Research On Growth Of Large CsB₃O₅ Crystal And Its Applications

High-average power all-solid-state 355 nm laser sources are desired for applications in micromachining of dielectrics and metals because of the advantages of high reliability and low maintenance cost. The third harmonic generation (THG) of the Nd:YAG laser radiation through sum-frequency generation of fundamental and second-harmonic in nonlinear optical crystal is one of the most promising methods to generate high-power 355 nm light. At present, LiB3O5 crystal (LBO) is most generally used for THG of Nd:YAG laser due to its relatively large nonlinear coefficient and high damage threshold. CsB3O5 crystal (CBO) has shown superior 355 nm generation. The THG conversion efficiency of CBO is about twice that of LBO.Currently, the main problems of CBO Crystal are crystal growth instability, optical scattering centers limited the quality, the crystal surfaces are easy to be fogged in atmospheric environment because of hygroscopic. In this dissertation, we focus on the above problems and the main results are as following:1. More stable growth conditions of larger CBO crystals were found. The polycrystalline material of CBO was synthesized by liquid-state reaction method.High quality CBO crystals with less optical scattering centers were grown by means of seed-submerged growth technique from a 4-mol% Cs2O-enriched melt. It was confirmed that the negative temperature gradient is effective for CBO crystal growth. The optical homogeneity of CBO crystal achievesΔn ~ 4.3×10-6/cm. The damage threshold of CBO was measured with a value of 10.371 GW/cm2 @ 1064nm, 7.5ns, this result approaches that of LBO and higher than that of BBO.2. The defects of CBO crystal were studied. Chemical etching method is used to reveal the dislocation on the surfaces of CBO crystal. The morphology of etching pits and strips are observed by microscopy. The growth defects in CBO crystals were investigated by synchrotron radiation X-ray topography method. The defects were removed or reduced by adjustment of material ratio, temperature gradient and cooling rate.3. Anti-reflection coating for the CBO crystal was used. The reflectance of CBO THG device at 1064 nm, 355 nm and 532nm was reduced to 0.06%, 0.16% and 0.11%. The THG conversion efficiency was increased two 21. 87%, this was 2.4% higher than the device without anti-reflection coating.4. Different crystallographic surfaces of CBO crystal were etched by chemical etching. Through comparison of the etching patterns of CBO crystal and crystal structure along different directions, it was confirmed that there are a lot of channels in the (010) plane. Water molecules enter the CBO crystal through channels react with CsB3O5, producing Cs2B4O7?5H2O and H3BO3. Moisture-proof films were fabricated by silane coupling agent and ultraviolet polymers. The moisture-proof film can work at 150℃which is higher than the CBO devices work temperature.