Abstract
Femtosecond optical parametric oscillators (OPOs) produce broadband mid-infrared (mid-IR) light with excellent spatial coherence and spectral brightness, making them well suited for open-path spectroscopy [1]. Here, we present some of the first examples of stand-off chemical detection using a broadband mid-IR OPO, with spectral coverage from 2700–3200 cm−1. Our principal approach employs Fourier-transform infrared (FTIR) spectroscopy, in which idler radiation from the OPO enters a scanning Michelson interferometer before being launched towards a target (Fig. 1a), typically of concrete or chemical agent resistant coating (CARC) paint. The technique has allowed us to identify the presence of both airborne chemicals (Fig. 1b, c) and liquids adhered to the target surface. The light returned from the target is typically backscattered over a 20–40° angular range, before collection by a 50-mm-diameter lens and detection on a PbSe or HgCdZnTe detector.
© 2015 IEEE
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