Three-layer composite glass slab lasers were fabricated using optical contact and thermal fusion methods, and their characteristics were examined in an attempt to develop a high-peak-power glass laser able to deliver a high-quality beam at a high repetition rate operation. The optical characteristics, laser characteristics, and limitation of the output of these composite slabs and the monolithic slab are compared. It is found that thermal birefringence effects were reduced in the case of the composite slabs in comparison to the monolithic slab at the same output during repetitive operation, thereby maintaining a high level of beam quality. A doping amount of Nd/sub 2/O/sub 3/ of 6 wt.% was optimum for increasing the single pass gain of the composite slabs. An optimum thickness of doping layer exists for keeping gain high while maintaining thermal birefringence effects at a low level. >