Diffusion bonding of single crystal Nd:YAG with another Nd:YAG or undoped YAG involves precision polishing, assembly by optical contacting and heat treatment. Preliminary data on bonding kinetics indicate an approximate (time)1/5 dependence which describes bulk sintering. Optical homogeneity across the interface did not exhibit a discontinuity for composites of Nd:YAG/Nd:YAG while a step at the Nd:YAG/undoped YAG interface is assumed to be due to a difference in refractive index. Parallel to the interface, stress birefringence values of up to about 5 nm/cm have been observed for Nd:YAG/Nd:YAG and about 20 nm/cm for Nd:YAG/undoped YAG. Corresponding values perpendicular to the interface are about 2 to 3 nm/cm for both types of composites. Reflectivity of about 3% and scattering of about 5% has been measured at 89 degrees incident angle while values below 0.03 and 0.05% respectively have been estimated for normal incidence.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.