Giant nonlinear refraction in gold island films

Giant nonlinear refraction has been experimentally observed in gold island films. The real part of the third-order nonlinear susceptibility χ⁽³⁾(ω: ω,-ω, ω) reaches a value of about 10^?4 CGS units. The mechanism of nonlinearity of the refractive index can be associated with the resonance enhancement of the factor of the local optical field at the pump wavelength due to the excitation of surface plasmons, as well as with the contribution of the heating of conduction electrons in an ensemble of metal particles.