  The device physics of parallel-wire superconducting nanowire single photon
detectors is based on a cascade process. Using nano-optical techniques and a
parallel wire device with spatially-separate pixels we explicitly demonstrate
the single- and multi-photon triggering regimes. We develop a model for
describing efficiency of a detector operating in the arm-trigger regime. We
investigate the timing response of the detector when illuminating a single
pixel and two pixels. We see a change in the active area of the detector
between the two regimes and find the two-pixel trigger regime to have a faster
timing response than the one-pixel regime.
