Study of Semiconductor nano structures by means of coherent phonon

相干声子是由超短激光脉冲在固体系统中脉冲产生的周期性晶格振动。通过产生相干声子，可以在时域上测量晶格振动。此外，利用可编程飞秒脉冲序列，可以选择性地激发特定模式到较大的振幅，该技术可以应用于精确声子光谱和相变的实现。本课题通过构建连续波绿色固体激光器泵浦的锁模钛蓝宝石激光器、基于级联迈克尔逊干涉仪的脉冲列发生器和测量单元，制备了相干声子光谱仪。然后将光谱仪应用于超晶格样品和石墨。从而阐明了这些样品中相干声子产生和探测机制的细节，大大提高了仪器技术和分析方法。脉冲序列发生器可以在飞秒到几十皮秒的宽时间范围内产生间隔精确、控制良好的脉冲序列。利用该脉冲序列，证明了超晶格和石墨样品中晶格振动的相干控制。

Coherent phonons are the periodic lattice vibration impulsively generated by the ultra short laser pulses in the solid state system. By generating the coherent phonon, the lattice vibration can be measured in time domain. Moreover by applying the programmable femtosecond pulse train, specific mode can be selectively excited to large amplitude and the technique can be applied to the precise phonon spectroscopy and the realization of phase transition.In this project, a coherent phonon spectrometer is prepared by constructing a mode locked titanium sapphire laser pumped by a cw green solid laser, a pulse train generator based on cascaded Michelson interferometers, and a measuring unit. Next the spectrometer is applied to the superlattice sample and graphite. As a result, the details of the generation and detection mechanisms of coherent phonons in these samples are clarified and the instrumentation technique and analysis method has been greatly improved. The pulse train generator can produce precise interval and well controlled pulse train in wide time range from femtoseconds to several tens of picoseconds. By using this pulse train, coherent control of lattice vibration in superlattice and graphite samples is demonstrated.