| PhD Viva

Name of the Speaker: Mr. Sooraj M S (EE17D055)
Guide: Dr. Balaji Srinivasan
Online meeting link: https://meet.google.com/top-uodg-ssh
Date/Time: 24th June 2025(Tuesday), 4:00 PM
Title: Investigation on Coherent Beam Combination Techniques for Enhanced Beam Combination Efficiency and Scalability.

Abstract :

High-power laser sources are essential for a wide range of applications, including material processing, medical treatments, defense systems, and space exploration. Coherent Beam Combination (CBC) of multiple fiber lasers enables power scaling beyond single-laser limits while maintaining excellent beam quality. This work investigates the design, simulation, and experimental realization of scalable CBC systems, focusing on non-intrusive off-center feedback methods for phase synchronization.

Initial efforts focused on filled-aperture CBC using diffractive optical elements (DOEs) to combine beams in two-dimensional arrays. Simulations and high-power experiments identified sensitivities to input non-uniformities and limitations in DOE-based CBC systems. Phase locking was successfully achieved using the stochastic parallel gradient descent (SPGD) algorithm with a non-intrusive higher diffraction order-based feedback. Expanding to tiled-aperture CBC, alternative off-center feedback strategies that exploit the inherent far-field symmetry of periodic arrays were developed for non-intrusive feedback phase control. The effects of various non-uniformities were investigated in a tiled 7-beam system, and the proposed off-center feedback methods were experimentally validated. Additionally, a modular tiled array configuration with nested-loop phase control was introduced to enhance scalability, extending off-center feedback to both sub-array and sequential full-system phase locking.