Effects of nonlinear absorption on the Z-scan technique through beam dimension measurements

Abstract

Recently we have proposed a novel Z-scan technique for measuring refractive nonlinearities, based on the direct measurement of the variations of the beam dimensions in the far field. In the present work this approach is extended to the case of simultaneous presence of nonlinear refraction and absorption, enabling the complete characterization of the materials regarding their nonlinear optical properties. In more detail we have found that nonlinear absorption induces asymmetry on the peak-valley configuration of the Z-scan curves, both in the cases of circular and elliptic Gaussian beams. We have also shown that this asymmetry grows exponentially with the values of the nonlinear phase shift and the nonlinear absorption coefficient. Further, we have found that the effects of nonlinear absorption on the Z-scan curves can be suppressed by multiplying the radius Z-scan plot with an open Z-scan curve. This result can be used for determining the nonlinear refractive index of the material through a simplified relation.