Dynamics of structural phase transition studied by picosecond time-resolved X-ray diffraction

我们研究了阶段过渡的动力学，是由脉冲激发引起的，并使用了一种可成像时间解决的X射线干扰技术。脉冲X射线在真空室中产生了10^17 W/cm^2的金属目标，并从窗口中提取出来。X射线是由L-N_2冷却的X射线电荷耦合设备指示的样本和不同的X射线。用水泵和探测器技术进行了时间解决的测量。一个300-ps激光束在样品上辐射，功率密度为3.3 GW/cm^2，令人兴奋。所用的样本是硅晶体（Si（111））。时间分辨率的X射线差分每隔50秒的时间间隔，每隔一个时间分辨率为10秒。晶格退化相关的激光加热和声学声子传播，由电子系统向晶格系统转移的能量，被直接观察到。在样品位置增加X射线强度的情况下，一个X射线聚焦系统是用约翰逊曲线晶体构建的。X射线聚焦于一个斑点大小，其直径为100米，强度更高，强度更高。新构建的X射线分化系统可以观察到接近4个学位的地点。

We investigated dynamics of a phase transition, which is induced by impulsive excitation, using a picosecond time-resolved X-ray diffraction technique. The pulsed X-rays were generated by focusing femtosecond laser beams onto metal targets at 10^17 W/cm^2 in a vacuum chamber, and extracted from a Be window. The X-rays were directed to a sample and the diffracted X-rays were detected by the L-N_2 cooled X-ray charge-coupled device. Time-resolved measurements were performed using a pump and probe technique. A 300-ps laser beam was irradiated on the sample at power density of 3.3 GW/cm^2 for excitation. The sample used was a silicon crystal (Si(111)). The time-resolved X-ray diffraction was obtained every 50 ps of time interval with a time-resolution of 10 ps. Lattice deformation corresponds to laser heating and acoustic-phonon propagation, which followed by the energy transfer from an electronic system to a lattice system, was directly observed. In order to increase the X-ray intensity at the sample position, an X-ray focusing system was constructed using a Johansson curved crystal. The X-rays were focused at a spot size with a diameter of 100・m and 400-times higher intensity. The newly constructed X-ray diffraction system can observe approximately 4 degrees at the spot.