A well-isolated vibrational state of CO₂verified by near-infrared saturated spectroscopy with kHz accuracy

Abstract

Quantitative determination of atmospheric CO2 concentration by remote sensing relies on accurate line parameters.

MOLECULAR TRANSITION FREQUENCES OF CO₂ NEAR 1.6 μ WITH KHZ-LEVEL UNCERTAINTIES

“…This interaction was accounted for in the global fit, significantly reducing uncertainties in the spectroscopic parameters of the (30012) state. We find excellent agreement with literature values, including better than 1 kHz RMS deviation with a recent saturation cavity ring-down study of the ( 30013) ← (00001) band [2]. Agreement is excellent with CDSD 2019 [3] and HITRAN 2016 [4] for the (30013) ← (00001) band, but much poorer for the (30012) ← (00001) band.…”

Comb coherence-transfer and cavity ring-down saturation spectroscopy around 1.65 μm: kHz-accurate frequencies of transitions in the 2ν3 band of 12CH4

“…16 However, only recent advances in laser technology and introduction of high sensitivity detection techniques, such as cavity ring-down spectroscopy (CRDS), make saturation spectroscopy attractive for a wide range of problems in high precision molecular spectroscopy and optical metrology. 6,[17][18][19][20][21][22][23][24][25][26][27] It is important to underline that application of high-finesse optical resonators for saturation spectroscopy demands laser radiation of high spectral purity. A first reason is that Lamb dips are spectrally narrow: Lorentzian widths of less than 500 kHz are typically observed.…”

“…Such approaches are quite complex to implement but were successfully exploited by a few research groups for high precision saturation spectroscopy in the near infrared range. 18,20,22,24 In a related scheme developed by our group, ultra narrow and stable emission from a DFB DL is obtained owing to optical feed-back from a low drift isolated Paper PCCP cavity and is the basis for a tunable source for CRDS saturation spectroscopy. 6 Beating with an OFC is still used for long term absolute frequency calibration.…”

“…Comb-linked frequency-stabilized CRDS was used by the same group (Beijing group, hereafter) to determine the position of the R9 components with an average accuracy of 5 kHz. 59 Very recently, the Beijing group performed new Lamb dip measurements in the R6 region and reported the center of 18 Lamb dips (including the six R6 components) with an accuracy between 15 and 60 kHz (5 Â 10 À7 and 2 Â 10 À6 cm À1 ). 20 Finally, in Liu et al, 58 a detailed study of the R9 region was performed in Hefei (China) by saturated CRDS: 32 dip centers were determined in the 6105.3-6107.3 cm À1 spectral interval, with an accuracy of a few kHz, extending significantly the eleven dip Beijing measurements in the region.…”

“…16 However, only recent advances in laser technology and introduction of high sensitivity detection techniques, such as cavity ring-down spectroscopy (CRDS), make saturation spectroscopy attractive for a wide range of problems in high precision molecular spectroscopy and optical metrology. 6,17–27…”