Two-photon absorption laser induced fluorescence with various laser intensities for density measurement of ground state neutral xenon

Abstract Electrostatic plasma thrusters such as ion engines and Hall thrusters commonly use xenon as a propellant and several measurement techniques for xenon ions and metastable neutrals have been applied to evaluate the characteristics of the thrusters. Although density measurements of ground state neutral xenon can provide crucial information on the ionization characteristics and help explain charge exchange phenomenon, much less research is available due to its technical difficulty. Two-photon absorption laser induced fluorescence is promising because it allows access to ground state xenon atoms by using around 220–260 nm wavelength lasers which have become more readily available lately. In this study, observation of the fluorescence following two-photon excitation from a room temperature (cold) xenon gas cell is conducted with 249 and 252 nm wavelength excitation at xenon pressures of 0.1 and 10 Torr. The fluorescence signals are obtained against a wide range of laser intensities, and the resulting fluorescence response comprises of a few regimes – weak-excitation, saturation, and an intermediate regime. The natural lifetime and quenching rate are evaluated by analyzing the fluorescence decay, and the result is consistent with published literature. Finally, actual application to ground tests of Hall thrusters is discussed based on the experimental results, especially with respect to their fluorescence responses.