Microtube-Czochralski (μT-CZ) growth of bulk benzophenone single crystal for nonlinear optical applications

Microtube-Czochralski technique was employed to grow large size benzophenone single crystal for the first time. In conventional Czochralski pulling technique, the growth of bulk single crystal will be initiated by a pre-grown seed, whereas in microtube-Czochralski technique a microtube that is made out of a metal such as stainless steel (8 μm ID) can be used to grow bulk single crystal. A specially designed furnace having inert gas atmosphere, condensation free enclosure and in situ annealing facility was employed. Benzophenone crystal having cubic facet (15 mm) with high optical quality was grown when the following vital growth parameters are set to the corresponding optimized values such as pulling rate: 1-2 mm/h, seed rotation rate: 5-10 rpm and the axial thermal gradient: 8 °C/cm. The grown crystals were cut and polished. Thin plate like polished samples were used to justify the optical quality of the grown samples by UV-VIS-NIR spectroscopy. Powder SHG measurement shows that the grown samples exhibit three times higher second harmonic generation than potassium dihydrogen phosphate (KDP).