Single-Shot Measurement of Electron Density Distribution Under Ultrashort Laser Pulse Irradiation

Ultrashort pulsed laser processing has attracted attention as a technique for microfabrication of transparent materials. As laser processing removes materials through excitation of electrons, quantitative evaluation of electronic excitation is important for understanding laser processing. In a previous study, the electron density distribution after laser irradiation was estimated based on experimental measurements of the refractive index and attenuation coefficient distributions. However, due to the lack of reproducibility of the phenomenon and the effect of scattering, precise measurement has not been realized [1]. In this study, we developed a single-shot imaging method that can simultaneously capture three spatial distributions: the refractive index distribution and the attenuation coefficient distributions at two wavelengths. This method enables precise electron density measurement that is not limited by reproducibility and takes into account the effects of scattering.