First-principle calculation of two-photon absorption in BaTiO3

We have derived a formula of third-order nonlinear optical susceptibility χ(3)(−ω;ω,−ω,ω). Under a scissor approximation by using a first-principle band structure approach, we have calculated the third-order nonlinear susceptibility χ(3), dielectric constant ɛ, and the nonlinear optical absorption for BaTiO3. The imaginary parts of the nonlinear susceptibility, dielectric constant, and two-photon absorption coefficient were calculated and discussed. The calculated two-photon absorption coefficient β equals 0.17 cm/GW, is in good agreement with the experimental value of 0.1 cm/GW under 596 nm laser excitation.