Initial temporal and spatial changes of the refractive index induced by focused femtosecond pulsed laser irradiation inside a glass
Initial temporal and spatial changes of the refractive index induced by focused femtosecond pulsed laser irradiation inside a glass
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DOI：
10.1103/physrevb.71.024113
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发表时间：
2005-01-01
影响因子：
3.7
通讯作者：
Terazima, M
中科院分区：
文献类型：
--
作者：
Sakakura, M;Terazima, M
采用瞬态透镜（TrL）方法，研究了飞秒激光脉冲在钠钙玻璃中聚焦区折射率随时间和空间的变化，时间分辨率为亚皮秒。在TrL信号中，观察到具有约800 ps周期的振荡直到约2000 ps。为了解释这种振荡现象，计算了短脉冲激光作用下材料的热弹性响应。据发现，基于热弹性计算计算的TrL信号再现观察到的振荡信号非常好，即使计算的密度在焦点区域不振荡。振荡的基本特征可以用压力波的产生和从照射区域向外传播来解释。基于压力波的传播和相位恢复方法，玻璃内部的折射率分布的时间演化是从探测光束变形（TrL图像）在不同的延迟时间之间的泵浦和探测脉冲。在20-100和500-700 ps范围内观察到激光聚焦区折射率增加的两个阶段，这可能导致玻璃内部激光聚焦区的折射率永久增加。讨论了激光脉冲宽度对激光辐照区材料变形过程的影响。该研究清楚地显示了飞秒激光辐照后玻璃内部材料变形动力学的初始过程。
The temporal and spatial developments of the refractive-index change in a focal region of a femtosecond-laser pulse inside a soda-lime glass is investigated by the transient lens (TrL) method with a time resolution of subpicosecond. In the TrL signal, the oscillation with about an 800-ps period is observed until about 2000 ps. In order to explain the oscillation, the thermoelastic response of a heated material by a short pulsed laser is calculated. It is found that the TrL signal calculated based on the thermoelastic calculation reproduces the observed oscillating signal very well, even though the calculated density at the focal region does not oscillate. The essential feature of the oscillation can be explained in terms of the pressure wave generation and propagation in the outward direction from the irradiated region. Based on the pressure-wave propagation and the phase-retrieval method, the temporal evolution of the refractive-index distribution inside a glass is obtained from the probe-beam deformation (TrL image) at various delay times between the pump and probe pulses. Two phases of the refractive-index increase at the laser focal region were observed in a range of 20-100 and 500-700 ps, which may cause a permanent refractive-index increase in the laser focal region inside a glass. We discuss the effect of the laser pulse duration on the material deformation process in the laser-irradiated region. This study clearly shows the initial process of the material deformation dynamics inside a glass after femtosecond laser irradiation.