Broadband Mid-Infrared Stand-Off Reflection–Absorption Spectroscopy Using a Pulsed External Cavity Quantum Cascade Laser. Issue 7 (July 2017)

• Record Type: Journal Article
• Authors: Liu, Xunchen; Chae, Inseok; Miriyala, Naresh; Lee, Dongkyu; Thundat, Thomas; Kim, Seonghwan
• Is Part Of: Applied spectroscopy. Volume 71:Issue 7(2017)
• Page Start: 1494
• Page End: 1505
• Publication Date: 2017-07
• Subjects: Stand-off detection -- quantum cascade laser -- 1, 3, 5-trinitroperhydro-1, 3, 5-triazine -- cyclotrimethylene trinitramine -- RDX -- mid-infrared; Spectrum analysis -- Periodicals; 543.505
• DOI: 10.1177/0003702817693233
• Languages: English
• ISSNs: 0003-7028

Abstract

Broadband mid-infrared molecular spectroscopy is essential for detection and identification of many chemicals and materials. In this report, we present stand-off mid-infrared spectra of 1, 3, 5-trinitro-1, 3, 5-triazine or cyclotrimethylene trinitramine (RDX) residues on a stainless-steel surface measured by a broadband external cavity quantum cascade laser (QCL) system. The pulsed QCL is continuously scanned over 800 cm −1 in the molecular fingerprint region and the amplitude of the reflection signal is measured by either a boxcar-averager-based scheme or a lock-in-amplifier-based scheme with 1 MHz and 100 kHz quartz crystal oscillators. The main background noise is due to the laser source instability and is around 0.1% of normalized intensity. The direct absorption spectra have linewidth resolution around 0.1 cm −1 and peak height sensitivity around 10 −2 due to baseline interference fringes. Stand-off detection of 5–50 µg/cm 2 of RDX trace adsorbed on a stainless steel surface at the distance of 5 m is presented.