Large diameter LaBGeO5 single crystal growth for QPM device with long interaction length

We focused on LaBGeO5 (LBGO) single crystal as a novel ferroelectric material for quasi-phase-matching (QPM) devices which are suitable for UV generation. In order to enhance the conversion efficiency of periodically poled LBGO (PP-LBGO), it is required to grow large diameter crystal to obtain PP-LBGO device with long interaction length. However, poly-crystallization were easily happened during LBGO single crystal growth process, and there were several difficulties to increase the diameter. In order to investigate the cause of poly-crystallization, a part of polycrystalline LBGO was characterized by powder X-ray diffractometer. As a result of the measurement, the polycrystalline parts slightly contained La2Ge2O7 phase. By considering the evaporation of B from the melt and optimizing growth conditions, LBGO single crystals with a diameter greater than 30 mm were successfully grown.