Reflectance of silicon photomultipliers (SiPMs) is an important aspect to understand large scale SiPM-based detector systems and evaluate the performance of SiPMs. We design and produce a new experimental setup to measure the reflectance in air or in a liquid at visible wavelengths for various samples. With the new setup, we establish the measurement methods and validate its measurement results. The systematic errors are estimated to be 1.9% and 3.4% for measuring the reflectance in air and in a liquid, respectively. The reflectance of two SiPMs, NUV-HD-lowCT and S14160-60-50HS manufactured by Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics K.K. (HPK) respectively, is measured 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 two times larger than that of the HPK device. This indicates that the two manufacturers are using different designs of anti-reflective coating on the SiPM surfaces. The reflectance is reduced by about 10% when the SiPMs are immersed in LAB, compared with that measured in air. The profiles of the reflected light beams are also measured by a charge-coupled device (CCD) camera.

硅光电倍增管（SiPM）的反射率是了解大型基于SiPM的检测器系统并评估SiPM性能的重要方面。我们设计并产生了一种新的实验装置，用于测量各种样品在可见波长下在空气或液体中的反射率。使用新设置，我们可以建立测量方法并验证其测量结果。用于测量在空气和液体中的反射率的系统误差估计分别为1.9％和3.4％。Fondazione Bruno Kessler（FBK）和Hamamatsu Photonics KK（HPK）分别制造的两种SiPM NUV-HD-lowCT和S14160-60-50HS的反射率是在线性烷基苯（LAB）和空气中可见波长下测量的。我们的结果表明，FBK SiPM在空气中的反射率在14％到23％的范围内变化，取决于波长和入射角，是HPK设备的两倍和两倍。这表明两家制造商在SiPM表面上使用了不同的抗反射涂层设计。与空气中测量的相比，将SiPM浸入LAB时，反射率降低了约10％。反射光束的轮廓也由电荷耦合器件（CCD）相机测量。