Silicon microcavity arrays with open access and a finesse of half a million

Optical resonators are essential for fundamental science,applications in sensing and metrology,particle cooling,and quantum information processing.Cavities can significantly enhance interactions between light and matter.For many applications they perform this task best if the mode confinement is tight and the photon lifetime is long.Free access to the mode center is important in the design to admit atoms,molecules,nanoparticles,or solids into the light field.Here,we demonstrate how to machine microcavity arrays of extremely high quality in pristine silicon.Etched to an almost perfect parabolic shape with a surface roughness on the level of 2A and coated to a finesse exceeding F=500,000,these new devices can have lengths below 17μm,confining the photons to 5μm waists in a mode volume of 88λ^(3).Extending the cavity length to 150μm,on the order of the radius of curvature,in a symmetric mirror configuration yields a waist smaller than 7μm,with photon lifetimes exceeding 64 ns.Parallelized cleanroom fabrication delivers an entire microcavity array in a single process.Photolithographic precision furthermore yields alignment structures that result in mechanically robust,pre-aligned,symmetric microcavity arrays,representing a lightmatter interface with unprecedented performance.