Progress towards a strontium optical lattice clock at NPL

The ¹S₀ - ³P₀ transition at 698 nm in neutral strontium has the potential to be an extremely precise optical frequency standard [1] and is one of several candidates for a future redefinition of the second. Recent measurements of this transition at three national laboratories around the world have fractional frequency uncertainties in the 10¹⁵ range and agree to within a hertz [2,3,4]. To realise fully the potential accuracy of this frequency standard, in depth studies of systematic effects need to be performed in order to characterise them at the level necessary for a redefinition of the second. At the National Physical Laboratory we are developing a compact, diode laser based optical lattice clock. We intend to study the clock transition in both ⁸⁸Sr and ⁸⁷Sr with focus on the uncertainties in the frequency shifts due to blackbody radiation. The setup incorporates a novel permanent magnet based Zeeman slower [5].