Micro-optical grayscale excitation lenses for atom and ion trapping

摘要

Designing and integrating micro-optical components into atom and ion traps are enabling steps toward miniaturizing trap dimensions in quantum computation applications. The micro-optic must have a high numerical aperture for precise illumination of the ion and should not introduce scatter. Due to the extreme optical efficiency requirements in trapped ion and atom-based quantum information processing, even slight losses from integrated micro-optics are detrimental. We have designed and fabricated aspheric micro-lenses through grayscale transfer into a fused silica in an effort to realize increased transmissive efficiency and decreased scatter compared to an equivalent diffractive optical element. The fabricated grayscale lens profile matched the desired lens profile well, and the measured and predicted optical performances were in good agreement. The pattern was transferred via coupled plasma reactive-ion etching smoothly into the fused silica with a RMS roughness ～ 35 nm. The micro-lens had a diameter of 88 um and 14.2 um sag, with an as-designed focal length of 149 um and spot diameter of 2.6 um. The maximum measured efficiency was ～80% (86% of theoretical, possibly due to rms roughness). This realized efficiency is superior to the equivalent diffractive lens efficiency, designed to the same use parameters. The grayscale approach demonstrated an increase in collection efficiency, at the desired optical focal length, providing the potential for further refinement.