, and identifying defects in the container itself.
2. Discussion of the Related Art
As is known to those skilled in the art, the detection of potentially 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 reasons, 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.
Listed below are various publications that are referenced throughout this application by the convention, author [reference number].    1. ATHERTON, KATHRYN, et al., “Generation and Detection of Broadband Laser Generated Ultrasound From Low Power Laser Sources”, Photonics 2000: International Conference on Fiber Optics and Photonics, Proceedings of SPIE, vol. 4417, pgs. 19-32, 2001.    2. BLOUIN, ALAIN, et al., “Detection of Ultrasonic Motion of a Scattering Surface by Two-Wave Mixing in a Photorefractive GaAs Crystal”, Applied Physics Letters, vol. 65, no. 8, pgs. 932-934, Aug. 22, 1994.    3. CAMPAGNE, BENJAMIN, et al., “Compact and Fast Response Ultrasonic Detection Device Based on Two-Wave Mixing in a Gallium Arsenide Photorefractive Crystal”, Review of Scientific Instruments, vol. 72, no. 5, pgs. 2478-2482, May 2001.    4. DELAYE, PHILIPPE, “Heterodyne Detection of Ultrasound From Rough Surfaces Using a Double Phase Conjugate Mirror”, Applied Physics Letters, vol. 67, no. 22, pgs. 3251-3253, Nov. 27, 1995.    5. DELAYE, PHILIPPE, et al., “Detection of Ultrasonic Motion of Scattering Surface by Photorefractive InP:Fe Under an Applied dc Field”, J. Opt. Soc. Am. B, vol. 14, no. 7, pgs. 1723-1734, July 1997.    6. GLASS, A. M., et al., “Four-Wave Mixing in Semi-Insulating InP and GaAs Using the Photorefractive Effect”, Applied Physics Letters, vol. 44, no. 10, pgs. 948-950, May 15, 1984.    7. GOLOVAN, L. A., et al., “Efficient Nonlinear Optical Conversion in Porous GaP—The Effect of Light Localization”, Photonic Crystal Materials and Devices II, Proceeding of SPIE, vol. 5360, pgs. 333-338, 2004.    8. HONDA, TOKUYUKI, et al., “Optical Measurement of Ultrasonic Nanometer Motion of Rough Surface by Two-Wave Mixing in Bil2SiO20”, Jpn. J. Appl. Phys., vol. 34, part 1, no. 7A, pgs. 3737-3740, July 1995.    9. IIDA, YASUHIRO, et al., “Detection of Small In-Plane Vibrations Using the Polarization Self-Modulation Effect in GaP”, Journal of Optics A: Pure and Applied Optics, vol. 5, pgs. S457-S461, 2003.    10. ING, R. K, et al., “Broadband Optical Detection of Ultrasound by Two-Wave Mixing in a Photorefractive Crystal”, Applied Physics Letters, vol. 59, no. 25, pgs. 3233-3235, Dec. 16, 1991.    11. ING, R. K., et al., “Ultrasound Detection on Rough Surfaces Using Heterodyne Photorefractive Interferometer: Applications to NDE”, IEEE Ultrasonic Symposium, pgs. 681-684, 1996.    12. JARASIUNAS, KESTUTIS, et al., “Nonresonant Four-Wave Mixing in Photorefractive CdTe Crystals Using a Picosecond Parametric Generator”, Review of Scientific Instruments, vol. 69, no. 11, pgs. 3776-3779, November 1998.    13. KAMSHILIN, ALEXEI, A., et al., “Adaptive Interferometer Using Self-Induced Electro-Optic Modulation”, Applied Physics Letters, vol. 77, no. 25, pgs. 4098-4100, Dec. 18, 2000.    14. KAMSHILIN, ALEXEI, A., et al., “Linear Sensing of Speckle-Pattern Displacements Using a Photorefractive GaP Crystal”, Applied Physics Letters, vol. 74, no. 18, pgs. 2575-2577, May 3, 1999.    15. KAMSHILIN, ALEXEI, A., et al., “Polarization Self-Modulation of the Nonstationary Speckle Field in A Photorefractive Crystal”, Optics Letters, vol. 24, no. 12, pgs. 832-834, Jun. 15, 1999.    16. KOBOZEV, OLEG, et al., “Fast Adaptive Interferometer in a GaP Crystal Using a Near-Infrared Laser Diode”, Journal of Optics A: Pure and Applied Optics, vol. 3, pgs. L9-L11, 2001.    17. KURODA, K. et al., “Photorefractive Effect in GaP”, Optics Letters, vol. 15, no. 21, pgs. 1197-1199, Nov. 1, 1990.    18. PENG, LEILEI, et al., “Adaptive Optical Coherence-Domain Reflectometry Using Photorefractive Quantum Wells”, J. Opt. Soc. Am. B, vol. 21, no. 11, pgs. 1953-1963, November 2004.    19. RAITA, ERIK, et al., “Fast Photorefractive Response in B12SiO20 in the Near Infrared”, Optics Letters, vol. 25, no. 17, pgs. 1261-1263, Sep. 1, 2000.    20. SCRUBY, C. B., et al., Laser Ultrasonics: Techniques and Applications, Adam Hilger, Bristol, England, 1990.    21. SHCHERBIN, K. et al., “Photorefractive Recording in AC-Biased Cadmium Telluride”, Journal of Alloys and Compounds, Elsevier, vol. 371, pgs. 191-194, 2004.    22. SMULKO, et al., Sensors and Materials Volume 16, in press, 2004.    23. STEPANOV, S., et al., Photorefractive Materials and Their Applications: Fundamental Phenomena, ed. P. Gunter, et al., Springer, Berlin, pg. 263.    24. VON BARDELEBEN, H. J., et al., “Defects in Photorefractive CdTe:V: An Electron Paramagnetic Resonance Study”, Applied Physics Letters, vol. 63, no. 8, pgs. 1140-1142, Aug. 23, 1993.    25. ZIARI, MEHRDAD, et al., “Enhancement of the Photorefractive Gain at 1.3-1.5 μm in CdTe Using Alternating Electric Fields”, J. Opt. Soc. Am. B, vol. 9, no. 8, pgs. 1461-1466, August 1992.
The disclosures of all these publications in their entirety 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 interferometers. For example, Kamshilin et al. introduced an interferometric technique for linear detection of small ultrasonic out-of-plane vibrations of a rough surface. This technique is based on the polarization self-modulation (PSM) effect in 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 (Bi12TiO20) by Kamshilin et al., and in photorefractive GaP crystals by Kobozev et al. [16].
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. 5,533,399 discloses a “Method and Apparatus for Non-Destructive Measurement of Elastic Properties of Structural 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.”
However, what is needed is a cost-effective, accurate way to make measurements of things (e.g., containers, fluid-filled containers, etc.), and fulfill one or more of the following inspection conditions: portable, stand-off, non-invasive, continuous, real-time, non-radiological, and non-consumable.