Large optical nonlinearities in $BiMnO3$ thin films

Large third-order optical nonlinearities were observed in epitaxial thin films of $BiMnO3$ grown on $SrTiO3$ substrates. Using 140 fs laser pulses at 900 nm, a negative nonlinear refractive index $(nI∼−0.53 cm2/GW)$ and a nonlinear absorption coefficient $(αI∼−0.08 cm/kW)$ for $BiMnO3$ are measured at room temperature. Large electric-field-induced enhancement of three to four orders of magnitude in the second-harmonic response at 450 nm is observed with effective nonlinear coefficients of $deff∼40(115) pm/V$ at 300 (473) K under applied fields of ∼707 (177) V/mm, respectively, from a 110 nm multivariant thin film.