Simulation and compensation of thermal lensing in optical systems.

High-power optical systems are used in a number of industrial applications. One difficulty in designing such systems is that the beam itself is a significant source of heat, which changes the optical properties of the system. To reduce this effect, we propose a new thermal lensing compensation technique based on a detailed analysis of the optical properties of the high-power optical system. To this end, we have developed a new ray tracing simulation technique that accurately models optical propagation through inhomogeneous, anisotropic, and deformed media. This model enables the performance of systems in physically realistic situations to be evaluated efficiently. Experimental comparisons were conducted to validate the simulation. We found excellent agreement between the simulation and the measured data. We have validated the simulation technique for a single lens setup and a complex optical scanner system.

Far field calculation of distorted Gaussian beams.

Far field calculations of beams, such as laser beams, are often applied in optical engineering. Current beam propagation methods fail in certain range parameters due to high storage requirements of the algorithms. This paper presents a new beam propagation method for far field calculations of distorted Gaussian beams in a homogeneous medium including optical elements, such as lenses. The method works even in the case of a large distance from the observation plane to the beam waist and can be applied to larger divergence angles. This new simulation technique factors out the phase of the Gaussian TEM00 beam and solves the resulting partial differential equation by suitable finite difference or finite element discretization methods.

3D simulation and beam quality improvement of a pulsed Cr,Tm,Ho:YAG laser.

Simulation and experimental improvement of a pulsed Cr,Tm,Ho:YAG (CTH:YAG) laser is presented. In order to simulate the CTH-Laser a generalized version of the Dynamic Mode Analysis (gDMA) is introduced, which includes an abstract formalism to describe arbitrary rate equations. This novel version of DMA enables the coupling between individual modes of the resonator and the complex excitation dynamics of the CTH state system. With the proposed method gDMA a full 3D simulation was conducted and the beam quality of the generated pulses could be calculated for various crystal diameters. Based upon the simulation results the crystal diameter was decreased in experiment. This reduction led to an improvement of M2 from 36 to 27, which is in good agreement with the experimental results. Additionally, the pulse energy depending on the pump power exhibits a close agreement with the experimental measurements. Moreover, the strength of each interionic mechanism in Cr,Tm,Ho:YAG is analyzed and the back transfer from Holmium to Thulium is identified to be the most dominant loss source for stimulated emission at 2090 nm. All in all, the presented extension of DMA represents an accurate and efficient method to simulate the amplification of higher order modes in gain media with strong interionic mechanisms.

An image processing approach to approximating interface textures of microcrystalline silicon layers grown on existing aluminum-doped zinc oxide textures.

We present an algorithm for generating a surface approximation of microcrystalline silicon (µc-Si) layers after plasma enhanced chemical vapor deposition (PECVD) onto surface textured substrates, where data of the textured substrate surface are available as input. We utilize mathematical image processing tools and combine them with an ellipsoid generator approach. The presented algorithm has been tuned for use in thin-film silicon solar cell applications, where textured surfaces are used to improve light trapping. We demonstrate the feasibility of this method by means of optical simulations of generated surface textures, comparing them to simulations of measured atomic force microscopy (AFM) scan data of both Aluminum-doped zinc oxide (AZO, a transparent and conductive material) and µc-Si layers.

Three-dimensional finite element computation of laser cavity eigenmodes [corrected].

A new method for computing eigenmodes of a laser resonator by the use of finite element analysis is presented. For this purpose, the scalar wave equation (delta + k2)E(x, y, z) = 0 is transformed into a solvable three-dimensional eigenvalue problem by the separation of the propagation factor exp(-ikz) from the phasor amplitude E(x, y, z) of the time-harmonic electrical field. For standing wave resonators, the beam inside the cavity is represented by a two-wave ansatz. For cavities with parabolic optical elements, the new approach has successfully been verified by the use of the Gaussian mode algorithm. For a diode-pumped solid-state laser with a thermally lensing crystal inside the cavity, the expected deviation between Gaussian approximation and numerical solution could be demonstrated clearly.