Photoacoustic spectroscopy for trace vapor detection and standoff detection of explosives

Abstract

The Army is investigating several spectroscopic techniques (e.g., infrared spectroscopy) that could allow for an adaptable sensor platform. Current sensor technologies, although reasonably sized, are geared to more classical chemical threats, and the ability to expand their capabilities to a broader range of emerging threats is uncertain. Recently, photoacoustic spectroscopy (PAS), employed in a sensor format, has shown enormous potential to address these ever-changing threats. PAS is one of the more flexible IR spectroscopy variants, and that flexibility allows for the construction of sensors that are designed for specific tasks.PAS is well suited for trace detection of gaseous and condensed media. Recent research has employed quantum cascade lasers (QCLs) in combination with MEMS-scale photoacoustic cell designs. The continuous tuning capability of QCLs over a broad wavelength range in the mid-infrared spectral region greatly expands the number of compounds that can be identified. We will discuss our continuing evaluation of QCL technology as it matures in relation to our ultimate goal of a universal compact chemical sensor platform. Finally, expanding on our previously reported photoacoustic detection of condensed phase samples, we are investigating standoff photoacoustic chemical detection of these materials. We will discuss the evaluation of a PAS sensor that has been designed around increasing operator safety during detection and identification of explosive materials by performing sensing operations at a standoff distance. We investigate a standoff variant of PAS based upon an interferometric sensor by examining the characteristic absorption spectra of explosive hazards collected at 1 m.

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

“…A research group at the U.S. Army Research Laboratory (ARL) has been focused on the research of laser interferometer-based PAS sensor used for standoff hazardous materials detection [150][151][152][153]. The simplified schematic diagram of their PAS sensor setup is shown in Figure 6, the components remain basically the same with the exception of a laser Doppler vibrometer (LDV) that replaces the traditional microphone.…”

Recent Developments in Spectroscopic Techniques for the Detection of Explosives

“…Due to the importance of rapid, automatic, and non-contact detection of explosives for homeland security and environmental safety [8], a variety of spectroscopic technologies have been employed to detect trace quantities of explosives; for example, terahertz (THz) spectroscopy [9,10], laser induced breakdown spectroscopy (LIBS) [11,12,13,14,15,16], Raman spectroscopy [17,18,19,20,21,22], ion mobility spectrometry (IMS) [23,24,25,26], nuclear magnetic resonance (NMR) [27,28,29,30], nuclear quadrupole resonance (NQR) [31,32,33], laser-induced thermal emissions (LITE) [34,35], infrared (IR) spectroscopy [36,37,38], mass spectrometry [39,40,41,42,43,44,45,46], optical emission spectroscopy (OES) [47,48], photo-thermal infrared imaging spectroscopy (PT-IRIS) [49,50,51], photoacoustic techniques [52,53,54], FT-FIR spectroscopy [55], microwave [56], and millimeter-wave [57], etc. Various electromagnetic radiations such as X-ray [58] and γ rays [59] have also been employed in explosive detection.…”