Focusing characteristic change and processing characteristic evaluation of femtosecond-to-picosecond pulse lasers above the air ionization threshold

Abstract

The utilization of ultrashort pulse lasers surpassing the air ionization threshold may result in detrimental focusing due to nonlinear optical phenomena. In the context of ultrashort pulse laser processing, alterations in focusing characteristics can lead to reduced processing efficiency and quality. In this study, numerical simulations were conducted to visualize the focusing characteristics across pulse durations ranging from femtoseconds to picoseconds. The distribution of fluence and the position of maximum focus during laser focusing are found to be dependent on the pulse duration, and correction of the irradiation position is crucial for achieving proper processing. The intensity and fluence achieved under high numerical aperture (NA) conditions are determined by the combination of NA and pulse duration. These findings are crucial in selecting optimal laser conditions and achieving optimal control of the processing position in high-energy laser processing applications.