Influence of strong light beams on the nonlinear refraction and absorption coefficients of transparent materials

We explore the effective nonlinear (NL) optical response of transparent materials illuminated by strong light beams with two different setups to study the influence of the numerical aperture (NA) corresponding to the collecting lens on the measured coefficients in the open and closed aperture Z-scan transmittance. For that, we have reproduced experiments in CS2 at 532nm in the picosecond regime using D4σ-Z-scan method. It is found that measurement of high order NL coefficients is not possible after a limit defined by the self-focusing of light inside the cell and that stimulated light scattering is not significant to explain alone the saturation behaviour that occurs in the NL refraction measurements. Indications are given for future Z-scan based experiments that may clarify the new boundary conditions to be respected for the measurement.