Reduction of optical intensity noise by means of two-photon absorption

We demonstrate an all-optical intensity noise reduction technique by using two-photon absorption of ZnSe in a Z-scan configuration. We measure the nonlinear transmission and the shot-to-shot energy fluctuations of 860-nm intense femtosecond laser pulses. At a 40% nonlinear transmission level the noise in the pulse train is reduced to 24%. This yields an additional 40% reduction in the relative pulse energy fluctuation. A realistic theoretical treatment is presented and is found to be in good agreement with experimental results. (C) 2003 Optical Society of America.