Progress in fabrication of nonlinear optical borate crystals for UV generation

Summary form only given. All-solid-state UV lasers have been in demand for various industrial and medical applications because of the convenient operation procedure and cost effectiveness as alternative to corrosive gas-based excimer laser. The performance of such lasers seems to depend on the capability and reliability of the UV frequency converter. In this decade, CsLiB/sub 6/O/sub 10/ (CLBO) and Gd/sub x/Y/sub 1-x/Ca/sub 4/O(BO/sub 3/)/sub 3/ (GdYCOB) have been developed by the authors group. CLBO is the most effective nonlinear optical crystal to generate the high-power fourth- and fifth-harmonics of the Nd:YAG laser. GdYCOB is the first material which can achieve the noncritical phase-matching (NCPM) condition for THG of the Nd:YAG laser. The NCPM condition is advantageous owing to its large angular acceptance and the elimination of walk-off between fundamental and harmonic light. On the other hand, reliability is very important for actual application of these crystals. We present techniques to improve the durability of NLO crystals for high-power UV light generation. For instance, we found that removal of the surface polishing compound by means of ion beam etching can improve the surface durability of CLBO. Also, we discuss the photo-induced damages in GdYCOB and their solution.