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

摘要

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 μm 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.