Noise suppression in femtosecond mid-infrared light sources

An experimental and theoretical study of intrinsic correlations and noise-suppression mechanisms in two-stage femtosecond mid-IR light sources is presented. The setup, based on parametric amplification in BBO and subsequent difference-frequency mixing in AgGaS(2), delivers approximately 100-fs mid-IR pulses with 1-2-muJ energy. Exceptionally low pulse-energy fluctuations of only 0.2% in the mid-IR (lambda approximately 3-6 mum) are found, which are much smaller than the Ti:sapphire amplifer noise. The noise suppression is analyzed and found to stem from the interplay between dispersion and pump depletion.