Spectroscopy of neutral 174Yb in a one-dimensional optical lattice

We report spectroscopy of the ¹S₀ - ³P₀ clock transition in neutral ¹⁷⁴Yb atoms confined to a one-dimensional optical lattice at the ac Stark shift-canceling wavelength of 759.35 nm. Spectroscopic linewidths as narrow as 4 Hz, full width at half-maximum, are shown with good contrast and signal-to-noise ratios. An upper limit on frequency instability is demonstrated to be 3 × 10^-15 at one second by measuring with respect to another stable laser through a Ti:sapphire femtosecond laser frequency comb.