11-{\mu}s Time-resolved, Continuous Dual-Comb Spectroscopy with Spectrally Filtered Mode-locked Frequency Combs

TL;DR

This paper introduces a high-speed dual-comb spectroscopy technique achieving 11 microseconds time resolution by spectrally filtering mode-locked fiber combs, enabling rapid, high-resolution measurements of gases in dynamic environments.

Contribution

The authors demonstrate a novel method of spectrally filtering fiber mode-locked combs to significantly increase DCS acquisition speed and resolution, enabling real-time measurements of fast-changing systems.

Findings

Achieved 11 μs time-resolved dual-comb spectroscopy.

Measured methane spectra during rapid compression cycles.

Captured single-shot CO spectra in 11 μs.

Abstract

Broadband dual-comb spectroscopy (DCS) based on portable mode-locked fiber frequency combs is a powerful tool for in situ, calibration free, multi-species spectroscopy. While the acquisition of a single spectrum with mode-locked DCS typically takes microseconds to milliseconds, the applications of these spectrometers have generally been limited to systems and processes with time changes on the order of seconds or minutes due to the need to average many spectra to reach a high signal-to-noise ratio (SNR). Here, we demonstrate high-speed, continuous, fiber mode-locked laser DCS with down to 11 $\mu$s time resolution. We achieve this by filtering the comb spectra using portable Fabry-Perot cavities to generate filtered combs with 1 GHz tooth spacing. The 1 GHz spacing increases the DCS acquisition speed and SNR for a given optical bandwidth while retaining a sufficient spacing to resolve absorption features over a wide range of conditions. We measure spectra of methane inside a rapid compression machine throughout the 16 ms compression cycle with 133 cm$^{-1}$ bandwidth (4000 comb teeth) and 1.4 ms time resolution by spectrally filtering one of the combs. By filtering both combs, we measured a single-shot, 25 cm$^{-1}$ (750 comb teeth) spectrum of CO around 6330 cm$^{-1}$ in 11 $\mu$s. The technique enables simultaneously high-speed and high-resolution DCS measurements, and can be applied anywhere within the octave-spanning spectrum of robust and portable fiber mode-locked frequency combs.