Control of heating in fiber lasers by doping management

Although high-power double-clad fiber lasers (HPDCFL's), doped by rare-earth ions, can satisfy current extreme power requirements they suffer from a high thermal loading, which could lead to irreversible damages inside the core as well as the polymer coatings of the fiber lasers since the materials used for low-index polymer coatings are very sensitive to high thermal loads. This study is a theoretical analysis of doping management in aspect of thermal load, according to the thermal conductive equations taking into account natural and geometrical properties of the fiber medium as well as pump beam intensity profile. Thermal differential equations, derived for the core and the clad for top hat beam intensity profile, have been solved by separation of variable method. Derived radial and longitudinal differential equations are Second-Order Homogenous Linear Differential Equations and Bessel Differential Equations, respectively, solved in relation to the specific conditions on the boundaries. The thermal distribution functions of both the core and the clad have been considered from two different points: constant and variable absorption coefficients. Although the doping management approach in this thesis is presented just for Ytterbium doped continuous-wave, it is thought that be applicable to the other rare-earth ions.