超高压下冲击波速度直接测量技术

针对超高压下透明材料的高压离化机理,分析了透明材料中冲击波直接诊断技术的基本方法. 利用Drude-自由电子气模型,分析了不同冲击压力下冲击波阵面反射率的变化. 从理论上比较了不同探针光波长反射率的区别,发现探针光波长为660 nm时比探针光波长为532 nm时获得的冲击波阵面反射率要高. 对探测器"致盲"问题也进行了研究. 通过分析反射信号的时间顺序和强度大小,发现"致盲"效应是由X光对透明窗口离化引起的. 同时,发现方波驱动脉冲平台的前沿到达时刻和X光离化效应出现的时刻相同,冲击波信号到达时刻晚于X光离化时刻. 通过实验结果,得到蓝宝石中冲击波速度为35 km/s时,其波阵面的反射率约为40%. 通过理论分析和实验数据比对的方法,验证了蓝宝石中的减速曲线. 给出了加蓝宝石窗口后的测速公式. 经过和实验对比,确认了测速公式的正确性. 关键词： 冲击波 光学诊断 成像 干涉仪

Direct measurement technique for shock wave velocity under super high pressure

With the ionization mechanism for the transparent material under the super high pressure, the basic measurement method of shock wave has been analyzed. With the Drude-free electron model, the change in reflectivity of shock wave front under different pressures has been analyzed. The reflectivity of shock wave front for different probe lasers has been compared in theory. And it was found that the reflectivity of shock wave front for 660 nm of probe laser is higher than that for 532 nm. The effect of the detector was found to be caused by the X-ray ionization of the transparent material after analyzing the reflectivity data in space-time scale. From the experiment data, it is found that the beginning of "blank" effect coincides with the start point of laser pulse. The shock wave is later than the "blank" effect under the square laser pulse. In the experiment, the reflectivity of shock wave front is about 40% when the shock velocity is 35 km/s. The theoretical decreasing curve of shock velocity in the sapphire window is confirmed by the experiment data. The formula to calculate the shock wave velocity in the transparent material was deduced and verified.