Infrared backscatter imaging spectroscopy of trace analytes at standoff

Abstract

We are developing a proximal noncontact detection technique for trace amounts of hazardous materials using diffuse reflectance infrared spectral signatures. Spectroscopy is performed at a distance by tuning a quantum cascade laser system through its wavelength range (6-11 μm) as the active illumination source and collecting a portion of the diffusely reflected light from the target onto an MCT focal plane array. The signals from each collected frame are binned and processed into an image hypercube that contains spectral and spatial information. The primary motivation of this work is to protect the loss of life by detecting trace explosives on contaminated surfaces before attacks occur. Here, we present results from backscatter experiments on trace samples with low loading and fill factors on glass substrates and compare them with a conventional benchtop analysis technique, FTIR diffuse reflectance. The backscatter results illustrate the ability to detect explosives at 1 m distance at the nanogram level, which is beyond the capability of the benchtop FTIR diffuse reflectance measurement.

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

“…A new heterodyne interferometric method for optical signal detection in photoacoustic or photothermal spectroscopy has been demonstrated and characterized recently, which enables high sensitivity and three-dimensional spatial gas distribution measurement [249]. Moreover, LAS has been combined with hyperspectral imaging, named infrared backscatter imaging spectroscopy [250,251], for the detection of trace amount of hazardous materials. Like CT-TDLAS, other standoff LAS-based detection techniques can also be combined with CT technology to measure 2D or even 3D information for threat localization [252].…”

Setup and Analysis of a Mid-Infrared Stand-Off System to Detect Traces of Explosives on Fabrics

“…The invention of quantum cascade lasers (QCLs) has particularly enabled the detection of trace materials at distances of up to one hundred meters [ 14 ], as QCLs exhibit an increased output power of up to hundreds of milliwatts. Stable operation in a large spectrum of wavelengths, mode-hop-free tuning, and a narrow line width at various operating conditions are other factors that make QCLs interesting for detection of hazardous substances [ 15 , 16 , 17 ] and gas analysis [ 18 , 19 ].…”

“…A classification algorithm for fast data analysis needs to be trained using a large variety of data that have to be generated by measurements and can be helped by the development of a reliable model to augment the data. Each of these aspects has its disadvantages: An enormous number of measurements is needed, which is laborious and makes taking all possible influencing factors (e.g., types of fabrics, geometries …) into a model with a high enough accuracy impossible [ 16 , 21 , 22 ]. In a first step toward such automatic detection and classification, the IR spectra of a variety of explosives such as trinitrotoluene (TNT) and royal demolition explosive (RDX) were measured at several angles of incidence, on multiple substrates and using varied amounts of sample material.…”

Standoff Detection of Oil and Powder Mixtures at 12 Meters Using a Tunable Quantum Cascade Laser-Based System with a Close Focus Telescope and Uncooled Infrared Detector

“…Although QCLs have yet to travel to another planet as part of a NASA exploration mission, there is great interest in the technology as investigators continue to advance its use in standoff applications involving chemical detection [4][5][6][7][8][9][10][11][12][13][14][15][16] and as the technology continues to evolve. As an example, Galán-Freyle Lawrence Livermore National Laboratory, Livermore, CA, USA and coworkers 17 have reported using three integrated mid-IR QCLs to cover a spectral range of 990-1600 cm À1 .…”