Pulse duration dependency of the X-ray emission during materials processing with ultrashort laser pulses

Abstract

The potentially hazardous soft x-ray emission with photon energies of 5 keV and above are part of the emission spectrum during material processing with ultrashort laser pulses. The emission spectrum and the spectral power density are determined by the fraction of the hot electrons in the laser plasma, whose temperature is mainly defined by the irradiance. The interaction of the laser with the plasma intensifies with growing plasma expansion during the laser pulse and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, the pulse duration is one of the predominant parameters, which determine the emission of ionizing radiation. The H(0.07) dose rate was measured to investigate the influence of the pulse duration. In an existing analytical model, the fraction of hot electrons was extended to be a function of the pulse duration. The comparison between experimental data and calculations clearly verify the predictions of the model.