Material surface treatment for design of composite optical elements

The quality of surface preparation of various laser materials for the purpose of creating composite elements is studied. It is shown that the flatness of the samples should be no worse than $\lambda$/10, and the roughness - no more than 1.0 nm. Parameters of ion etching that do not lead to roughness degradation are found: Ar ions, $E_{ion}$ = 800 eV and grazing angle $\theta$ = 5$^\circ$. Composite elements were created from yttrium aluminium garnet doped with ytterbium ions (Yb:YAG), as well as a magnetoactive TGG crystal with single crystals of sapphire.