Adam J. Fleisher, David A. Long, Zachary D. Reed, David F. Plusquellic, Joseph T. Hodges
Multiheterodyne spectroscopy performed with two stabilized optical frequency combs (OFCs) has shown great potential as a fast, accurate, and high-resolution substitute for existing interferometry methods that require lengthy integration times and precision moving parts (e.g., Fourier transform spectroscopy). The inclusion of long interaction paths between a probe comb and a gas-phase sample, either via an open-air path or an enhancement cavity, has yielded impressive sensitivities for several small molecules important for precise atmospheric monitoring. In order to achieve appropriate sensitivities, however, these initial demonstrations required several high-bandwidth phase-lock loops and software-controlled phase corrections to maintain relative OFC laser coherence for an integration time ≈1 s. In this letter, we demonstrate a frequency-agile alternative approach to dual-comb spectroscopy using two electro-optic modulator (EOM) combs originating from a single continuous-wave (CW) laser capable of >1 hour of coherent real-time averaging. The OFCs of 52 GHz optical bandwidth (256 teeth) were generated using compact step recovery diodes, passive electronic devices that provided low-phase-noise harmonics for efficient comb-cavity coupling, and therefore the sensitivity to simultaneous monitor CO2, CO and H2O over a 10 km effective path in as little as 10 μs.
, Long, D.
, Reed, Z.
, Plusquellic, D.
and Hodges, J.
Coherent cavity-enhanced dual-comb spectroscopy, Optics Express, [online], https://doi.org/10.1364/OE.24.010424
(Accessed June 3, 2023)