Strain-induced improvements on linear and nonlinear optical properties of SrB4O7 crystal

Although the high nonlinearity, strontium tetraborate crystal SrB4O7 is angular non-phasematched in UV SHG process due to its low birefringence. In this Letter, we revealed that its birefringence can be significantly enhanced by uniaxial strain based on the first principles computations. The birefringence is thirteen and sixteen times larger than those of unstrained crystal at -10% a-axial compressive and 10% a-axial tensile strain, respectively. The compressive strain also effectively improve the static second-order coefficients and shift the optical absorption edge towards the UV side, which would shed light on the modulations of UV/VUV nonlinear optical crystals by directionally external stress.