Femtosecond relaxation dynamics of excitons localized by disorder in semiconductors

1)研制了一种被动锁模染料激光系统。染料激光器以100兆赫的速率产生一列100秒的脉冲。波长调谐范围为580 ~ 620 nm.2)利用温度相关光子回波法测量了GaSe中激子的相弛豫时间。发现在30 k以上的声子散射引起了光学失相。3)GaSe中自由激子的辐射寿命与相位相关时间密切相关。这一结果为最近的理论预测提供了直接的实验证明。4)在GaSe的自由激子线上进行了两种不同的烧孔实验：脉冲传播延迟实验和泵探实验。这两个结果都支持了堆叠无序导致部分激子局域化的观点。5)我们提出了两种研究飞秒过程的新方法：泵浦探测和使用时间非相干光的上转换方法。6)利用一种新颖的泵浦探针技术，以亚皮秒精度研究了CdSe中热载流子的时间行为。其中利用光纤中的自相位调制效应来延长探测脉冲的光谱宽度。泵引起的变化可以用电子空穴等离子体的形成和随后等离子体的热松弛来解释。7)研究了短周期GaAs/AlAs超晶格的光致发光光谱随静水压力和单轴压力的变化规律。发现最低激发态是Xz处的间接激发态。

1) We made a passively mode-locked dye laser system. The dye laser produces a train of 100 fs pulses at the rate of 100 MHz. The wavelength tuning range is 580-620 nm.2) The phase relaxation time of the exciton in GaSe was measured by using temperature-dependent photon echo method. It is found that the optical dephasing is caused by phonon scattering above 30 K.3) A close correlation was found between the radiative lifetime and the phase correlation time of the free excitons in GaSe. This result gives a direct experimental proof of the recent theoretical prediction.4) We made two different hole burning experiments in the free exciton line in GaSe: pulse propagation delay and pump-probe experiments. Both results support arguments for partial exciton localization by stacking disorder.5) We proposed two new methods to investigate femtosecond processes: pump-probe and upconversion methods using temporally incoherent lights.6) Temporal behavior of hot carriers in CdSe was investigated with subpicosecond accuracy, by using a novel pump-probe technique. in which the self-phase modulation effect in an optical fiber is utilized to extend the spectral width of the probe pulse. Pump-induced changes is explained by the formation of an electron-hole plasma and a succeeding thermal relaxation of the plasma.7) Photoluminescence spectra of short-period GaAs/AlAs superlattices were studied as a function of hydrostatic and uniaxial pressure at 20 K. It is found that lowest excited state is an indirect exciotns at Xz.