Achieving kilometric absorption paths using intracavity laser absorption spectroscopy detected by FTS (FT-ICLAS); Development and applications

摘要

We have built an intracavity laser absorption spectrometer based on a pulsed Ti:Sa laser synchronized to a commercial continuous scan interferometer. A two generation times technique was used to improve the signal-to-noise ratio. Overtone absorption spectra will illustrate the technique. Intracavity laser absorption spectroscopy (ICLAS) is based on a laser operated in transient regime leading to a broadband multimode emission. A sample cell is inserted inside the cavity. As the laser modes are building up, the intracavity absorption increases. Recording absorption at time t_(g) (generation time) after switching the pump laser on, allows the equivalent absorption path length inside the sample to become l_(eq)=(l/L) c t_(g), with l and L the resonator and cell lengths, respectively, and c the speed of light. Several kilometers equivalent absorption could be achieved. This technique, first described in the early 70's [1]is mainly based on Ar~(+) pumped Ti:Sapphire lasers, covering the NIR region (e.g. [2-4]); dye lasers in the visible and UV range (e.g. [5-7]); and more recently VECSEL lasers were developed, allowing the lower energy range to be also investigated using ICLAS (e.g [8]), down to some 9500 cm~(-1), so far. For these initial developments, the spectra were mainly recorded using grating spectrometers.