Numerical Analytic Prediction and Experimental Validation of Focused ArF Laser Pulse Absorption Process in Air

Abstract

In order to understand the single-photon absorption process of focused ArF laser pulse in air, numerical simulations and spectroscopic experiments were carried out. The partial saturation of the laser spectrum and the depopulation of oxygen molecule at high vibrational levels in the ground state during laser emission was taken into consideration in the numerical simulation (relaxation-free model). The analytical results showed that these two effects caused the substantial decrease in the absorption coefficient, and the comparison of absorbance between the simulations and the measurement results revealed that analytical results with relaxation-free model were in better agreement than the results with the thermal equilibrium model, in which the depopulation effect was not considered. However, in the high temperature condition, the difference in the transmitted energy between experimental and analytical results was larger. It was found that the experimental ArF laser spectrum has a self-absorption region, which was not considered in the simulations. The difference in transmission due to these effects is likely to be enhanced at high temperature. The absorption spectra calculated with the relaxation-free model and the thermal equilibrium model were compared with the measured spectra in longer wavelength beyond the region influenced by the self-absorption. Better agreement was found for the relaxation-free model, leading to the conclusion that the spectral partial saturation and the depopulation of oxygen molecule were important to understand the absorption process of pulsed ArF laser light in air.