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

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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.