Simultaneous frequency stabilisation of 399 nm and 556 nm lasers via fluorescence spectroscopy of an atomic beam: application to laser cooling of Yb

Experimental studies of ultracold ytterbium atoms generally involve the frequency stabilisation (locking) of lasers to two transitions - at 399 and 556 nm - in order to implement laser cooling. Here we present a simple and robust apparatus that generates narrow fluorescence signals with a high signal-to-noise ratio at both wavelengths. The design utilises easily acquired vacuum parts, optics and electronics, requires very little laser power and is applicable to other alkaline earth and lanthanide elements. We demonstrate the stability and precision of the frequency stabilisation at 556 nm by presenting sensitive measurements of the gravitational sag of an ytterbium MOT as a function of laser power.