| Summary: | Thesis (Ph.D.)--Boston University === PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. === The concept of optical excitation and detection of nanoscale mechanical motion
has led to a variety of tools for non-destructive materials characterization and remote
sensing. These techniques, commonly referred to as laser ultrasonics, offer the benefit
of high-bandwidth, highly localized measurements, and also allow for the ability to
investigate nanoscale devices. The impact of laser ultrasonic systems has been felt in
industries ranging from semiconductor metrology to biological and chemical sensing.
In this thesis, we develop a variety of techniques utilizing a frequency domain laser
ultrasonic approach, where amplitude modulated continuous wave laser light is used
instead of traditional pulsed laser sources, and we apply these systems in free-space,
optical fiber based. and integrated on-chip configuration. In doing so , we demonstrate
the ability to efficiently transduce various types of mechanical motion including
surface and bulk acoustic waves, guided acoustic waves, and resonant motion from
nanomechanical systems (EMS). First, we develop a superheterodyne free-space ultrasonic
inspection system in an effort to characterize tiurface acoustic wave dispersion
in thin-film material systems. We utilize a similar system to study negative refraction
and focusing behavior of guided elastic waves in a thin metal plate, providing a novel
approach for the study of negative index physics. Furthermore, we develop a nearfield
optical technique using optical fibers to simultaneously t ransduce the motion
of 70 NEMS resonators using a single channel. This multiplexed approach serves as
a crucial step in moving NEMS technology out of the research laboratory. Finally,
we go on to study opto-mechanical interactions between optical whispering gallery
mode (WGM) resonators and integrated EMS devices on the same chip, using the
enhanced interactions to tudy optical forces acting on the nanoscale mechanical devices. This integrated system provides a very efficient mechanical sensing platform as well as a robust test-bed for the study of new optical interactions including the presence of both attractive and repulsive optical forces. The overall goal of the work is to further the state-of-the art for optically transduced nano mechanical sensing as well as to advance the understanding of optomechanical interactions of nanoscale devices. === 2031-01-01
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