Electric-field-induced optical second-harmonic generation in KTaO3and SrTiO3

Electric-field-induced optical second-harmonic generation (SHG) has been studied for KTa${\mathrm{O}}_3$ and SrTi${\mathrm{O}}_3$ in the temperature range from 300 to 4.2 K. The results can be summarized by the fourth-order Miller constants (in units of ${10}^{-11\mathrm{}}$ esu): for KTa${\mathrm{O}}_3$, $\left|{\Delta }_{1111}\right|=2.2\mathrm{}\pm 30\%$ and $\left|{\Delta }_{1122}\right|=0.77\mathrm{}\pm 33\%$; for SrTi${\mathrm{O}}_3$, $\left|{\Delta }_{1111}\right|=0.56\mathrm{}\pm 34\%$ and $\left|{\Delta }_{1122}\right|=0.77\mathrm{}\pm 36\%$. The anisotropy of the SHG coefficients varies considerably among these isomorphous crystals: the ratios $\left|\frac{d_{33}}{d_{31}}\right|$ are 2.86 ± 6%, 0.74 ± 5%, and 0.37 ± 15% for KTa${\mathrm{O}}_3$, SrTi${\mathrm{O}}_3$, and BaTi${\mathrm{O}}_3$, respectively. This is discussed in terms of Levine's bond-charge model of nonlinear optical susceptibilities.