We show the effects of double pulse processing with a pico-second laser for internal modification of transparent materials. In recent years, the need for laser processing of transparent materials has been growing. Many applications for such laser processing exist, such as the formation of through-silicon via, scribing glass and creating optical wave guides. Creation of photonic devices and circuits are also expected. A large amount of applied research on the processing of transparent materials has been conducted, but many of the processing mechanisms remain unexplained. In general, fluence thresholds are related to free-electron density caused by multi-photon ionization and avalanche ionization. Additionally, the internal fluence threshold of transparent materials is lower than surface fluence thresholds. We applied the double pulse method to the internal modification of transparent materials, and investigated how the second pulse affects the generation of microcracks. We used a pico-second laser with a 532-nm wavelength for the first pulse and a 1064-nm wavelength for the second pulse. The target was fused silica glass. In this paper, we show our experimental results and discuss the processing mechanism of the double pulse method. We call it the double pulse explosion drilling method. Moreover, we discover a processing method that can be applied to the high-rate drilling and scribing of transparent materials.
A. Tamura, T. Nishio, H. Suhara, and N. Nagayama, "Double pulse explosion drilling of transparent materials," Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 105200M (Presented at SPIE LASE: January 31, 2018; Published: 19 February 2018); https://doi.org/10.1117/12.2287648.
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