Cavity-enhanced saturated absorption spectroscopy of the (30012) − (00001) band of 12C16O2

Abstract

The (30012) ← (00001) band of 12C16O2 in the 1.6 μm region is used for satellite observation of carbon dioxide in the Earth’s atmosphere. Here, we report a Doppler-free spectroscopy study of this band with comb-locked wavelength-modulated cavity-enhanced absorption spectroscopy. Frequencies of 18 transitions with the rotational quantum numbers up to 42 were determined with sub-kHz accuracy, corresponding to a fractional uncertainty at the 10−12 level. With this precision, we revealed an anomalous decrease of the line shift and an increase of the line broadening for the Lamb dips of CO2 in the low-pressure regime compared to values obtained from Doppler-limited spectra at higher pressures.

12CO2 transition frequencies with kHz-accuracy by saturation spectroscopy in the 1.99–2.09 μm region

“…As a result, the pressure shift is observed to evolve from a value of ∼−0.23 kHz Pa −1 (or −7.8 × 10 −4 cm −1 atm −1 ) at very low pressure to an high pressure value which has a 10 times larger amplitude (−2.24 kHz Pa −1 or −7.57 × 10 −3 cm −1 atm −1 ) according to HITRAN2020. 49 This variation is similar to that reported in Tan et al 14 for the P(10) transition of the 30012-00001 band of 12 CO 2 : a pressure shift of −0.35 ± 0.08 kHz Pa −1 was measured below 4 Pa, i.e. a four times smaller than the −1.7 kHz Pa −1 pressure shift coefficient recommended in the HITRAN database.…”

“…In particular, transition frequencies with kHz-accuracy were determined both in the Doppler limited regime 8,9,12,13 and in the saturation regime. 10,14…”

“…These missions are increasingly demanding in terms of high quality spectroscopic data for the CO 2 absorption bands in the 1.6 and 2.0 mm regions used for these measurements. In the former spectral region, numerous line profile studies [2][3][4][5][6] as well as highly accurate frequency measurements [7][8][9][10][11][12][13][14] have been reported so far. In particular, transition frequencies with kHz-accuracy were determined both in the Doppler limited regime 8,9,12,13 and in the saturation regime.…”

Absolute frequency metrology of buffer-gas-cooled molecular spectra at the 10-12 accuracy level

“…In this configuration, we address the acetylene (ν 1 +ν 3 ) R(1)e ro-vibrational line at 6561.0941 cm −1 in a 20-K cell specimen, demonstrating absolute line-center frequency measurements with an overall (statistical + systematic) fractional uncertainty as low as 6 × 10 −12 . In fact, by equaling the highest accuracy levels obtained so far with long-standing methodologies involving room-temperature samples [25][26][27][28][29][30], our achievement marks the birth of frequency metrology on cold spectra.…”

Absolute frequency metrology of buffer-gas-cooled molecular spectra at 1 kHz accuracy level

“…In this configuration, by way of example, we address the acetylene (ν 1 + ν 3 ) R(1)e ro-vibrational line at 6561.0941 cm −1 in a 20-K cell specimen, demonstrating absolute line-center frequency measurements with an overall (statistical + systematic) uncertainty as low as 1.2 kHz (6 × 10 −12 in fractional terms). In fact, by ranking with the highest accuracy levels obtained so far with deep-rooted methodologies involving room-temperature cell samples, either in the Doppler-limited 33,34 or Doppler-free regime [35][36][37][38][39][40] , our achievement finally opens a metrological perspective to the spectroscopy of buffer-gas-cooled molecules.…”