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arXiv · 2605.08425

In-Situ Measurement of Beam Divergence in a High Efficiency SNSPD Platform

Daniel W. Sorensen·Martin J. Stevens·Lynden K. Shalm·Dileep V. Reddy
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Abstract

We implement a time-of-flight imaging technique utilizing a differential-readout SNSPD to spatially resolve detection events in a fiber-coupled detector platform. We measure the spatial detection profiles for ultra-high numerical aperture fiber, standard single-mode fiber, and thermally-expanded core fiber (mode-field diameters 4.1{\mu}m, 10.4{\mu}m, 30{\mu}m respectively) in an active area surrounded by an all-dielectric optical stack designed for near-unity detection efficiency. We see no beam divergence in all but the smallest fiber optic modes. This contradicts previously-held beliefs that beam divergence during the detection process necessitates activate areas much larger than coupled optical modes, opening new paths toward smaller and better-optimized detectors.

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Daniel W. Sorensen, Martin J. Stevens, Lynden K. Shalm, Dileep V. Reddy. 2026-05-08. In-Situ Measurement of Beam Divergence in a High Efficiency SNSPD Platform. https://arxiv.org/abs/2605.08425

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