Since the first direct detection of gravitational wave signals from the coalescence of a pair of stella-mass black holes on 14 September 2015, a global network of terrestrial interferometric detectors, with kilometer-scale arms, have opened a new window through which the astrophysical universe can be probed. This success was the result of decades of exploratory work done on smaller-scale prototype interferometers. Even though the detection of astrophysical gravitational wave signals has become almost a routine event, prototype interferometers remain an essential tool in developing technologies for future generations of kilometer-scale detectors. They are unique in that they are large enough to probe physics that cannot be easily investigated on the table-top, but have no obligation to function as an observatory, and so can be readily modified for a wide variety of experiments. This thesis focuses on one direction in which prototype interferometry can be taken, serving as a testbed for testing the laws of quantum mechanics at the macroscopic scale. While this is in itself an interesting experimental program, it can make a direct contribution to the field of gravitational wave astronomy since future generations of terrestrial detectors are expected to be limited in their sensitivity due to measurement limits set by the Heisenberg uncertainty principle. Techniques to evade these limits can be demonstrated on a prototype interferometer, before embarking on an expensive program to implement them at the scale necessary for kilometer-scale observatories.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/4H7V-W213, author = {Korth, William Zachary}, title = {Mitigating Noise in Interferometric Gravitational Wave Detectors}, school = {California Institute of Technology}, year = {2019}, doi = {10.7907/4H7V-W213}, url = {https://resolver.caltech.edu/CaltechTHESIS:05292019-020613259}, abstract = {Gravitational waves, first predicted by Einstein in 1916, eluded detection for nearly a century. These faint ripples in the fabric of spacetime, with typical strain amplitudes at the Earth on the order of |h| ∼ 10−22, carry secrets of the universe untold by electromagnetic radiation. Following decades of research and development, a network of terrestrial interferometric detectors succeeded in measuring the passing of a gravitational wave (GW150914) for the first time in 2015. Individual detectors within this network are currently said to be operating in a “second-generation” configuration; over the next decade, planned upgrades will take these detectors beyond this into a new generation. This thesis concerns the characterization and reduction of noise in one of these second-generation detectors, Advanced LIGO, as well as efforts underway to improve its sensitivity in the coming years.
The first part of this thesis is a detailed overview of gravitational waves, the history of gravitational wave detection, and a reasonably thorough description of the Advanced LIGO detector. Particular attention is paid to a pedagogical motivation of the optical configuration of Advanced LIGO with reference to its forebears. This part ends with an overview of the sources of noise limiting the sensitivity of Advanced LIGO, and an exposition of plans to reduce their influence in the future.
The second part describes the development of a laser gyroscope for use in tilt sensing in Advanced LIGO, starting with a motivation of the work based on limitations in the area of seismic noise sensing and cancellation.
The third part recounts the design, fabrication, testing, installation and commissioning of an important component of the Advanced LIGO detector: the output mode cleaner (OMC).
The fourth part outlines a proposed scheme for reduction of quantum noise in gravitational wave detectors and other experiments. In particular, this scheme allows for the operation of a so-called “optical spring” cavity in such a way as to be largely immune from the deleterious effects of quantum radiation pressure noise.
The fifth and final part describes progress towards a direct measurement of thermal noise in thin silicon ribbons, which is pertinent to the design of suspensions in future cryogenic gravitational wave detectors.
This thesis has the internal LIGO document number P1900035.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/Z9DZ06HS, author = {Quintero, Eric Antonio}, title = {Improving the Performance and Sensitivity of Gravitational Wave Detectors}, school = {California Institute of Technology}, year = {2018}, doi = {10.7907/Z9DZ06HS}, url = {https://resolver.caltech.edu/CaltechTHESIS:10162017-190056286}, abstract = {The field of observational gravitational wave astronomy has begun in earnest, starting with the detection of the strain signal from the binary black hole merger GW150914 by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015. The current incarnation of the LIGO observatories, known as Advanced LIGO, has achieved strain sensitivities on the order of 10−23/√Hz in the hundreds of Hz region, which has enabled unambiguous detection of astrophysical gravitational wave signals. Nevertheless, the scientific output from the LIGO observatories is constrained by the instrumental performance and sensitivity, as there remain many more distant and exotic sources to be observed.
This thesis describes a few topics in experimental gravitational physics, broadly unified by the desire to improve the performance and sensitivity of gravitational wave interferometers. First, it describes an experimental effort to search for a novel form of nonlinear mechanical noise that may be relevant for the ultimate performance of the mirror sus- pension systems used throughout the instrument. Next, it summarizes work done at the CalTech 40m LIGO controls prototype to realize its fully operational state, and a novel automated controls algorithm developed and tested there that may be useful in simplifying the control of current and future interferometers. Finally, it describes work done on a system to identify and subtract unwanted noise couplings out of recorded aLIGO strain data in an automated fashion. The noise subtraction system applied to GW150914 is demonstrated to reduce the uncertainties of the black hole mass parameters by about 10%.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/F38W-6N47, author = {Ni, Xiaoyue}, title = {Probing Microplastic Deformation in Metallic Materials}, school = {California Institute of Technology}, year = {2018}, doi = {10.7907/F38W-6N47}, url = {https://resolver.caltech.edu/CaltechTHESIS:09202017-020239229}, abstract = {Metallic materials deform through discrete displacement bursts that are commonly associated with abrupt dislocation activities, i.e. avalanches, during plastic flow. Dislocations might be active prior to the textbook yielding, but it is unclear whether these activities can be discerned as smaller strain events, i.e. microplasticity. Novel experimental approaches involving nanomechanical experiments are developed to detect and to quantify microplastic deformation that occurs during compression of micron- and sub-micron sized single crystalline copper nano-pillars. The experiment, focusing on metals’ pre-yield regime, reveals an evolving dissipation component in the storage and loss moduli that likely corresponds to a smooth transition from perfect elasticity to avalanche-dominated plastic deformation. This experimental investigation is corroborated by mesoscopic plasticity simulations, which apply to a minimal model that combines fast avalanche dynamics and slow relaxation processes of dislocations. The model’s predictions are consistent with the microscopic experiments and provide constitutive relationship predicting microplastic crackling noise being upconverted by small stress perturbations. Another experimental investigation on unload-reload cyclic behavior of copper nano-pillars post yielding shows a decaying microplastic hysteresis with emergent power laws and scaling features, which signifies an ever-explored reversible-to- irreversible transitions in metal deformation, as seen in other nonequilibrium systems. To study microplasticity in macroscopic metallic samples, an instrument is custom-built based on Michelson interferometer and achieves unprecedented high displacement noise resolution of 10−14m/√Hz in the frequency range of 10 – 1000 Hz. The macroscopic experiment has resolved a driving-modulated microplastic noise in bulk cantilever steel samples under nominal elastic loading. The characteristics of the noise resemble those of the microplastic noise predicted from the micromechanical simulations developed from microscopic experiments.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Greer, Julia R.}, } @phdthesis{10.7907/Z9PG1PQ9, author = {Hall, Evan Drew}, title = {Long-Baseline Laser Interferometry for the Detection of Binary Black-Hole Mergers}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z9PG1PQ9}, url = {https://resolver.caltech.edu/CaltechTHESIS:01302017-113507797}, abstract = {Late in 2015, gravitational physics reached a watershed moment with the first direct detections of gravitational waves. Two events, each from the coalescence of a binary black hole system, were detected by the Laser Interferometer Gravitational-wave Observatory (LIGO). At present, LIGO comprises two 4 km laser interferometers, one in Washington and the other in Louisiana; a third detector is planned to be installed in India. These interferometers, known as Advanced LIGO, belong to the so-called “second generation” of gravitational-wave detectors. Compared to the first-generation LIGO detectors (Initial and Enhanced LIGO), these instruments use multi-stage active seismic isolation, heavier and higher-quality mirrors, and more laser power to achieve an unprecedented sensitivity to gravitational waves. In 2015, both Advanced LIGO detectors achieved a strain sensitivity better than 10-23/Hz1/2 at a few hundred hertz; ultimately, these detectors are designed to achieve a sensitivity of a few parts in 10-24/Hz1/2 at a few hundred hertz.
This thesis covers several topics in gravitational physics and laser interferometry. First, it presents the design, control scheme, and noise performance of the Advanced LIGO detector in Washington during the first observing run (O1). Second, it discusses some issues relating to interferometer calibration, and the impact of calibration errors on astrophysical parameter estimation. Third, it discusses the prospects for using terrestrial and space-based laser interferometers as dark matter detectors.
This thesis has the internal LIGO document number P1600295.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/Z91V5BWT, author = {Yeaton-Massey, David Joseph}, title = {Cryogenic Silicon Optical Reference Cavities}, school = {California Institute of Technology}, year = {2016}, doi = {10.7907/Z91V5BWT}, url = {https://resolver.caltech.edu/CaltechTHESIS:01042016-150434876}, abstract = {Thermodynamical fluctuations in temperature and position exist in every physical system, and show up as a fundamental noise limit whenever we choose to measure some quantity in a laboratory environment. Thermodynamical fluctuations in the position of the atoms in the dielectric coatings on the mirrors for optical cavities at the forefront of precision metrology (e.g., LIGO, the cavities which probe atomic transitions to define the second) are a current limiting noise source for these experiments, and anything which involves locking a laser to an optical cavity. These thermodynamic noise sources scale physical geometry of experiment, material properties (such as mechanical loss in our dielectric coatings), and temperature. The temperature scaling provides a natural motivation to move to lower temperatures, with a potential huge benefit for redesigning a room temperature experiment which is limited by thermal noise for cryogenic operation.
We design, build, and characterize a pair of linear Fabry-Perot cavities to explore limitations to ultra low noise laser stabilization experiments at cryogenic temperatures. We use silicon as the primary material for the cavity and mirrors, due to a zero crossing in its linear coefficient of thermal expansion (CTE) at 123 K, and other desirable material properties. We use silica tantala coatings, which are currently the best for making high finesse low noise cavities at room temperature. The material properties of these coating materials (which set the thermal noise levels) are relatively unknown at cryogenic temperatures, which motivates us to study them at these temperatures. We were not able to measure any thermal noise source with our experiment due to excess noise. In this work we analyze the design and performance of the cavities, and recommend a design shift from mid length cavities to short cavities in order to facilitate a direct measurement of cryogenic coating noise.
In addition, we measure the cavities (frequency dependent) photo-thermal response. This can help characterize thermooptic noise in the coatings, which is poorly understood at cryogenic temperatures. We also explore the feasibility of using the cavity to do macroscopic quantum optomechanics such as ground state cooling.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/Z9Q81B1F, author = {Martynov, Denis V.}, title = {Lock Acquisition and Sensitivity Analysis of Advanced LIGO Interferometers}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z9Q81B1F}, url = {https://resolver.caltech.edu/CaltechTHESIS:05282015-142013480}, abstract = {Laser interferometer gravitational wave observatory (LIGO) consists of two complex large-scale laser interferometers designed for direct detection of gravitational waves from distant astrophysical sources in the frequency range 10Hz - 5kHz. Direct detection of space-time ripples will support Einstein’s general theory of relativity and provide invaluable information and new insight into physics of the Universe.
Initial phase of LIGO started in 2002, and since then data was collected during six science runs. Instrument sensitivity was improving from run to run due to the effort of commissioning team. Initial LIGO has reached designed sensitivity during the last science run, which ended in October 2010.
In parallel with commissioning and data analysis with the initial detector, LIGO group worked on research and development of the next generation detectors. Major instrument upgrade from initial to advanced LIGO started in 2010 and lasted till 2014.
This thesis describes results of commissioning work done at LIGO Livingston site from 2013 until 2015 in parallel with and after the installation of the instrument. This thesis also discusses new techniques and tools developed at the 40m prototype including adaptive filtering, estimation of quantization noise in digital filters and design of isolation kits for ground seismometers.
The first part of this thesis is devoted to the description of methods for bringing interferometer to the linear regime when collection of data becomes possible. States of longitudinal and angular controls of interferometer degrees of freedom during lock acquisition process and in low noise configuration are discussed in details.
Once interferometer is locked and transitioned to low noise regime, instrument produces astrophysics data that should be calibrated to units of meters or strain. The second part of this thesis describes online calibration technique set up in both observatories to monitor the quality of the collected data in real time. Sensitivity analysis was done to understand and eliminate noise sources of the instrument.
Coupling of noise sources to gravitational wave channel can be reduced if robust feedforward and optimal feedback control loops are implemented. The last part of this thesis describes static and adaptive feedforward noise cancellation techniques applied to Advanced LIGO interferometers and tested at the 40m prototype. Applications of optimal time domain feedback control techniques and estimators to aLIGO control loops are also discussed.
Commissioning work is still ongoing at the sites. First science run of advanced LIGO is planned for September 2015 and will last for 3-4 months. This run will be followed by a set of small instrument upgrades that will be installed on a time scale of few months. Second science run will start in spring 2016 and last for about 6 months. Since current sensitivity of advanced LIGO is already more than factor of 3 higher compared to initial detectors and keeps improving on a monthly basis, upcoming science runs have a good chance for the first direct detection of gravitational waves.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/Z94F1NNP, author = {Driggers, Jennifer Clair}, title = {Noise Cancellation for Gravitational Wave Detectors}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z94F1NNP}, url = {https://resolver.caltech.edu/CaltechTHESIS:06052015-123753277}, abstract = {The LIGO gravitational wave detectors are on the brink of making the first direct detections of gravi- tational waves. Noise cancellation techniques are described, in order to simplify the commissioning of these detectors as well as significantly improve their sensitivity to astrophysical sources. Future upgrades to the ground based detectors will require further cancellation of Newtonian gravitational noise in order to make the transition from detectors striving to make the first direct detection of gravitational waves, to observatories extracting physics from many, many detections. Techniques for this noise cancellation are described, as well as the work remaining in this realm.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, } @phdthesis{10.7907/7202-WT21, author = {Chalermsongsak, Tara}, title = {High Fidelity Probe and Mitigation of Mirror Thermal Fluctuations}, school = {California Institute of Technology}, year = {2014}, doi = {10.7907/7202-WT21}, url = {https://resolver.caltech.edu/CaltechTHESIS:05282014-211250693}, abstract = {
Thermal noise arising from mechanical loss in high reflective dielectric coatings is a significant source of noise in precision optical measurements. In particular, Advanced LIGO, a large scale interferometer aiming to observed gravitational wave, is expected to be limited by coating thermal noise in the most sensitive region around 30–300 Hz. Various theoretical calculations for predicting coating Brownian noise have been proposed. However, due to the relatively limited knowledge of the coating material properties, an accurate approximation of the noise cannot be achieved. A testbed that can directly observed coating thermal noise close to Advanced LIGO band will serve as an indispensable tool to verify the calculations, study material properties of the coating, and estimate the detector’s performance.
This dissertation reports a setup that has sensitivity to observe wide band (10Hz to 1kHz) thermal noise from fused silica/tantala coating at room temperature from fixed-spacer Fabry–Perot cavities. Important fundamental noises and technical noises associated with the setup are discussed. The coating loss obtained from the measurement agrees with results reported in the literature. The setup serves as a testbed to study thermal noise in high reflective mirrors from different materials. One example is a heterostructure of AlxGa1−xAs (AlGaAs). An optimized design to minimize thermo–optic noise in the coating is proposed and discussed in this work.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Adhikari, Rana}, }