Cavity-Enhanced Frequency-Comb-Based Optical-Optical Double-Resonance Spectrometer
Résumé
Optical-optical double resonance spectroscopy (OODR) using a continuous wave (CW) pump and a frequency comb probe is a powerful tool for measuring and assigning hot-band transitions with high selectivity and accuracy [1]. In the first demonstration of the technique, we detected transitions in the 3ν3 ← ν3 range of methane with ~1.7 MHz accuracy, using a 3.3 μm CW pump and 1.67 μm comb probe, and a liquid-nitrogen-cooled single pass cell containing the sample [2]. Later on, we introduced a room-temperature enhancement cavity to increase the absorption sensitivity for the comb probe and reach sub-MHz accuracy on probe transition frequencies [3]. However, the transmitted comb probe coverage was limited by the dispersion of the cavity mirrors and the offset frequency (fceo) was monitored but not actively stabilized, which complicated the data averaging process.