Contributed Review: Quantum cascade laser based photoacoustic detection of explosives

Abstract

Detecting trace explosives and explosive-related compounds has recently become a topic of utmost importance for increasing public security around the world. A wide variety of detection methods and an even wider range of physical chemistry issues are involved in this very challenging area. Optical sensing methods, in particular mid-infrared spectrometry techniques, have a great potential to become a more desirable tools for the detection of explosives. The small size, simplicity, high output power, long-term reliability make external cavity quantum cascade lasers (EC-QCLs) the promising spectroscopic sources for developing analytical instrumentation. This work reviews the current technical progress in EC-QCL-based photoacoustic spectroscopy for explosives detection. The potential for both close-contact and standoff configurations using this technique is completely presented over the course of approximately the last one decade.

Standoff Photoacoustic Spectroscopy of Explosives

“…3,4,9 Investigating solid samples using the photoacoustic technique is advantageous as it allows optical absorption measurements to be made for optically opaque samples and is insensitive to scattered light. This unique capability of photoacoustic spectroscopy for the investigation of solid samples is attractive, [10][11][12][13][14] especially in comparison to commonly used passive IR reflectance techniques. Reflectance data can depend strongly on the refractive index of the sample, the particle size and size distribution, packing density, and sample homogeneity.…”

Deep Ultraviolet Standoff Photoacoustic Spectroscopy of Trace Explosives

“…This contrasts with previous QCTF-based approaches, which indirectly produce a photoacoustic response by focusing the IR scattered light from the explosive target onto a tuning fork. 14,16,17 In this investigation, we developed an instrument for the standoff detection of trace explosives by using deep UV PAS with a sensitive microphone. We use a laser wavelength of 213 nm, which is near to the peak absorptions of most explosives to induce a PAS response.…”

Optical frequency comb Faraday rotation spectroscopy

“…Laser-based spectroscopy for quantitative gas detection offers high sensitivity, high species specificity and the possibility of performing real-time measurements in situ without sample consumption. Laser-based gas sensors have found applications in fields ranging from fundamental science [1] and environmental monitoring [2][3][4] to medical diagnostics [5,6] and security [7,8]. However, the inherently limited optical bandwidths of these sensors have mostly restricted them to single species detection in spectral regions that are free from spectral interferences.…”