CAVITY-LOCKED RING-DOWN SPECTROSCOPY

We have performed cavity ring-down spectroscopy by locking a high-fine sse resonator to the probe laser. We have obtained combination overton e spectra of water vapor in the ambient environment with a baseline no ise of 5x10(-9) cm(-1) for decay constants (R = 99.93% reflectors) of 1 mu s. This cavity-locked approach ensures single transverse mode exc itation, reduces shot-to-shot fluctuations in the decay constant to 4 x 10(-3), and eliminates oscillations in spectral backgrounds. This ap proach also allows ring-down decay acquisition rates limited only by t he ring-down and buildup constants of the resonator, and holds the pro mise of offering truly shot-noise-limited cavity ring-down spectroscop y measurements. (C) 1998 American Institute of Physics.