Figure 3

Spatial 1D and 2D distributions of the relative photoresponse (i.e.PCR, recorded at 0.5 p.e. threshold) of SiPMs to the single-photon-level light focal spot. (a) 1D and (b) 2D distribution of the PCR of the SiPM from Fondazione Bruno Kessler (FBK), Italy (model = NUV-HD-LF), with 35 μm Gm-APD cell pitch(The inset is the optical microscope photograph of the SiPM surface); (c) 1D and (d) 2D distribution of the PCR of the SiPM from novel device laboratory (NDL),China (model = EQR1011-1010C-T), with 10 μm Gm-APD cell pitch(the black solid square with rounded corners is the layout of the active region²⁹); (e) 1D and (f) 2D distribution of the PCR of the Hamamatsu SiPM, Japan (model = S12571-010C) with 10 μm Gm-APD cell pitch(The inset is the secondary electron microscopy (SEM) image of the SiPM surface¹⁸). ((a,c,e) is corresponding to the function h(x, y) in Eq. (1)).