Abstract
Dual-comb spectroscopy (DCS) offers high sensitivity and wide spectral coverage without the need for bulky spectrometers or mechanical moving parts. And DCS in the mid-infrared (mid-IR) is of keen interest because of inherently strong molecular spectroscopic signatures in these bands. We report GHz-resolution mid-IR DCS of methane and ethane that is derived from counter-propagating (CP) soliton microcombs in combination with interleaved difference frequency generation. Because all four combs required to generate the two mid-IR combs rely upon stability derived from a single high-Q microcavity, the system architecture is both simplified and does not require external frequency locking. Methane and ethane spectra are measured over intervals as short as 0.5 ms, a time scale that can be further reduced using a different CP soliton arrangement. Also, tuning of spectral resolution on demand is demonstrated. Although at an early phase of development, the results are a step towards mid-IR gas sensors with chip-based architectures for chemical threat detection, breath analysis, combustion studies, and outdoor observation of trace gases.
Highlights
Dual-comb spectroscopy (DCS) offers high sensitivity and wide spectral coverage without the need for bulky spectrometers or mechanical moving parts
Dual-comb spectroscopy (DCS) works by mapping an optical comb of frequencies into radio-frequencies by multi-heterodyne beat with a second comb having a slightly different repetition rate
Comb generation in the mid-infrared has traditionally used methods that rely upon mode-locked pulse generation, including difference-frequency-generation (DFG), optical parametric oscillation, and supercontinuum generation[3,4]; and there is considerable progress using such systems for mid-IR DCS5–14
Summary
Dual-comb spectroscopy (DCS) offers high sensitivity and wide spectral coverage without the need for bulky spectrometers or mechanical moving parts. We report GHz-resolution mid-IR DCS of methane and ethane that is derived from counter-propagating (CP) soliton microcombs in combination with interleaved difference frequency generation. Offering high repetition rates and chip integration are soliton microcombs[20,21]. On account of their compact size, these devices operate readily in the X to millimetre-wave bands. The two GHz-rate mid-IR combs are generated by interleaved difference-frequency-generation (iDFG)[33] applied to four near-IR combs. These four combs are linked to counterpropagating (CP) solitons[34] formed within a single microcavity
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