Nonlocal response of optical thermal nonlinearity

In this work, we analyse experimentally the nonlocal response of a thermal nonlinearity medium and provide quantitative description in the terms of a nonlocal response function. We demonstrate that the nonlocal response function is well localized despite the infinite range of nonlocal interaction, and it does not depend on the material parameters but only on the sample´s boundaries. Our method is based on the pump-probe excitation technique combined with quantitative measurement of the light-induced nonlinear refractive index by holographic interferometry. Our technique is versatile and can be used in characterization of the thermal nonlinear response of various materials, for application in nonlinear devices based on infiltrated photonic crystal fibers and photonic crystals.