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Ultrafast nonlinear optical properties of semiconductors in low dimension

低维半导体的超快非线性光学特性

基本信息

批准号：
02044021
负责人：
MASUMOTO Yasuaki
金额：
$ 4.22万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02044021/
关键词：
CdSe Hot electron Femtosecond Pump-probe-spectroscopy Exciton BiI_3 Coherent phenomenon Coherent phonon effect 積層欠陥

项目摘要

An extensive study by means of femtosecond pump-and-probe spectroscopy has clarified the ultrafast dynamics of photogenerated carriers in a CdSe thin film. Under band-to-band excitation, a nonthermalized hot carrier distribution was observed immediately upon excitation. This distribution was observed in a 200 meV broad energy range extending from the pump energy to its low energy side. From the ratio of nonthermalized to the total carriers, the thermalization time was estimated to be 20-40 fs.Under resonant excitation of the A-exciton, a 42 meV energy broadening of the B-exciton structure was observed. This broadening is caused by collisions between the A-exciton and the B-exciton. This is an example of the scattering process between different kinds of excitons. Analysis indicates that the A-exciton-B-exciton scattering time is 31 fs. This time is well explained by a simple theory based on the rigid-sphere scattering model.Under resonant excitation of the B-exciton, a fast recovery of the bleaching was observed at the B-exciton. The recovery time of 0.9 ps is explained as the transformation time of B-excitons into A-excitons by LO phonon emission. The obtained time constant agrees with the calculated scattering time based on the Frohlich interaction within an order of magnitude.Resonant coherent lattice vibrations in a BiI_3 layered crystal are observed around the indirect absorption edge by femtosecond pump and probe measurements. Coherent optical phonons that are impulsively excited by femtosecond pump pulses modulate the phase of probe pulses. The corresponding shift of the probe spectrum swings with the period of phonon oscillation, which continues for more than 100 periods. We speculate that the coherent phonon-assisted indirect exciton transitions have also contributed to the data.

利用飞秒泵浦-探测光谱技术对CdSe薄膜中光生载流子的超快动力学行为进行了深入的研究。带到带激发下，非热化的热载流子分布观察后立即激发。在从泵浦能量延伸到其低能量侧的200 meV宽能量范围内观察到这种分布。根据非热化载流子与总载流子的比率，估计热化时间为20-40 fs。在A激子的共振激发下，观察到B激子结构的42 meV能量展宽。这种加宽是由A激子和B激子之间的碰撞引起的。这是不同种类激子之间散射过程的一个例子。分析表明A激子-B激子散射时间为31 fs。在B激子的共振激发下，在B激子处观察到漂白的快速恢复。0.9ps的恢复时间被解释为通过LO声子发射的B激子到A激子的转变时间。利用飞秒抽运和探测技术，在BiI_3层状晶体的间接吸收边附近观察到了共振相干晶格振动。飞秒泵浦脉冲激发的相干光学声子调制探测脉冲的相位。探测谱的相应位移随声子振荡的周期摆动，该周期持续超过100个周期。我们推测，相干声子辅助的间接激子跃迁也有助于数据。