High-power lasers are essential for various commercial, industrial, and military applications. In recent years, there has been a notable trend towards up-scaling laser systems for long-distance propagation. Fiber lasers have revolutionized the laser industry due to their impressive efficiency, durability, and capacity to generate high-power beams in the kilowatt range. Nevertheless, the output power of a single fiber laser is constrained by factors like non-linear effects and excessive heating. Thus, beam combination is a viable solution to generate a high-power beam by combining several low-power lasers. Various methods for combining beams can be employed, including incoherent, coherent, and spectral beam combination techniques. In incoherent beam combinations, lasers are adjusted and combined individually, without consideration of their phase. On the other hand, coherent beam combination requires precise phase matching of the beams and involves sophisticated optical and electronic circuits. Spectral beam combination combines lasers of different wavelengths using diffractive optical elements. Coherent and spectral beam combination methods often lead to increased complexity and cost of the beam combination system. Therefore, incoherent beam combinations are frequently used, especially in directed energy applications, where high intensities at longer distances are essential. Through this technique, high-power laser beams can be generated without requiring precise phase control, making them more practical and cost-effective.

This thesis outlines the design and analysis of a multi-channel incoherent beam combination (IBC) system, investigating the behavior of laser beams propagating in atmospheric turbulence. It presents various initial architectures for the IBC system. and devises a fiber-actuator-based optical channel design to steer high-power laser beams effectively. To improve system efficiency, this thesis optimizes the initial beam waist and power of each laser beam across different atmospheric conditions. Furthermore, to enhance the combined intensity of the IBC system, it introduces collimated, inclined, and focused-inclined directing mechanisms. Additionally, this thesis delves into the modeling and analysis of alignment errors in fiber lasers and collimating lens arrays, addressing challenges and optimizing system performance. The proposed system optimizes beam-directing channel length and minimizes heat generation, ensuring improved efficiency and suitability for scenarios with moving target locations.

This thesis also introduces the incorporation of a higher-order Gaussian beam a high-power incoherent beam combination system. Various higher-order Gaussian beams like Hermite Gaussian (HG) and Laguerre Gaussian (LG) beams can be used for beam combination to generate high intensity at various distances with limited. hardware requirements. It provides optimal combination efficiency with minimal hardware requirements. Theoretical modeling and detailed analysis of Hermite and Laguerre Gaussian beams in atmospheric turbulence are conducted, investigating the influence of atmospheric parameters like jitter, turbulence, wind speed, and thermal blooming on beam spreading. This thesis further investigates the impact of steady-state thermal blooming on Laguerre Gaussian beams as they propagate through the atmosphere, considering various modes of LG beams. Additionally, it analyzes how atmospheric turbulence, beam wander, residual mechanical jitter, beam quality, and thermal blooming. and bore-sight error collectively influence the intensity and spot size of the beams. Our findings presented in this thesis hold significance for the design of various beam combination systems and have implications for applications in industrial, military, communication, and information transmission within atmospheric propagation scenarios.

Keywords: Incoherent beam combination, Gaussian Beam, Collimated beam, inclined beam, Focused-inclined beam, Hermite Gaussian, Laguerre Gaussian, Beam spreading, Atmospheric turbulence, Beam wander, Atmospheric Strehl ratio, Jitter, Thermal blooming.