NUMERICAL-ANALYSIS OF Z-SCAN EXPERIMENTS BY USE OF A MODE EXPANSION

The Z-scan analysis technique has been developed to permit characteriz ation of nonlinear refractive indices and nonlinear absorption of non- Gaussian laser beams by a numerical approach. The new approach is base d on a mode expansion of the electric field of the laser beam into Gau ssian-Laguerre or Gaussian-Hermite modes. The individual modes are pro pagated within the nonlinear sample under the influence of the intensi ty-dependent phase shifts. The resulting electric field at the exit pl ane is expanded as a new sum of Gaussian-Laguerre or Gaussian-Hermite modes. From the final mode expansion the field distribution at the det ector plane is calculated. The method also makes it possible to simula te a variety of complex optical limiting devices, such as stacks of sa mples with different material parameters and thick samples with a vari ation of material parameters along the z axis. A series of test simula tions is presented and compared with experimental Z-scan data of solut ions of substituted phthalocyanine molecules. (C) 1998 Optical Society of America.