Temperature Measurements through Femtosecond Nitric Oxide Laser Induced Fluorescence

This study presents a method for measuring gas temperature using femtosecond (fs) Nitric Oxide (NO) Laser-Induced Fluorescence (LIF). A femtosecond laser system, tuned to excite the NO A-X (0,0) transition, was utilized to generate the LIF signal. LIFBASE was used to calculate the signal ratio between the fluorescence collected when the fs laser was tuned to two distinct frequencies: one sensitive and the other insensitive to gas temperature changes. To validate this technique, an air capacitively coupled plasma (CCP) system was used to create variable temperature conditions. LIFBASE simulations revealed a linear relationship between the LIF signal ratio and temperature for the explored range. The simulation also showed that the signal ratio is invariant to pressure changes. This simulated relationship was used to measure 335 K and 795 K temperatures for plasmas driven by 16 W and 30 W RF power, respectively. These results demonstrate the feasibility of using fs lasers for NO LIF thermometry.