Standoff detection using coherent backscattered spectroscopy

• US 20080258071A1
• Filed: 10/02/2007
• Published: 10/23/2008
• Est. Priority Date: 10/02/2006
• Status: Abandoned Application

• Current Assignee: Alexander Schill, Bradley R. Arnold, Dustin Levy, Lisa Kelly
• Original Assignee: Alexander Schill, Bradley R. Arnold, Dustin Levy, Lisa Kelly
• Inventors: Kelly, Lisa, Schill, Alexander, Arnold, Bradley R., Levy, Dustin
• Application Number:
  US11/906,436
• Publication Number:
  US 20080258071A1
• Time in Patent Office: Days
• US Class Current: 250/373
• CPC Class Codes: G01J 3/443 Emission spectrometry
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 2021/6421 Measuring at two or more wavelengths
• CPC Class Codes: G01N 21/6402 Atomic fluorescence; Laser induced fluorescence

Abstract

Provided herein are methods for detecting vapor-phase materials and/or photofragments thereof including energetic materials and decomposition products thereof, molecules or analytes at a stand-off distance. The methods provide for the stimulation of the ground state vapor phase to an excited state using a high fluence temporally and spatially focused ultraviolet laser pulse. The detection of back-scattered amplified spontaneous emission from the excited state vapor-phase material indicates the presence of the vapor phase materials.

Claims

1. A method for detecting the presence of a vapor-phase analyte at a distance, comprising:

a) selecting a wavelength absorbed by an analyte of interest;

b) generating a laser pulse of the selected ultraviolet wavelength from a laser source;

c) stimulating vapor-phase molecules of the analyte from a ground state to an excited state within a cylindrical volume via the laser pulse at a defined distance from the laser source; and

d) detecting coherent backscattered amplified spontaneous emission from the excited state molecules within the cylindrical volume thereby detecting the presence of the vapor-phase analyte.

2. The method of claim 1, further comprising:

stimulating a photoproduct of the excited state molecules within the cyclindrical volume with another laser pulse t wavelength after step (c).

3. The method of claim 2, wherein another laser pulse has a different wavelength.

4. The method of claim 1, further comprising:

ablating or thermally desorbing the analyte from a solid surface prior to step (a).

5. The method of claim 1, further comprising:

creating a spectral fingerprint from the detected backscattered amplified spontaneous emission.

6. The method of claim 1, wherein the selected wavelength is an ultraviolet wavelength.

7. The method of claim 1, wherein the selected wavelength is a spontaneously generated harmonic ultraviolet wavelength.

8. The method of claim 7, wherein the ultraviolet wavelength is generated from within a spectral range of about 213 nm to about 1200 nm.

9. The method of claim 1, wherein a detection distance is about 0.01 km to about 1 km.

10. The method of claim 1, wherein the laser pulse has a pulse width of about 150 fs to about 8 ns.

11. The method of claim 1, wherein a lower detection limit of the vapor-phase analyte is about 1 ppm.

12. The method of claim 1, wherein the analyte is a combustible material, a volatile solvent, a flammable solvent, a taggant, a stimulant, a gas, a gas mixture, or a solid.

13. The method of claim 12, wherein the combustible material is a TATP decomposition product, a nitro-aromatic compound, a nitroamine, or other nitro-containing compounds.

14. The method of claim 1, wherein the stimulated molecule is a photoproduct of the vapor-phase analyte.

15. The method of claim 1, wherein detection of backscattered amplified spontaneous emission is in real time.

16. A method for real-time stand-off detection of an energetic material, comprising:

(a) temporally focusing a high fluence ultraviolet laser pulse on a site of interest at a stand-off distance from a laser source;

(b) stimulating vapor-phase molecules associated with the energetic material to an excited state within a cylindrical volume at the site of interest via the laser pulse;

(c) detecting coherent backscattered amplified spontaneous emission from the excited state molecules within the cylindrical volume; and

(d) identifying the vapor-phase molecule from the backscattered amplified spontaneous emission upon the detection thereof, thereby detecting the energetic material at a stand-off in real-time.

17. The method of claim 16, further comprising:

stimulating a photoproduct of the excited state molecules within the cyclindrical volume with another high fluence ultraviolet laser pulse after step (b).

18. The method of claim 17, wherein another laser pulse has a different wavelength.

19. The method of claim 18, wherein the laser pulse has a wavelength or a harmonic wavelength generated from within a spectral range of about 213 nm to about 1200 nm.

20. The method of claim 16, wherein the stand-off distance is about 0.01 km to about 1 km.

21. The method of claim 16, wherein the temporally focused laser pulse has a pulse width of about 150 fs to about 8 ns.

22. The method of claim 16, wherein a lower detection limit of the vapor-phase molecules is about 1 ppm.

23. The method of claim 16, wherein the energetic material is a TATP decomposition product, a nitro-aromatic compound, a nitroamine, or other nitro-containing compound.

24. The method of claim 23, wherein the energetic material comprises an improvised explosive device.

25. The method of claim 16, wherein the stimulated molecule is a photoproduct of the vapor-phase molecule.