Temperature dependence of the air-broadened line-shape parameters of the 1.27 µm O2-band

Abstract

Satellite missions are considering the atmospheric O₂ band at 1.27 µm to determine the air-column. A prerequisite of these demanding atmospheric applications is an accurate knowledge of the spectroscopy of this band, in particular of the line profiles and their temperature dependence. In the present work, fifty-five transitions of the 1.27 µm band of O₂ have been studied with a cavity ring down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator. The comb-coherence transfer (CCT) technique was applied to obtain a RF tunable narrow-line comb-disciplined laser source from a set of distributed feedback laser diodes and a simple electro-optic modulator. High-quality spectra were obtained with a high-finesse cavity regulated at 253, 273 and 333 K. For each transition and each temperature, series of synthetic dry air spectra were recorded for five pressures, from 50 to 750 Torr. The line-shape parameters were retrieved thanks to a multi-spectrum fit procedure with a quadratic speed-dependent Nelkin-Ghatak profile and first-order line-mixing effect when required. For each transition, the temperature dependence exponents and coefficients of the different line profile parameters together with their values at the reference temperature of 296 K were determined. Absolute positions and intensities are provided by the fit with an average accuracy of 240 kHz (or 8 × 10^–6 cm^-1) and 0.2 %, respectively. An effect of intensity depletion with pressure on the order of 0.4 % atm^-1 is evidenced. Comparison with literature, in particular with the HITRAN2020 database is discussed.