Broadband Mid-Infrared Stand-Off Reflection-Absorption Spectroscopy Using a Pulsed External Cavity Quantum Cascade...

Area of Science:

• Spectroscopy
• Chemical detection
• Materials science

Background:

• Mid-infrared molecular spectroscopy is crucial for identifying chemicals and materials.
• Detection of trace amounts of hazardous materials like explosives is a significant challenge.

Purpose of the Study:

• To present stand-off mid-infrared spectra of 1,3,5-trinitro-1,3,5-triazine (RDX) residues.
• To evaluate a broadband external cavity quantum cascade laser (QCL) system for RDX detection.
• To demonstrate stand-off detection capabilities for RDX on stainless steel surfaces.

Main Methods:

• Utilized a broadband external cavity quantum cascade laser (QCL) system for spectral measurements.
• Scanned the QCL over 800 cm⁻¹ in the molecular fingerprint region.
• Employed boxcar-averager and lock-in amplifier schemes for signal detection, measuring RDX residues on stainless steel at a 5m distance.

Main Results:

• Achieved direct absorption spectra with linewidth resolution of approximately 0.1 cm⁻¹.
• Demonstrated peak height sensitivity around 10⁻² despite baseline interference fringes.
• Successfully performed stand-off detection of 5-50 µg/cm² of RDX trace on stainless steel from 5m.

Conclusions:

• The broadband QCL system is effective for stand-off mid-infrared spectroscopic analysis of RDX residues.
• The developed spectroscopic method shows promise for sensitive and remote detection of explosive traces.