Femtosecond relaxation dynamics of excitons localized by disorder in semiconductors

1)研制了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串100飞秒的脉冲。波长调谐范围为580-620 nm。2)用变温光子回波法测量了GaS中激子的位相弛豫时间。3)GASE中自由激子的辐射寿命与位相关联时间密切相关。这一结果为最近的理论预测提供了直接的实验证明。4)我们在GASE自由激子线上进行了两种不同的烧孔实验：脉冲传输延迟实验和泵浦探测实验。5)我们提出了两种新的方法来研究飞秒过程：泵浦-探测方法和利用时间非相干光的上转换方法。6)利用一种新的泵浦-探测技术，以亚皮秒的精度研究了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用电子空穴等离子体的形成和随后等离子体的热弛豫来解释。7)研究了20K下短周期GaAsAlAs超晶格的光致发光光谱随流体静压和单轴压力的变化，发现在XZ处最低激发态是一种间接激发。

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.