, Volume 108, Issue 4, pp 721-725

Doppler-limited H2O 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

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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.