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 2 Å and coated to a finesse exceeding F = 500,000, these new devices can have lengths below 17 µm, confining the photons to 5 µm waists in a mode volume of 88λ 3 . Extending the cavity length to 150 µm, on the order of the radius of curvature, in a symmetric mirror configuration yields a waist smaller than 7 µm, 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 light-matter interface with unprecedented performance.

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This work reports on the nanomechanical metrology of vertically aligned gallium nitride micropillar arrays with high homogeneity and well‐controlled geometry. The GaN micro‐building blocks are top‐down fabricated by combining photolithography, inductively coupled plasma dry reactive ion etching (ICP‐DRIE) with SF6/H2 gases, and post‐wet chemical etching treatment by a KOH‐based solution. A nanoindenter with a three‐sided pyramid Berkovich tip is employed to precisely measure the mechanical properties of the GaN micropillars directly from their top surfaces, hence an additional preparatory work to transfer them on a foreign substrate is not necessary. From the obtained experimental results, the insight of the indentation pop‐in phenomenon on the micropillars is carefully investigated. Besides, a confocal laser scanning microscope (CLSM) and an atomic force microscope (AFM) are utilized to confirm the high homogeneity of the micropillar arrays before indentation and to characterize the morphologies of their top surfaces after stress relaxation, respectively. Therefore, the obtained experimental results can be employed as the prior knowledge to be compared with the bulk counterparts, in which the GaN micropillars can be further developed for mechanical force sensors, since the performed measurement techniques have provided the existent mechanical circumstance of the microstructures when a vertical force is applied.