Multi-pixel photon counter (MPPC) has been widely used in the field of weak light detection due to their various advantages in recent years. However, their parasitic effects such as optical crosstalk limit their further improvement in photoelectric performance. A deep understanding of the generation and propagation mechanism of optical crosstalk in MPPC is one of the prerequisites for further improving the performance of MPPC. The mechanism of the non-uniform spatial distribution phenomenon of the prompt optical crosstalk effect (POCE) in MPPC was investigated in-depth. The experimental results show that the optical crosstalk probability (Pct) in MPPC without optical isolation trench shows obviously non-uniformity within the avalanche photo diode (APD) cell, nevertheless, for the MPPC with optical isolation trench, the uniformity of spatial distribution of Pct in APD cells is greatly improved. Therefore, the different propagation distances of crosstalk photons emitted from different positions of the source APD cell to the nearest neighbor APD cell along a straight line, are the main reason of non-uniform spatial distribution of Pct in MPPC. According to the experimental results, it can also be inferred that the emission of crosstalk photons is spatially localized during an avalanche of an APD cell, and most of the crosstalk photons are emitted during the early stage of the avalanche. The results of this paper not only have reference value for further understanding the mechanism of optical crosstalk effect in MPPC, but also be beneficial for guiding to optimize the structure and process design of MPPC, and thus improving the performance of MPPC.
Raman spectrometry was employed to study the characteristics of Raman spectra of polyethylene terephthalate (PET), which were treated with sodium hydroxide, sulfuric acid and copper sulfate, respectively. Raman spectra under different conditions were obtained and the characteristics of the Raman spectra were analyzed. The morphology structures were observed under different conditions using Atomic Force Microscope. The results show that the spectral intensity of PET treated with sodium hydroxide is higher than that untreated between 200-1750 cm-1, while the intensity of PET treated with sodium hydroxide is lower than that untreated beyond 1750 cm-1 and the fluorescence background of Raman spectra is decreased. The spectral intensity of PET treated with sulfuric acid is remarkably reduced than that untreated, and the intensity of PET treated with copper sulphate is much higher than that untreated.
In this work it is shown the benefit of using waveform integration of the avalanche pulses of MPPC for enhancing the photon number resolving capability of Multi-Pixel Photon Counter (MPPC). Up to 47 photon equivalent peaks can be distinguished in the Photon-Number-Resolving (PNR) spectrum with a repetition frequency of 80 MHz, which is the largest reported number obtained at room temperature as far as we know.
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