Characterization of Photonic Materials Using Thermal Lens Technique

The subject of Photonics is concerned with the generation,control and utilization of photons for performing a variety of tasks.It came to existence as a consequence of the harmonious fusion of optical methods with electronic technology.Wide spread use of laser based methods in electronics is slowly replacing elecrtons with photons in the field of Communication,Control and Computing .Therefore,there is a need to promote the R & D activities in the area of Photonics and to generate well trained manpower in laser related fields.Development and characterization of photonic materials is an important subject of research in the field of Photonics.Optical and thermal characterization of photonic materials using thermal lens technique is a PhD thesis in the field of Photonics in which the author describes how thermal lens effect can be used to characterize themal and optical properties of photonic materials.Plausibility of thermal lens based logic gates is also presented in this thesis.

Mathematical Modelling of the Dynamics of Granular Materials in a Rotating Cylinder

The current study is aimed at the development of a theoretical simulation tool based on Discrete Element Method (DEM) to 'interpret granular dynamics of solid bed in the cross section of the horizontal rotating cylinder at the microscopic level and subsequently apply this model to establish the transition behaviour, mixing and segregation.The simulation of the granular motion developed in this work is based on solving Newton's equation of motion for each particle in the granular bed subjected to the collisional forces, external forces and boundary forces. At every instant of time, the forces are tracked and the positions velocities and accelarations of each partcle is The software code for this simulation is written in VISUAL FORTRAN 90 After checking the validity of the code with special tests, it is used to investigate the transition behaviour of granular solids motion in the cross section of a rotating cylinder for various rotational speeds and fill fraction.This work is hence directed towards a theoretical investigation based on Discrete Element Method (DEM) of the motion of granular solids in the radial direction of the horizontal cylinder to elucidate the relationship between the operating parameters of the rotating cylinder geometry and physical properties ofthe granular solid.The operating parameters of the rotating cylinder include the various rotational velocities of the cylinder and volumetric fill. The physical properties of the granular solids include particle sizes, densities, stiffness coefficients, and coefficient of friction Further the work highlights the fundamental basis for the important phenomena of the system namely; (i) the different modes of solids motion observed in a transverse crosssection of the rotating cylinder for various rotational speeds, (ii) the radial mixing of the granular solid in terms of active layer depth (iii) rate coefficient of mixing as well as the transition behaviour in terms of the bed turnover time and rotational speed and (iv) the segregation mechanisms resulting from differences in the size and density of particles.The transition behaviour involving its six different modes of motion of the granular solid bed is quantified in terms of Froude number and the results obtained are validated with experimental and theoretical results reported in the literature The transition from slumping to rolling mode is quantified using the bed turnover time and a linear relationship is established between the bed turn over time and the inverse of the rotational speed of the cylinder as predicted by Davidson et al. [2000]. The effect of the rotational speed, fill fraction and coefficient of friction on the dynamic angle of repose are presented and discussed. The variation of active layer depth with respect to fill fraction and rotational speed have been investigated. The results obtained through simulation are compared with the experimental results reported by Van Puyvelde et. at. [2000] and Ding et at. [2002].The theoretical model has been further extended, to study the rmxmg and segregation in the transverse direction for different particle sizes and their size ratios. The effect of fill fraction and rotational speed on the transverse mixing behaviour is presented in the form of a mixing index and mixing kinetics curve. The segregation pattern obtained by the simulation of the granular solid bed with respect to the rotational speed of the cylinder is presented both in graphical and numerical forms. The segregation behaviour of the granular solid bed with respect to particle size, density and volume fraction of particle size has been investigated. Several important macro parameters characterising segregation such as mixing index, percolation index and segregation index have been derived from the simulation tool based on first principles developed in this work.

Non-destructive evaluation of photovoltaic materials and solar cells using Photoluminescence

Photoluminescence (PL) spectroscopy is an optical technique that has emerged successful in the field of semiconductor material and device characterization. This technique is quite a powerful one which gives idea about the defect levels in a material, the band gap of the material, composition as well as material quality. Over the recent years it has received an elevation as a mainstream characterization technique. This thesis is an attempt to characterize each individual layer used in a thin film solar cell with special focus on the electrical properties. This will be highly beneficial from the lab as well as industrial point of view because electrical measurements generally are contact mode measurements which tend to damage the surface. As far as a thin film solar cell is concerned, the constituent layers are the transparent conducting oxide (TCO), absorber layer, buffer layer and top electrode contact. Each layer has a specific role to play and the performance of a solar cell is decided and limited by the quality of each individual layer. Various aspects of PL spectroscopy have been employed for studying compound semiconductor thin films [deposited using chemical spray pyrolysis (CSP)] proposed for solar cell application. This thesis has been structured in to seven chapters