Optical Generation of Coherent Hypersonics in the 100GHz to THz Range

这项拟议的研究将把产生和检测相干超高频超声波的光学技术从100 GHz范围扩展到太赫兹范围。太赫兹波的产生将通过使用AlGaAs层和GaAs层交替的特殊设计的量子阱结构来完成。这个量子井结构将被设计成声场的静态图像。热电子和空穴载流子的亚皮秒光激发以及随后量子井结构所规定的图案中载流子的非辐射弛豫将导致与势垒周期相同的波长的相干声波的选择性激发。这些结构将被设计成提供与太赫兹频率相对应的声波波长。声波幅度的检测将通过使用专门设计的单量子井层(光学探测器层)来完成，通过激子共振的调制来跟随声应变幅度。光驱动应变场的理论模型，通过非辐射弛豫和光致伸缩效应，将与实验研究并行进行。这些高频声学在界面和周期井结构内的传播和传输也将被讨论。这项工作将提供一种全光声换能器，与二极管泵浦的微激光源兼容，作为下一代成像声学设备。

The proposed research will extend the optical technique of generating and detecting coherent ultrahigh frequency ultrasonics from the 100 GHz range to the THz range. The generation of THz waves will be accomplished by using specifically engineered quantum-well structures of alternating AlGaAs and GaAs layers. This quantum-well structure will be designed to be a static image of a sound field. Subpicosecond optical excitation of hot electron and hole carriers and subsequent non-radiative relaxation of the carriers in the pattern prescribed by the quantum well structure will lead to selective excitation of coherent acoustic waves with the same wavelength as the well period. The structures will be designed to provide acoustic wavelengths corresponding to THz frequencies. The detection of the acoustic wave amplitude will be accomplished by using a specifically designed single quantum well layer (optical detector layer) to follow the acoustic strain amplitude through the modulation of the exciton resonance. Theoretical modelling of the optically driven strain fields, through both non-radiative relaxation and photostriction effects, will be carried out in parallel with the experimental studies. The propagation and transmission of these high frequency acoustics at interfaces and within the periodic well structure will also be treated. This work will provide an all optical acoustic transducer, compatible with diode pumped micro laser sources, as a future generation of acoustic devices for imaging.