Femtosecond relaxation dynamics of excitons localized by disorder in semiconductors

1）我们制作了被动锁模染料激光系统。染料激光器以 100 MHz 的速率产生一串 100 fs 脉冲。波长调谐范围为580-620 nm。2)采用温度相关光子回波法测量了GaSe中激子的相位弛豫时间。研究发现，光学相移是由30 K以上的声子散射引起的。3)GaSe中自由激子的辐射寿命与相位相关时间之间存在密切的相关性。这一结果为最近的理论预测提供了直接的实验证明。4)我们在GaSe中的自由激子线中进行了两种不同的烧孔实验：脉冲传播延迟和泵浦探针实验。这两个结果都支持了通过堆积无序进行部分激子局域化的论点。5) 我们提出了两种研究飞秒过程的新方法：泵浦探针和使用时间不相干光的上转换方法。6) 通过使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扩展探测脉冲的光谱宽度。泵浦引起的变化可以通过电子空穴等离子体的形成和随后的等离子体热弛豫来解释。7)研究了短周期GaAs/AlAs超晶格的光致发光光谱作为20 K下静水压力和单轴压力的函数。发现最低激发态是Xz处的间接激子。

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.