SEARCH Articles Figures Tables Nonlinear optical , second Nonlinear optical susceptibilities Nonlinear second order Nonlinear second-order optical nonlinearity Nonlinear second-order optical susceptibility origin Nonlinear susceptibility Optical nonlinearity second-order Optical susceptibility Second nonlinear optics Second-order nonlinear optical Second-order nonlinear optics Second-order nonlinear susceptibility Susceptibility second-order