Phase matching for second harmonic generation in KNbO3:Ta crystals with Nd:YAG- and GaAs-laser wavelengths

Noncritical phase-matched second harmonic generation was measured in optically biaxial KNb1−xTaxO3 mixed crystals in the orthorhombic phase. For Nd:YAG-(1064 nm) the coefficient d31 of the tensor of the nonlinear susceptibility was applied, while for the GaAs-laser (905 nm) the coefficient d32 was used. For both laser wavelengths the phase-matching temperature decreases with increasing Ta-concentration. Noncritical phase-matching at room temperature can be reached with the GaAs-laser for a Ta concentration of ≊9%. The corresponding value for the Nd:YAG laser is ≊14%.