Abstract

The last three years 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~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 shown¹ efficient cavity injection and obtained atmospheric molecular spectra with a good repetition rate (5Hz) and a detection limit better than 5.10⁻⁸/cm.

© 2000 IEEE