Quantum Cascade Lasers with Submicrosecond Tuning Speed for the Detection of High Explosives and Chemical Warfare Agents

Project Overview

Military convoys in theater need to perform chemical detection while in transit. This proposed study will determine the feasibility of detecting chemical compounds at standoff distances. For this work, we have designed and demonstrated a quantum cascade laser- (QCL-) based standoff system for chemical identification at distances of 12 meters in indoor ambient light conditions. In the system, light is collected using a 10-inch Dall Kirkham telescope directly coupled via zinc selenide (ZnSe) optics to an uncooled infrared detector. A tunable quad-QCL operating in quasi-continuous wave (1 megahertz (MHz)) mode between 8.45 to 10.03 microns (~1182 to 1000 cm^-1) serves as the wavelength source for remotely interrogating mineral, powder, and thin film oil samples including powder mixtures (6, 12.5, 25, 50 and 100% w/w) of potassium bromide (KBr) and crystalline quartz prepared using resonant acoustic mixing. The mixture dependence of the highly transparent KBr and strongly absorbing and scattering quartz was found to fit a modified version of the Schatz reflectance model for compacted powder mixtures. All reflectance measurements were normalized against a gold-coated diffuse reflector reference. A polystyrene reference standard was used to confirm the QCL wavelength tuning accuracy.

Mission Impact

This technology is applicable to aging and compatibility of materials (solid, liquid, or gas) in support of stockpile stewardship and life extension programs efforts and high explosives science to enable measurements of transient or rapidly changing processes in real time and in situ. Furthermore, this technology provides a unique sensing capability for threat reduction in theater and the homeland in response to high explosives, chemical agents, and feedstocks. The acousto-optic tuning quantum cascade laser (AOT-QCL) fast scan capability could localize objects of forensic interest for identification.

Publications, Presentations, and Patents

J. Chance Carter, Phillip H. Paul, Joshua M. Ottaway, Peter Haugen, Anastacia M. Manuel, "Standoff Detection of Oil and Powder Mixtures at 12 Meters Using a Tuneable Quantum Cascade Laser-Based System with a Close Focus Telescope and Uncooled Infrared Detector," in press for January 2022 publication in special issue of Applied Spectroscopy.