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Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics / CHRISTOPHER DAWSON

Swansea University Author: CHRISTOPHER, DAWSON

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DOI (Published version): 10.23889/SUthesis.56947

Abstract

In levitated optomechanics, nano-scale objects are optically trapped so that their motion can be studied. These trapped nanoparticles are held in a 3D quadratic potential and act as damped harmonic oscillators; they are thermally and mechanically decoupled from the apparatus and their position is me...

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Published: Swansea 2020
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Bateman, James E.
URI: https://cronfa.swan.ac.uk/Record/cronfa56947
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first_indexed 2021-05-24T09:46:28Z
last_indexed 2021-05-25T03:28:06Z
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spelling 2021-05-24T11:52:52.1634530 v2 56947 2021-05-24 Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics cf74d57adc25af60a7fc1a571ee1cb48 CHRISTOPHER DAWSON CHRISTOPHER DAWSON true false 2021-05-24 In levitated optomechanics, nano-scale objects are optically trapped so that their motion can be studied. These trapped nanoparticles are held in a 3D quadratic potential and act as damped harmonic oscillators; they are thermally and mechanically decoupled from the apparatus and their position is measured interfer-ometrically to picometre accuracy. These systems are well suited to sensing and metrology applications, as any external disturbance of the particle can be observed using the scattered trapping light.When examining the motion of a levitated nanoparticle, it’s position is recorded and used to estimate a power spectral density (PSD), from which state parameters can be estimated. In this thesis an experi-mental setup is presented, optimised for maximum collection of particle position information in 1D, using a fibre-based parabolic mirror trap and heterodyne measurement system in order to produce spectra with minimal noise and unwanted artefacts.A novel application of the Middleton expansion from RF engineering is used to generate a complete power spectrum that depends on the physical parameters of the system. This method treats the particle as a stochastic harmonic oscillator, phase modulated by a Gaussian random process with known PSD. We reproduce the PSD of intensity at a detector, a quantity that is sinusoidally dependent on particle posi-tion. This technique generates a single, full PSD using modified Bessel functions, and does not depend on assumptions about the relative phases of the interfered fields, highlighting the non-linear dependence of measured signal on position. Theoretical spectra are fitted to a measured PSD and the phase modulation depth is extracted; this is used to calculate the particle oscillation amplitude and, by an equipartition ar-gument, the centre of mass temperature to mass ratio. State parameters are tracked as environmental conditions change and an increase in centre of mass temperature as a function of decreasing background gas pressure is observed. E-Thesis Swansea Optomechanics, Levitated Optomechanics, Fibre optics, Signal Processing, Optics, Photonics, Motion control, Spectral Analysis 1 3 2020 2020-03-01 10.23889/SUthesis.56947 COLLEGE NANME COLLEGE CODE Swansea University Bateman, James E. Doctoral Ph.D College of Science 2021-05-24T11:52:52.1634530 2021-05-24T10:43:07.3407442 College of Science Physics CHRISTOPHER DAWSON 1 56947__19975__0bd3afe44dc446fcbf2f4d2489c4ae5b.pdf Dawson_Christopher_PhD_Thesis_Final_Redacted_Signature.pdf 2021-05-24T11:49:19.9667543 Output 42015616 application/pdf E-Thesis – open access true Copyright: The author, Christopher Dawson, 2020. true eng
title Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
spellingShingle Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
CHRISTOPHER, DAWSON
title_short Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
title_full Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
title_fullStr Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
title_full_unstemmed Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
title_sort Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics
author_id_str_mv cf74d57adc25af60a7fc1a571ee1cb48
author_id_fullname_str_mv cf74d57adc25af60a7fc1a571ee1cb48_***_CHRISTOPHER, DAWSON
author CHRISTOPHER, DAWSON
author2 CHRISTOPHER DAWSON
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department_str Physics{{{_:::_}}}College of Science{{{_:::_}}}Physics
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description In levitated optomechanics, nano-scale objects are optically trapped so that their motion can be studied. These trapped nanoparticles are held in a 3D quadratic potential and act as damped harmonic oscillators; they are thermally and mechanically decoupled from the apparatus and their position is measured interfer-ometrically to picometre accuracy. These systems are well suited to sensing and metrology applications, as any external disturbance of the particle can be observed using the scattered trapping light.When examining the motion of a levitated nanoparticle, it’s position is recorded and used to estimate a power spectral density (PSD), from which state parameters can be estimated. In this thesis an experi-mental setup is presented, optimised for maximum collection of particle position information in 1D, using a fibre-based parabolic mirror trap and heterodyne measurement system in order to produce spectra with minimal noise and unwanted artefacts.A novel application of the Middleton expansion from RF engineering is used to generate a complete power spectrum that depends on the physical parameters of the system. This method treats the particle as a stochastic harmonic oscillator, phase modulated by a Gaussian random process with known PSD. We reproduce the PSD of intensity at a detector, a quantity that is sinusoidally dependent on particle posi-tion. This technique generates a single, full PSD using modified Bessel functions, and does not depend on assumptions about the relative phases of the interfered fields, highlighting the non-linear dependence of measured signal on position. Theoretical spectra are fitted to a measured PSD and the phase modulation depth is extracted; this is used to calculate the particle oscillation amplitude and, by an equipartition ar-gument, the centre of mass temperature to mass ratio. State parameters are tracked as environmental conditions change and an increase in centre of mass temperature as a function of decreasing background gas pressure is observed.
published_date 2020-03-01T04:23:15Z
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score 10.829975