Biophotons Contribute to Retinal Dark Noise

The discovery of dark noise in retinal photoreceptors resulted in a long-lasting controversy over its origin and the underlying mechanisms.Here,we used a novel ultra-weak biophoton imaging system（UBIS） to detect biophotonic activity（emission） under dark conditions in rat and bullfrog（Rana catesbeiana） retinas in vitro.We found a significant temperature-dependent increase in biophotonic activity that was completely blocked either by removing intracellular and extracellular Ca^（2＋）together or inhibiting phosphodiesterase 6.These findings suggest that the photon-like component of discrete dark noise may not be caused by a direct contribution of the thermal activation of rhodopsin,but rather by an indirect thermal induction of biophotonic activity,which then activates the retinal chromophore of rhodopsin.Therefore,this study suggests a possible solution regarding the thermal activation energy barrier for discrete dark noise,which has been debated for almost half a century.

Signal-to-noise ratio of Raman signal measured by multichannel detectors

Raman spectroscopy has been widely used to characterize the physical properties of two-dimensional materials(2DMs).The signal-to-noise ratio(SNR or S/N ratio)of Raman signal usually serves as an important indicator to evaluate the instrumental performance rather than Raman intensity itself.Multichannel detectors with outstanding sensitivity,rapid acquisition speed and low noise level have been widely equipped in Raman instruments for the measurement of Raman signal.In this mini-review,we first introduce the recent advances of Raman spectroscopy of 2DMs.Then we take the most commonly used CCD detector and IGA array detector as examples to overview the various noise sources in Raman measurements and analyze their potential influences on SNR of Raman signal in experiments.This overview can contribute to a better understanding on the SNR of Raman signal and the performance of multichannel detector for numerous researchers and instrumental design for industry,as well as offer practical strategies for improving spectral quality in routine measurement.

Consistency test of PMT SPE spectrum from dark-noise pulses and LED low-intensity light

Photomultiplier tube(PMT)has been an essential instrument for low background experiments,and the accuracy of single photoelectron(SPE)calibration will directly affect the energy reconstruction of the detector.The SPE spectrum can be acquired from the charge distribution of dark-noise pulses or the low-intensity light signal triggered by LED.However,there are arguments on whether the two methods are consistent.In this paper,the Hamamatsu R5912-20mod PMT and the EMID642KNFL PMT have been tested adopting the two methods with signal waveform recording electronics.As comparison,traditional charge-to-digital conversion system is also used to test SPE spectrum.The results show that they are consistent when the PMTs are working at typical recommended high voltage(HV).

Analysis of proton and γ-ray radiation effects on CMOS active pixel sensors

Radiation effects on complementary metal-oxide-semiconductor（CMOS） active pixel sensors（APS） induced by proton and γ-ray are presented. The samples are manufactured with the standards of 0.35 μm CMOS technology. Two samples have been irradiated un-biased by 23 MeV protons with fluences of 1.43 × 10^11 protons/cm^2 and 2.14 × 10^11 protons/cm-2,respectively, while another sample has been exposed un-biased to 65 krad（Si） ^60Co γ-ray. The influences of radiation on the dark current, fixed-pattern noise under illumination, quantum efficiency, and conversion gain of the samples are investigated. The dark current, which increases drastically, is obtained by the theory based on thermal generation and the trap induced upon the irradiation. Both γ-ray and proton irradiation increase the non-uniformity of the signal, but the nonuniformity induced by protons is even worse. The degradation mechanisms of CMOS APS image sensors are analyzed,especially for the interaction induced by proton displacement damage and total ion dose（TID） damage.

Characterization of 3-inch photomultiplier tubes for the JUNO central detector

Background Jiangmen Underground Neutrino Observation(JUNO)is one of the largest experimental facilities for neutrino detecting.As its main structure,the central detector contains 20 kiloton liquid scintillator filled in an acrylic shell,and there are 18,00020-inch photomultiplier tubes(PMTs)and 25,0003-inch PMTs covering the shell.Purpose As an independent photon detection system,3-inch PMTs have been required to have excellent resolution for the single photoelectron detection,high quantum efficiency,small transit time spread and low dark noise rate.Methods Two kinds of 3-inch PMTs from HZC Photonics and Hamamatsu have been investigated as candidates.A dedicated test system for 3-inch PMTs has been designed,and various characterization parameters have been studied.Conclusion The preliminary results show these PMTs can meet the requirements of JUNO.