Suitability of Tunable Diode Laser Absorption Spectroscopy Experiments for Low Density Flows

In this report we investigate the suitability of different gases for TDLAS of low density hypersonic nozzle-exit flows, but tunnel results are not be presented yet. Oxygen (for an Earth atmosphere), carbon dioxide (for a Martian atmosphere) and seeded rubidium are the considered candidates for TDLAS measurements. We demonstrate the design of a simple, minimum-path-length TDLAS system that can be used to measure the temperature and velocity of a hypersonic nozzle flow. This system is tested in laboratory air, and the absorption signals are then scaled using an in-house code to predict absorption in rarefied flows in the shock tunnel, comparing between different candidate optical configurations. A design for TDLAS measurements inside a hypersonic facility is discussed, along with the challenges associated with hypersonic ground test facilities.