Single-beam velocimetry with dual frequency comb absorption spectroscopy.

Laser absorption Doppler velocimeters use a crossed-beam configuration to cancel errors 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.

Thermometry and velocimetry in a ramjet using dual comb spectroscopy of the O A-band.

Dual comb spectroscopy (DCS) of near-infrared HO absorption has been demonstrated in the past for low-uncertainty flow measurements in ground test ramjets. However, HO is scarce at actual ramjet flight altitudes, so oxygen is a preferable absorption target. Here, we demonstrate DCS of the O A-band (13000-13200 cm) and fit temperature and velocity across different flow conditions in a ground-test ramjet, demonstrating precisions of 3-5% and 7-11% respectively in five minutes and total uncertainty estimates of 7-9% and 8-12% respectively.