Second Z-scan in materials with nonlinear refraction and nonlinear absorption

The Z-scan technique is a popular method for measuring optical nonlinearities using a single laser beam. We describe a simplified second Z-scan technique for cases where nonlinear refraction is accompanied by nonlinear absorption to separately evaluate the nonlinear refraction and the nonlinear absorption by performing straightforward measurement with the aperture removed. We divide the normalized transmittance of the closed aperture (S < 1) Z-scan by that of the open-aperture (S = 1) Z-scan. It is found that not only the ratio rho of the imaginary part chi(I)((3)) to the real part chi(R)((3)) of the third-order nonlinear susceptibility chi((3)) but also the linear transmittance S of the aperture has a great influence on the performance of the second Z-scan. Some useful results, which determine whether a second Z-scan can be performed or not, have been obtained for the rho dependence of the critical linear transmittance S-c of the aperture and S dependence of the critical ratio rho(c). These results may be applied to timely adjusted experimental conditions in order to obtain highly accurate data. We demonstrate this method on a CH3OH solution of Co2L3 with 7 ns laser pulses.