Single-Beam Velocimetry with Dual Frequency Comb Absorption Spectroscopy

TL;DR

This paper introduces a portable dual comb spectrometer-based single-beam velocimetry method that simplifies measurements and maintains high accuracy, demonstrated on a supersonic ramjet engine.

Contribution

It presents a novel single-beam velocimetry technique using dual comb spectroscopy with high stability and a new water vapor absorption database, reducing complexity compared to traditional crossed-beam methods.

Findings

Single-beam measurements within 19 m/s of crossed-beam results

Achieved high frequency accuracy with GPS-referenced dual comb spectrometer

Demonstrated application on supersonic ramjet engine inlet flow

Abstract

Laser absorption Doppler velocimeters use a crossed-beam configuration to cancel error due to laser frequency drift and absorption model uncertainty. This configuration complicates the spatial interpretation of the measurement since the two beams sample different volumes of gas. Here, we achieve single-beam velocimetry with a portable dual comb spectrometer (DCS) with high frequency accuracy and stability enabled by GPS-referencing, and a new high-temperature water vapor absorption database. We measure the inlet flow in a supersonic ramjet engine and demonstrate single-beam measurements that are on average within 19 m/s of concurrent crossed-beam measurements. We estimate that the DCS and the new database contribute 1.6 and 13 m/s to this difference respectively.