Assessment of Multiphoton Absorption in Inert Gases for the Measurement of Gas Temperatures

Abstract

A spatially resolved optical technique to measure gas temperature was assessed. The technique relies on multiphoton absorption in inert gases. In contrast to laser-induced fluorescence, absorption is insensitive to collisional deactivation, and, in contrast to one-photon absorption, multiphoton absorption only occurs around the focus point of a typical laser beam. Multiphoton absorption features both the merits of being insensitive to quenching and of being a spatially resolved technique. In a case study we assessed two-photon absorption in xenon upon exciting the 5p6 1S0 → 5p56p[5/2]2 transition in xenon at a wavelength of 256 nm. The amount of light absorbed by xenon is related to the number density of the gas, and if the gas pressure is known then the gas temperature can be inferred from the number density. Two-photon absorbance was measured as a function of xenon number density and was used to validate a theoretical model of the absorption process. We discuss the circumnavigation of experimental challenges in applying this technique and analyze its precision in terms of the inferred gas temperature.