Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 24 for “"Gaussian beams"”.
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Propagation of Gaussian Beams Through a Modified von Karman Phase Screen
Gaussian beam propagation through discrete phase screens and an extended random media has been studied extensively over the last four decades. In this thesis, we numerically examine the effects of a discrete phase screen during Gaussian beam propagation on the scintillation index for a single beam …
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Quasi-Optical Approaches to the Diffraction and Scattering of Gaussian Beams
Made available in DSpace on 2014-12-10T19:06:30Z (GMT). No. of bitstreams: 1 7105108.pdf: 3612962 bytes, checksum: 1571753387d0860f663108222f61fda6 (MD5) Previous issue date: 1970
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The broken non-abelian X-ray transform and inverse problems for connections at high fixed frequency
… both problems by using special quasimodes called Gaussian beams. Gaussian beams are approximate solutions of (Δ_A - λ^2)u = 0 that are supported on a small neighbourhood of a geodesic. We develop the theory of Gaussian beams on a vector bundle in Chapter 4. Our approach is novel because we view …
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Generation of high power single-cycle and multiple-cycle terahertz pulses
… THz outputs are very close approximations to Gaussian beams, and can be well collimated and focused into samples for time-resolved spectroscopic experiments. This may allow for explorations in coherent nonlinear spectroscopy in the THz region such as the photon echo and multidimensional …
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Modeling and Numerical Approximations of Optical Activity in the Chemical Oxygen-Iodine Laser
… utilize the theory of paraxial wave optics and Gaussian beams. Doing so allows us to incorporate physical effects such as diffusion/diffraction and refraction into the model. After describing the optical model, we present numerical methods for obtaining approximate solutions to the model in the …
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Laser Scanning Imaging for Increased Depth-Of-Focus
… heterodyne scanning system using a difference-of-Gaussians (DoG) pupil. The object is illuminated by the combined beam which consists of two Gaussian beams with different waists, frequencies, and amplitudes. This system does not block most light like the annular pupil system and can obtain high …
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Effects Of Atmospheric Turbulence On The Propagation Of Flattened Gaussian Optical Beams
… model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects upon the scintillation of the beam and upon beam wander are determined. A comparison of these results is made with the like effects on a standard TEM00 Gaussian …
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Generation and imaging of structural laser beams for optical trapping of airborne particles and light-matter interaction applications.
Recently emerged non-diffracting optical Bessel-Gaussian beams have extended the `optical toolbox' in laser interaction with matter studies, providing many techniques that are not possible using conventional Gaussian beams. The research work performed under this thesis focuses on the design, …
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Generation and imaging of structural laser beams for optical trapping of airborne particles and light-matter interaction applications.
Recently emerged non-diffracting optical Bessel-Gaussian beams have extended the `optical toolbox' in laser interaction with matter studies, providing many techniques that are not possible using conventional Gaussian beams. The research work performed under this thesis focuses on the design, …
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Experimental Investigation of Particle Lag behind a Shock Wave using a Novel Laser Doppler Accelerometer
… of a new Laser Doppler probe using non Gaussian beams to obtain a prolonged measurement volume. This volume covers a major part of the particle lag after a shock wave. An experimental investigation on particle acceleration and drag, using different types and sizes of seeding material, …
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Three-Dimensional Microscopy by Laser Scanning and Multi-Wavelength Digital Holography
… the depth of focus by using Bessel rather than Gaussian beams is discussed. Then, a phase-imaging technique to quantitatively study the three-dimensional structure of reflective and transmissive microscopic samples is presented. The method, based on the simultaneous dual-wavelength digital …
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Adaptive Mode Matching in Advanced LIGO and Beyond
… for operating at higher power and mode matching Gaussian beams in the dual-recycled Michelson interferometer for the Advanced LIGO era and beyond. The first two chapters discuss the fundamentals of gravitational waves and the LIGO detector configurations. The third chapter introduces the reader …
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Low Loss Orientation-Patterned Gallium Arsenide (OPGaAs) Waveguides for Nonlinear Infrared Frequency Conversion
… normally associated with tight focusing of Gaussian beams. However, device performance in OPGaAs waveguides has been limited by large propagation losses resulting from the unique nature of the material. In this dissertation I report an OPGaAs/OPAlxGa1-xAs embedded ridge waveguide design …
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Experimental application and numerical study of reflectometry in the Alcator C-Mod tokamak
… The Huygens source technique is used to generate Gaussian beams and separate the reflected waves from the total field. Simulations based on realistic 2-D geometry of the Alcator C-Mod reflectometer provide a calibration curve by which we can relate the QC fluctuations in reflectometry signals to …
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Light-Matter Interactions and Devices Enabled By Novel Engineered Photonic Media
… it becomes possible to manipulate the optical beams having complex structures with novel properties instead of simple conventional Gaussian beams; or to build materials having complex micro or nanoscale structures that cannot be found in the natural world. The goal of this thesis is to …
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Fractality and topology of optical singularities
… generated compact vortex knots and links in real Gaussian beams. These results were achieved through the use of algebraic knot theory and random search optimisation algorithms. Finally, polarisation singularity densities are measured experimentally which confirm analytic predictions.
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On the initial value problem in general relativity and wave propagation in black-hole spacetimes
… thesis investigates the behaviour of so-called Gaussian beam solutions of the wave equation - highly oscillatory and localised solutions which travel, for some time, along null geodesics. The main result of this part of the thesis is a characterisation of the temporal behaviour of the energy of …
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Modeling of a compact terahertz source based on the two-stream instability.
… relies on low-energy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region …
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Scattering of acoustic energy from rough deep ocean seafloor: A numerical modeling approach
… Simulation Technique) combines solutions from Gaussian beams, viscoelastic finite-differences, and Kirchhoff extrapolation, to simulate large offset scattering problems. Several scattering hypotheses based on finite-difference simulations of short-range acoustic scattering from realistic …
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The Calderón problem for connections
… is based on our proof of existence of Gaussian Beams on $M_0$, which are a family of smooth approximate solutions to $d_A^*d_Au = 0$ depending on a parameter $\tau \in \mathbb{R}$, bounded in $L^2$ norm and concentrating in measure along geodesics when $\tau \to \infty$, whereas the …
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