Hybrid Photodiode Research Articles

Testbeam results on particle identification with aerogel used as RICH radiator

We present the results obtained by exposing samples of silica aerogel of different thickness and optical properties to pion and proton beams with momenta between 6 and 10 GeV/c in the PS testbeam facility at CERN. Two large diameter pad hybrid photodiodes with 2048 channels, produced at CERN, have been used as photon detectors. Separate Cherenkov rings produced by the different particles were reconstructed obtaining pion/proton separation over the whole momentum range. The number of photoelectrons was measured as a function of aerogel thickness and was found to be in agreement with Monte Carlo expectations.

X-Y position readout of a YAP:Ce crystal matrix using wavelength-shifting fibers

A set of preliminary test results of a detector prototype for positron emission tomography applications is presented. The detector is made of a YAP:Ce finger crystal (2/spl times/2/spl times/30 mm/sup 3/ each) matrix coupled to a set of square section wavelength-shifting fibers (one fiber for each matrix row and one fiber for each matrix column) read by a position-sensitive detector. The recognition of each fiber allows the determination of the x-y position of the scintillation event. The light yield of the system has been investigated: all possible light loss factors have been taken into account to evaluate the expected signal. Experimental measurements with a single-pixel hybrid photodiodes have been performed. We have measured about ten photoelectrons for a deposit of 511 keV in the scintillator for each coordinate. Preliminary position measurements with a small 5/spl times/5 matrix are presented.

Position reconstruction in a scintillator coupled to proximity focused HPDs using the light division method

The light generated by an ionizing particle crossing a scintillator is collected by means of light guides coupled to two proximity focused Hybrid Photo Diodes (HPDs) and used to measure the position along the slab. Two scintillators with dimensions (20×3.1×0.23) cm 3 and (60×5×0.5) cm 3 have been tested with a collimated 90 Sr source. The relation between reconstructed position and nominal position of the source is linear through all the scintillator length. The accuracy in the position depends on the attenuation length, the number of photoelectrons and the signal-to-noise ratio of the HPD. The resolutions obtained with a MIP for the two slabs are σ z=3.8 cm and σ z=15.9 cm , respectively. This method will be used in the inner scintillator array of the FINUDA experiment.

A prototype RICH detector using multi-anode photo multiplier tubes and hybrid photo-diodes

The performance of a prototype Ring Imaging Cherenkov Detector is studied using a charged particle beam. The detector performance, using CF 4 and air as radiators, is described. Cherenkov angle precision and photoelectron yield using hybrid photo-diodes and multi-anode PMTs agree with simulations and are assessed in terms of the requirements of the LHCb experiment.

Performance of a prototype RICH detector using hybrid photo-diodes

A prototype Ring-Imaging Cherenkov detector has been operated in a charged particle test beam. Cherenkov photons are imaged onto a plane of hybrid photo-diode detectors. The geometrical arrangement of the prototype and data-taking conditions are described. An analysis of the detector performance, using silica aerogel, air and C 4F 10 gas radiators, is presented. The photon yields and observed Cherenkov angle resolutions are found to be in good agreement with Monte Carlo simulation and satisfy the requirements of the RICH 1 detector in the LHCb experiment.

Performance results of a prototype depth-encoding PET detector

The results of a feasibility study for a high-resolution PET detector system are presented. The detector is based on the use of etched LSO scintillation crystals viewed from just one end. The authors have demonstrated that this configuration yields Depth-of-Interaction (DOI) information whilst also preserving good energy and coincidence-time resolution. A prototype detector was built using a 4/spl times/4 crystal array coupled to 61-pixel hybrid photodiodes. The measurements demonstrate a DOI resolution of 5/spl sim/7 mm FWHM in a 30 mm deep detector. The signal level was measured to be in the range 250 to 600 photoelectrons depending on the location of the 511 keV energy deposit in the crystal. A resolving-time of less than 5 ns FWHM was estimated based on indirect measurements. The technique depends on the assumption that all of the events detected above a selected threshold value are, in fact, full-energy deposits. The validity of this assumption and the impact of the photons scattered in the object have been studied using a Monte Carlo simulation of the proposed small animal PET imager.

RICH detectors for the LHCb experiment

The LHCb experiment is being designed to study CP violation in the B-meson system. It differs from other LHC experiments in its requirement for an excellent π/K separation in the momentum range 1– 150 GeV/c . This is accomplished by two RICH counters: RICH1 has a 5 cm-thick aerogel radiator and a 95 cm-long C 4F 10 radiator, while RICH2 has a 180 cm-long CF 4 radiator. Cherenkov photons are focused by spherical mirrors onto photodetectors. Three photodetector options are under study: a 127 mm diameter Pad Hybrid Photodiode (HPD) with a 2048 silicon pad sensor and analog readout, a 80 mm diameter Pixel HPD with a 1024-pixel silicon sensor and binary readout, and Hamamatsu's multianode photomultiplier (MaPMT). Recent test beam results on the performance of both RICH and photodetector prototypes show good agreement with the design. Cherenkov ring pattern recognition based on a global log-likelihood method is being developed to satisfy the hadron identification requirements.

An evaluation of the new compact hybrid photodiodes R7110U-07/40 from Hamamatsu in high-speed light detection mode

The main parameters of hybrid photodiodes (HPD) are constantly improving. In the new 20mm ∅ HPDs from Hamamatsu an avalanche diode (AD) serves as anode. Due to high gain of the used ADs the HPDs show a total gain of 6−8×104 at nominal HV. This allows one to use HPDs with very fast low-noise voltage amplifiers and to detect fast pulses (down to the single photoelectron level) with very good amplitude resolution. Of special interest are HPDs of the type R7110U-40 with GaAsP photocathode which provide a quantum efficiency of ∼40% in maximum at ∼500nm. Results on the evaluation of the above-mentioned HPDs and their comparison with HPDs from INTEVAC will be presented.

Magnetic field effects on Hybrid PhotoDiode single electron response

Hybrid PhotoDiodes (HPDs) are very simple photo detectors which cover the applicability field of Photo Multipliers but show some better features. In particular HPDs show a very good photon counting capability, due to their peculiar one-stage gain process. It was found that HPD's photoelectron spectrum has a low-energy continuum which could be attributed to a backscattering process from the diode surface. In order to clearly distinguish the exact role of backscattering, the single photoelectron response (SER) of a 61 pixel proximity focused HPD was measured in standard conditions and in a 5 kG axial magnetic field. The results clearly indicate that the backscattering process gives the greatest contribution to the low-energy continuum spectrum. Monte Carlo simulations, using the EGS4 code, supported the analysis and allowed some interpretation of the effect, which greatly depends on diode surface characteristics, such as contact layer thickness.

HPD for linear colliders

Hybrid Photo Diode (HPD) is an attractive photodevice with many advantages. The HPD is considered as a candidate photodevice for the calorimetry in future linear collider experiments. HAPD, which uses avalanche photo diode (APD) as the anode is very useful for its much larger gain than usual HPDs. We report results of R&D on Hamamatsu R7110U HAPD.

Highly segmented large-area hybrid photodiodes with bialkali photocathodes and enclosed VLSI readout electronics

We report on the principles, design, fabrication, and operation of a highly segmented, large-area hybrid photodiode, which is being developed in the framework of the LHCb RICH project. The device consists of a cylindrical, 127 mm diameter vacuum envelope capped with a spherical borosilicate UV-glass entrance window, with an active-to-total-area fraction of 81%. A fountain-focusing electron optics is used to demagnify the image onto a 50 mm diameter silicon sensor, containing 2048 pads of size 1×1mm2. The sensor pads are read out by 16 analogue multiplexed readout chips enclosed in the vacuum envelope. A large ultra-high vacuum plant for the evaporation of visible-light transmittive bialkali (K2CsSb) photocathodes and subsequent tube encapsulation has been built and successfully operated. The characteristics and performance of the first HPDs have been measured to be in full agreement with expectations.

A compact readout system for multi-pixel hybrid photodiodes

The excellent properties of the recently developed multi-pixel hybrid photodiodes (M-HPD) will be easier to exploit following the development of the new hybrid read-out circuits described in this paper. This system will enable all of the required read-out functions to be accommodated on a single board into which the M-HPD is plugged. The design and performance of a versatile system is described in which a trigger-signal, derived from the common-side of the silicon anode in the M-HPD, is used to trigger the readout of the 61-anode pixels in the M-HPD. The multi-channel amplifier section is based on the use of a new, commercial VLSI chip, whilst the read-out sequencer uses a chip of our own design. The common anode signal is processed by a fast amplifier and discriminator to provide a trigger signal when a single event is detected. In the prototype version, the serial analogue output data-stream is processed using a PC-mounted, high speed ADC. Results obtained using the new read-out system in a compact gamma-camera and with a small muon tracking-chamber demonstrate the low-noise performance of the system. The application of this read-out system in other position-sensitive or multi-anode photomultiplier tube applications are also described.

Development of a micro-array-type electron multiplier

This paper describes the development of a micro-array-type electron multiplier (MAEM) and its application to preamplification of a hybrid photo diode (HPD) system. The MAEM consists of several dynode plates fabricated by micromachining techniques. In our simulation of the electron multiplication process in the HPD system, 4500 gain is easily obtained with the total voltage of 6 kV. No spread of electron charges into the neighboring channels is observed in the MAEM device. Consequently, very high position resolution can be achieved if the pixel-type PD is used with the MAEM. The simulation also showed small fluctuation of the electron transit time of 23 ps in the MAEM, thus very high timing resolution can be achieved.

Large area hybrid photodiodes

Hybrid Photodiodes (HPD) represent one of the most promising options for high granularity single photon detection. HPD's are photodetectors consisting of a photocathode, which is deposited on the inner side of the entrance window, and a solid state sensor encapsulated in a vacuum envelope. HPD's combine the high sensitivity of photomultiplier tubes with the excellent space and energy resolution of solid state detectors. After reviewing the physical principles of HPD's the article gives a short overview of the history of this detector. A number of commercially available devices will be discussed. Current and future applications in high energy physics lie in the fields of scintillator readout (calorimetry, fibre tracking) and Cherenkov light detection. It is for the latter application that various large area Hybrid Photodiodes are currently under development.

A fast preamplifier for proximity focused HPDs

Abstract The proximity focused hybrid photo diode (HPD), a new type of light detector insensitive to uniform magnetic fields, will be employed in the inner region of the FINUDA detector coupled to a simple, cheap, low noise and low input impedance fast preamplifier (PA): the design and the performances are presented and discussed.

Development of RICH detectors and large-area hybrid photodiodes for the LHCb experiment

The LHCb experiment is being designed to study CP violation in the B meson sector. It differs from other LHC experiments in its excellent particle identification capability. This is accomplished by two focused RICH counters: RICH 1 has 5 cm thick aerogel and 95 cm long C 4F 10 radiators while RICH 2 uses 180 cm long CF 4 radiator. The combined system will give π/K separation in the momentum range 1–150 GeV/ c. Spherical mirrors are used to focus the Cherenkov light on detection planes equipped with photodetectors. One photodetector option is the large-area Hybrid Photodiode (HPD). An HPD consists of a cylindrical vacuum envelope of 127 mm diameter capped with a spherical borosilicate glass entrance window. Electrodes demagnify the image onto a silicon sensor comprising 2048 pads, each with a surface of 1 mm 2. A large UHV evaporation plant for the production of HPDs with visible light bialkali photocathodes (K 2CsSb) has been built and successfully operated producing photocathodes with good quantum efficiency and stability. A Cold Indium sealing technique has been developed and proven to provide excellent vacuum tightness.

Evaluation of the performances of the FINUDA inner trigger detector

A barrel detector of 12 thin scintillator slabs viewed by Hybrid Photo Diodes (HPDs) will be employed in the interaction region of the FINUDA experiment as inner trigger detector. This device, designed to work in a 1.1 T uniform magnetic field, will provide a fast first level trigger to discriminate ( K +, K −) pairs from Φ decay from background events, the common stop for drift chambers and straw tubes and the start signal for Time-of-Flight (ToF) measurements. The performances of a module tested with a 90 Sr radiation source, are presented.

Latest beam test results from RICH prototypes using hybrid photo detectors and multi anode PMTs

Beam tests were performed in 1998 to investigate the performance of a prototype of the downstream RICH of the LHCb using hybrid photo-diodes and multi anode PMTs. The angular resolutions obtained from these photodetectors under various experimental configurations are compared with the expectations from simulation.

Evolution of the RICH technique

This paper presents recent advances in development of Ring Imaging Cherenkov counters. Work on bare and protected reflective CsI photocathodes is reviewed and compared with gaseous UV photosensors. Development of multipixel-visible light-vacuum photosensors allows much improved Cherenkov angular resolution (by factor 10) relative to the available gaseous UV photosensors. The Hybrid PhotoDiode and MultiAnode PMT concepts are reviewed with prototype realizations described and test results compared with expectations. The use of the Gas Electron Multiplier (GEM) with gaseous RICH counters is presented and discussed. Its advantages for single electron detection are shown by new experimental data.

The AQUA-RICH atmospheric neutrino experiment

We describe a 125 m diameter spherical detector containing 1 Mt of water, capable of high rate observation of atmospheric neutrino events (30 000/y). The ring imaging Cherenkov (RICH) technique is used to measure velocity, momentum and direction of particles produced by neutrinos interacting in water. The detector will be sited outdoors (under a 50 m water shield) in a natural (further excavated) pit, probably in Sicily. Spherical reflecting mirrors focus Cherenkov light produced by secondaries from interacting neutrinos. Photons are detected by 5310 hybrid photodiodes (HPDs) of 1 m diameter each with 396 pads of 45×45 mm 2 on the photocathode surface, demagnified to 9×9 mm 2 on the silicon sensor. For most tracks the ring width will be dominated by multiple scattering which should allow momentum to be determined. Hadrons of momentum p≤5 GeV/ c can be measured with σ p / p≤7% and muons of p≤32 GeV/ c with σ p / p≤1%. The ring center determines track direction with σ θx, σ θy≈6 mrad. Track reconstruction in water will require time resolution σ t <1 ns. Detection of oscillating muon signals (disappearance) is feasible with atmospheric neutrinos and precision measurement of oscillation parameters is feasible for 10 −2≤Δ m 2≤10 −4eV 2. Tau or sterile neutrino appearance experiments are also possible with atmospheric neutrinos. Other physics topics addressable with this detector are proton decay, supernova detection and search for astrophysical neutrino sources. A first test module of 3 tons water and 120 PMs (32 mm φ) will operate (5/99) with 1–3 GeV muons in a CERN-PS test beam to verify the momentum algorithm. A second (6 m) 3 test module with 216 tons of water and 25 HPDs (0.25 m φ) is designed to observe full multi-track images and test pattern recognition and ring reconstruction algorithms.