The Growth Of Large-sized BBO Crystals And The Exploration Of Nonlinear Optical Crystals

?-BaB₂O₄?BBO?, a new type of ultraviolet frequency doubling crystal which was discovered by Chinese scientists, has been widely used in laser frequency doubling,mixing, optical parametric oscillator, and etc., which has become one of the core materials in the field of modern nonlinear optical technology. However, the method of large BBO crystal growth is still a difficult problem, which becomes the bottle limitation for the further applications of BBO. Herein, according to the BaB₂O₄-Na F phase equilibrium diagram and the lever principle, we deduced the mathematical expression of BBO crystal growth, wishing to carry out the large BBO crystal growth steadily under the theoretical guidance.With several decades development of nonlinear optical?NLO? crystals, they are mostly satisfied with the light source in the uv-vis-near infrared band. However, we also lack of the NLO crystals in deep ultraviolet?especially below 200 nm? and far infrared?especially the 5?m- 20?m?. Therefore, the searching of NLO crystals still has a long way to go. Up to now, the "cooking" mode? the screening method of powder second harmonic generation effect?is the popular method for searching NLO crystals, which has the defects of "low efficiency with high cost". So, it is inevitable to looking for the scientific method of searching new NLO crystals. Here we want to find an efficient way to search new NLO crystals based on the theory of anionic groups by using the method of the plane-wave pseudopotential ab initio and the theory to guide practice from the ICSD database.The main contents of this paper are as follows:?1? According to the phase equilibrium diagram of BBO and the lever principle, we deduce the mathematic expression of the cooling rate for crystal growth, and research the pulling speed, cooling speed, liquid crystal radius line slope, the relationship between the melt composition and quality of cosolvent in the process of crystal growth. BBO crystal is grown steadily with more than 20 mm,which confirms the practicability of the theory to guide practice.?2? The optical properties of the Zn2?OH?PO4 crystal are calculated by using the anionic group theory and plane-wave pseudopotential ab initio method.Subsequently the Zn2?OH?PO4 crystal is synthesized by hydrothermal method and the measured second harmonic generation effect is in accordance with the theoretical calculation, which demonstrated how to looking for NLO crystals by the method of theory to guide practice.