Mapping the second and third order nonlinear susceptibilities in a thermally poled microimprinted niobium borophosphate glass

Abstract

Multiplex coherent anti-stokes Raman scattering (M-CARS) and second harmonic generation (SHG) techniques are used to map the real part of the nonresonant third order nonlinear optical susceptibility and the second order nonlinear optical susceptibility of a thermally microimprinted niobium borophosphate glass. In particular, such bimodal nonlinear imaging is employed in order to precisely evaluate how thermal poling can modify the amplitude of the nonresonant third-order nonlinearity of the sample. A systematic decrease of the M-CARS intensity is found in the poled areas with respect to the unpoled ones, suggesting therefore a reduction of the real part of the nonresonant third order nonlinear susceptibility within these regions. Such a reduction in the M-CARS intensity can be explained by sodium depletion in the subanodic zone and is mostly linked to the reduction of both the matter density and the linear refractive index, in agreement with earlier works on thermal poling on the same family of glasses.