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 ${\mathrm{AgGaS}}_2$, delivers $\approx 100‐\mathrm{fs}$ mid-IR pulses with $1–2‐\mathit{\mu }\mathrm{J}$ energy. Exceptionally low pulse-energy fluctuations of only 0.2% in the mid-IR $\left(\lambda \approx 3–6 \mathit{\mu }\mathrm{m}\right)$ 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.