The Influence Of Inhomogeneity Of Amplifier Medium On Laser Transmission

Because the cost for a high power laser system is very huge, it is necessary to make a design and numerical calculate before the system is built. So the work is widely developed all around the world. The most important part of a high power laser system is multi-pass amplifiers, and it plays a crucial role at the beam quality. Based on the Collins diffraction formula, we build a numeric model for the beam transformation through Inhomogeneous medium; we call it slice diffraction model. Using this model, we calculated the Fig. of some laser pulse and the beam. Such as Gaussian and super-Gaussian pulse and beams transmit in the homogeneous medium and inhomogeneous medium with square refractive index and gain distribution.Using this model, we calculate the pulse shape through laser amplifying medium, we find that if the intensity of the pulse is much lower than the saturation intensity of the medium, the shape of the pulse is little effected by the medium when transmit trough homogeneous or inhomogeneous medium. And if the intensity is above the saturation intensity, the pulse is distorted.Using this model,we calculate the beam shape through laser amplifying medium, we find that the dependence between the inhomogeneous medium and the output beam spatial distribution. Including the refractive index distribution, the gain coefficient distribution and the gain saturation; they all distort the laser spot greatly. Take square refractive index distribution medium and gain coefficient distribution medium for example; we calculate the output beam spatial intensity distribution, and get some rules between them which we interest in.