【作者】 陈磊；

【导师】 任乃飞；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2007， 硕士

【摘要】 飞秒激光的超短脉冲宽度、超高峰值功率和电场强度等独特性质决定了其在很多领域都具有广泛的应用。人们能够利用飞秒激光技术研究光与不同物质相互作用过程中的超快现象，特别是发生在皮秒和飞秒时域内的超快过程。例如用于制作超高速存储和读写以及应用于微机电系统中的超磁致伸缩材料的磁化与退磁过程。磁性薄膜瞬态反射率与电子动力学过程是飞秒超快探测技术研究热点，这些研究可以为各种超高速磁存储设备和高频化磁微器件提供充足的设计依据。利用磁控溅射方法制备了不同参数的TbDvFe薄膜，在不同的实验条件下进行了退火处理。利用SEM(扫描电镜)、XRD(X射线衍射)和AFM(原子力显微镜)等手段对薄膜样品进行了成份、形貌和结晶度的表征，并利用Scherrer公式对薄膜表面晶粒直径D进行计算，与SEM观测到的结果有较好的符合。利用实验室飞秒激光泵浦探测装置对TbDyFe薄膜进行瞬态反射率测试，研究了薄膜厚度、泵浦光功率和退火处理对样品反射率变化曲线的影响，由试验装置的时间分辨率得知反射率突变至极值的时间为100±33fs。结合菲涅耳反射公式和K-K变换，从薄膜反射率变化曲线计算出其介电常数的实部与虚部在时间零点前后的变化曲线，发现薄膜表面对光束反射作用增强的同时，其内部对激光脉冲的吸收也在增大，在大约1ps后样品介电常数实部与虚部的变化稳定在相对于初始状态较低的范围，薄膜对光束的反射和损耗作用恢复至稳定状态。结合双温模型与三温模型对TbDyFe薄膜受激光激发后的电子动力学过程进行了描述，并利用三温模型公式求解出薄膜内部电子、自旋与晶格系统的温度变化曲线。反射率突变至极值的时间比之前对Ni薄膜的研究结果要短，可以归结为掺杂在TbDyFe薄膜中稀土离子局域4f电子的作用和激光脉宽的缩短。试验中发现了薄膜中的回波效应，薄膜厚度的增加影响了回波出现的位置，使回波强度减弱并出现不规则变化。最后将实验结果与课题组内对GaAs样品的研究结果进行比较，分析了造成结果差异的原因。更多还原

【Abstract】 Femtosecond laser unique characters such as ultrashort pulse width, ultrahigh peak power and the electric field intensity has decided it will having broad application in many fields. Femtosecond laser technology was used to investigate ultrafast phenomenon in the interaction process between laser and different material, especially the ultrafast process occurred in picosecond and femtosecond time domain. Such as the magnetization and demagnetization process of ultrahigh speed memory and read-write system and the giant magnetostrictive material applying to the micro-electromechanical systems (MEMS). Transient reflectivity and electron dynamics of magnetic thin film is the key issue in femtosecond ultrafast measurement domain and it will provide various magnetic storage devices and high frequency micro-magnetic systems with more design basis.TbDyFe thin films with different thickness were prepared by magnetron sputter and they were annealed under different temperature and atmospheres (vacuum, nitrogen). The component、surface topography and crystallinity property of TbDyFe thin films were investigated by scanning electronic microscope (SEM)、X-ray diffraction (XRD) and atom force microscope (AFM) methods. The surface crystal gain diameters D of thin film were calculated by Scherrer formula and it has a good agreement with SEM observation result.Optical transient reflectivity change of TbDyFe thin films were measured by femtosecond laser pump-probe measurement technique in our laboratory in order to investigate the influence of thin film thickness、pump power and annealing process. Combine with Fresnel reflect formula and K-K transformation, real and imaginary part of the complex dielectric constant was derived from reflectivity relative change curves. It reveals that the film surface properties have rapid change after laser irradiation, at the same time, inside of thin film have more absorption to laser pulses. After 1ps, the thin film surface properties become steady but imaginary part of dielectric constant increasing gradually and the reflection and absorption of laser pulses in film recover to initial state.We described the electron dynamics process in TbDyFe thin film after femtosecond laser excitation combine with two-temperature and three-temperature model and use the three-temperature model equation to obtain the electron、spin and lattice system temperature variation curves. Extremum time of reflectivity shorter than former research results and we may ascribe this phenomenon to the local 4f electrons in rare earth ions that doping in thin film and improvement of the temporal resolution. The wavelike phenomenons are observed in equilibration process of the reflectivity change, particularly in 400nm and 600nm thin film. Thickness of the thin film determines the echo time and echo wave in 800 nm thin film is not obvious and regular. Last, experiment results were compared with GaAs crystal and the cause bring about difference was analyzed.更多还原