The magic carpet: an arbitrary spectrum wave maker for internal waves

Abstract: We present a novel apparatus for generating internal waves of arbitrary size and shape, including both phase-locked and propagating waves. It is an actively driven, flexible “magic carpet” in the base of a tank. Our wave maker is computer-controlled to enable easy configuration. The actuation of a smooth, flexible surface produces clean waveforms with a predictable spectrum, for which we derive a theoretical model. We demonstrate the versatility of our wave maker through an experimental study of linear and nonlinear, isolated, and combined internal waves, including some that are sufficiently nonlinear to break remote from their source. Graphic abstract

Wavefront modelling and sensing for advanced gravitational wave detectors

The Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) directly detected gravitational waves for the first time on the 14th of September 2015. In 2017 the detection of gravitational waves from a binary neutron star merger was subsequently followed up by observations by optical and radio astronomers — the first time an astrophysical event was observed by two completely separate astrophysical signals. This marked the beginning of multi-messenger astronomy. Since then 90 astrophysical events have been observed using gravitational waves. To increase the rate of event detection the sensitivity of gravitational wave detectors must be improved. Current state of the art gravitational wave detectors are optical interferometers in the dual recycled Fabry-Perot Michelson (DRFPMI) configuration with quantum squeezed light injected to reduce vacuum noise. Future plans to improve the sensitivity further rely on increasing the circulating laser power and improving the efficiency of quantum squeezing. Squeezing efficiency is drastically reduced by optical losses in the interferometer of which mode mismatch is a large component. Higher laser power introduces larger thermal distortions in the interferometer, which increase mode mismatch. This thesis covers topics relevant to optical modelling of coupled cavity interferometers such as the DRFPMI with a focus on mode mismatch. Novel applications in aLIGO commissioning based on existing mode mismatch sensing techniques using the output mode cleaner (OMC) are presented. A new mode mismatch sensing technique based on transverse higher order mode sidebands is demonstrated on an optical tabletop and its applications to mode mismatch sensing in aLIGO is discussed. A new optical modelling framework based on linear canonical transformations and signal flow graph theory is also presented.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

Cavity Optomechanics with High Stress Silicon Nitride Films

There has been a barrage of interest in recent years to marry the fields of nanomechanics and quantum optics. Mechanical systems provide sensitive and scalable architectures for sensing applications ranging from atomic force microscopy to gravity wave interferometry. Optical resonators driven by low noise lasers provide a quiet and well-understood means to read-out and manipulate mechanical motion, by way of the radiation pressure force. Taken to an extreme, a device consisting of a high-Q nanomechanical oscillator coupled to a high-finesse optical cavity may enable ground-state preparation of the mechanical element, thus paving the way for a new class of quantum technology based on chip-scale phononic devices coupled to optical photons. By way of mutual coupling to the optical field, this architecture may enable coupling of single phonons to real or artificial atoms, an enticing prospect because of the vast "quantum optics toolbox" already developed for cavity quantum electrodynamics. The first step towards these goals --- ground-state cooling of the mechanical element in a "cavity optomechanical" system --- has very recently been realized in a cryogenic setup. The work presented in this thesis describes an effort to extend this capability to a room temperature apparatus, so that the usual panoply of table-top optical/atomic physics tools can be brought to bear. This requires a mechanical oscillator with exceptionally low dissipation, as well as careful attention to extraneous sources of noise in both the optical and mechanical componentry. Our particular system is based on a high-Q, high-stress silicon nitride membrane coupled to a high-finesse Fabry-Perot cavity. The purpose of this thesis is to record in detail the procedure for characterizing/modeling the physical properties of the membrane resonator, the optical cavity, and their mutual interaction, as well as extraneous sources of noise related to multimode thermal motion of the oscillator, thermal motion of the cavity apparatus, optical absorption, and laser phase fluctuations. Our principle experimental result is the radiation pressure-based cooling of a high order, 4.8 MHz drum mode of the membrane from room temperature to ~ 100 mK (~ 500 phonons). Secondary results include an investigation of the Q-factor of membrane oscillators with various geometries, some of which exhibit state-of-the-art Q x frequency products of 3 x 10^13 Hz, and a novel technique to suppress extraneous radiation pressure noise using electro-optic feedback.</p