A hemispheric lens of a single crystal having a refractive index of 2.0 or over is used as a SIL lens of an optical system for optical recording. The single crystal is LiNbO3, LiTaO3, rutile phase TiO2, PbMoO4, TeO2, SrTiO3, ZrO2, SrNbO3, SrTaO3, CaNbO3, CaTaO3, CaTiO3, KNbO3, KTaO3, BaZrO3, SrZrO3, CaZrO3, KNbO3, KTaO3, BaZrO3, SrZrO3, CaZrO3, ZnWO4, ZnMoO4, CdWO4, CdMoO4, PbWO4, Bi20SiO12, Bi20GeO12, Bi4Si3O12, Bi4Ge3O12, GaP, ZnTe, ZnSe, Cu3TaSe4 or ZnS.