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Advances in optical and photonic devices Part 15

Tham khảo tài liệu 'advances in optical and photonic devices part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Silicon Photomultiplier - New Era of Photon Detection 269 Fig. 17. a b. Light generation in the silicon photomultiplier micro-cell in regions with high gradient of electric field a - the micro-cell in external light b - same micro-cell without external light. Optical crosstalk of silicon photomultiplier scales as the product of optical generation inside the triggered micro-cell during the avalanche breakdown process the total geometric cross section for the interaction between two micro-cells and the single photon sensitivity of micro-cells. The optical crosstalk probability is a function of silicon photomultiplier bias voltage and the distance between neighbourhood pixels. The optical crosstalk probability preliminary can be estimated by the ratio of the count rate at the second photoelectron level to the count rate at the single photoelectron level. The count rate at the single photoelectron level is measured by setting the threshold at half the single photon peak while the rate at the second photoelectron level is measured by setting the threshold at 1.5 times single photon peak height. The measurements were taken at 253K to reduce the primary dark rate. At room temperature were the dark rates are of the order of MHz there is a higher probability that two uncorrelated dark pulses or a dark pulse and an afterpulse event might coincide to produce a pulse with amplitude greater than the threshold setting for the second photoelectron level. At 253K the primary dark rate is of the order of a few 100kHz and the probability of uncorrelated events occurring simultaneously is minimized. Fig. 18. a b. shows the optic crosstalk probability measured at 253K for two silicon photomultiplier as a function of voltage over breakdown voltage left and the frequency of dark rate as a function of threshold right Stewart A. G. et al. 2008 . The crosstalk probability increases linearly with over-bias and as expected the silicon photomultiplier 2 SPM2 design has a higher crosstalk .