Cooled SPAD array detector for low light-dose fluorescence laser scanning microscopy

The single-photon timing and sensitivity performance and the imaging ability of asynchronous-readout single-photon avalanche diode (SPAD) array detectors have opened up enormous perspectives in fluorescence (lifetime) laser scanning microscopy (FLSM), such as super-resolution image scanning microscopy and high-information content fluorescence fluctuation spectroscopy (FFS). However, the strengths of these FLSM techniques depend on the many different characteristics of the detector, such as dark-noise, photon-detection efficiency, after-pulsing probability, and optical-cross talk, whose overall optimization is typically a trade-off between these characteristics. To mitigate this trade-off, we present a novel SPAD array detector with an active cooling system, which substantially reduces the dark-noise without significantly deteriorating any other detector characteristics. In particular, we show that lowering the temperature of the sensor to -15°C significantly improves the signal-to-noise ratio due to a 10-fold decrease in the dark-count rate compared to room temperature. As a result, for imaging, the laser power can be decreased by more than a factor of three, which is particularly beneficial for live-cell super-resolution imaging, as demonstrated in fixed and living cells expressing GFP-tagged proteins. For FFS, together with the benefit of the reduced laser power, we show that cooling the detector is necessary to remove artifacts in the correlation function, such as spurious negative correlations observed in the hot elements of the detector, i.e., elements whose dark-noise is substantially higher than the median value. Overall, this detector represents a further step towards the integration of SPAD array detectors in any FLSM system.

Robust diagnostics of dark counts for quantum networks

In this work, we study timestamps when registering counts of single-photon detectors in quantum communications. Post-pulse counts are analyzed based on several approaches. Explicit statistical accounting of the noise of quantum detectors allows you to most correctly select the mode of use of the detectors to realize the most efficient quantum communication with the highest signal to noise ratio. Direct statistical analysis and robust diagnostics of the noise of quantum detectors can be done by ranging the time's tags of quantum keys that are available for the online diagnostic system and analysis a significant amount of information about the quantum communication performance (the amount of dark noise and post-pulse counts, line interference, etc.). The conclusion is made about the proportion of dark noise and post-pulse counts in the total noise, and the limits of applicability of the theory are shown using a sequence of the ranged amplitudes. We offer non-parametric robust diagnostic of times tags in keys to increase the security of quantum networks, and also discuss the prospects of commercializing quantum-classical cloud-based security services.

Dark noise and retinal degeneration from D190N-rhodopsin

Numerous rhodopsin mutations have been implicated in night blindness and retinal degeneration, often with unclear etiology. D190N-rhodopsin (D190N-Rho) is a well-known inherited human mutation causing retinitis pigmentosa. Both higher-than-normal spontaneous-isomerization activity and misfolding/mistargeting of the mutant protein have been proposed as causes of the disease, but neither explanation has been thoroughly examined. We replaced wild-type rhodopsin (WT-Rho) in RhoD190N/WT mouse rods with a largely “functionally silenced” rhodopsin mutant to isolate electrical responses triggered by D190N-Rho activity, and found that D190N-Rho at the single-molecule level indeed isomerizes more frequently than WT-Rho by over an order of magnitude. Importantly, however, this higher molecular dark activity does not translate into an overall higher cellular dark noise, owing to diminished D190N-Rho content in the rod outer segment. Separately, we found that much of the degeneration and shortened outer-segment length of RhoD190N/WT mouse rods was not averted by ablating rod transducin in phototransduction—also consistent with D190N-Rho’s higher isomerization activity not being the primary cause of disease. Instead, the low pigment content, shortened outer-segment length, and a moderate unfolded protein response implicate protein misfolding as the major pathogenic problem. Finally, D190N-Rho also provided some insight into the mechanism of spontaneous pigment excitation.

Instrument Radiometric Processing for Earh Observation Satellite Optical Payload

The radiometric calibration procedure, applied on VNREDSat-1 raw data shall correct and minimize the radiometric non-uniform gain and offset, occurred by the nature of the optical payload. The procedure is based on the radiometric model, built to transform the incoming radiance into camera output signal. Within this radiometric model, the radiometric parameters such as dark noise and pixel response non-uniformity shall be separated. The output signal of dark noise shall be measured by capturing image scene of the ocean at night. The output signal of pixel response non-uniformity shall be measured by capturing image scene of uniform radiance image scene such as the dessert or grass field. All the radiometric calibration parameter after calculated shall be saved into a calibration file, which is kept on the control station and image processing station.