Thermometry and velocimetry in a ramjet using dual comb spectroscopy of the O2 A-band.

Dual comb spectroscopy (DCS) of near-infrared H2O absorption has been demonstrated in the past for low-uncertainty flow measurements in ground test ramjets. However, H2O is scarce at actual ramjet flight altitudes, so oxygen is a preferable absorption target. Here, we demonstrate DCS of the O2 A-band (13000-13200 cm-1) 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. The DCS measurements and uncertainty estimates are compared to predicted values for the test facility.