  We measure the detection efficiency of single-photon detectors at wavelengths
near 851 nm and 1533.6 nm. We investigate the spatial uniformity of one
free-space-coupled single-photon avalanche diode and present a comparison
between fusion-spliced and connectorized fiber-coupled single-photon detectors.
We find that our expanded relative uncertainty for a single measurement of the
detection efficiency is as low as 0.70 % for fiber-coupled measurements at
1533.6 nm and as high as 1.78 % for our free-space characterization at 851.7
nm. The detection-efficiency determination includes corrections for
afterpulsing, dark count, and count-rate effects of the single-photon detector
with the detection efficiency interpolated to operation at a specified detected
count rate.
