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Simulation of thermal, mechanical and optical behavior of yag ceramics with increasing Nd3+ concentration under lasing conditions.

Kenar, Necmettin
Two-dimensional thermal, mechanical and optical simulations are carried out to investigate the effect of Nd3+ concentration on thermal, mechanical and optical behavior of Nd:YAG ceramic laser materials under continuous wave laser operation. In the analyses, rods are pumped longitudinally with laser diodes, in three, six, nine and twelve fold structures. Rods having diameters of 3 and 6 mm are pumped with 808 nm and 885 nm sources separately having Nd+3 concentrations of 0.6, 1, 2, 3, 4 and 6 at. %. Total absorbed pump power are kept constant for all rods. Absorbed pump power distribution are obtained for each rod using ray tracing method and Beer’s Law. In the analysis, temperature dependent material properties are incorporated. Nonlinear numerical solutions of thermal and stress equations have been performed. Temperature and stress results are obtained to investigate the effect of Nd concentration on the optical properties of ceramic YAG laser material. Analysis results reveal that, increase in Nd3+ concentration of YAG ceramic laser material, decreases the temperature and stress developed during optical pumping. Rods pumped with 808 nm source have large temperature and stress values compared to 885 nm pumped ones. Optical path difference (OPD) of each ray passed trough the material is calculated using thermal and elastic strain results together with photo-elastic constants of Nd:YAG material. Focal length and depolarization of each rod is calculated numerically from OPD results. Focal length of each rod is found to increase, in contrary depolarization is found to decrease with increase in the dopant concentration.