INTRACAVITY LASER-ABSORPTION MEASUREMENTS AT ULTRAHIGH SPECTRAL RESOLUTION

Intracavity laser absorption spectroscopy with ultrahigh sensitivity a nd enhanced spectral resolution is demonstrated. It entails use of an intracavity etalon that selects equally spaced modes of the cavity. Th ese modes are reduced in intensity when they occur at spectral locatio ns where absorption that is due to intracavity species also occurs. We obtained absorption spectra by tuning the etalon in small steps acros s its free spectral range, recording intracavity spectra at each step, and summing the result. The maximum resolution is determined by the w idth of the etalon peaks, which was similar to 0.01 cm(-1). When the f inesse of the etalon is increased, the resolution equal to the width o f a single laser mode can be achieved. With this technique, spectra at Doppler-free resolution such as that required for studies of high vib rational-overtone transitions of molecules in supersonic jets are poss ible. (C) 1997 Optical Society of America.