Development and Implementation of a Novel Resonantly Ionized Photoemission Thermometry Technique for One-Dimensional Measurements

In this work, Resonantly Ionized Photoemission Thermometry (RIPT) is established and validated as a novel, non-intrusive, non-seeded, One-Dimensional (1D) line thermometry technique. The RIPT technique resonantly ionizes a target molecule via REMPI (Resonant Enhanced Multi-Photon Ionization) of selectively chosen rotational peaks within a resonant absorption band. Thus, efficiently ionizing and subsequently exciting local nitrogen molecules either by direct or indirect schemes. The excited nitrogen deexcites through photoemissions of the first negative band of N₂⁺[molecular nitrogen], specifically near 390, 425, and 430nm [nanometers], that is then acquired as a 1D line signal. The signal strength at all transitions shares a direct relationship with the line strength of the selectively excited rotational peak, which are temperature sensitive. The thermal distribution of the REMPI rotational levels is given by a statistically weighted (i.e., quantum degenerated) Boltzmann factor, thus with knowledge of the rotational spectrum, a statistical fit can be applied that relates the slope of the Boltzmann plots to a gas temperature.

The RIPT technique bypasses the need for a fully rotational-resolved spectrum of the ionized region, instead directly probing up to four rotational lines within the spectrum. By relation, the acquired photoemissions strength directly represents the line strengths at each of the probed rotational wavelengths enabling a rotational state distribution analysis to be applied via the photoemission intensities and generating Boltzmann plots at each probed peak. The slope of a statistical fit to the Boltzmann plots allows a gas temperature assignment. The groundwork is laid for both oxygen and nitrogen-based RIPT techniques through detailed calibration studies that will allow ease-of-use in future applications by scientists and researchers. Furthermore, the potential for 1D thermometry applications is realize for oxygen-based RIPT by implementation in various high-speed, low enthalpy flow environments.