Study of Picosecond Laser-Induced Shock Waves and Phase Transformation in Solids

1.由一个ZnO transducer产生的声学或冲击波的一代研究由一个Piezolectric transduceration and propagation characteristics of picosecond laser生成的声学或冲击波在Siwere研究。在等离子体形成区域，声学脉冲的传播速度超出了声音速度。在传播的早期阶段。冲击波的幅度对硅表面上激光生成等离子体的形成和扩展的影响。INTENSE ACOUSTIC WAVEES在玻璃上研究，光学方法波在其方向向表面平面传播，但在45左右向正常方向传播。在传播的早期阶段，波前端的速度在玻璃中产生了声音的速度。Moreover，这表明，剪切波的产生和传播行为对表面条件是非常敏感的。新的照相光谱学USING A Transparent TranSDUCER我们开发了一个新的照相声学光谱学系统，使用透明的传感器和研究的激光诱导的结构变化在固体的表面。在光辐射的前表面检测到的信号具有较大的价值，并与后表面进行了良好的信号到噪音比较。激光诱导的表面结构性更改使用这个系统是很明显的。高功率激光辐射后的表面转换器红外线在玻璃表面表面形成裂纹，并在高变焦激光辐射后的一个硅表面观察中的爆炸性晶体化。受辐射区域的损伤是由激光破坏和等离子体形成造成的，但裂缝和液体滴也出现在受辐射区域之外，超过了许多百万人的距离。延迟裂纹形成是由玻璃组成的化学反应引起的，大气水蒸汽在表面上的微裂纹被激光驱动的冲击波诱导。我们也观察到了一个-Si发起的冲击波的爆炸性水晶化。

1. GENERATION OF SHOCK WAVES STUDIED BY A PIEZOELECTRIC TRANSDUCERGeneration and propagation characteristics of picosecond laser-generated acoustic or shock waves in Si were studied by a ZnO transducer. In the Plasma formation region, the propagation velocity of acoustic pulses exceeds the sound velocity. At early stage of propagation. The amplitude of shock waves is affects by the formation and expansion of laser-generated plasma at the silicon surface.2. INTENSE ACOUSTIC WAVES IN GLASS STUDIED BY AN OPTICAL METHODLongitudinal waves propagate at the direction of the normal to the surface plane, but shear waves propagate at about 45 to the normal. At the early stage of propagation, the velocity of the wavefront exceeds the sound velocity in glass. Moreover, it is pointed out that the generation and propagation behavior of shear waves is very sensitive to the surface conditions.3. NEW PHOTOACOUSTIC SPECTROSCOPY USING A TRANSPARENT TRANSDUCERWe developed new photoacoustic spectroscopy system using a transparent transducer, and studied laser-induced structural changes at the surface of solids. The signal detected at the light-irradiated front surface has a large value and a good signal-to-noise ration compared with that at the back surface. Laser-induced surface structural changes are clearly observed using this system.4. SURFACE TRANSFORMATIONS AFTER HIGH-POWER LASER IRRADIATIONCrack formation in glass surfaces and explosive crystallization in a-Si were observed after high-Zower laser irradiation. The damage in the irradiated region was caused by laser ablation and plasma formation, but cracks and liquid drops also appeared outside the irradiated region over a distance of many millimeters. Delayed crack formation is caused by chemical reactions of component of glass with atmospheric water vapor at microcracks in the surface induced by laserーdriven shock waves. We also observed explosive crystallization of aーSi initiated by shock waves.