Gain Guiding Effect In An End Pumped Laser Amplifier

"Gain guiding" effect widely exists in all kinds of laser oscillators and amplifiers, in which the gain guiding effect improving the beam quality were verified. In this thesis, we focus on the gain guiding effect in an end-pumped laser amplifier. Through my theoretical model and experiment, it is illustrated that with the help of gain guiding effect, the beam quality emitted from MOPA laser system can be improved without any compensation. Firstly, considering thermal effect, gain guiding effect and gain saturation effect comprehensively, a novel model for laser amplifier in MOPA system is developed and numerically calculated. This model includes the beam propagation in an inhomogeneous medium, deducing the Maxwell's equations and proposing a novel slide algorithm base on Fast Fourier Transform. In addition, the gain in four level laser system and temperature were analyzed. According to the analysis, it was shown that the gain saturation and input power distribution could affect the gain profile, and the thermal spherical aberration must be considered in our following experiments. Finally, we took the M2 to evaluate the beam quality of output beam. Numerical simulations are performed to show the output beam quality and output power in a Nd:YVO4 laser amplifier with different input beam quality, different signal and pump beam radius, different input and pump power. Some useful conclusions are drawn for the design consideration of an effective amplifier. Several parameters, such as the beam filling factor, the ratio between input and output power, the absorption coefficient of active medium, have to be optimized. As well as, the thermal effect and gain guiding effect are the underlying reasons.Moreover, an experiment is performed for an end-pumped Nd:YVO4 laser amplifier. The experiment results approve the theoretical analyses and predictions.