Abstract: The present invention relates to an optical system for concentrating incoming light comprising a plurality of concentrating optical elements (100) with a front surface (102) arranged to receive incoming light and a back surface (103) arranged to exit light, wherein the front surface is larger than the back surface. Adjacent concentrating optical elements are separated by gaps (101) and the refractive index of the material in a concentrating optical element is higher than the refractive index of the gap. The geometry of the concentrating optical elements is optimized to enhance the light concentration.

Abstract: A method of producing a polycrystalline film of a metal compound, AlN or ZnO, on a substrate with a non-zero mean tilt of the c-axis relative to the surface normal of the substrate, is disclosed. The method comprises deposition of crystallites of said compound onto the substrate that has a suitable surface for crystal growth with tilted c-axis relative to the surface normal by operating a deposition system designed for sputtering of metal atoms from a target, in a gas mixture of inert gas and nitrogen or oxygen, respectively, at a process pressure such that the mean free path of sputtered metal atoms is comparable or larger than the target to substrate distance, the geometry of the deposition system being such that there exists at least one arbitrary area on the substrate where the distribution of the depositing flux is asymmetric relative to the surface normal at that area.