Second harmonic generation from the novel polar polymorph α/β-BaTeMo2O9 phases

Abstract

The second harmonic generation (SHG) and the first hyperpolarizability (β_ijk) of β-BaTeMo₂O₉ and α-BaTeMo₂O₉ phases have been calculated. Due to structure arrangement and hence the orientation of the dipole moments, β-phase exhibit larger SHG than that of α-phase although it produces high local SHG. The linear optical properties reveals that α-phase show larger anisotropy between the optical components along the polarization directions [100], [101] and [001] than that of β-phase. The anisotropy in the linear optical susceptibilities favors an enhanced phase matching conditions necessary for observation of SHG and optical parametric oscillation (OPO). It has been found that these materials exhibit positive uniaxial anisotropy and positive birefringence. We found that α-phase show higher uniaxial anisotropy and birefringence values than those of β-phase. The calculated SHG reveals that χ⁽²⁾₂₂₂(ω) is the dominant tensor compound for β-phase with d₂₂ of about 20.46 pm V⁻¹ which is higher than the experimental value of the well known KTiOPO₄ (KTP) single crystals. While χ⁽²⁾₃₂₂(ω) is the dominant tensor compound of α-phase with d₃₂ of about 0.11 pm V⁻¹. In addition, we have calculated the microscopic first hyperpolarizability, β_ijk, the vector components along the dipole moment direction for the dominant components of β-BaTeMo₂O₉ and α-BaTeMo₂O₉ phases at static limit and at λ = 1064 nm.