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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Static Polarizability Measurements and Inertial Sensing with Nanograting Atom Interferometry

Gregoire, Maxwell David, Gregoire, Maxwell David January 2016 (has links)
I used a Mach-Zehnder atom interferometer to measure the static electric-dipole polarizabilities of K, Rb, and Cs atoms with 0.11\% uncertainty. Static polarizability measurements serve as benchmark tests for 𝑎𝑏 𝑖𝑛𝑖𝑡𝑖𝑜 atomic structure calculations. Calculating atomic properties such as polarizabilities, van der Waals coefficients, state lifetimes, or oscillator strengths involves accurately calculating the valence electrons' electric-dipole transition matrix elements. Additionally, testing Cs atomic structure calculations helps interpret the results of parity non-conservation experiments, which in turn places constraints on beyond-the-standard-model physics. I discuss improvements to our experiment that allowed us to measure static polarizabilities with 0.11% uncertainty, and we present our results in the context of recent 𝑎𝑏 𝑖𝑛𝑖𝑡𝑖𝑜 and semi-empirical static polarizabilities and recent, high-precision measurements of excited state lifetimes and van der Waals C₆ coefficients. I also used our interferometer to develop a new technique for inertial sensing. High precision, portable, atom-interferometer gyroscopes and accelerometers are desirable for self-contained inertial navigation and in the future may be used for tests of General Relativity and searches for gravitational waves using satellite-mounted inertial sensors. Satellite-mounted atom interferometers are challenging to build because of size, weight, power, and reliability constraints. Atom interferometers that use nanogratings to diffract atoms are attractive for satellite-mounted inertial sensing applications because nanogratings weigh approximately nothing and require no power. We developed a new 𝑖𝑛 𝑠𝑖𝑡𝑢 measurement technique using our nanograting atom interferometer, and we used it to measure inertial forces for the benefit of our static polarizability measurements. I also review how to calculate the sensitivity of a nanograting atom interferometer, and I employed these calculations in order to design a portable, nanograting atom interferometer inertial sensor.
32

Accurate and Precise Calibration of Advanced LIGO Detectors in the Era of Gravitational Wave Astronomy

Karki, Sudarshan 30 April 2019 (has links)
The first direct detection of gravitational waves in 2015, and the multiple detections that followed ushered in the era of gravitational-wave astronomy. With these developments, the focus of the gravitational-wave community shifted from detection to precision measurement, requiring a factor of ten improvement in calibration accuracy to maximize the astrophysical information that can be extracted from these detected signals. This dissertation discusses the implementation and characterization of a radiation-pressure-based calibration system called the Photon calibrator that is used as the primary calibration reference for the Advanced LIGO detectors. It also discusses the techniques and procedures used to realize sub-percent accuracy calibration of absolute displacement fiducials introduced using the Photon calibrator system during Advanced LIGO’s first and second observing runs. Using the Photon calibrator systems, frequency dependent calibration of the interferometer responses was achieved at the level of 2-3% in magnitude and 3- 5 degrees in phase across the LIGO detection band. This level of calibration accuracy has already played a significant role in extracting astrophysical parameters from LIGO’s detections. With the LIGO and Virgo detectors operating at design sensitivity, updated rate estimates indicate that measurement of the Hubble constant with gravitational waves with 1% accuracy will be possible within the next decade. This will require absolute amplitude calibration of the detectors at the sub-1% level. This dissertation also discusses the improvements that have been implemented in the Photon calibrator systems that will reduce the uncertainty in absolute displacement to below 0.5%. The gravitational waves from the post-merger phase of binary neutron stars are expected to contain interesting features at frequencies up to few kHz, carrying rich information about neutron-star astrophysics. This dissertation discusses the calibration errors introduced by test mass deformations caused by calibration forces at frequencies above 1 kHz. The errors, estimated using Finite Element Analysis, is in reasonable agreement with measurement results in the 1 to 5 kHz band. These investigations have enabled the reduction of calibration uncertainty at these frequencies, which should enhance our ability to decipher the neutron star astrophysics encoded in the gravitational wave signals from the post-merger phase. This dissertation includes previously published co-authored material.
33

A system for automatic positioning and alignment of fiber-tip interferometer

Jalan, Mahesh 15 November 2004 (has links)
The research described in this thesis involves the design, development, and implementation of an automated positioning system for fiber-optic interferometric sensors. The Fiber-Tip Interferometer (FTI) is an essential component in the proven Thermo-Acousto-Photonic NDE technique for characterizing a wide range of engineering materials including polymers, semiconductors and composites. The need to adapt the fiber-optic interferometric system to an industrial environment and to achieve precision control for optimizing interferometric contrast motivated the development of an automated, self-aligning FTI system design. The design enables high-resolution positioning and alignment by eliminating manual subjectivity and allows significantly improved repeatability and accuracy to be attained. Opto-electronic and electromechanical devices including a GRIN lens, 2x2 fused bi-conical taper couplers, photodiodes, motor-controlled tip/tilt stages, oscilloscopes, and a PCI card, constitute a closed-loop system with a feedback controller. The system is controlled by and communicates with a computer console using LabVIEW, a graphical language developed by National Instruments. Specifically, alignment is quantified by scanning the voltage readings at various orientations of the GRIN lens. The experimental setup specific to achieving maximum interferometric contrast intensity when interrogating silicon wafers with various surface depositions is discussed. Results corresponding to the interferometric contrast data obtained at several different standoff distances (Fizeau Cavity magnitudes) demonstrate the robustness of the novel design.
34

Buried fiber optic intrusion sensor

Maier, Eric William 30 September 2004 (has links)
A distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the φ-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.
35

Dark Ages Lunar Interferometer (DALI): Deployment-Rover - Mobility System

Andersson, Erik, Bengtsson, Per-Johan January 2013 (has links)
This thesis is issued in collaboration with the Jet Propulsion Laboratory (JPL) in Pasadena, California. JPL's primary function is the construction and operation of robotic planetary spacecraft. At the time being JPL has 22 spacecraft and 10 instruments conducting active missions. The "Dark Ages" represent the last frontier in cosmology, the era between the genesis of the cosmic microwave background (CMB) and the formation of the first stars. During the Dark Ages, when the Universe was unlit by any star, the only detectable signal is likely to be that from neutral hydrogen (HI). The HI absorption occurs in dark matter-dominated overdensities, locations that will later become the birthplaces of the first stars. Tracing this evolution will provide crucial insights into the properties of dark matter and potentially reveal aspects of cosmic inflation. This could be accomplished using a radio telescope located on the far side of the Moon, the only site in the solar system shielded from human-generated interference and, at night, from solar radio emissions. Our objective has been the development of the concept of an autonomous rover that would be capable of deploying a large number of low frequency radio antennas on the lunar surface. This is an enabling task for the eventual creation of a radio telescope. The project at Halmstad University was divided into three sub-projects, where our area of responsibility has been the development of a concept of the rover's mobility system. The result of the project is the concept of a "Rocker-Bogie" suspension system, created in a 3D-environment. A concept which underwent a series of digital analyses and simulations to ensure the compliance with required specifications. / Detta examensarbete är utfört i samarbete med Jet Propulsion Laboratory (JPL) i Pasadena, Kalifornien. JPL's primära funktion är konstruktion och drift av robotiserade rymdfarkoster. För tillfället har JPL 22 rymdfarkoster och 10 instrument i aktiva uppdrag. Den "mörka tiden" representerar den sista utposten i kosmologi, eran mellan uppkomsten av den kosmiska bakgrundsstrålningen (CMB) och bildandet av de första stjärnorna. Under den "mörka tiden", när universum inte var upplyst av någon stjärna, var den enda detekterbara signalen sannolikt från neutralt väte (HI). HI-absorptionen sker i mörk materia-dominerade överdensiteter, platser som senare blir födelseplatserna för de första stjärnorna. Att spåra denna utveckling kommer att ge viktiga insikter i egenskaperna hos mörk materia och eventuellt ge information om universums expansion. Detta kan åstadkommas med hjälp av ett radioteleskop på baksidan av månen. Den enda platsen i vårt solsystem avskärmad från störningar från jorden, och på natten även från solens strålning. Vår uppgift har varit att utveckla ett koncept på en autonom rover som ska placera ut ett stort antal lågfrekvensantenner på månytan. Detta är ett nödvändigt steg för det eventuella anläggandet av ett radioteleskop. Projektet vid Högskolan i Halmstad delades upp i tre delprojekt, där vårt ansvarsområde har varit att utveckla ett koncept för roverns drivsystem. Resultatet av projektet ett koncept på ett "Rocker-Bogie"-hjulupphängningssystem, skapad i en 3D-miljö. Ett koncept som har genomgått en serie av digitala analyser och simuleringar för att säkerställa överensstämmelse med krav och önskemål.
36

The Effects and Applications of Erbium Doped Fiber Fabry-Perot Interferometers

Taylor, Justin K. 2009 May 1900 (has links)
Fiber Fabry-Perot Interferometers (FFPI) are optical sensors which can be used to measure changes in stress or temperature, but efforts continue to improve them. Calculations show that the response can be dramatically altered with a gain inducing medium in the cavity. In order to induce gain, a highly doped Erbium (Er) fiber is incorporated in the FFPI. A pump wavelength of 1480 nm is used with a wavelength near 1550 nm. The pump must be at a significantly higher power level than the signal for gain. In order to correctly interpret responses, it is necessary to characterize the response of the measurement equipment. This includes everything from the laser and photodetector to system losses and the titanium oxide coated fibers. Fabrication of FFPIs involves fusing titanium oxide coated fibers to standard single mode fibers. Directly fusing an Er - doped fiber to a titanium oxide coated fibers was not possible because of incompatible splice conditions required in each case. Instead, an intermediate standard single mode fiber was spliced between them. This lengthened the cavity. Experimental results from the Er - doped Fiber Fabry-Perot Interferometer verified the hypothesis that improvements are obtainable. Overall, the measurements showed a 1.3 dB improvement in the maximum-to-minimum Insertion Loss Ratio.
37

The Design and Fabrication of Asymmetric Mach-Zehnder Interferometer and Ring Cavity Filter

Li, Kuan-Jui 10 July 2006 (has links)
The goal of the thesis is to fabricate the integrated asymmetric Mach-Zehnder Interferometer and Optical waveguide Ring Resonator with simple fabrication process. A 1.49£gm symmetric quantum well InGaAlAs epitaxial wafer is used to fabricate the devices. In the asymmetric Mach-Zehnder Interferometer design, we design asymmetric straight waveguides with difference of optical path, and asymmetric bend waveguides with difference of curvature radius. By this design, we can observe the interference variation of output light by difference of optical path. Using these properties, it will get the index change caused by electric field and the loss of bend waveguide. In optical waveguide ring resonator design, we improve the problem of the length of original K=0.15 Multi-Mode Interference (MMI) by stepped-width waveguide. And we obtain different transmission spectrum by adjusting the splitting ratio of MMI couplers (K=0.85, 0.5, and 0.15) and cascading doudle rings. We apply K0=0.5, K1=0.15 and K2=0.5 MMIs to design and fabricate optical filters with square transmission spectrum. In fabrication process, we get smooth sidewall and highly perpendicularity waveguide by multi-step wet etch method. In order to reduce waveguide loss, we make deep etching for the outside of curve waveguide and MMI. Finally, we use polyimide to smooth out the sides of the ridge waveguides and evaporate metal pad over the polyimide.
38

A system for automatic positioning and alignment of fiber-tip interferometers

Jalan, Mahesh 15 November 2004 (has links)
The research described in this thesis involves the design, development, and implementation of an automated positioning system for fiber-optic interferometric sensors. The Fiber-Tip Interferometer (FTI) is an essential component in the proven Thermo-Acousto-Photonic NDE technique for characterizing a wide range of engineering materials including polymers, semiconductors and composites. The need to adapt the fiber-optic interferometric system to an industrial environment and to achieve precision control for optimizing interferometric contrast motivated the development of an automated, self-aligning FTI system design. The design enables high-resolution positioning and alignment by eliminating manual subjectivity and allows significantly improved repeatability and accuracy to be attained. Opto-electronic and electromechanical devices including a GRIN lens, 2x2 fused bi-conical taper couplers, photodiodes, motor-controlled tip/tilt stages, oscilloscopes, and a PCI card, constitute a closed-loop system with a feedback controller. The system is controlled by and communicates with a computer console using LabVIEW, a graphical language developed by National Instruments. Specifically, alignment is quantified by scanning the voltage readings at various orientations of the GRIN lens. The experimental setup specific to achieving maximum interferometric contrast intensity when interrogating silicon wafers with various surface depositions is discussed. Results corresponding to the interferometric contrast data obtained at several different standoff distances (Fizeau Cavity magnitudes) demonstrate the robustness of the novel design.
39

Buried fiber optic intrusion sensor

Maier, Eric William 30 September 2004 (has links)
A distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the φ-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.
40

Creating and Imaging Surface Acoustic Waves on GaAs

Mathew, Reuble 08 December 2009 (has links)
The versatility of surface acoustic wave (SAW) devices stems from the accessibility of the propagation path to modification and detection. This has led to the integration of SAWs in a variety of novel fields, including quantum information processing. The development of technologically competitive devices requires the use of gigahertz frequency SAWs. This thesis develops fabrication processes for high frequency interdigital transducers on gallium arsenide. Optically lithography was used to create linear and stepped transducers, with a minimum feature size of 2 um, that were driven at their fifth harmonic. The highest frequency achieved was 1435 MHz, but the power absorbed was less than 3% and insertion losses were greater than -80 dB. Further improvements in the design and fabrication are required if optically fabricated transducers are to be an alternative to transducers with narrower finger widths. Electron-beam lithography techniques were developed and used to create transducers with finger widths of 500 and 400 nm, with fundamental resonance frequencies of 1387 and 1744 MHz, respectively. The power absorbed was 3 to 6% with insertion losses greater than -45 dB. The performance characteristics can be improved by the removal of residual resist on the surface of the transducer. An indispensable tool for the characterization of one-port transducers is an all optical probe to measure the displacement field of a SAW. This work details the design and construction of a scanning Sagnac interferometer, that is capable of measuring the outward displacement of a surface. The spatial resolution of the interferometer was 2.4 +/- 0.2 um and the displacement sensitivity was determined to be 4 +/- 1 pm. The instrument was used to map the SAW displacement field from a 358 MHz transducer, with results showing the resonant cavity behaviour of the fingers due to Bragg reflections. It also allowed for the direct detection of the SAW amplitude as a function of the driving frequency of the transducer. The results showed good agreement with the related S21 scattering parameter. Lastly, the interferometer was used to image the attenuated propagation of SAWs through a phononic crystal. Results showed good agreement with theoretical simulations. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-12-08 12:28:35.962

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