Standoff Detection of High Explosive Materials at 50 Meters in Ambient Light Conditions Using a Small Raman Instrument

TLDR

The study aimed to design and demonstrate a standoff Raman system capable of detecting high‑explosive materials up to 50 m in ambient light. The system employs an 8‑in Schmidt–Cassegrain telescope, a fiber‑coupled f/1.8 spectrograph with a gated ICCD detector, and a 532‑nm Nd:YAG pulsed laser (10 Hz) to acquire spectra of samples containing up to 8 % explosives (RDX, TNT, PETN, nitrate‑ and chlorate‑containing materials) at 27 and 50 m, with laser‑power studies assessing heating and photodegradation effects. Raman signal intensity increased linearly with laser energy up to ~3 × 10⁶ W cm⁻² for all samples except TNT, which showed degradation at higher powers, and a 10‑µs detector gate width enabled spectral acquisition under high ambient light.

Abstract

We have designed and demonstrated a standoff Raman system for detecting high explosive materials at distances up to 50 meters in ambient light conditions. In the system, light is collected using an 8-in. Schmidt–Cassegrain telescope fiber-coupled to an f/1.8 spectrograph with a gated intensified charge-coupled device (ICCD) detector. A frequency-doubled Nd: YAG (532 nm) pulsed (10 Hz) laser is used as the excitation source for measuring remote spectra of samples containing up to 8% explosive materials. The explosives RDX, TNT, and PETN as well as nitrate- and chlorate-containing materials were used to evaluate the performance of the system with samples placed at distances of 27 and 50 meters. Laser power studies were performed to determine the effects of laser heating and photodegradation on the samples. Raman signal levels were found to increase linearly with increasing laser energy up to ∼3 × 10 6 W/cm 2 for all samples except TNT, which showed some evidence of photo- or thermal degradation at higher laser power densities. Detector gate width studies showed that Raman spectra could be acquired in high levels of ambient light using a 10 microsecond gate width.