Modulated-laser source induction system for remote detection of infrared emissions of high explosives using laser-induced thermal emission
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Fecha
2020
Autores
Galán-Freyle, Nataly J.
Pacheco-Londoño, Leonardo C.
Figueroa-Navedo, Amanda M.
Ortiz-Rivera, William
Castro-Suarez, John R.
Hernández-Rivera, Samuel P.
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Editor
Optical Engineering
Resumen
In a homeland security setting, the ability to detect explosives at a distance is a top
security priority. Consequently, the development of remote, noncontact detection systems continues
to represent a path forward. In this vein, a remote detection system for excitation of infrared
emissions using a CO2 laser for generating laser-induced thermal emission (LITE) is a
possible solution. However, a LITE system using a CO2 laser has certain limitations, such
as the requirement of careful alignment, interference by the CO2 signal during detection, and
the power density loss due to the increase of the laser image at the sample plane with the detection
distance. A remote chopped-laser induction system for LITE detection using a CO2 laser
source coupled to a focusing telescope was built to solve some of these limitations. Samples of
fixed surface concentration (500 μg∕cm2) of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) were
used for the remote detection experiments at distances ranging between 4 and 8 m. This system
was capable of thermally exciting and capturing the thermal emissions (TEs) at different times in
a cyclic manner by a Fourier transform infrared (FTIR) spectrometer coupled to a gold-coated
reflection optics telescope (FTIR-GT). This was done using a wheel blocking the capture of TE
by the FTIR-GT chopper while heating the sample with the CO2 laser. As the wheel moved, it
blocked the CO2 laser and allowed the spectroscopic system to capture the TEs of RDX.
Different periods (or frequencies) of wheel spin and FTIR-GT integration times were evaluated
to find dependence with observation distance of the maximum intensity detection, minimum
signal-to-noise ratio, CO2 laser spot size increase, and the induced temperature increment
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Palabras clave
Standoff detection, Laser-induced thermal emission, Highly energetic materials, Midinfrared emission spectroscopy, Carbon dioxide laser