We present a new cavity ring-down spectroscopy (CRDS) apparatus suitable for high-resolution absorption spectroscopy. The central feature of the spectrometer is a ring-down cavity whose comb of eigenfrequencies is actively stabilized with respect to a tuneable, frequency-stabilized reference laser. By using dichroic mirrors that are designed to have relatively high and low losses at the respective wavelengths of the reference laser and probe laser, the cavity stabilization dynamics are decoupled from frequency jitter of the probe laser. We use the cavity eigenfrequencies as markers in spectral scans and achieve a frequency resolution of 1 MHz. Five rovibronic transitions in the (2,0,1) vibrational band of water vapor near 0.935 m are probed with a continuous-wave external cavity diode laser, and their line strengths are determined and compared to literature values. Collisional narrowing effects and pressure shifting are observed, illustrating the applicability of the method for quantitative line shape studies of weakly absorbing systems.
Citation: Review of Scientific Instruments
Issue: No. 4
Pub Type: Journals
Absorption, cavity ring-down spectroscopy, laser spectroscopy, water vapor