Time-domain coherent phonon spectroscopy and dynamics of structural change

We have constructed a system for measurement of high frequency coherent oscillations of phonons and electrons in solids，using Ti：sapphire pulse lasers with~ten femtosecond duration.The characteristics of the constructed system has been evaluated by measurements of the coherent phonons in various materials and the SHG signals.The pulse duration of 16fs and reflectivity change(ΔR/R)of the order of 10-7 have been obtained。Using this system we were able to measure the coherent phonons in Ge with a good S/N ratio，which was so far difficult to observe them.We have examined coherent phonons in semimetals，superlattices，semiconductors，semiconductor-and semimetal-and materials which undergo phase transition.The results of our studies are as follows：(1)We have found from a comparison of the Raman and coherent phonon spectra that the decay of the coherent phonons is mainly governed by the energy relaxation and that the contribution of the pure depasing is very all in Bi.More r Bi/Sb superlattices，we have first observed coherent oscillations of optical modes confined in the constituent layers，Bi-Sb interface modes，folded longitudinal acoustic modes。The deviation of the observed frequency of the coherent folded modes from the calculated ones is attributed to elastic anomaly in very thin Bi layers.(3)We have produced pulse trains using spatial modulation filters and a grating pair and experimentally proved that the control of the amplitude of the coherent phonons and the selective excitation of specified phonon modes are possible for Bi/Sb mixed crequency of the coherent phonons and the selective excitation of specified phonon modes are possible for Bi/Sb mixed crystals.(4)We have folded modes of the braves of layers.We also determined carrier density dependence of coupled-mode decays and discussed the dynamics.(5)The coherent oscillations of folded longitudinal acoustic phonons are observed in GaAs-AlAs superlattices.We have obtained a clue for understanding the generation and detection mechanisms for the coherent phons.(6)We have observed coherent phonons in materials which undergo phase transitions in V I D22文件D2O文件D23文件D2，η-Mo文件D24文件D2O文件D211文件D2 and GeTe and obtained much information on the mechanisms of the generation and relaxation of the coherent phonons.Less：Less

We have constructed a system for measurement of high frequency coherent oscillations of phonons and electrons in solids, using Ti : sapphire pulse lasers with 〜 ten femtosecond duration. The characteristics of the constructed system has been evaluated by measurements of the coherent phonons in various materials and the SHG signals. The pulse duration of 16fs and reflectivity change (ΔR/R) of the order of 10-7 have been obtained. Using this system we were able to measure the coherent phonons in Ge with a good S/N ratio, which was so far difficult to observe them. We have examined coherent phonons in semimetals, superlattices, semiconductors, semiconductor- and semimetal-and materials which undergo phase transition.The results of our studies are as follows :(1) We have found from a comparison of the Raman and coherent phonon spectra that the decay of the coherent phonons is mainly governed by the energy relaxation and that the contribution of the pure dephasing is very small in Bi.(2) Fo … More r Bi/Sb superlattices, we have first observed coherent oscillations of optical modes confined in the constituent layers, Bi-Sb interface modes, folded longitudinal acoustic modes. The deviation of the observed frequency of the coherent folded modes from the calculated ones is attributed to elastic anomaly in very thin Bi layers.(3) We have produced pulse trains using spatial modulation filters and a grating pair and experimentally proved that the control of the amplitude of the coherent phonons and the selective excitation of specified phonon modes are possible for Bi/Sb mixed crystals.(4) We have first observed both the upper and lower branches of coherent LO-phonon plasmon coupled modes in GaAs and InP. We also determined carrier density dependence of coupled-mode decays and discussed the dynamics.(5) The coherent oscillations of folded longitudinal acoustic phonons are observed in GaAs-AlAs superlattices. We have obtained a clue for understanding the generation and detection mechanisms for the coherent phonons.(6) We have observed coherent phonons in materials which undergo phase transitions in VィイD22ィエD2OィイD23ィエD2, η-MoィイD24ィエD2OィイD211ィエD2 and GeTe and obtained much information on the mechanisms of the generation and relaxation of the coherent phonons. Less