Exploring Carbon New phases by Laser-Induced Shock Waves

基于激波枪技术的SCARQ （shock compression and rapid quenching）方法制备了金刚石的亚稳相，即非晶和纳米晶金刚石，并将该方法应用于本研究开发的激光激波技术。研究了两种激光冲击法；一种是直接利用激光诱导烧蚀压力，另一种是利用激光驱动飞片冲击，后者是利用高功率Nd: YAG脉冲激光和放置在一定距离上的冲击PMMA窗口来加速薄铝箔。飞机的到达时间由条纹相机检测。到达时间的空间变化显示出随激光能量分布的弯曲飞片形状，从而导致速度分布。此外，这些分布强烈依赖于与激光焦点的距离。因此，很难将焦点光斑尺寸减小到0.1 mm以下，而0.1 mm是实现50 GPa金刚石转变压力所需的值。对这些实验数据进行了基于一维水代码的计算机模拟。利用拉曼散射研究了富勒烯薄膜在激光冲击压缩下的结构变化。一些样品转化为富勒烯聚合物，并对富勒烯的光致结构变化进行了研究。为了研究材料在冲击下的动态反应过程，研制了一种精确测量冲击温度的红外辐射计。为了确定红外辐射计，对四氯化碳的冲击温度进行了低于10 GPa的测量，结果证实了该系统可以测量低于1000 K的相对中等冲击温度。然而，由于该系统的冲击压缩面积小，在激光冲击的情况下，该系统可能在更高的温度下可用。

Metastable phases of diamond, amorphous and nanocrystalline diamond, were produced by SCARQ (shock compression and rapid quenching) method based on the shock-gun technology, This method was also applied to a laser-shock technology, which was developed in this study. Two-types of laser-shock method were investigated ; one was the direct use of laser-induced ablation pressures, and the other was the use of the laser-driven flyer impact, For the latter, thin aluminum foils were accelerated by a high power Nd : YAG pulse laser and impacted PMMA window placed at a certain distance. Arrival time of the flyers was detected by a streak camera. Spatial changes in the arrival time revealed the curved flyer shape depending on the laser energy distribution which resulted in velocity distribution. Moreover, these profiles were strongly dependent on the distance from focal point of laser. Therefore, it was difficult to reduce the focal spot size less than 0.1 mm whose value was required for achieving the diamond transition pressure of 50 GPa. These experimental data were described by computer simulation based on one-dimensional hydro-code.The structural change of fullerene films subjected to laser-shock compression using the laser was investigated by Raman scattering. Some samples transformed into fullerene polymer, and the photo-induced structural change of fullerene was also investigated.An infrared radiometer for the accurate measurement of shock temperature was developed in order to investigate shock-induced, dynamic reaction processes of materials. To determine the IR-radiometer, the shock temperature measurements of carbon tetrachloride were conducted below 10 GPa, and the results confirmed that the system was available to measure relatively moderate shock temperatures lower than 1000 K.However, the system might be available at higher temperature in the case of laser-shock because of the small shock-compressed area.