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.

通过飞秒泵和探针光谱的一项广泛的研究阐明了CDSE薄膜中光生载体的超快动态。在带对波段的激发下，激发后立即观察到非热的热载体分布。在200 meV的宽能范围内观察到了这种分布，从泵能量延伸到其低能侧。从非热载体与总载流子的比率相比，估计热载体为20-40 fs.在A-EXCITON的共振激发下，观察到B-Exciton结构的42 MeV能量扩大。这种扩展是由A-Exciton和B-Exciton之间的碰撞引起的。这是不同类型激子之间散射过程的一个例子。分析表明A-Exciton-B-Exciton散射时间为31 fs。这次是通过基于刚性散射模型的简单理论很好地解释的。在B-Exciton的共振激发下，在B-Exciton上观察到了漂白的快速恢复。 0.9 ps的恢复时间被解释为通过LO Phonon发射将B-Excitons转换为A-Excitons。获得的时间常数与基于弗洛希（Frohlich）相互作用在数量级内相互作用的计算散射时间一致。通过飞秒泵和探测测量值，在间接吸收边缘周围观察到BII_3分层晶体中的共振相干晶格振动。飞秒泵脉冲冲动激发的相干光子声子调节了探针脉冲的相。探针光谱随着声音振荡周期的相应偏移，该周期持续了100多个周期。我们推测，相干的语音辅助间接激子转变也有助于数据。