Proposal for electro-optically tunable Kerr-Lens in BBO crystal by cascaded second-order process

In this report, a linear electro-optically tunable non-phase matched second-order nonlinear process is transformed into a cascaded second-order nonlinear process in a bulk BBO crystal to generate the effect of electro-optically tunable Kerr-type nonlinearity. A phase mismatch condition is created by applying an electric field to the x-z plane of the crystal which introduces a nonlinear phase shift between the launched and reconverted fundamental waves from the generated second harmonic wave. The sign of this nonlinear phase shift is easily changed by changing the polarity of applied electric field. The nonuniform radial intensity distribution of incident Gaussian beam introduces a curvature to the fundamental wavefront which focuses or defocuses the incident beam while propagating through the medium. Hence, a positive or negative lens is established within the crystal. The focal length of that lens is also tuned by tuning the applied electric field. The maximum calculated effective nonlinear refractive index due to nonlinear phase shift is ±6.6508 × 10−14 cm2/W.