Development of high power yb doped fiber laser systems with 915nm pumped

High-power fiber lasers (HPFL) have taken their place as widely used laser sources in industry (metalworking, cutting, welding, engraving, etc.), medical (additive manufacturing) and defense fields, with their excellent beam quality, high output power and high conversion efficiency. Their superiority over other types of lasers in terms of maintenance and repair costs has been one of the research subjects that have been studied intensively by researchers in recent years. The power scalability of HPFLs is limited by nonlinear effects such as stimulated Raman scattering (SRS) and transverse mode instability (TMI). Because the SRS effect is proportional to the fiber length and fiber core diameter, studies show that it can be overcome with fibers with shorter fiber length and larger core diameter. These methods also cause higher temperature zones and other modes to form, resulting in TMI limit effects. However, although the exact cause of the TMI effect is not known, there are studies showing that it can also limit the SRS effect. In recent years, it is seen that pumping methods at different wavelengths (976nm, 980nm, 1018nm, 1030nm) are used, active fibers with high doping rate are used, and special components that are difficult to obtain commercially are used. At the same time, photo-darkening effect, spontaneous emission is seen in these methods and the formation of high-cost structures is encountered. This thesis presents an experimental demonstration of a high-power output fiber laser on HPFLs with a wavelength of 915nm using commercially available and lower cost components. The system is built with commercially available components with an all-fiber structure. Since the positive results of the effect of bending methods of fibers on TMI have been reported, the bend diameter of the active fiber was determined as 12 cm. The setup is designed on a hybrid master oscillator power amplifier (MOPA) concept and it has been shown that the targeted output power can be achieved by aiming the signal power produced in the master oscillator to have high beam quality. Optical efficiency was measured as >75% with 3600W pump power (slope efficiency) and beam quality (M2) was <1.5 in the amplifier region, and no non-linear effects were observed. As far as we know, this is the first study showing a ytterbium doped fiber laser system with 915nm pump, 1080nm output wavelength, 3kW output power and diffraction limited beam quality, with the structure we established and the method we presented.