Study of Semiconductor nano structures by means of coherent phonon

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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.