Calculation of second-order nonlinear optical coefficients of KTiOPO4 and KTiOAsO4

The second-order nonlinear optical tensor coefficients of both KTiOPO4 (KTP ) and KTiOAsO4 (KTA) are calculated from the chemical bond viewpoint. All c onstituent chemical bonds of both crystals are considered, and contribution s of each type of bond to the total linearity and nonlinearity are determin ed. Calculated results agree satisfactorily with experimental data in both signs and numerical values. The calculation shows that though TiO6 groups a nd P(1)O-4 or As(1)O-4 groups have relatively larger linear contributions, they can only produce an advantageous environment for KOx (x = 8, 9) groups and P(2)O-4 or As(2)O-4 groups in nonlinear optical contributions. The ori gin of nonlinearity of KTP family crystals comes from the KOx (x = 8, 9) an d P(2)O-4 groups in their crystal structures. Furthermore, the difference i n optical nonlinearities of KTP type crystals is analyzed, based on the det ailed calculation of nonlinearities of both KTP and KTA. (C) 1999 Academic Press.