Study of Semiconductor nano structures by means of coherent phonon

相干声子是超短激光脉冲在固态系统中产生的周期性晶格振动。通过产生相干声子，可以在时域内测量晶格振动。本课题利用连续绿色固体激光器泵浦的钛蓝宝石锁模激光器，基于级联迈克尔逊干涉仪的脉冲序列发生器，和测量单元。接下来，将光谱仪应用于超晶格样品和石墨。结果，这些样品中相干声子的产生和检测机制的细节得到澄清，仪器技术和分析方法有了很大的改进。该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精确的间隔和良好的控制脉冲序列。利用该脉冲序列，在超晶格和石墨样品中实现了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.