Quantitative modeling of complex molecular response in coherent cavity-enhanced dual-comb spectroscopy

TL;DR

This paper develops a complex-valued electric field model for cavity transmission in coherent cavity-enhanced dual-comb spectroscopy, validated with near-infrared spectra of CO and CO2, achieving high-precision measurement of a vibrational band.

Contribution

It introduces a novel transmission model for CE-DCS that accounts for the non-interacting local oscillator, differing from previous Fourier-transform models.

Findings

Validated model with near-infrared spectra of CO and CO2.

Achieved measurement of CO2 vibrational band with 770 kHz uncertainty.

Demonstrated high-finesse cavity measurement precision.

Abstract

We present a complex-valued electric field model for experimentally observed cavity transmission in coherent cavity-enhanced (CE) multiplexed spectroscopy (i.e., dual-comb spectroscopy, DCS). The transmission model for CE-DCS differs from that previously derived for Fourier-transform CE direct frequency comb spectroscopy [Foltynowicz et al., Appl. Phys. B 110, 163-175 (2013)] by the treatment of the local oscillator which, in the case of CE-DCS, does not interact with the enhancement cavity. Validation is performed by measurements of complex-valued near-infrared spectra of CO and CO$_2$ by an electro-optic frequency comb coherently coupled to an enhancement cavity of finesse $F=19600$. Following validation, we measure the $30012\leftarrow00001$ $^{12}$C$^{16}$O$_2$ vibrational band origin with a combined standard uncertainty of 770 kHz (fractional uncertainty of $4\times10^{-9}$).