# Direct magneto-optical compression of an effusive atomic beam for high resolution focused ion beam application

G. ten Haaf, T.C.H. de Raadt, G.P. Offermans, J.F.M. van Rens, P.H.A. Mutsaers, E.J.D. Vredenbregt, S.H.W. Wouters

An atomic rubidium beam formed in a 70 mm long magneto-optical compressor, directly loaded from a collimated Knudsen source, is analyzed using laser-induced fluorescence. The longitudinal velocity distribution, the transverse temperature and the flux of the atomic beam are reported. The equivalent transverse reduced brightness of an ion beam with similar properties as the atomic beam is calculated because the beam is developed to be photoionized and applied in a focused ion beam. In a single magneto-optical compression step an equivalent transverse reduced brightness of $(1.0\substack{+0.8\\-0.4})$ $\times 10^6$ A/(m$^2$ sr eV) was achieved with a beam flux equivalent to $(0.6\substack{+0.3\\-0.2})$ nA. The temperature of the beam is further reduced by applying sub-Doppler cooling behind the magneto-optical compressor. This increased the equivalent brightness to $(6\substack{+5\\-2})$ $\times 10^6$ A/(m$^2$ sr eV). When fully ionized this will be a six times improvement over the liquid metal ion source, which would improve the resolution in focused ion beam nanofabrication.