• Mark F Witinski, Romain Blanchard, Christian Pfluegl, Laurent Diehl, Biao Li, Kalyani Krishnamurthy, Brandt C Pein, Masud Azimi, Peili Chen, Gokhan Ulu, Greg Vander Rhodes, Chris R Howle, Linda Lee, Rhea J Clewes, Barry Williams, and Daryoosh Vakhshoori.
• Opt Express. 2018 Apr 30; 26 (9): 12159-12168.

AbstractThis article presents new spectroscopic results in standoff chemical detection that are enabled by monolithic arrays of Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), with each array element at a slightly different wavelength than its neighbor. The standoff analysis of analyte/substrate pairs requires a laser source with characteristics offered uniquely by a QCL Array. This is particularly true for time-evolving liquid chemical warfare agent (CWA) analysis. In addition to describing the QCL array source developed for long wave infrared coverage, a description of an integrated prototype standoff detection system is provided. Experimental standoff detection results using the man-portable system for droplet examination from 1.3 meters are presented using the CWAs VX and T-mustard as test cases. Finally, we consider three significant challenges to working with droplets and liquid films in standoff spectroscopy: substrate uptake of the analyte, time-dependent droplet spread of the analyte, and variable substrate contributions to retrieved signals.

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