High-speed mass flux measurements using mid-infrared electro-optic dual-comb spectroscopy.

Abstract

We demonstrate a tunable, high-speed mid-infrared dual-comb spectrometer for high-time-resolution measurements of mass flux in gases. The spectrometer combines near-infrared electro-optic combs with a singly resonant, continuous-wave optical parametric oscillator. Compared with mode-locked combs, these electro-optic combs provide watt-class power, adjustable tooth spacing, rapid acquisition, and narrower spectral bandwidth. Single-shot measurements of CO2 temperature, velocity, and concentration in a pulsed jet, combined with pressure data, yield transient mass flux. We achieve 1 µs time resolution with 19 teeth (∼1.5 GHz spacing, ∼1 cm-1 bandwidth) and demonstrate 20 ns single-shot methane absorption measurements, highlighting our approach's flexibility, speed, and sensitivity.

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