Optical System for Growing Optical Isolator Single Crystals by the Laser Diode Floating Zone Method

For growing optical isolator crystals, an optical system was designed, set up and characterized. It consists of four identical beam shaping optics which collimate the ingoing radiation emerging from a 600 µm fiber and create a specifically homogenized intensity profile at the position of the feed rod. The characterization of the system includes the measurement of the beam profile and efficiency of the optics, as well as a high-power endurance test. After the tests, the system was integrated into an optical floating zone furnace and commissioned together with four fiber-coupled 3-kW diode laser modules. In this configuration, the system is applied to grow single crystals of a novel optical isolator material based on Tb2O3 (terbium oxide). Crystals with a maximum diameter of 14 mm and a maximum length of 200 mm were grown and samples were cut from the crystals and polished. Moreover, the Verdet constants of the rotator samples were measured. The measured values lie within a range of 50 rad T-1m-1 to 114 rad T-1m-1.