Theory, development and testing of a novel six degree of freedom sensor using optical interferometry

This thesis describes the design, development and testing of a novel sensor based on optical interferometry that measures displacement to 6 degree of freedom (DoF). It starts with an in-depth mathematical analysis of the behaviour of the radiant flux over the active area of a rectangular photodetector under varying mirror tilt angle, width of photodetector active area, distance of photodetector from beam centre, distance of the photo-detector from the optical origin and light source wavelength. Findings not evident in the literature are presented, such as flux behaviour beyond the first modulation amplitude zero and the effect of fringe contraction and expansion on the flux at varying distance from beam centre and optical origin. The outcome of the analysis was crucial for deciding to use image sensors rather than photodetectors for this displacement sensor. Obtaining tilt and rotation information from the interferogram is discussed as well as the orthogonal design of the sensor. The mathematics for deriving the position vectors of displaced mirrors from the fringe analysis is given in detail. An experiment rig was built to test the sensor that included an XYZ translation stage as well as a Tilt/Rotation stage, which together provided a means of displacing the interferometer cube mirror to 6 DoF. The experiment rig integrated a 3 DoF tilt/rotation optical lever system designed specifically to accurately measure pitch, roll and yaw of the 6 DoF displacement sensor. Experimental data showed the optical lever system and 6 DoF sensor to have better than 0.01° correlation for pitch, roll and yaw over the test range of ±0.5° angular displacements. The accuracy and resolution of measuring linear displacement using optical interferometry is already well known, therefore this research adds a novel way of including angular displacement to that capability to provide displacement measurement to 6 DoF using 3 interferometers

The AXAF technology program: The optical flats tests

The results of a technology program aimed at determining the limits of surface polishing for reflecting X-ray telescopes is presented. This program is part of the major task of developing the Advanced X-ray Astrophysical Facility (AXAF). By studying the optical properties of state-of-the-art polished flat surfaces, conclusions were drawn as to the potential capability of AXAF. Surface microtopography of the flats as well as their figure are studied by X-ray, visual, and mechanical techniques. These techniques and their results are described. The employed polishing techniques are more than adequate for the specifications of the AXAF mirrors

LOLA: Lunar Optical Long-baseline Array. 1992-1993 space design

In the fall of 1992, the design and analysis of a lunar-based optical interferometer telescope array was initiated by a group of students in the Department of Aerospace Engineering at Virginia Tech. This project was undertaken at the suggestion of the Space Exploration Initiative Office at the NASA Langley Research Center. The original array design requirements, listed below, centered on the primary objective of resolving earth-type planets about stars out to a distance of ten parsecs: spectrum coverage spanning wavelengths from five nm to five mm, with a primary operating mode in the visible spectrum; a total collecting area providing a signal-to-noise ratio (SNR) of no less than 10.0 for a median wavelength of 500 nm; the individual array elements must be identical and have a maximum optical diameter of 2.0 m; and lunar site selection is limited to ten degrees north and south of the lunar equator on the lunar far side while not closer than 15 degrees to either near-side limb. Following construction by astronaut crews, array operation will be conducted from earth and astronomical observations will not be conducted during the lunar day. The entire system is designed for minimum achievable mass. The majority of the original design requirements for the telescope array were met

Hyperspectral colour imaging and spectrophotometric instrumentation

The trichromatic nature of commercial photography is strictly connected with the nature of human colour vision, although the characteristics of usual colour imaging devices are quite different from the human visual system. The increase in the number of colour channels for spectral (either multispectral or hyperspectral) imaging is an active field of research with many potential applications in different fields. Each element of the captured scene is specified in the spectral image by the spectral reflectance factor. This measurement is independent of the particular illumination of the scene and allows the colorimetric computation in a device-independent colour space for any chosen illuminant and any observer. This thesis describes the project and construction of a compact spectrophotometric camera, which can be used in both portable and in-situ applications. The compactness is made possible by a suitable image spectral scanning based on an Induced Transmission Filter (ITF). This filter is made by a set of thin-film coatings of dielectric materials with high and low refraction index, whose shape like a wedge induces a wavelength selective transmittance, continuously variable along one direction and uniform in the perpendicular direction. Such a filter, classified as Linearly Variable Filter (LVF), operates continuously from 430nm to 940nm and allows hyperspectral imaging. In traditional scanners the whole apparatus is moved along a path as long as the scene, whereas in this instrument the camera body is still and the LVF is the only moving part. The sequence of operations for wavelength and radiometric calibrations are discussed. The expected acquisition times and number of images as a function of the spectral sampling step are considered. The resulting properties make the instrument easy to use and with short acquisition times. Moreover, overviews of the historic evolution of colour vision fundamentals, colour spaces and spectral imaging technology are given for introducing the reader to the essential concepts useful for the understanding of the text

Design and construction of a fibre interferometer for the study of MEMS and NEMS to temperatures below 1 K

Optical interferometry offers a powerful tool for the study of the mechanical motion of micro- and nano-electromechanical systems (MEMS and NEMS). By examining the modulation of reflected light the displacement can be measured with sub-nanometre precision. Recent work with fibre interferometers carried out by other groups has studied the motion of nanomechanical systems down to temperatures as low as 1 K. Dissipation measurements in the last few years of a number of devices fabricated from high-stress amorphous silicon nitride have shown a marked increase in quality factors when compared to similar low-stress devices. The high quality factors and small masses of these devices have attracted a great deal of interest within the nanomechanical and optomechanical communities. Measurements of dissipation in nanomechanical resonators carried out in Nottingham to date have used the magnetomotive effect to detect nanomechanical motion. This has required that a layer of metal be applied to the high-stress silicon nitride, modifying the mechanical properties. In this thesis we present an overview of the design and construction of an optical detection system designed to study MEMS and NEMS devices from room temperature to liquid helium temperatures. Optical detection is able to measure the displacement of purely dielectric structures and as such is an ideal method with which to measure dissipation in these high-Q silicon nitride resonators, complementing the other nanomechanical measurement techniques available within Nottingham. Using this system, measurements have been made on a number of micro- and nano-electromechanical systems fabricated using processes developed during this work. Confocal images of these devices obtained using the fibre interferometer show a spatial resolution of 0.75 um, a value close to the diffraction limit of the system. Micromechanical quartz tuning forks have been measured to confirm the frequency response of the interferometer, with a value for the piezo-electro-mechanical coupling constant of 2.18 +/- 0.06 uC/m obtained that is in very good agreement with the values published in the literature. Nanomechanical measurements of 200 um square high-stress silicon nitride membranes have revealed thermoelastic damping to be the limiting dissipation mechanism for these resonators at room temperature. Using elastic theory it is possible to quantify the fQ floor predicted by thermoelastic damping seeing good agreement with experimental data. At lower temperatures inter-membrane coupling was observed, with acoustic vibrations from neighbouring membranes coupling into and being amplified by the membrane under observation. Discrepancies in quality factor between the observed and unobserved membranes are most likely due to optomechanical damping of the observed membrane by the laser. This inter-membrane coupling offers a powerful technique for the indirect observation of the flexural modes of nearby membranes without optically damping the response

Development of Technologies for Active Wavefront Control of Advanced Gravitational Wave Detectors

The era of gravitational-wave astronomy started with the detection of a binary black hole coalescence on the 14th of September 2015 by the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO). By the end of 2017, a total number of 11 gravitational wave events have been detected by LIGO and Virgo detectors. One of these events, GW17081, produced by the coalescence of a binary neutron star signaled the dawn of multi-messenger gravitational astronomy, revealing invaluable information about the physics occurring in such cataclysmic event. The work presented in this thesis is part of the ongoing global effort to improve the sensitivity of current detectors and thus improve both the detection rates and the information that can be gleaned from each detection. The sensitivity of terrestrial interferometric detectors are broadly limited by coating thermal noise and quantum noise. Increasing the circulating laser power and injecting vacuum-squeezed light are employed to reduce the quantum noise. However, the ability to implement these measures and their efficacy is fundamentally limited by absorption-induced wavefront distortion within the interferometer. At the time of writing this thesis, aLIGO detectors are struggling to increase the input power above approximately 30 W and the current observed level of squeezing at aLIGO Livingston and Hanford Observatories are 3dB and 2.2 dB respectively, partly due to wavefront mismatch. New technologies are urgently required to diagnose these issues. In this thesis, I will will describe the development of a new technologies for the solution of this problem: an advanced “phase camera” that can examine individual RF sideband fields used to control and sense the interferometer and new adaptive optics for active wavefront control and mode-matching within the interferometer. The new phase camera measures the complex amplitude of a coherent field that is frequency-offset from a reference field, and records the transverse profile with high spatial and temporal resolution. Furthermore, it does so without the use of scanning mirrors and thus is suitable for use during both detector commissioning and low-noise operation. This thesis also describes the development of new thermally-actuated mirrors for adaptive wavefront control and mode matching in aLIGO. The two designs presented are the thermal-bimorph mirror and the compression-fit mirror. Both of which show a large and linear actuation range, and low higher-order aberrations. They are currently scheduled for deployment to assist with mode matching between the squeezed light source and the signal recycling cavity of aLIGO and can be extended to other optical interfaces during the detectors A+ upgrade.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

Theoretical Analysis of Interferometer Wave Front Tilt and Fringe Radiant Flux on a Rectangular Photodetector

This paper is a theoretical analysis of mirror tilt in a Michelson interferometer and its effect on the radiant flux over the active area of a rectangular photodetector or image sensor pixel. It is relevant to sensor applications using homodyne interferometry where these opto-electronic devices are employed for partial fringe counting. Formulas are derived for radiant flux across the detector for variable location within the fringe pattern and with varying wave front angle. The results indicate that the flux is a damped sine function of the wave front angle, with a decay constant of the ratio of wavelength to detector width. The modulation amplitude of the dynamic fringe pattern reduces to zero at wave front angles that are an integer multiple of this ratio and the results show that the polarity of the radiant flux changes exclusively at these multiples. Varying tilt angle causes radiant flux oscillations under an envelope curve, the frequency of which is dependent on the location of the detector with the fringe pattern. It is also shown that a fringe count of zero can be obtained for specific photodetector locations and wave front angles where the combined effect of fringe contraction and fringe tilt can have equal and opposite effects. Fringe tilt as a result of a wave front angle of 0.05° can introduce a phase measurement difference of 16° between a photodetector/pixel located 20 mm and one located 100 mm from the optical origin

Interferometric observations of hot stars

Accurate determination of fundamental stellar properties is crucial in understanding and testing models of stellar structure and evolution. To date, most stars with independent determinations of stellar properties based on high-resolution observations by optical interferometers belong to stars of type F5 or later, and most of measurements for early type stars come almost exclusively from the seminal observations with the Narrabri Stellar Intensity Interferometer (NSII) 50 years ago. Additionally, stellar rotation, generally overlooked in standard stellar models for decades, can play a central role for early-type stars, given their frequent high rotation rates. In this case, determination of fundamental stellar properties requires accurate diameter estimates at a range of position angles, and a more detailed modelling of the stellar surface. Recent development of 2D stellar models including a self-consistent rotation description (incorporating differential rotation) in stars with radiative envelopes has provided a method to describe the effects of rotation that links them to fundamental properties,based on a small set of parameters determining the stellar structure (mass,composition,rotation). In this thesis I have determined fundamental stellar properties for 14 new stars with spectral types earlier than F6. For 10 of them, the effects of stellar rotation may be neglected, whereas the other 4 exhibit fast rotation. In order to derive stellar parameters for these stars, I have incorporated state-of-the-art 2D models into a code capable of generating a model synthesizing all observables into a robust and self-consistent framework. Using interferometry,star distances,photometry and spectroscopy in the ultraviolet,visible and infrared, the derived fundamental stellar parameters, together with rotation dependent evolutionary tracks,are used to determine mass and age of the stars,corrected for the bias induced by the star rotation axis orientation

Research and Development of Methods and Instrumentation for the Calibration of Vertical Angle Measuring Systems of Geodetic Instruments

This research deals with the methods and instrumentation for calibration of vertical angle measuring systems of geodetic instruments. Two different methods are proposed in the thesis. First method is based on the vertical angle measuring system calibration using trigonometric method where 1 m reference scale with 1mm grating is utilized. Two ways of application of this method are analyzed in the thesis as well as uncertainty sources and their impact on measurement results are provided in the table of the uncertainty budget. Another method for vertical angle measuring system calibration is based on the new setup of the reference means. New proposed apparatus is designed to fit the instrument under calibration in horizontal position. Therefore, this setup enables to perform calibration of vertical angle measuring systems using horizontal angle measuring system calibration techniques. The special mirror mount was attached to the telescope of the calibrated instrument and the change of the telescope position was measured by the electronic autocollimator. The analysis of the uncertainty budget is presented in this thesis. The dissertation consists of introduction, 3 chapters, general conclusions and references. The introduction reveals the topicality of the thesis, investigated problem and object of the research. The aim and tasks as well as research methodology, scientific novelty, practical significance of the results and defended statements are also presented in the introduction. Chapter 1 revises scientific papers on the subject of the dissertation. Analysis of standards, methods and instrumentation for the calibration of angle measuring systems are provided in this Chapter. Chapter 2 describes the main principles of two proposed methods. The instrumentation and measurement procedure are analyzed as well as uncertainty evaluation model is designed. Chapter 3 is focused on the experiment of the practical application of both proposed methods. The uncertainty sources are analyzed and specified in the tables of uncertainty budgets. The experimental results of the calibration of vertical angle measuring systems of the total station are revealed. Research results are presented in 7 publications of scientific journals: 3 publications in journals indexed in ISI Web of Science data base with the impact factor, 4 – in other international scientific journals indexed in SCOPUS, Compendex databases. 5 papers are published in the proceedings of international conferences. 1 national patent regarding method for calibration of vertical angle measuring systems using reference scale was registered in the State Patent Bureau of the Republic of Lithuania