Co膜中多次超快瞬态反射突变现象研究

飞秒激光泵浦瞬态热反射技术是研究金属薄膜超快动力学的有效手段，这种技术具有两大突出特点：首先，可以揭示飞秒激光激发的微观电、声子的传输过程是一个非平衡热输运过程。其次，反射率瞬态变化实验中电子运动的超短时间分辨可以用来研究热过程中电子的非平衡相互作用情况。利用磁控溅射真空镀膜技术，在玻璃衬底和硅衬底上蒸镀了不同厚度的Co单层膜，Cr，Co双层膜以及Ag，Co双层膜。利用飞秒激光瞬态反射技术研究了Co膜及其双层膜的瞬态反射率响应。结果表明，在同一厚度的Co膜样品上，施加不同的泵浦光功率时，Co膜内电子的加热时间与泵浦光功率的大小无关，均为0.1344 ps。而对于不同厚度的Co膜，电子的热化时间与薄膜厚度直接相关。此外，发现与以往研究结果不同的是，在泵浦光功率足够大时，玻璃衬底上的Co膜在飞秒激光脉冲泵浦下会出现两次或三次瞬态反射率下降现象，Co膜厚度决定了Co膜内瞬态反射率突变的次数，即Co膜内电子的超快动力学变化次数。

Research on Several Times of Abruptly Changes in the Ultrafast Transient Reflectivity in Co Films

In the present paper, cobalt films, chromium and cobalt double layer films, and silver and cobalt double layer films were deposited by magnetron sputtering technique. The transient reflectivity response in cobalt thin films and their double layer films was studied by using femtosecond laser pump-probe transient reflection experimental technology. The result shows that, under the condition of the cobalt films of the same thickness, when the pump power increases, the heating time of the electrons in cobalt thin films is independent of the pump power, and is 0.134 4 ps. And for the cobalt films of different thickness, the electron thermalization time is directly related to the film thickness. In addition, when the laser pulse power is high enough, two or three transient reflectivity decline signals on glass substrate films are found which is different with previous researches, when the cobalt films were thin, there are three times of transient reflectivity abruptly decline signals, and when the cobalt films were thick, there are two times of transient reflectivity abruptly decline signals, so the thickness of the cobalt films determines the times of the changes of the ultrafast dynamics in cobalt films.