Doppler-limited HO and HF absorption spectroscopy by sweeping the 1,321-1,354 nm range at 55 kHz repetition rate using a single-mode MEMS-tunable VCSEL.

A single longitudinal mode micro-electro-mechanical system-tunable vertical cavity surface-emitting laser (VCSEL) was used to measure H $$_{2}$$O and HF absorption spectra in the 1,321-1,354 nm range at 55 kHz repetition rate ( $$\sim $$740 MHz/ns tuning rate). Pulse delay referencing was used to achieve an absorbance noise level of 0.004 (RMS), within a factor of 2.6 of the shot noise limit. The measured linewidths approach the low-pressure feature linewidths ( $$\sim$$790 MHz) characteristic of the gases studied, highlighting the single-mode nature of the VCSEL throughout each rapid wavelength sweep. At even higher tuning rates, molecular features became asymmetric and broad, consistent with rapid passage and Fourier effects. [ABSTRACT FROM AUTHOR]