Gain and absorption saturation coupling in end pumped Tm:YVO4 and Tm,Ho:YLF CW amplifiers

In this paper we theoretically investigate the coupling between gain and absorption saturation in quasi three level CW longitudinally pumped amplifier exhibiting up-conversion and ground state depletion. Numerical computations are performed for both Tm:YVO4 and Tm,Ho:YLF crystals. We show that the absorption of the pump strongly increases with increasing intensity of the amplified wave. We also investigate the effect of the up-conversion process and we find that, at high laser intensity level, quite comparable results are found with and without up-conversion. Last, we investigate the round trip amplification of a low intensity laser beam when both the laser and the pump beams are Gaussian and we analyse the amplified beam shape as a function of the ratio of the pump and the laser beam waist size. (C) 2000 Elsevier Science B.V. All rights reserved.