Determination of the optimum phase-matching directions for GdCOB and YCOB crystals

Summary form only given.The nonlinear optical coefficients of GdCa/sub 4/O(BO/sub 3/)/sub 3/ (GdCOB) and YCa/sub 4/O(BO/sub 3/)/sub 3/ (YCOB) have been calculated by using the revised Gaussian 92 program on the basis of the anionic group theory. Meantime, the d/sub 11/, d/sub 12/, d/sub 32/ and d/sub 33/ coefficients of the crystals were also measured by the Maker fringes method at /spl lambda/=1064 nm, while d/sub 13/ and d/sub 31/ were evaluated from measurement of the Maker fringes. It was found that the coefficients determined by the Maker fringes are in agreement with the theoretical values. On the basis of the d/sub ij/ coefficients and the Sellmeier equations, the effective second harmonic generation (SHG) coefficients d/sub eff/ of GdCOB and YCOB as a function of phase-matching angles /spl theta/ and /spl Phi/ have been determined. It is interesting that directions of the maximum effective SHG coefficients both GdCOB and YCOB are not in the principal plane but located out of the X-Z plane, for example, in the positions /spl theta/=65.9/spl deg/, /spl Phi/=36.5/spl deg/ and /spl theta/=66.3/spl deg/, /spl Phi/=143.5/spl deg/ for YCOB. It is also worth noting that the largest d/sub eff/ of GdCOB and YCOB in the region of 0/spl deg//spl les//spl theta//spl les/90/spl deg/, 90/spl deg//spl les//spl Phi//spl les/180/spl deg/ are larger than those in 0/spl deg//spl les//spl theta//spl les/90/spl deg/, 0/spl deg//spl les//spl Phi//spl les/90.