Nonlinear ellipse rotation measurements in optical thick samples

Nonlinear refractive indices of several optical glasses were measured by means of the nonlinear ellipse rotation method in a tightly focused laser beam condition, leading to the improvement of the spatial resolution which allows probing the local refractive nonlinearity with better accuracy. The use of a short focal length results in a Rayleigh range shorter than the sample thickness, and this feature can be explored to measure two stacked samples in a single run. In this way, it is possible to simultaneously probe a reference and an unknown sample, improving significantly the refractive nonlinearity determination. Several optical glasses were characterized by this method using fused silica as reference.