Sensitive multiplex spectroscopy in the molecular fingerprint 2.4 μm region with a Cr2+:ZnSe femtosecond laser

An ultrashort-pulse Cr2+:ZnSe laser is a novel broadband source for sensitive high resolution molecular spectroscopy. A 130-fs pulse allows covering of up to 380 cm(-1) spectral domain around 2.4 mu m which is analyzed simultaneously with a 0.12 cm(-1) (3.6 GHz) resolution by a Fourier-transform spectrometer. Recorded in 13 s, from 70-cm length absorption around 4150 cm(-1), acetylene and ammonia spectra exhibit a 3800 signal-to-noise ratio and a 2.4.10(-7) cm(-1). Hz(-1/2) noise equivalent absorption coefficient at one second averaging per spectral element, suggesting a 0.2 ppbv detection level for HF molecule. With the widely practiced classical tungsten lamp source instead of the laser, identical spectra would have taken more than one hour. (C) 2007 Optical Society of America.