Chemical identification by flash spectroscopy

• US 7,023,545 B2
• Filed: 06/12/2003
• Issued: 04/04/2006
• Est. Priority Date: 06/12/2003
• Status: Active Grant

• Current Assignee: Textron Systems Corporation (Textron Inc)
• Original Assignee: Textron Systems Corporation (Textron Inc)
• Inventors: Slater, Richard C.
• Primary Examiner(s): Toatley, Jr., Gregory J.
• Assistant Examiner(s): GEISEL, KARA E
• Application Number:
  US10/460,101
• Publication Number:
  US 20040252300A1
• Time in Patent Office: 1,027 Days
• Field of Search: 356/326, 356/328, 372/72
• US Class Current: 356/326
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation

Abstract

A light source produces a pump wave that is used to pump a parametric device. The parametric device is configured at or near its degeneracy point and produces a broadband output. The broadband output is directed to a remote location where chemical agents may be located. The broadband output may be transmitted through or scattered from the remote location and chemical agents located at the remote location may absorb portions of the broadband output. The broadband output may be collected and dispersed to produce channels or sub-bands that are detected by a detector array. The detector array may multiplex the intensities of the sub-bands and produce an absorption spectrum. The absorption spectrum may be compared to a library of known chemical agents and the presence of a chemical agent at the remote location can be determined in or near real time.

Claims

1. A flash spectroscopy standoff chemical detection system comprising:

a light source;

a parametric device configured to receive a pump wave from said light source at a degeneracy point of said parametric device;

a broadband output produced by said parametric device, wherein said broadband output is transmitted to a remote location and wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of about 5 percent to about 25 percent of a central broadband output wavelength; and

a spectrometer operable to receive said broadband output from said remote location and to produce an absorption spectrum.

2. The system of claim 1, wherein said broadband output comprises an idler wave and a signal wave.

3. The system of claim 2, wherein said idler wave is substantially equal to said signal wave.

4. The system of claim 1, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of about 10 percent to about 20 percent of a central broadband output wavelength.

5. The system of claim 1, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of greater than 200 cm⁻

1.

6. The system of claim 1, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of greater than 300 cm⁻

1.

7. The system of claim 4, wherein said pump wave has a central wavelength equal to about one-half of said central broadband output wavelength.

8. The system of claim 2, wherein a central wavelength of one of said idler wave and said signal wave is between about 8 microns to about 12 microns.

9. The system of claim 2, wherein a central wavelength of one of said idler wave and said signal wave is between about 3 microns to about 5 microns.

10. The system of claim 1, wherein said spectrometer comprises an optical dispersion element configured to receive said broadband output and to disperse said broadband output into a plurality of sub-bands after said broadband output has been received from said remote location.

11. The system of claim 10, wherein said spectrometer comprises a detector array configured to receive said sub-bands, said detector array operable to produce a multiplexed absorption spectrum from said sub-bands.

12. The system of claim 11, wherein said detector array comprises a 1D array.

13. The system of claim 12, wherein said detector array comprises 128 detector elements.

14. The system of claim 12, wherein said detector array comprises 256 detector elements.

15. The system of claim 11, wherein said detector array comprises a 2D array.

16. The system of claim 15, wherein said detector elements are configured in a 128 by 128 configuration.

17. The system of claim 11, further comprising a matched filter corresponding to a known chemical agent.

18. The system of claim 1, wherein said pump wave has a wavelength between about four microns to about five microns.

19. The system of claim 1, wherein said parametric device comprises collimating or transmission optics.

20. The system of claim 1, wherein said parametric device comprises an optical parametric generator.

21. The system of claim 1, wherein said parametric device comprises an optical parametric oscillator.

22. The system of claim 1, wherein said light source comprises a carbon monoxide or carbon dioxide gas laser.

23. The system of claim 1, wherein said light source comprises a diode laser.

24. The system of claim 23, wherein said light source comprises a quantum cascade diode laser producing a pump wave having a 4.5-micron wavelength.

25. The system of claim 23, wherein said light source comprises an AlInAs/InGaAs quantum cascade diode laser.

26. The system of claim 1, wherein said parametric device is configured in a Type I configuration.

27. The system of claim 1, wherein said parametric device is configured in a Type II configuration.

28. The system of claim 1, wherein said parametric device is made of cadmium germanium arsenide (CdGeAs₂).

29. The system of claim 1, wherein said parametric device is made of silver gallium selenide (AgGaSe₂).

30. The system of claim 1, wherein said parametric device is made of periodically twinned gallium arsenide (PTGaAs).

31. The system of claim 11, wherein said detector array comprises a quantum well infrared photodetector (QWIP).

32. A method of standoff chemical detection comprising the steps of:

supplying a pump wave to a parametric device configured at a degeneracy point;

producing a broadband output, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of about 5 percent to about 25 percent of a central broadband output wavelength;

directing said broadband output to a remote location containing a chemical agent;

detecting said broadband output from said remote location; and

producing a chemical absorption spectrum of said chemical agent.

33. The method of claim 32, wherein said step of detecting further comprises the step of dispersing said broadband output into two or more sub-bands.

34. The method of claim 33, further comprising the step of detecting an intensity of each of said two or more sub-bands.

35. The method of claim 34, wherein said step of producing said chemical absorption spectrum comprises a step of multiplexing said intensities of said two or more sub-bands.

36. The method of claim 32, further comprising the step of comparing said chemical absorption spectrum to one or more known absorption spectra.

37. The method of claim 32, further comprising the step of determining the presence of a known chemical at said remote location.

38. A flash spectroscopy chemical detection system comprising:

means for producing a pump wave;

means for degenerately amplifying said pump wave and producing a broadband output, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of about 5 percent to about 25 percent of a central broadband output wavelength;

means for directing said broadband output to a remote location;

means for detecting said broadband output from said remote location; and

means for identifying a chemical agent.

39. The system of claim 38, wherein said means for identifying further comprises means for producing a chemical absorption spectrum.

40. The system of claim 38, wherein said means for identifying comprises means for dispersing said broadband output into two or more sub-bands.

41. The system of claim 40, wherein said means for identifying further comprises means for detecting an intensity of each of said two or more sub-bands.

42. The system of claim 41, wherein said means for identifying further comprises means for multiplexing said intensities of said two or more sub-bands to produce said absorption spectrum.

43. The system of claim 42, wherein said means for identifying further comprises means for correlating said absorption spectrum with a known chemical absorption spectrum.

44. The system of claim 38, wherein said broadband output has a bandwidth or linewidth with a full-width half-maximum value of greater than 200 cm⁻

1.