Yüksek ışın kaliteli yüksek güçlü İterbiyum katkılı fiber lazerlerin geliştirilmesi

High power ber laser (HPFL) systems have drawn considerable interest for the last decades in health, industry, and especially defense applications due to their compactness, robustness, and high directionality. In this respect, the defense industry is currently in high demand for HPFL systems in the naval, air force, and ground operations. As an example, they have been implemented to the battleship, armored vehicles, and most currently to the drones. Outstanding features of these systems allow us to utilize them in various applications; however, this great demand brings some shortcomings. For example, power scaling of high-power fiber lasers has been impeded by non-linear interactions such as Stimulated Raman Scattering (SRS) and Transverse Mode instability (TMI). Regarding these non-linear interactions, I have built high-power fi ber laser oscillators and amplifier systems based on both commercial and homemade self-fabricated Ytterbium (Yb)-doped large mode area active (LMA) fibers. Amplifi er systems have been built based on the Master Oscillator Power Ampli er (MOPA) configuration and the average power reaches up to 1 kW power level. Besides, the ber oscillator system has been built with a power level up to 2 kW power level and M2 value of 1.2, the beam quality parameter of the ber laser system. To understand and investigate the TMI effect on the fiber laser system and the fiber itself, I have intended to observe the intensity change of the probe lasers and the color center formation inside a homemade active fi ber in the presence of TMI. Then, I have rebuilt the system to eliminate the TMI effect and repeated the same experiments to ensure that the TMI effect was responsible for the difference. For that purpose, I have installed a ber laser system whose ber has been coiled in a large bending diameter to ensure the existence of the TMI effect. I have utilized two different probe lasers with 645 nm and 520 nm central wavelengths, respectively. I have coupled these probe lasers to the ber laser system via free-space arrangements. Afterward, I have repeated the same experiment only with the 520 nm probe laser ensuring the absence of the TMI effect by rebuilding the laser structure. Finally, I have taken data about the intensity change of the probe lasers for both cases and compared them. Having benefitted from the experience of these studies, to suppress the SRS and TMI, I have fabricated a new type of generation Yb-doped LMA active fiber having an ultra-low numerical aperture (NA) around 0.034. Then I have built a monolithic MOPA system based on this fiber with a 1 m bending diameter. In addition, I have obtained 1 kW maximum power with a diffraction-limited beam quality with an M2 value of 1.16. Additionally, I have studied the side-pump combining technique, which is one of the mitigation methods for TMI. It allows us to pump the active fiber from both sides, thus decreasing the thermal load on ber. Finally, I have studied the side pump combiner on both homemade self-fabricated Photonic Crystal Fiber (PCF) and ultra-low NA active ber in a (1 + 1) x 1 pumping configuration with 95% and 89% pump coupling efficiencies, respectively.