Cavity ring down with optically coupled diode laser applied to ultra-sensitive atmospheric trace detection

Summary form only given. During the last three years of the 1990s we have been developing CW-cavity ring down spectroscopy using single mode distributed feedback (DFB) diode lasers for application to trace gas detection. This technique relies on the measurement of the photon lifetime in a high finesse (F/spl sim/10.000) optical cavity. A difficult point in CW-CRDS is to perform the injection of the laser radiation (typical linewidth 10 MHz) into the narrow cavity resonances (typical linewidth 10 kHz). This has to be done while maintaining as high as possible a scanning rate of the laser frequency. Our approach is to develop optical servo-control of the laser to the cavity modes. By using optical feedback from a three mirrors cavity (V-cavity), we have shown efficient cavity injection and obtained atmospheric molecular spectra with a good repetition rate (5 Hz) and a detection limit better than 5.10/sup -8//cm.