Study On The Effects Of Amplified Spontaneous Emission On The Q-Switched Solid-State Lasers

Based on the theory about radiation and absorbability of matters, using the rateequations of the four levels laser system, this paper discusses the effects of amplifiedspontaneous emission(ASE) on the Q-switched solid-state lasers with end uniform andnonuniform pumping.In the case of end uniform pumping, this paper mainly discusses the effects of ASEon the population inversion, the fluorescence lifetime, the pumping efficiency and so on.There are three most important factors to influence the ASE. They are the averagedistance of photons propagating in the laser matters, the repetition rate of Q-switch andthe pump power. The effects of them are different. The strongest effect will be causedby the average distance, then by the repetition rate, at last by the pump power. Theaverage distance will be sure when the laser system is given. In comparison with thesituation of ignoring ASE, when the repetition rate is 1kHz and the pump power is200w/mm2, the population inversion decreases 32.4%, the fluorescence lifetime curtails82μs, the pumping efficiency decreases 10%. The conclusion is that lower repetitionrate or higher pump power could affact stronger ASE.In the case of end nonuniform pumping, this paper mainly discusses the effects ofASE on the peak power of output pulse, the pulse width, the optical to opticalconversion efficiency and so on. Here use Gaussian beam as the input beam model. Incomparison with the situation of ignoring ASE, when the repetition rate is 1kHz and thepump power is 200w/mm2, the peak power decreases 30.8%, the pulse width stretches5%, the optical to optical conversion efficiency decreases 26.3%. The effects of ASE onthe power characteristic of output is more strong than the time characteristic. Generally,ignoring the effect of ASE on the pulse width, the shape of pulse and the building timeof pulse is reasonable. Moreover, ASE will cause the distributed energy fromnonuniform to uniform.