Abstract

Cavity ringdown spectroscopy (CRDS) with continuous-wave (cw) laser excitation has added superior frequency resolution to the capability of conventional pulsed CRDS, making it a more powerful workhorse to be used for the absolute quantification of trace-level species. Among many versatile variants of cw-CRDS implementation, a simple approach proposed by Romanini et al. utilizing a cavity dither operational] have witnessed a wide acceptance to researchers in this field, perhaps for its practical simplicity. The cavity dither technique has easily resolved the problem of resonant coupling of a cw laser light into a high-finesse cavity. Employing further controlled sequences in the cavity scan has led to a novel method to allow for both the appreciable amount of laser light injection into a cavity and the subsequent laser decoupling, without the need for any additional fast switching optics to initiate cavity decay output. [2] In this method, the laser injection into a cavity is accomplished during the slow cavity scan across a cavity resonance, which is then followed by a quick cavity scan away from the cavity resonance to establish antiresonance condition. Obstructing laser coupling via a destructive optical interference has produced ringdown signals, free of any modulating waveforms, to show single-exponential decay with theoretical decay constants.

© 2007 IEEE