Alignment and optimization of optical tweezers on trapped ions

This paper presents a routine to align an optical tweezer on a single trapped ion and use the ion as a probe to characterize the tweezer. We find a smallest tweezer waist of $2.3(2)\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{m}$, which is in agreement with the theoretical minimal attainable waist of $2.5(2)\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{m}$ in our setup. We characterize the spatial dependence of the tweezer pattern in terms of its Rabi frequency on an optical transition in the ion. We find a peak Rabi frequency of $390(70)\phantom{\rule{4pt}{0ex}}\mathrm{MHz}$ in the center of the tweezer and a suppression factor of 19(3) in the immediate surrounding of the ion. We investigate the effects of optical forces and coherent population trapping on the ion. We show that the challenges posed by these forces can be overcome, and that the number of tweezers can be easily scaled up to reach several ions by using a spatial light modulator.