Simultaneous measurements of nonlinear refraction and nonlinear absorption using a 4f imaging system

A method is reported to simultaneously measure the nonlinear absorption and refraction coefficients of materials using a nonlinear-imaging technique with a phase object. In this technique, the sign and magnitude of both the nonlinear absorption and refraction can be acquired conveniently from the analysis of three experiment images: the linear image, the nonlinear image and the image without sample. In order to validate our approach, we demonstrate this method for ZnSe at 532 nm where two-photon absorption is present and the nonlinear refractive index n ₂ is negative. The values of β (nonlinear absorption coefficient) and n ₂ we measured are very close to the values found in other literature.