Nanostructured antireflective coatings for trapped ion quantum computing experiments

The next generation quantum computing experiments are either based on trapped ions or neutral atoms. In the latter experiment that atoms exhibit a laser-induced excitation to Rydberg states which is typically carried out in glass cells that must operate under ultra-high vacuum conditions. The experimental setup requires the entry of laser light of numerous wavelengths at different angles of incidence into the glass cell. The optical spectrum ranges from the UV to near infrared range (310-820nm) and the angles of incidence (AOI) can reach up to 60°. Especially at high AOI, the Fresnel reflections occurring at each glass interface can reach non-negligible levels. The paper presents an AR solution called AR-plas2, which is based on nanostructures with very low effective refractive indices that can be stacked on top of each other and allow the combination with classical interference coatings within a closed process. This opens great design opportunities with outstanding AR properties in terms of residual reflectance, AOI tolerance as well as polarization neutrality in comparison to conventional AR coatings. Processing is performed in a commercial box coater and is based on the nanostructuring of organic layers by an APS plasma source. Subsequent coating with a dielectric capping layer and post treatment steps that remove the organic compounds lead to overall dielectric nanostructures with very low absorption values in the range of <2ppm (1064nm). An AR coating with an Rave(310-820nm)<0.2% for AOI=6° and Rave(310-820nm)<0.3% for AOI=45° with extremely low polarization splitting that was realized on basis of the AR-plas2 technology will be presented.