Coherent acoustic phonon generation and development of terahertz cryogenic acoustic microscope

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Wilson 0622060 The objective of this research is to investigate a new technique for the generation of high-frequency (terahertz) acoustic waves by pulsed millimeter-wave laser radiation. The approach will be to first demonstrate the feasibility of the acoustic wave generation technique, followed by testing the reverse process whereby coherent terahertz acoustic waves can be made to induce pulses of electromagnetic radiation, in preparation for the development of an acoustic microscope capable of subsurface imaging with nanometer-scale resolution. Intellectual MeritThe proposed research involves a challenging set of experimental measurements in a novel phonon generating system that consists of a doping semiconductor superlattice excited by terahertz laser pulses. The research would certainly enhance the knowledge base concerning the generation and detection of high-frequency phonons. The envisioned acoustic microscope could have a very high spatial resolution approaching the nanometer-scale range. Broader Impacts The primary application of the proposed research is towards the development of a cryogenic acoustic microscope that uses superfluid helium as the transmitting fluid between phonon source/detector and sample to be imaged. Such a microscope, if it possessed nanometer scale accuracy, could provide new methods for non-invasive imaging of interfaces, substrate surfaces, and doping profiles in semiconductor nanostructures, with potential applications in biological materials and sensors. Furthermore, by providing modern research opportunities at a West Virginia state (primarily undergraduate) university, located in a traditionally economically disadvantaged area, larger numbers of Appalachian undergraduates may decide to pursue advanced degrees and careers in the physical sciences and engineering.