Sakakura Masaaki, Yoshimura Kouhei, Kurita Torataro, Shimizu Masahiro, Shimotsuma Yasuhiko, Fukuda Naoaki, Hirao Kazuyuki, Miura Kiyotaka
Opt Express. 2014 Jun 30;22(13):16493-503. doi: 10.1364/OE.22.016493.
Local melting and modulation of elemental distributions can be induced inside a glass by focusing femtosecond (fs) laser pulses at high repetition rate (>100 kHz). Using only a single beam of fs laser pulses, the shape of the molten region is ellipsoidal, so the induced elemental distributions are often circular and elongate in the laser propagation direction. In this study, we show that the elongation of the fs laser-induced elemental distributions inside a soda-lime glass could be suppressed by parallel fsing of 250 kHz and 1 kHz fs laser pulses. The thickness of a Si-rich region became about twice thinner than that of a single 250 kHz laser irradiation. Interestingly, the position of the Si-rich region depended on the relative positions between 1 kHz and 250 kHz photoexcited regions. The observation of glass melt during laser exposure showed that the vortex flow of glass melt occurred and it induced the formation of a Si-rich region. Based on the simulation of the transient temperature and viscosity distributions during laser exposure, we temporally interpreted the origin of the vortex flow of glass melt and the mechanism of the formation of the Si-rich region.
通过以高重复率（>100kHz）聚焦飞秒（fs）激光脉冲，可在玻璃内部诱导局部熔化和元素分布的调制。仅使用单束飞秒激光脉冲时，熔化区域的形状为椭圆形，因此诱导的元素分布通常呈圆形且在激光传播方向上拉长。在本研究中，我们表明，通过250kHz和1kHz飞秒激光脉冲的平行飞秒作用，可以抑制钠钙玻璃内部飞秒激光诱导的元素分布的拉长。富硅区域的厚度比单次250kHz激光照射时变薄了约两倍。有趣的是，富硅区域的位置取决于1kHz和250kHz光激发区域之间的相对位置。激光曝光期间对玻璃熔体的观察表明，发生了玻璃熔体的涡旋流动，并诱导形成了富硅区域。基于激光曝光期间瞬态温度和粘度分布的模拟，我们从时间上解释了玻璃熔体涡旋流动的起源以及富硅区域形成的机制。
