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

TL;DR

This paper demonstrates a magneto-optical method to produce a high-brightness atomic beam from rubidium, which can be photoionized for improved focused ion beam applications, potentially surpassing liquid metal ion sources.

Contribution

The study introduces a direct magneto-optical compression technique to generate a high-brightness atomic beam suitable for focused ion beam nanofabrication, achieving significant brightness improvements.

Findings

Achieved an equivalent transverse reduced brightness of 1.0×10^6 A/(m^2 sr eV) with a flux of 0.6 nA.

Further reduced temperature increased brightness to 6×10^6 A/(m^2 sr eV).

Potential for a sixfold brightness improvement over liquid metal ion sources.

Abstract

An atomic rubidium beam formed in a 70 mm long two-dimensional magneto-optical trap (2D MOT), 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 two-dimensional magneto-optical trapping 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 with an optical molasses after the 2D MOT. This increased the equivalent brightness to $(6\substack{+5-2})$$\times 10^6$ A/(m$^2$ sr eV). For currents below 10 pA, for which disorder-induced heating can be suppressed, this number is also a good estimate of the ion beam brightness that can be expected. Such an ion beam brightness would be a six times improvement over the liquid metal ion source and could improve the resolution in focused ion beam nanofabrication.