Optimization of two-lens coupling structure for a tandem-set solid-state laser system

This is a serial report on birefringence compensation for a LD-side-pumped solid-state laser (LSPSSL) system. In this paper, a coupling system with two coupling lenses and a normal 90° rotator has been analyzed in detail to obtain a perfect compensation of birefringence in two tandem-set rods. The optimum configuration can be determined by selecting a suitable coupling geometry as well as the focal lengths of two coupling lenses. By using the optimum conditions, almost all the birefringence can be removed in a tandem-arranged rod system. We also found that there are many coupling structures which can realize a complete compensation of birefringence if the thermally induced characteristics of two rods are absolutely equivalent. For two rods with different thermally induced features, the optimum structure is unique with the best birefringence elimination. These conclusions are different from the general expressions of clearing up the depolarization loss in many published references