Spatial visualization of electron wavefunctions and acoustic phonon transduction in semiconductor quantum wells and related applications

1)利用表面吸收探测光脉冲和波长调谐泵浦光脉冲对2势垒和3势垒的GaAs/GaAlAs样品进行了太赫兹声子产生和探测实验。这些首次在皮秒声学领域(高达0.3 THz)的光谱实验被成功地用理论模型来描述这些多层膜中声子的产生和检测。我们还对光谱产生效率进行了表征。2)在时间和空间分辨率方面，我们使用较短的(~400飞秒)光脉冲来演示频率高达0.5太赫兹的探测。我们还开发了一种新的光学偏振敏感斜入射技术，对铬进行了测试，以分离不同的信号贡献，并模拟了该样品的声子脉冲形状。3)研制了一种新型的超快Sagnac干涉仪，空间分辨率为1μm，适用于半导体，涉及单一聚焦对象。4)为了帮助解释量子阱结果，我们研究了3种不同样品的超快声子产生。我们演示了利用各向异性剪切和电子扩散展宽产生的皮秒剪切脉冲。5)在量子阱样品上测试了一种基于光致发光的新的检测方案。结果表明，要实现对声子脉冲的探测，需要更高的探测灵敏度，而不是在表面。

1)THz phonon generation and detection experiments were done on 2-well and 3-well GaAs/GaAlAs samples with surface-absorbed probe optical pulses and wavelength-tuned pump optical pulses. These first spectroscopic experiments in the domain of picosecond acoustics (up to 0.3 THz) were successfully treated with theoretical models to describe the phonon generation and detection in these multilayers. We also characterized the spectral generation efficiency.2)Improvements in temporal and spatial resolution were achieved using shorter (〜400 fs) optical pulses to demonstrate detection at frequencies up to 0.5 THz. We also developed a new optical-polarization-sensitive oblique-incidence technique, tested on Cr, to separate different signal contributions, and modelled the phonon pulse shapes for this sample.3)A Novel ultrafast Sagnac interferometer was developed for picosecond phonon detection with 1 μm spatial resolution, applicable to semiconductors, involving a single focusing objective.4)Bulk GaAs picosecond acoustics was implemented to help interpret the quantum well results, we investigated ultrafast phonon generation in 3 different GaAs samples. We demonstrate the generation of picosecond shear pulses using anisotropic cuts and pulse-broadening by electron diffusion.5)A novel detection scheme based photoluminescence was extensively tested on quantum well samples. The results show that we require a higher detection sensitivity to achieve detection of phonon -pulses detection within a quantum well rather than at the surface.