CW CAVITY RING DOWN SPECTROSCOPY

Until now, applications of cavity ring down spectroscopy (CRDS) employ ed pulsed laser sources. Here, we demonstrate that a commercial single -frequency CW laser can also be conveniently employed, allowing to gai n in spectral resolution, signal intensity and data acquisition rate. As a demonstration, we measured a section of the weak HCCH overtone tr ansition near 570 nm, and compare to existing photoacoustic data. Our high quality and reproducible Doppler-limited spectra display a (rms) noise-equivalent absorption of 10(-9)/cm or 5 x 10(-8) per pass throug h the sample. Most interesting applications of CW-CRDS include high re solution spectroscopy at low pressure, sub-Doppler absorption spectros copy in a supersonic jet, and trace-gas detection using compact diode laser sources.