Quantum cascade laser based standoff photoacoustic chemical detection

Abstract

Standoff chemical detection with a distance of more than 41 feet using photoacoustic effect and quantum cascade laser (QCL) operated at relatively low power, less than 40 mW, is demonstrated for the first time. The option of using QCL provides the advantages of easy tuning and modulation besides the benefit of compact size, light weight and low power consumption. The standoff detection signal can be calibrated as a function of different parameters such as laser pulse energy, gas vapor concentration and detection distance. The results yield good agreements with theoretical model. Techniques to obtain even longer detection distance and achieve outdoor operations are in the process of implementation and their projection is discussed.

Stand-Off Chemical Detection Using Photoacoustic Sensing Techniques—From Single Element to Phase Array

“…Figure 4b shows the TNT absorption spectrum measured by the CO 2 laser scan with a corresponding absorption peak at 10.65 µm. Similarly, we use IPA vapor (0.13% volume) as a safer experimental substitute of the explosive, which has a strong absorption peak at around 7.9 µm [26]. The emission wavelength of the laser is set accordingly.…”

“…We also evaluated and characterized PA signal and found that it is linearly dependent on laser optical power, chemical vapor density and 1/R where R is the radius with the target chemical as the center. For further details, the reader is encouraged to see our work reported in [26]. Based on these findings, we were able to determine and setup the right parameters for extending our work to the outdoor experiment as described in the following section.…”

“…For example, we demonstrated PA standoff detection of TNT (trinitrotoluene), RDX (research department explosives) and nerve gas stimulant i.e., IPA (isapropanol) vapor. Figure 2 shows one such experiment where QCL was targeted at TNT and a microphone, with the parabolic sound reflector, detected the TNT with a strong SNR (above 10 dB) from a standoff detection distance of 8 feet [24][25][26][27]. Moreover, we improved our PA sensing systems' performance by replacing a single microphone element with an acoustic beam array of multiple microphone elements.…”

Widely Tunable Monolithic Mid-Infrared Quantum Cascade Lasers Using Super-Structure Grating Reflectors

“…Optical sources in the mid-infrared (mid-IR) wavelength range are important for applications including trace gas sensing, explosive detections, spectroscopy and free space communications [1][2][3][4]. Mid-IR quantum cascade laser (QCL) is in unique position to be utilized for these applications.…”

High sensitivity gas sensor based on IR spectroscopy technology and application

“…Presently, the usefulness of the laser spectroscopy approach is limited by the availability of convenient tunable sources in the spectroscopically important "fingerprint" region from 3 μm to 20 μm [1]. Recent measurements with QC-DFB (distributed feedback quantum cascade laser) lasers [2,3] have demonstrated the usefulness of these devices for highly selective real-time trace gas concentration measurements based on the absorption spectroscopy with the sensitivity of several ppb [4][5][6][7][8][9][10][11].…”