Self -pumped Gaussian beam -coupling and stimulated backscatter due to reflection gratings in a phot...

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" Self -pumped Gaussian beam -coupling and stimulated backscatter due to reflection gratings in a photorefractive material "
Mohammad Abu Saleh P. P. Banerjee

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	54353
Doc. No	:	TL24307
Call number	:	‭3271402‬
Main Entry	:	Mohammad Abu Saleh
Title & Author	:	Self -pumped Gaussian beam -coupling and stimulated backscatter due to reflection gratings in a photorefractive material\ Mohammad Abu Saleh
College	:	University of Dayton
Date	:	2007
Degree	:	Ph.D.
student score	:	2007
Page No	:	176
Abstract	:	When overlapping monochromatic light beams interfere in a photorefractive material, the resulting intensity fringes create a spatially modulated charge distribution. The resulting refractive index grating may cause power transfer from one beam (the pump) to the other beam (the signal). In a special case of the reflection grating geometry, the Fresnel reflection of the pump beam from the rear surface of the crystal is used as the signal beam. It has been noted that for this self-pumped, contra-directional two-beam coupling (SPCD-TBC) geometry, the coupling efficiency seems to be strongly dependent on the focal position and spot size, which is attributed to diffraction and the resulting change in the spatial overlaps between the pump and signal. In this work a full diffraction based simulation of SPCD-TBC for a Gaussian beam is developed with a novel algorithm. In a related context involving reflection gratings, a particular phenomenon named six-wave mixing has received some interest in the photorefractive research. The generation of multiple waves during near-oblique incidence of a 532 nm weakly focused laser light on photorefractive iron doped lithium niobate in a typical reflection geometry configuration is studied. It is shown that these waves are produced through two-wave coupling (self-diffraction) and four-wave mixing (parametric diffraction). One of these waves, the stimulated photorefractive backscatter produced from parametric diffraction, contains the self-phase conjugate. The dynamics of six-wave mixing, and their dependence on crystal parameters, angle of incidence, and pump power are analyzed. A novel order analysis of the interaction equations provides further insight into experimental observations in the steady state. The quality of the backscatter is evaluated through image restoration, interference experiments, and visibility measurement. Reduction of two-wave coupling may significantly improve the quality of the self-phase conjugate.
Subject	:	Pure sciences; Backscatter; Gaussian beam-coupling; Photorefractive; Reflection gratings; Self-pumped; Optics; 0752:Optics
Added Entry	:	P. P. Banerjee
Added Entry	:	University of Dayton