Effect of gain medium's volume of amplifier on DF amplification system with MOPA configuration

The interaction of amplified spontaneous emission (ASE) flux and coherent laser flux in cuboid DF amplifiers are studied, by using a finite difference method and an iterative arithmetic. The influence of gain medium's volume on amplification ratio and energy extraction efficiency is discussed in detail. The simulation results in the amplifier which gain zone is cuboid and the small gain coefficient is distributed as parabola indicated that the amplification ratio and energy extraction efficiency increase as the increase of gain medium length, but they decrease as the increase of gain medium's width; the amplification ratio and energy extraction efficiency are increased with the increase of gain medium length when the gain medium's volume is definite; although the amplification ratio and energy extraction efficiency will decrease with the increase of gain medium's height, but the energy extraction from the amplifier will increase when the gain medium's length is definite.