Frequency-comb infrared spectrometer for rapid, remote chemical sensing.

We demonstrate real-time recording of chemical vapor fluc-tuations from 22m away with a fast Fourier-transform infrared (FTIR) spectrometer that uses a laser-like infrared probing beam generated from two 10-fs Ti:sapphire lasers. The FTIR's broad 9-12 microm spectrum in the "molecular fingerprint" region is dispersed by fast heterodyne self-scanning, enabling spectra at 2cm-1 resolution to be recorded in 70 micros snapshots. We achieve continuous acquisition at a rate of 950 IR spectra per second by actively manipulating the repetition rate of one laser. Potential applications include video-rate chemical imaging and transient spectroscopy of e.g. gas plumes, flames and plasmas, and generally non-repetitive phenomena such as those found in protein folding dynamics and pulsed magnetic fields research.