研究目的
To study the controllable photon energy deposition in laser irradiation of fused silica by temporally shaped femtosecond laser pulse trains and to understand the underlying mechanisms.
研究成果
The study demonstrates that photon energy deposition efficiency in processing of fused silica can be controlled by temporally shaped femtosecond pulse with different sub-pulse interval and intensity ratio arrangements. The results show that the decreasing pulse trains exhibit the highest photon energy deposition efficiency under high fluence, while the unshaped pulse produces higher energy deposition efficiency under lower fluence. These results are explained by a plasma model taking into account the ionization process and its feedback on the photon energy deposition.
研究不足
The study assumes that under same experimental conditions, the more photon energy deposited into fused silica, the greater degree of permanent modification, and thus the larger etching crater volume after being etched by HF. The effect of chemical etching on the laser irradiated sample is a very complicated process and certainly beyond the scope of the current study.
1：Experimental Design and Method Selection:
The study used temporally shaped femtosecond laser pulse trains with different envelope shapes (increasing, plain, and decreasing pulse trains) to irradiate fused silica samples. The photon energy deposition efficiency was analyzed by measuring the morphology of the etching craters created by laser irradiation followed by chemical etching in hydrofluoric acid (HF) solution.
2：Sample Selection and Data Sources:
Highly polished fused silica samples (10 × 10 × 1 mm3) were used. After each single shot exposure, the sample was moved to a fresh position using a computer-controlled, six-axis moving stage.
3：List of Experimental Equipment and Materials:
A Ti:sapphire regenerative amplifier system for fs laser source, a commercial pulse shaper (MIIPS-HD), a half-wave plate combined with a polarizer for pulse energy control, a 20× microscope objective for focusing, a scanning electron microscope (SEM; S-480, Hitachi, Japan) and an atomic force microscope (AFM; Bruker, EDGE, Germany) for morphology evaluation.
4：Experimental Procedures and Operational Workflow:
The laser beam was focused on the upper surface of the sample. After irradiation, the sample was immersed in 6% HF solution assisted with ultrasonic bath to visualize the permanent modification induced by laser irradiation. The morphology of the etched craters was evaluated using SEM and AFM.
5：Data Analysis Methods:
The photon energy deposition efficiency was quantitatively evaluated based on the depth and volume of etching craters. Micro-Raman Spectroscopy was employed to study internal changes of fused silica sample irradiated by fs pulse.
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