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.

An Experimental Determination of Critical Power for Self-Focusing of Femtosecond Pulses in Air Using Focal-Spot Measurements

“…The explanation will be provided in the following section. Furthermore, the change in the ablation area serves as an indicator of the laser intensity, which enables the exploration of the evolution of the laser beam along its propagation direction [44]. Therefore, by systematically analyzing the variation of the ablation area in relation to the propagation distance as the input energy gradually increases, we can explore the evolution of the laser intensity and, subsequently, determine the critical power for self-focusing of femtosecond pulses.…”

“…Among these methods, the ablation spot method is widely used for characterizing laser filamentation [42,43]. Recently, Nishibata et al conducted a study on the focusing properties of ultrashort laser pulses in laser processing by analyzing the irradiation and ablation areas [44]. Their findings indicate that the ablation technique can effectively demonstrate the evolution of intensity or fluence in the laser focal region.…”

Nonlinear propagation calculation-based irradiation process control for several mJ ultrashort pulse laser processing

“…Instead, to amplify the peak fluence, one must either escalate the NA or extend the pulse duration. 28) Figure 3 illustrates the transition of spot area in the propagation direction near the focal point for each energy. Error bars are given by the maximum and minimum measured four radius in the vertical and horizontal directions from the center of the ablation, and plots were averaged.…”