The Optically-Coupled Current-Mirror (OCCM) is a novel feedback circuit architecture that allows linear transmission of analog signals via optical fibers. Its most distinctive feature is that the ...input stage is galvanically isolated and passive, as it consists just on the back-to-back connection of a LED and a photodiode. Only those components are required to be in close contact with the detector, and no power supply is required to be brought to the input stage. All active components are located at a safe distance, therefore saving them from being exposed to radiation, as it is common in most experiments at particle accelerators. We have investigated the properties of the OCCM when its passive input stage is cooled to cryogenic temperatures. Results have been extremely interesting as, for instance, the sharp increase in open-loop gain observed when cooling to 77 K, due to an enhanced LED efficiency. This translates into a higher dynamic range and still better linearity, opening new opportunities for the transmission of current signals generated in cryogenic detectors.
The transmission of analog signals via fiber optics is a subject of interest for applications with detectors operating at cryogenic temperature, at ground or on space borne instruments. For those ...detectors, both thermal and galvanic decoupling shall be required. For a better understanding of the cryogenic performance of cooled optoelectronic devices, we have investigated an infrared AlGaAs LEDs, a Si p-i-n photodiode, a Si photodiode, and an avalanche photodiode (APD). Results of a study related to the photodiode's dark currents at low temperature is presented. In fact, we have clearly measured a strong reduction of the dark current when these devices are cooled down
During the investigation of cryogenic properties of recently developed Ge JFETs we have applied the technique known in literature as low frequency noise versus temperature spectroscopy (LFN versus ...T). Using this method we have determined the energy levels of traps associated to Lorentzian noise found in the 30 to 40 K temperature range. To perform this task we have developed a computer-controlled experimental setup able to set the temperature within /spl plusmn/5 mK in the range 4 to 300 K during a spectral noise measurement. An approach for the calculation of the uncertainties that affect the evaluation of traps parameter is presented.
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 x 10(19) electron volts ...and the positions of active galactic nuclei (AGN) lying within approximately 75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar spatial distribution are possible sources.
The scintillation yields of CaF
2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these ...studies we have constructed the first “scintillating bolometer” where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from
α-particles in the energy region of interest for searches on double beta decay of
48Ca can be achieved.
An optocoupler with differential input and balanced output was realized to make galvanic decoupling of a particle detector located in a high common mode disturbance environment. The circuit ...configuration incorporates a true differential optocoupled feedback, with low bias current in LEDs and photodiodes. The present circuit improves by a factor two the dynamic range of a previous solution. Large Common Mode (CMRR) and Power Supply (PSRR) Rejection Ratio, low crossover distortion, high dynamic range, low noise and power dissipation have been achieved.
The optically coupled current mirror (OCCM) is a novel optoelectronic architecture that replicates at ground potential a current flowing in an isolated conductor. The mirroring action is done without ...need to bring any power to the potential of the conductor where the current flows, as its input stage is completely passive. This feature is particularly important when the conductor is at high voltage (HV), a typical case being the photomultiplier tubes (PMTs) biased with positive HV, or when the number of channels is very large as it is the case of many particle physics experiments. The OCCM has been used to equip the two prototype telescopes, each one comprising 440 PMTs, of the ultra-high-energy cosmic-ray experiment Pierre Auger. Despite that the PMT's anodes were at HV, the DC or slowly varying component of the anode current was measured with high resolution, clearly revealing the presence of faint stars, planets, and other similar objects which determine the sky background light. In this paper we describe the principle of operation of the OCCM and its application to the measurement of the anode current of PMTs biased with cathode grounded, as well as the first results obtained with the OCCM on linear transmission of 2-/spl mu/s-width pulses, via fiber optics.
The fluorescence detector (FD) of the Southern Pierre Auger Observatory consists of four groups of six telescopes, concentrated in four different buildings at the periphery of the 3000 km/sup 2/ ...observatory site. Each telescope consists of a 3.5/spl times/3.5-m/sup 2/ mirror of 3.4-m radius, an aperture of 2.2-m diameter covered by a UV filter, a corrector ring in its periphery, and an array of PMTs, disposed as a matrix of 20 columns by 22 rows in its focal surface. The pointing accuracy should be verified regularly during the whole life of the experiment, estimated to be about 20 years. Recording background-light tracks left by stars gives important information for this scope. In addition, the response along known tracks of many PMTs can be mapped by averaging the signals left by the same star in different nights. During the engineering array phase of the experiment, all PMTs have been equipped with the optically-coupled current-mirror, a novel optoelectronic system developed to perform a highly sensitive measurement of the dc or slowly varying component of the anode current, despite the fact that the PMT is biased with cathode grounded. We proved that the FD telescopes are extremely sensitive, even to 5.4 visual magnitude stars that could be clearly recorded despite the fact that a UV filter was present at the telescope aperture.
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