Experimental and theoretical investigation of thermal lensing effects in mode-locked femtosecond Z-scan experiments

We show that the closed aperture refractive Z-scan signatures using high-repetition rate ultrafast laser systems are strongly influenced by thermal lensing. We demonstrate that a stationary thermal lens develops even in the case of very low linear absorption. In addition, we have developed a stationary thermal lens model using the Gaussian decomposition method and applied it for the first time to Z-scan experiments and find good agreement between theory and experiment. (C) 2002 Elsevier Science B.V. All rights reserved.