Stress- and growth-induced anisotropic birefringences in garnet films

From optical wave-guide experiment in rare-earth and bismuth-substituted iron garnet films, it is shown that the optical birefringence Δn presents important contributions Δnσ and Δ nG arising from stress-induced (photoelastic) and growth-induced birefringences which depend on the chemical composition, growth temperature TG and orientation of the film. The dependence of Δn σ on TG is directly associated with the variation of the segregation coefficients of the different ions substituted in the garnet which changes their content and therefore the lattice mismatch between the films and the substrates. On the other hand ΔnG seems to be independent on TG. In (110)-oriented Bi-YIG films anisotropic behaviours have been observed for Δnσ. The different contributions to Δn are determined and discussed from theoretical models.