Nonlinear optics in atomic ytterbium

We have performed degenerate four-wave mixing experiments with cryogenically-cooled atomic ytterbium. We use buffer-gas cooling to prepare high optical density samples at a temperature of 5~K, cold enough to resolve the different isotopes and hyperfine transitions. We observe four-wave mixing. With cross-polarized pump and probe beams, we observe a conjugate beam only when the laser is closely detuned from the $^1S_0 (F=1/2) \rightarrow ^1P_1 (F=1/2)$ transition of the $^{171}$Yb ($I=1/2$) isotope. Progress towards the generation of squeezed light will be discussed.