  Reflectance of silicon photomultipliers (SiPMs) is an important aspect to
understand the large scale SiPM-based detector systems and evaluate the
performance of SiPMs. We report the reflactance of two SiPMs, NUV-HD-lowCT and
S14160-60-50HS manufactured by Fondazione Bruno Kessler (FBK) and Hamamatsu
Photonics K.K. (HPK) respectively, in linear alkylbenzene (LAB) and in air at
visible wavelengths. Our results show that the reflectance of the FBK SiPM in
air varies in the range of 14% to 23% , depending on wavelengths and angle of
incidence, which is 2 time larger than that of the HPK device. This indicates
that the two manufacturers are using different designs of anti-reflective
coating on SiPMs' surfaces. The reflectance is reduced by about 10% when SiPMs
are immersed in LAB, compared with that measured in air. The profiles of
reflected light beams are also measured by a charge-coupled device (CCD) camera
for the two SiPMs.
