Visible Light Photon Counters Research Articles

Single-Photon Detection Timing Jitter in a Visible Light Photon Counter

Visible light photon counters (VLPCs) offer many attractive features as photon detectors, such as high quantum efficiency and photon number resolution. We report measurements of the single-photon timing jitter in a VLPC, a critical performance factor in a time-correlated single-photon counting measurement, in a fiber-coupled closed-cycle cryocooler. The measured timing jitter is 240 ps full-width-at-half-maximum at a wavelength of 550 nm, with a dark count rate of 25 000 counts per second. The timing jitter increases modestly at longer wavelengths to 300 ps at 1000 nm, and increases substantially at lower bias voltages as the quantum efficiency is reduced.

Enhanced quantum efficiency of the visible light photon counter in the ultraviolet wavelengths

The visible light photon counter (VLPC) is a very high quantum efficiency (QE, 88% at 694 nm) single photon detector in the visible wavelengths. The QE in the ultraviolet (UV) wavelenghths is poor in these devices due to absorption in the degenerate front contact. We introduce the ultraviolet photon counter (UVPC), where the QE in the near UV wavelength range (300-400 nm) is dramatically enhanced. The degenerate Si front contact of the VLPC is replaced with a Ti Schottky contact, which reduces the absorption of incident photons within the contact layer. We demonstrate a system QE of 5.3% at 300 nm and 11% at 370 nm for a UVPC with a Ti Schottky contact and a single layer MgF(2) antireflection coating.

The MICE scintillating-fibre tracker

The international Muon Ionization Cooling Experiment (MICE) collaboration will carry out a systematic investigation of the ionization cooling of a muon beam. An ionization cooling channel is required to compress the phase-space volume occupied by the muon beam prior to acceleration in the baseline conceptual designs for both the Neutrino Factory and the Muon Collider. Muons entering and leaving the cooling channel will be measured in two solenoidal spectrometers, each of which is instrumented with a scintillating-fibre tracker. Each tracker is composed of five planar scintillating fibre stations, each station being composed of three planar layers of 350 micron scintillating fibres. The devices will be read out using the Visible Light Photon Counters (VLPCs) developed for use in the D0 experiment at the Tevatron. The design of the system will be presented along with the status of the tracker-construction project. The expected performance of prototypes of the full tracker will be summarised.

Generation of photon number states

The visible light photon counter (VLPC) has the capability to discriminate photon number states, in contrast to conventional photon counters which can only detect the presence or absence of photons. We use this capability, along with the process of parametric down-conversion, to generate photon number states. We experimentally demonstrate generation of states containing 1, 2, 3 and 4 photons with high fidelity. We then explore the effect the detection efficiency of the VLPC has on the generation rate and fidelity of the created states.

Gain dispersion in visible light photon counters as a function of counting rate

We present measurements of light signals using visible light photon counters (VLPC), that indicate an increase in gain dispersion as the counting rate increases. We show that this dispersion can be understood on the basis of a recent observation of localized field reduction in VLPCs at high input rates.

Localized field reduction and rate limitation in visible light photon counters

We observe the effect of localized field reduction (LFR) in visible light photon counters (VLPCs) by measuring the bias current of the device after a light pulse, and find it consistent with being produced by avalanches that have an average transverse dimension of ≈12μm2. The characteristic recovery time for the device after an avalanche is measured to be ≈3.5ms, and is a function of bias voltage and temperature. A simple model is presented to describe the performance drop of the VLPCs with rate as a consequence of LFR.

Concept of High Speed Astronomical Instrumentation Based on Visible Light Photon Counters

The domain of high speed optical astrophysics is still quite unexplored. The availability of 10 meter diameter telescopes offers the unique possibility to investigate variability of faint objects at submillisecond time scales. In this paper I describe the concepts of a photometer and a spectrometer for high speed astronomical observations. The instruments are based on a photon counting detector developed for high energy physics, the Visible Light Photon Counter (VLPC). The detector has a quantum efficiency in the visible as high as 88% and performs photon counting with sub microsecond time resolution. The photometer is built using VLPC arrays. Adding a grating a VLPC array can be used in a time resolved spectrograph with medium resolution. This paper develops, starting from experimental data, the concept of the two VLPC based instruments and their application to time resolved photometry and spectroscopy of compact objects (pulsars, cataclysmic variables, low mass X-ray binary systems etc) and optical counterparts of Gamma Ray Bursts. The high speed optical observations are the ideal complement to X/γ rays and gravitational wave studies. The application of the instruments to the optical photometry of pulsars, the spectrophotometry of the prompt optical flash from Gamma Ray Bursts and the study of binary systems are discussed in detail: in the last two applications the instruments offer better opportunities than existing instruments.

Observation of fast scintillation of cryogenic PbI/sub 2/ with VLPCs

At cryogenic temperatures (/spl sim/10 K), undoped lead iodide (PbI/sub 2/) has material and scintillation properties that are very attractive for positron emission tomography (PET). However, the PbI/sub 2/ emissions are quenched at temperatures >40 K, so close optical coupling between the scintillator and photodetector requires a photodetector that also operates at cryogenic temperatures. This suggests the visible light photon counter (VLPC), which operates at similar temperatures and combines high gain and high quantum efficiency. We proximity couple (0.001 in air gap) PbI/sub 2/ crystals with 1.0-2.5 mm dimensions to a 1 mm diameter VLPC and cool the system to 8.5 K. Signals with short (<10 ns) duration are observed. When excited with 511 keV photons, a coincidence timing resolution of 1.3 ns full-width at half-maximum is measured. While a clear photopeak is observed for 122 keV excitation, no clear photopeak is seen under 511 keV excitation (possibly due to the poor optical quality of the PbI/sub 2/ crystals). While the present configuration must be scaled-up considerably, a cryogenic PbI/sub 2//VLPC combination may eventually become the basis for a practical time-of-flight PET camera.

High-efficiency photon-number detection for quantum information processing

The visible light photon counter (VLPC) features high quantum efficiency (QE) and low pulse height dispersion. These properties make it ideal for efficient photon-number state detection. The ability to perform efficient photon-number state detection is important in many quantum information processing applications, including recent proposals for performing quantum computation with linear optical elements. In this paper, we investigate the unique capabilities of the VLPC. The efficiency of the detector and cryogenic system is measured at 543 nm wavelengths to be 85%. A picosecond pulsed laser is then used to excite the detector with pulses having average photon numbers ranging from 3-5. The output of the VLPC is used to discriminate photon numbers in a pulse. The error probability for number state discrimination is an increasing function of the number of photons, due to buildup of multiplication noise. This puts an ultimate limit on the ability of the VLPC to do number state detection. For many applications, it is sufficient to discriminate between 1 and more than one detected photon. The VLPC can do this with 99% accuracy.

Hybrid photon detectors

Abstract Hybrid photon detectors detect light via vacuum photocathodes and accelerate the emitted photoelectrons by an electric field towards inversely polarized silicon anodes, where they are absorbed, thus producing electron–hole pairs. These, in turn, are collected and generate electronic signals on their ohmic contacts. This review first describes the characteristic properties of the main components of hybrid photon detectors: light entrance windows, photocathodes, and silicon anodes. Then, essential relations describing the trajectories of photoelectrons in electric and magnetic fields and their backscattering from the silicon anodes are derived. Depending on their anode configurations, three families of hybrid photon detectors are presented: hybrid photomultiplier tubes with single anodes for photon counting with high sensitivity and for gamma spectroscopy; multi-anode photon detector tubes with anodes subdivided into square or hexagonal pads for position-sensitive photon detection; imaging silicon pixel array tubes with finely segmented anodes for photon-sensitive imaging devices. Some of the hybrid photon detectors’ applications and achievements in radiation detection are discussed and compared with competing devices such as photomultipliers, image intensifiers, photodiodes, silicon drift chambers, charge coupled devices, visible light photon counters, and photographic emulsions.

Characterization and performance of visible light photon counters (VLPCs) for the upgraded DØ detector at the Fermilab Tevatron

The upgraded DØ detector at the Tevatron collider will use about 100 000 pixels of Visible Light Photon Counters (VLPCs) readout for its scintillating fiber tracker and preshower detectors. VLPCs are solid state photodetectors that are operated at the temperature of a few degrees Kelvin, capable of detecting single photons. All VLPC chips were characterized in the presence of a 20 MHz background of photoelectrons. The acceptance rate was 87%. The operating bias ranges from 5.8 to 8.0 V, the gain from 20 000 to 60 000, and the threshold from 5 to 15 fC. All 8 pixels belonging to one chip have very similar efficiencies, thresholds and gains.

Cosmic-ray tests of the DØ preshower detector

The DØ preshower detector consists of scintillator strips with embedded wavelength-shifting fibers, and a readout using Visible Light Photon Counters. The response to minimum ionizing particles has been tested with cosmic-ray muons. We report results on the gain calibration and light-yield distributions. The spatial resolution is investigated taking into account the light sharing between strips, the effects of multiple scattering and various systematic uncertainties. The detection efficiency and noise contamination are also investigated.

The new scintillating fiber detector of E835 at Fermilab

A cylindrical scintillating fiber detector for the measurement of the polar coordinate /spl theta/ has been built for experiment E835 at Fermilab. This is the first detector used in a high-energy physics experiment that exploits scintillating fibers and visible light photon counters (VLPCs). It combines the high granularity, flexibility, and fast response of the scintillating fibers with the high quantum efficiency of the VLPCs. Complete results about tracking resolution, detection efficiency, time resolution, long-term stability, and reliability are given.

The new scintillating fiber detector of E835 at Fermilab

The scintillating fiber tracker for the measurement of the polar coordinate θ for experiment E835 at Fermilab has been upgraded, by adding two extra layers (240 fibers each), at R ≈9 cm from the beam axis. Photons from the fibers are detected by Visible Light Photon Counters (VLPCs). The high granularity, flexibility and fast response of the scintillating fibers, combined with the high quantum efficiency of the VLPCs, allow high rate capability, high efficiency, good tracking and time resolution. Signals from the outer two layers are used to provide θ information to the first-level trigger.

The Fermilab E835 scintillating fiber detector

A cylindrical scintillating-fiber tracker for the measurement of the polar coordinate θ has been built for experiment E835 at Fermilab. This detector combines the high granularity, flexibility and fast response of the scintillating fibers with the high quantum efficiency of the Visible-Light Photon Counters (VLPC). Complete results about the tracker performance are given: tracking and timing resolution, photoelectron yield per mip, detection efficiency single-double track discrimination.

Development of a high-quantum-efficiency single-photon counting system

A high-quantum-efficiency single-photon counting system has been developed. In this system, single photons were detected by a visible light photon counter operated at 6.9 K. The visible light photon counter is a solid state device that makes use of avalanches across a shallow impurity conduction band in silicon. Threefold tight shielding and viewports that worked as infrared blocking filters were used to eliminate the dark count caused by room-temperature radiation. Corrected quantum efficiencies as high as 88.2%±5% (at 694 nm) were observed, which we believe is the highest reported value for a single-photon detector. The dark count increased as the exponential of the quantum efficiency with changing temperature or bias voltage, and was 2.0×104 cps at the highest quantum efficiency.

Results from the E835 scintillating fiber detector

A cylindrical scintillating-fiber tracker for the measurement of the polar coordinate θ has been built for experiment E835 at Fermilab. This detector combines the high granularity, flexibility and fast response of the scintillating fibers with the high quantum efficiency of the Visible-Light Photon Counters (VLPC). Complete results about the tracker performance are given: tracking and timing resolution, photoelectron yield per mip, detection efficiency, single–double-track discrimination.

The E835 scintillating fiber tracking detector

This paper describes the scintillating fiber tracking detector designed and built for the Fermilab experiment E835. This detector uses Visible Light Photon Counters (VLPC) readout system and is in use at the p ¯ accumulator ring at Fermilab. A description of the components of the detector and preliminary results of its performances are given.

Time resolution and linearity measurements for a scintillating fiber detector instrumented with VLPCs

The time resolution for charged particle detection is reported for a typical scintillating fiber detector instrumented with Rockwell HISTE-IV Visible Light Photon Counters (VLPC). The resolution measurements are shown to agree with a simple Monte-Carlo model, and the model is used to make recommendations for improved performance. In addition, the gain linearity of a sample of VLPC devices was measured. The gain is shown to be linear for incident light intensities which produce up to approximately 600 photoelectrons per event.

Scintillating pad detectors

We have been investigating the performance of scintillating pad detectors, individual small tiles of scintillator that are read out with wavelength-shifting fibers and visible light photon counters, for application in high luminosity colliding beam experiments such as the DO Upgrade. Such structures could provide "pixel" type readout over large fiducial volumes for tracking, preshower detection and triggering.