Abstract

We investigate the remote detection of explosives via a technique that vaporizes and photodissociates the condensed-phase material and detects the resulting vibrationally excited NO fragments via laser- induced fluorescence. The technique utilizes a single 7ns pulse of a tunable laser near 236.2nm to perform these multiple processes. The resulting blue-shifted fluorescence (226nm) is detected using a photomultiplier and narrowband filter that strongly block the scatter of the pump laser off the solid media while passing the shorter wavelength photons. Various nitro-bearing compounds, including 2,6-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX) were detected with a signal-to-noise of 25dB. The effects of laser fluence, wavelength, and sample morphology were examined.

© 2008 Optical Society of America

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References

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  1. D. S. Moore, “Instrumentation for trace detection of high explosives,” Rev. Sci. Instrum. 75, 2499-2512 (2004).
    [Crossref]
  2. S. Singh, “Sensors--An effective approach to the detection of explosives,” J. Hazard. Mater. 144, 15-28 (2007).
    [Crossref] [PubMed]
  3. T. Arusi-Parpar, D. Helfinger, and R. Lavi, “Photodissociation followed by laser-induced fluorescence at atmospheric pressure and 20 C: a unique scheme for remote detection of explosives,” Appl. Opt. 40, 6677-6681 (2001).
    [Crossref]
  4. D. Helfinger, T. Arusi-Parpar, Y. Ron, and R. Lavi, “Application of a unique scheme for remote detection of explosives,” Opt. Commun. 204, 327-331 (2002).
    [Crossref]
  5. T. Arusi-Parpar and Izhak Levy, “Remote detection of explosives by enhanced pulsed laser photodissociation/laser-induced fluorescence method,” Standoff Detection of Suicide Bombers and Mobile Subjects, H. Schubert and A. Rimski-Korsakow, eds. (Springer, 2006), pp. 59-68.
    [Crossref]
  6. J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
    [Crossref]
  7. C. Lenchitz and R. Velicky, “Vapor pressure and heat of sublimation of three nitrotoluenes,” J. Chem. Eng. Data 15, 401 (1970).
    [Crossref]
  8. J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program,” SRI International Report MP 99-009 (1999).
  9. J. Luque and D. R. Crosley, “Transition probabilities and electronic transition moments of the A2∑+−X2\scale 90%Π and D2∑+ −X2\scale 90%Π systems of nitric oxide” J. Chem. Phys. 111, 7405 (1999).
    [Crossref]
  10. Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
    [Crossref] [PubMed]
  11. J. Cabalo and R. Sausa, “Detection of RDX by laser surface photofragmentation-fragment detection spectroscopy,” Appl. Spectrosc. 57, 1196-1199 (2003).
    [Crossref] [PubMed]
  12. H.-S. Im and E. R. Bernstein, “Photodissociation of NO2 in the region 217-237 nm: Nascent NO energy distribution and mechanism,” J. Phys. Chem. A 106, 7565-7572 (2002).
    [Crossref]
  13. C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
    [Crossref]
  14. M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
    [Crossref]
  15. H. S. Im and E. R. Bernstein, “On the initial steps in the decomposition of energetic materials from excited electronic states,” J. Chem. Phys. 113, 7911-7918 (2000).
    [Crossref]
  16. M. Kuklja, “Thermal decomposition of solid cyclotrimethylene trinitramine,” J. Phys. Chem. B 105, 10159-10162 (2001).
    [Crossref]
  17. J. Cabalo and R. Sausa, “Trace detection of explosives with low vapor pressure emissions by laser surface photofragmentation-fragment detection spectroscopy with an improved ionization probe,” Appl. Opt. 44, 1084-1091 (2005).
    [Crossref] [PubMed]
  18. F. J. Owens, “Calculation of energy barriers for bond rupture in some energetic molecules,” J. Mol. Struct., Theochem 370, 11-16 (1996).
    [Crossref]
  19. L. Nagli and M. Gaft, “Raman scattering spectroscopy for explosives identification,” Proc. SPIE 6552, 65502Z (2007)
  20. M. Gaft and L. Nagli, “UV gated Raman spectroscopy for standoff detection of explosives,” Opt. Mater. 30, 1747-1754 (2008).
    [Crossref]
  21. National Research Council, Existing and Potential Standoff Explosive Detection Techniques (National Academies, 2004).
  22. J. Steinfeld and J. Wormhoudt, “Explosives detection: a challenge for physical chemistry,” Annu. Rev. Phys. Chem. 49, 203-232 (1998).
    [Crossref]
  23. A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
    [Crossref]

2008 (2)

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

M. Gaft and L. Nagli, “UV gated Raman spectroscopy for standoff detection of explosives,” Opt. Mater. 30, 1747-1754 (2008).
[Crossref]

2007 (2)

L. Nagli and M. Gaft, “Raman scattering spectroscopy for explosives identification,” Proc. SPIE 6552, 65502Z (2007)

S. Singh, “Sensors--An effective approach to the detection of explosives,” J. Hazard. Mater. 144, 15-28 (2007).
[Crossref] [PubMed]

2006 (1)

M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
[Crossref]

2005 (2)

J. Cabalo and R. Sausa, “Trace detection of explosives with low vapor pressure emissions by laser surface photofragmentation-fragment detection spectroscopy with an improved ionization probe,” Appl. Opt. 44, 1084-1091 (2005).
[Crossref] [PubMed]

Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
[Crossref] [PubMed]

2004 (1)

D. S. Moore, “Instrumentation for trace detection of high explosives,” Rev. Sci. Instrum. 75, 2499-2512 (2004).
[Crossref]

2003 (1)

2002 (2)

H.-S. Im and E. R. Bernstein, “Photodissociation of NO2 in the region 217-237 nm: Nascent NO energy distribution and mechanism,” J. Phys. Chem. A 106, 7565-7572 (2002).
[Crossref]

D. Helfinger, T. Arusi-Parpar, Y. Ron, and R. Lavi, “Application of a unique scheme for remote detection of explosives,” Opt. Commun. 204, 327-331 (2002).
[Crossref]

2001 (2)

2000 (2)

H. S. Im and E. R. Bernstein, “On the initial steps in the decomposition of energetic materials from excited electronic states,” J. Chem. Phys. 113, 7911-7918 (2000).
[Crossref]

J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
[Crossref]

1999 (1)

J. Luque and D. R. Crosley, “Transition probabilities and electronic transition moments of the A2∑+−X2\scale 90%Π and D2∑+ −X2\scale 90%Π systems of nitric oxide” J. Chem. Phys. 111, 7405 (1999).
[Crossref]

1998 (1)

J. Steinfeld and J. Wormhoudt, “Explosives detection: a challenge for physical chemistry,” Annu. Rev. Phys. Chem. 49, 203-232 (1998).
[Crossref]

1996 (1)

F. J. Owens, “Calculation of energy barriers for bond rupture in some energetic molecules,” J. Mol. Struct., Theochem 370, 11-16 (1996).
[Crossref]

1985 (1)

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

1970 (1)

C. Lenchitz and R. Velicky, “Vapor pressure and heat of sublimation of three nitrotoluenes,” J. Chem. Eng. Data 15, 401 (1970).
[Crossref]

Arusi-Parpar, T.

D. Helfinger, T. Arusi-Parpar, Y. Ron, and R. Lavi, “Application of a unique scheme for remote detection of explosives,” Opt. Commun. 204, 327-331 (2002).
[Crossref]

T. Arusi-Parpar, D. Helfinger, and R. Lavi, “Photodissociation followed by laser-induced fluorescence at atmospheric pressure and 20 C: a unique scheme for remote detection of explosives,” Appl. Opt. 40, 6677-6681 (2001).
[Crossref]

T. Arusi-Parpar and Izhak Levy, “Remote detection of explosives by enhanced pulsed laser photodissociation/laser-induced fluorescence method,” Standoff Detection of Suicide Bombers and Mobile Subjects, H. Schubert and A. Rimski-Korsakow, eds. (Springer, 2006), pp. 59-68.
[Crossref]

Bar, I.

J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
[Crossref]

Bernstein, E. R.

M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
[Crossref]

Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
[Crossref] [PubMed]

H.-S. Im and E. R. Bernstein, “Photodissociation of NO2 in the region 217-237 nm: Nascent NO energy distribution and mechanism,” J. Phys. Chem. A 106, 7565-7572 (2002).
[Crossref]

H. S. Im and E. R. Bernstein, “On the initial steps in the decomposition of energetic materials from excited electronic states,” J. Chem. Phys. 113, 7911-7918 (2000).
[Crossref]

Cabalo, J.

Crosley, D. R.

J. Luque and D. R. Crosley, “Transition probabilities and electronic transition moments of the A2∑+−X2\scale 90%Π and D2∑+ −X2\scale 90%Π systems of nitric oxide” J. Chem. Phys. 111, 7405 (1999).
[Crossref]

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program,” SRI International Report MP 99-009 (1999).

Edwards, B.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Gaft, M.

M. Gaft and L. Nagli, “UV gated Raman spectroscopy for standoff detection of explosives,” Opt. Mater. 30, 1747-1754 (2008).
[Crossref]

L. Nagli and M. Gaft, “Raman scattering spectroscopy for explosives identification,” Proc. SPIE 6552, 65502Z (2007)

Golden, D.

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

Gonzalez, A.

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

Greenfield, M.

M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
[Crossref]

Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
[Crossref] [PubMed]

Guo, Y. Q.

M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
[Crossref]

Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
[Crossref] [PubMed]

Helfinger, D.

Im, H. S.

H. S. Im and E. R. Bernstein, “On the initial steps in the decomposition of energetic materials from excited electronic states,” J. Chem. Phys. 113, 7911-7918 (2000).
[Crossref]

Im, H.-S.

H.-S. Im and E. R. Bernstein, “Photodissociation of NO2 in the region 217-237 nm: Nascent NO energy distribution and mechanism,” J. Phys. Chem. A 106, 7565-7572 (2002).
[Crossref]

Kuklja, M.

M. Kuklja, “Thermal decomposition of solid cyclotrimethylene trinitramine,” J. Phys. Chem. B 105, 10159-10162 (2001).
[Crossref]

Kunz, R. R.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Larson, C.

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

Lavi, R.

Lenchitz, C.

C. Lenchitz and R. Velicky, “Vapor pressure and heat of sublimation of three nitrotoluenes,” J. Chem. Eng. Data 15, 401 (1970).
[Crossref]

Levy, Izhak

T. Arusi-Parpar and Izhak Levy, “Remote detection of explosives by enhanced pulsed laser photodissociation/laser-induced fluorescence method,” Standoff Detection of Suicide Bombers and Mobile Subjects, H. Schubert and A. Rimski-Korsakow, eds. (Springer, 2006), pp. 59-68.
[Crossref]

Luque, J.

J. Luque and D. R. Crosley, “Transition probabilities and electronic transition moments of the A2∑+−X2\scale 90%Π and D2∑+ −X2\scale 90%Π systems of nitric oxide” J. Chem. Phys. 111, 7405 (1999).
[Crossref]

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program,” SRI International Report MP 99-009 (1999).

McMillen, D.

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

Moore, D. S.

D. S. Moore, “Instrumentation for trace detection of high explosives,” Rev. Sci. Instrum. 75, 2499-2512 (2004).
[Crossref]

Nagli, L.

M. Gaft and L. Nagli, “UV gated Raman spectroscopy for standoff detection of explosives,” Opt. Mater. 30, 1747-1754 (2008).
[Crossref]

L. Nagli and M. Gaft, “Raman scattering spectroscopy for explosives identification,” Proc. SPIE 6552, 65502Z (2007)

Owens, F. J.

F. J. Owens, “Calculation of energy barriers for bond rupture in some energetic molecules,” J. Mol. Struct., Theochem 370, 11-16 (1996).
[Crossref]

Palmacci, S.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Ron, Y.

D. Helfinger, T. Arusi-Parpar, Y. Ron, and R. Lavi, “Application of a unique scheme for remote detection of explosives,” Opt. Commun. 204, 327-331 (2002).
[Crossref]

Rosenwaks, S.

J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
[Crossref]

Rothschild, M.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Sausa, R.

Shu, J.

J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
[Crossref]

Singh, S.

S. Singh, “Sensors--An effective approach to the detection of explosives,” J. Hazard. Mater. 144, 15-28 (2007).
[Crossref] [PubMed]

Steinfeld, J.

J. Steinfeld and J. Wormhoudt, “Explosives detection: a challenge for physical chemistry,” Annu. Rev. Phys. Chem. 49, 203-232 (1998).
[Crossref]

Velicky, R.

C. Lenchitz and R. Velicky, “Vapor pressure and heat of sublimation of three nitrotoluenes,” J. Chem. Eng. Data 15, 401 (1970).
[Crossref]

Wormhoudt, J.

J. Steinfeld and J. Wormhoudt, “Explosives detection: a challenge for physical chemistry,” Annu. Rev. Phys. Chem. 49, 203-232 (1998).
[Crossref]

Wynn, C. M.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Zayhowski, J. J.

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Annu. Rev. Phys. Chem. (1)

J. Steinfeld and J. Wormhoudt, “Explosives detection: a challenge for physical chemistry,” Annu. Rev. Phys. Chem. 49, 203-232 (1998).
[Crossref]

Appl. Opt. (2)

Appl. Phys. B (1)

J. Shu, I. Bar, and S. Rosenwaks, “The use of rovibrationally excited NO photofragments as trace nitrocompound indicators,” Appl. Phys. B 70, 621-625 (2000).
[Crossref]

Appl. Spectrosc. (1)

Chem. Phys. Lett. (1)

M. Greenfield, Y. Q. Guo, and E. R. Bernstein, “Ultrafast photodissociation dynamics of HMX and RDX from their excited electronic states via femtosecond laser pump-probe techniques,” Chem. Phys. Lett. 430, 277-281 (2006).
[Crossref]

J. Chem. Eng. Data (1)

C. Lenchitz and R. Velicky, “Vapor pressure and heat of sublimation of three nitrotoluenes,” J. Chem. Eng. Data 15, 401 (1970).
[Crossref]

J. Chem. Phys. (3)

J. Luque and D. R. Crosley, “Transition probabilities and electronic transition moments of the A2∑+−X2\scale 90%Π and D2∑+ −X2\scale 90%Π systems of nitric oxide” J. Chem. Phys. 111, 7405 (1999).
[Crossref]

Y. Q. Guo, M. Greenfield, and E. R. Bernstein, “Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX,” J. Chem. Phys. 122, 244310 (2005).
[Crossref] [PubMed]

H. S. Im and E. R. Bernstein, “On the initial steps in the decomposition of energetic materials from excited electronic states,” J. Chem. Phys. 113, 7911-7918 (2000).
[Crossref]

J. Hazard. Mater. (1)

S. Singh, “Sensors--An effective approach to the detection of explosives,” J. Hazard. Mater. 144, 15-28 (2007).
[Crossref] [PubMed]

J. Mol. Struct., Theochem (1)

F. J. Owens, “Calculation of energy barriers for bond rupture in some energetic molecules,” J. Mol. Struct., Theochem 370, 11-16 (1996).
[Crossref]

J. Phys. Chem. (1)

A. Gonzalez, C. Larson, D. McMillen, and D. Golden, “Mechanism of decomposition of nitroaromatics. Laser-powered homogeneous pyrolysis of substituted nitrobenzenes,” J. Phys. Chem. 89, 4809-4814 (1985).
[Crossref]

J. Phys. Chem. A (1)

H.-S. Im and E. R. Bernstein, “Photodissociation of NO2 in the region 217-237 nm: Nascent NO energy distribution and mechanism,” J. Phys. Chem. A 106, 7565-7572 (2002).
[Crossref]

J. Phys. Chem. B (1)

M. Kuklja, “Thermal decomposition of solid cyclotrimethylene trinitramine,” J. Phys. Chem. B 105, 10159-10162 (2001).
[Crossref]

Opt. Commun. (1)

D. Helfinger, T. Arusi-Parpar, Y. Ron, and R. Lavi, “Application of a unique scheme for remote detection of explosives,” Opt. Commun. 204, 327-331 (2002).
[Crossref]

Opt. Mater. (1)

M. Gaft and L. Nagli, “UV gated Raman spectroscopy for standoff detection of explosives,” Opt. Mater. 30, 1747-1754 (2008).
[Crossref]

Proc. SPIE (2)

L. Nagli and M. Gaft, “Raman scattering spectroscopy for explosives identification,” Proc. SPIE 6552, 65502Z (2007)

C. M. Wynn, S. Palmacci, R. R. Kunz, J. J. Zayhowski, B. Edwards, and M. Rothschild, “Experimental demonstration of remote detection of trace explosives,” Proc. SPIE 6954, 695407 (2008).
[Crossref]

Rev. Sci. Instrum. (1)

D. S. Moore, “Instrumentation for trace detection of high explosives,” Rev. Sci. Instrum. 75, 2499-2512 (2004).
[Crossref]

Other (3)

T. Arusi-Parpar and Izhak Levy, “Remote detection of explosives by enhanced pulsed laser photodissociation/laser-induced fluorescence method,” Standoff Detection of Suicide Bombers and Mobile Subjects, H. Schubert and A. Rimski-Korsakow, eds. (Springer, 2006), pp. 59-68.
[Crossref]

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program,” SRI International Report MP 99-009 (1999).

National Research Council, Existing and Potential Standoff Explosive Detection Techniques (National Academies, 2004).

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Figures (8)

Fig. 1
Fig. 1

Schematic of steps and energy levels associated with the vaporization/PD-LIF detection process. Solid explosives (bottom of figure) are vaporized and dissociated into diatomic NO fragments in the first two (simultaneous) steps. The resultant NO fragments (top of figure) are optically excited (Step 3) from their vibrationally excited electronic ground state to an electronically excited state. The blue-shifted fluorescence (Step 4) is used for detection.

Fig. 2
Fig. 2

Experimental detection setup. The primary components used were a variable-wavelength pulsed UV laser (the light from which was focused on the sample with a UV lens), a narrowband filter strongly rejecting the laser scatter, and a PMT photodetector. The explosive samples were placed on fused silica substrates.

Fig. 3
Fig. 3

Absorption cross section as a function of wavelength for explosives in acetonitrile solutions.

Fig. 4
Fig. 4

Blue-shifted fluorescence signal of various explosives as a function of pump laser wavelength. (a)–(d) The laser beam directly strikes the explosives (solid or liquid). (e) The open circles are a background measurement in which the laser strikes the silica substrate without explosives, and the closed circles are a measurement in which the laser probes only the vapor headspace above liquid DNT (but not the liquid itself). (f) The predicted fluorescence of NO assuming excitation from its first vibrationally excited state; two different rotational temperatures are displayed.

Fig. 5
Fig. 5

Blue-shifted fluorescence signal of liquid DNT as a function of pump laser wavelength ( 22 mJ / cm 2 / pulse ). The markers are experimental data for liquid DNT, and the lines are the predicted NO fluorescence. The predicted NO fluorescence pumped at wavelengths below 237 nm is for excitation from v = 1 with a rotational temperature of 1000 K . The predicted NO fluorescence pumped at wavelengths above 237 nm is for excitation from v = 2 with a rotational temperature of 5000 K . The inset is a close-up near v = 1 .

Fig. 6
Fig. 6

Fluence dependence of the fluorescence signal of various explosives at fixed pump laser wavelengths. Dashed curves indicate either (a) cubic or (b) quadratic behavior. In (c) both quadratic and cubic behavior are indicated.

Fig. 7
Fig. 7

Blue-shifted fluorescence signal of liquid DNT as a function of pump laser wavelength at various laser fluences. Signals have been normalized to their peak values at 236.2 nm . Symbols are experimental data, while the curves are predicted NO fluorescence for two different rotational temperatures.

Fig. 8
Fig. 8

TNT cross section as a function of fluence for PD-LIF (squares) and Raman detection (upper and lower bounds denoted by dashed lines). The Raman cross sections are from [19, 20]. Note PD-LIF cross section estimates assume that the number of particles probed per pulse was constant with fluence and equal to the measured value at 10 mJ / cm 2 .

Tables (1)

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Table 1 Structures and Physical Properties of Compounds under Study a

Equations (2)

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N photon = F n σ eff η .
σ eff = σ abs η NO σ exc σ fl .

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