Elasto-optic effects characterize the dependency of optical birefringence on strain. Thus, by changing the strain, one can control the optical properties of the sample. Large elasto-optic effects are desirable to improve the sensitivity of elasto-optic devices, their performances, and lower their energy consumption. Yet, the microscopic mechanisms underlying elasto-optic conversion effects are not well understood. For example, the temperature dependencies of the elasto-optic effect as well as the effect of the concentration in solid solutions have not been investigated from first principles. Here, we develop a coupled density functional theory and effective Hamiltonian numerical method to compute and understand the elasto-optic response of ferroelectric materials at finite temperature. In particular, we apply such scheme to calculate the elasto-optic response of ${\mathrm{BaTiO}}_3$ and ${\mathrm{Ba}}_{1-\mathrm{x}}{\mathrm{Sr}}_{\mathrm{x}}{\mathrm{TiO}}_3$ compounds in their tetragonal phase near room temperature, and report how elasto-optic coefficients can be significantly enhanced in the visible range. We also demonstrate that, and explain why, this effect can be enlarged in the THz-frequency range.

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• Dielectric properties
• Ferroelectricity
• Optical & microwave phenomena
• Optical conductivity
• Strain
• Density functional theory