Z-scan investigation of doubly doped surface layer of lithium niobate

摘要

We experimentally investigate the photorefractive nonlinearity within lithium niobate samples with surface doping by combinations of copper (Cu) and iron (Fe). In the configuration of closed Z-scan we use either helium - neon laser irradiation with wavelength of 633 nm or continuous wave semiconductor laser with wavelength of 650 nm. Light power in experiments ranges from 1 to 4 mW. We observe very strong Z - scan response in the closed scheme at the transient stage and the different temporal behavior of this response for different locations of the light beam waist with respect to the doped surface of samples studied. The approach of thin light - induced nonlinear lens is used to estimate the Z - scan response in the steady state in dependence on the nonlinear sample position. We also use this approach to compare the observed distortions of the light beam due to its spatial self - action with expected change of the beam profile.