Superconducting nanowire single photon detectors (SNSPDs) are typically used as single-mode-fiber-coupled single-pixel detectors, but large area detectors are increasingly critical for applications ranging from microscopy to free-space quantum communications. Here, we explore changes in the rising edge of the readout pulse for large-area SNSPDs as a function of the bias current, optical spot size on the detector, and number of photons per pulse. We observe a bimodal distribution of rise times and show that the probability of a slow rise time increases in the limit of large spot sizes and small photon number. In the limit of low bias currents, the dark-count readout pulse is most similar to the combined large spot size and small-photon-number bright-count readout pulse. These results are consistent with a simple model of traveling microwave modes excited by single photons incident at varying positions along the length of the nanowire.
@article{arxiv.2006.00126,
title = {Position Sensitive Response of a Single-Pixel Large-Area SNSPD},
author = {Claire E. Marvinney and Brian E. Lerner and Alexander A. Puretzky and Aaron J. Miller and Benjamin J. Lawrie},
journal= {arXiv preprint arXiv:2006.00126},
year = {2021}
}