Heat Distribution in High Power Yb Doped Fiber Laser by Considering Photo-darkening Effect

Several effects, such as optical nonlinear and thermal effects can change and reduce the output power of high-power fiber laser. In this paper, the photodarkening effect as an additional loss factor in the high-power fiber lasers was added in the rate equations, and the pump power variation relation was rewritten under the new conditions. By considering the complete form of the heat transfer function, including conductive and radiative heat transfer, the generated heat in the double clad fiber laser with the bidirectional pump scheme for different cavity geometry was determined. In this work, the photodarkening loss is added to the rate equations as power decreasing factor which is suggested as a stretched exponential function. The effects of core radius, the first clad size, input power, and output reflectors coefficient, and laser cavity length in the heat generation was calculated, also the contribution of each heat production factor including Quantum defect, photodarkening, and propagation loss was determined in heat generation. It was shown that the share of photodarkening heat caused from pump power and propagation loss affected from pump power in heat generation in the Double clad fiber laser is negligible. But the photodarkening heat affected from signal power is the main factor in heat generation at the central points of fiber laser.