Standoff Detection of Solid Traces by Single-Beam Nonlinear Raman Spectroscopy Using Shaped Femtosecond Pulses

TL;DR

This paper presents a novel single-beam, standoff CARS spectroscopy method using shaped femtosecond pulses for detecting trace materials like explosives from over 10 meters away under ambient light.

Contribution

It introduces a simple, highly sensitive, single-beam CARS technique with spectral resolution below 20cm-1 for remote detection of hazardous substances.

Findings

Successful detection of explosives and nitrates at >10m distance

Utilization of nonresonant background for signal amplification

High spectral resolution achieved with broadband phase-shaped pulses

Abstract

We demonstrate a single-beam, standoff (>10m) coherent anti-Stokes Raman scattering spectroscopy (CARS) of various materials, including trace amounts of explosives and nitrate samples, under ambient light conditions. The multiplex measurement of characteristic molecular vibrations with <20cm-1 spectral resolution is carried out using a single broadband (>550cm-1) phase-shaped femtosecond laser pulse. We exploit the strong nonresonant background signal for amplification of the weak backscattered resonant CARS signal by using a homodyne detection scheme. This facilitates a simple, highly sensitive single-beam spectroscopic technique, with a potential for hazardous materials standoff detection applications.