Z-scan measurements using high repetition rate lasers: how to manage thermal effects

We demonstrate the effectiveness of a simple method for using Z-scan technique with high repetition rate lasers managing cumulative thermal effects. Following Falconieri [J. Opt. A, 1 (1999) 662], time evolution of Z-scan signal is recorded. We use data time correlation to extrapolate with accuracy the instantaneous nonlinear optical response of the sample. The method employed allows us to clearly evaluate the order of the absorption process underlying the thermo-optical nonlinearities. Using a 76 MHz repetition rate laser with 120 fs pulsewidth we measure third order nonlinearities and thermal properties of CS2 and toluene in accordance with values obtained with low repetition rate light sources.