Direct loading of a large Yb MOT on the transition

Abstract

We report a robust technique for laser frequency stabilisation that enables the reproducible loading of in excess of 109 Yb atoms from a Zeeman slower directly into a magneto-optical trap (MOT) operating on the transition, without the need for a first stage MOT on the transition. We use a simple atomic beam apparatus to generate narrow fluorescence signals on both the 399 nm transition used for the Zeeman slower and the 556 nm transition. We present in detail the methods for obtaining spectra with a high signal-to-noise ratio and demonstrate error signals suitable for robust frequency stabilisation. Finally we demonstrate the stability and precision of our technique through sensitive measurements of the gravitational sag of the Yb MOT as a function of the intensity of the laser cooling beams, which are in good agreement with theory. These results will be important for efficient loading of the atoms into an optical dipole trap.