Investigation of Efficiencies for Laser-Sustained Plasma in Argon Seeded with UV-Absorbing Gas

Laser-Thermal Propulsion (LTP) suffers from low thermal efficiency due to radiative losses from the plasma core to the bulk propellant. This study experimentally investigates seeding argon propellant with UV-absorbing gases (NO2, SO2) to enhance radiation capture. Plasmas were sustained with a 3-kW pulsed laser in argon at 5-10 bar. Optical emission spectroscopy and pressure analysis were used to diagnose plasma properties and quantify efficiency. Results demonstrate gas seeding significantly contributes to increased system thermal efficiency. At 10 bar, peak efficiency almost doubles, reaching 23-24%, compared to a 13-16% unseeded baseline. Spectroscopy confirmed attenuation of plasma emission in the corresponding seed gas absorption bands. Efficiency gains are shown to saturate and decline past critical concentrations, as excessive seeding gas reduces electron temperature via inelastic and electronegative processes.