Abstract
We report the development of a non-contact no-reagents system operating in the eye-safe 1560-1800 nm wavelength range for standoff trace detection of explosives and high-speed imaging. Experimental results are provided for a number of chemicals including explosives on a variety of surfaces at sub-microgram per cm2 concentration. Chemically specific images were collected at 0.06 ms per pixel. Results from this effort indicate that the combination of modern industrial fiber lasers and nonlinear optical spectroscopy can address next generation eye-safe trace detection of chemicals including explosives.
Highlights
Trace detection of explosives has been an ongoing challenge for decades, and despite technical advances, direct contact using swabs analysed by ion mobility remain in use
A range of compounds including explosives deposited on a variety of unclean surfaces including bare metal, painted car panels, automotive glass and nylon fabric were identified at a rate of 0.06 ms per pixel
When the backscatter CARS signal is detected by a spectrometer or an optical spectrum analyzer, we can acquire a CARS spectrum; in the absence of a spectrometer we are able to obtain a spectrum with a single photodiode by scanning the phase of the input laser
Summary
Trace detection of explosives has been an ongoing challenge for decades, and despite technical advances, direct contact using swabs analysed by ion mobility remain in use. Near-infrared wavelength lasers have been considered impractical because the spontaneous Raman signal from a 1550 nm laser would be 1477 times weaker than the signal from a 250 nm laser, based on the inverse 4th-power wavelength dependence mentioned above Stimulated processes, such as coherent anti-Stokes Raman scattering (CARS), do not have the same wavelength dependence because they are stimulated by the field. A broadband source, Fig. 1(b), can be used to obtain CARS signals from a single laser shot by using different spectral regions for the pump, Stokes, and probe [3, 5, 21] In this process the probe beam is modulated by the coherent vibrations leading to emission proportional to the third-order susceptibility, χ(3), which can be written as [22, 23]. In a published comparison CARS was shown to produce a 105-106 times greater signal than spontaneous Raman scattering [26]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
