Development of high-beam quality high power Ytterbium-doped fiber lasers

buir.advisorOrtaç, Bülend
dc.contributor.authorMidilli, Yakup
dc.date.accessioned2022-02-18T07:55:50Z
dc.date.available2022-02-18T07:55:50Z
dc.date.copyright2022-01
dc.date.issued2022-01
dc.date.submitted2022-02-09
dc.descriptionCataloged from PDF version of article.en_US
dc.descriptionThesis (Ph.D.): Bilkent University, Department of Materials Science and Nanotechnology, İhsan Doğramacı Bilkent University, 2022.en_US
dc.descriptionIncludes bibliographical references (leaves 125-147).en_US
dc.description.abstractHigh power fiber 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 highpower 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 fiber laser oscillators and amplifier systems based on both commercial and homemade selffabricated Ytterbium (Yb)-doped large mode area active (LMA) fibers. Amplifier systems have been built based on the Master Oscillator Power Amplifier (MOPA) configuration, and the average power reaches up to 1 kW power level. Besides, the fiber 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 fiber 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 fiber 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 fiber laser system whose fiber 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 fiber laser system via freespace 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 benefited 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 fiber. Finally, I have studied the side pump combiner on both homemade self-fabricated Photonic Crystal Fiber (PCF) and ultra-low NA active fiber in a (1 + 1) x 1 pumping configuration with 95% and 89% pump coupling e ciencies, respectively.en_US
dc.description.provenanceSubmitted by Betül Özen (ozen@bilkent.edu.tr) on 2022-02-18T07:55:50Z No. of bitstreams: 1 B160772.pdf: 17077633 bytes, checksum: bc9a64cec780784d2cfa7b9bba117b1f (MD5)en
dc.description.provenanceMade available in DSpace on 2022-02-18T07:55:50Z (GMT). No. of bitstreams: 1 B160772.pdf: 17077633 bytes, checksum: bc9a64cec780784d2cfa7b9bba117b1f (MD5) Previous issue date: 2022-01en
dc.description.statementofresponsibilityby Yakup Midillien_US
dc.embargo.release2022-08-09
dc.format.extentxix, 157 leaves : illustrations, charts ; 30 cm.en_US
dc.identifier.itemidB160772
dc.identifier.urihttp://hdl.handle.net/11693/77488
dc.language.isoEnglishen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectOptical fibersen_US
dc.subjectFiber lasersen_US
dc.subjectAmplifiersen_US
dc.subjectOscillatorsen_US
dc.subjectUltra-low numerical apertureen_US
dc.subjectTransverse mode instabilityen_US
dc.subjectSide pump combining techniqueen_US
dc.titleDevelopment of high-beam quality high power Ytterbium-doped fiber lasersen_US
dc.title.alternativeYüksek ışın kaliteli yüksek güçlü İterbiyum katkılı fiber lazerlerin geliştirilmesien_US
dc.typeThesisen_US
thesis.degree.disciplineMaterials Science and Nanotechnology
thesis.degree.grantorBilkent University
thesis.degree.levelDoctoral
thesis.degree.namePh.D. (Doctor of Philosophy)

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