Beam shaping and amplifiers
Date
2024
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Abstract
Tailored or structured laser light has received much attention from the photonics community globally. Structured forms of laser light have the potential to enhance many aspects of laserenabled processes across a myriad of applications, such as industrial manufacturing processes, optical communication, quantum computing, medical sciences, and space sciences. While the laser itself is well over 60 years old, the range of obtainable "structured" laser outputs has been restricted for many decades since its inception. With recent advances in micro-mechanical electro-optics, liquid crystal display, and advanced lithographic processing technologies, it is possible for us to create highly complex forms of structured light with exotic spatial, phase, and polarization characteristics. As we make the inevitable transitions towards updating the existing laser technology with structured light systems, there are certain parameters that need to be met such as average laser power, which is crucial for performing micro and macro material processing, accounting for 15% of the global demand for lasers. Therefore, in addition to the selection of structured light, there is a clear need for obtaining high-power structured light which generally involves the need for optical power amplifiers.
This dissertation explores the generation, power scaling, and characterization of structured light for application areas that demand high-power laser outputs. To fully characterize the process of power scaling of structured laser light, an accurate 3D numerical model is required. Here we present a new 3D model for an end-pumped cylindrical rod Master Oscillator Power Amplifier (MOPA) system, using contemporary analytical expressions and novel approximations which demonstrate significant improvements over current comparative 3D modelling approaches. Then, we explore the amplification of structured light fields, in the form of higher-order Laguerre-Gaussian modes, using a novel polarization-based dual-pass MOPA. This system was specifically developed to maximize amplification efficiency while maintaining the purity and complex structures of high-order Laguerre-Gaussian modes and showed excellent agreement with the 3D simulated results. Finally, we investigate the thermallyinduced aberrations resulting from end-pumping bulk solid-state gain media. We show that amplification of higher-order Laguerre-Gaussian modes in this aberrated system, specifically those possessing orbital angular momentum, results in the separation of the phase singularities, otherwise known as "vortex splitting". We fully study this effect and describe the cause and rectification of this phenomenon
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2023