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

A liquid helium cryostat has been designed and operated for the purpose of testing visible light photon counter (VLPC) chips at 6.5 K. To achieve the desired operational characteristics for the VLPC devices their operating temperature is restricted to 6.5 K +/− 0.1 K. They will be used in a scintillating fiber tracker being proposed as part of an upgrade of the DO detector at Fermilab. The final version of the scintillating fiber tracker will contain roughly 100000 VLPC channels. Two cryostats with identical thermal design (a 128 channel and a 3072 channel design) have been built to perform the initial VLPC testing. The heat transfer needed to maintain the VLPC at its operating temperature occurs by conduction across an annular helium gas gap to a liquid helium reservoir. Helium boiloff is used to intercept conduction heat leak to the liquid reservoir. ANSYS finite element heat transfer analysis was utilized in the thermal design of the cryostat. The cryostat design and thermal performance (predicted and measured) are presented.

This paper reviews the research work on the Visible Light Photon Counters (VLPC) that have been developed for the scintillating fiber tracking at high luminosity colliders and high rate fixed target experiments. The devices originated from the joint work between UCLA and Rockwell International Science Center. The VLPCs are capable of counting photons very efficiently down to a single photon level with high avalanche gain, producing pulses at very high rates with very short rise times. Due to small gain dispersions they can be used in counting photons with high quantum efficiencies, therefore they are excellent devices for charged particle tracking using small diameter scintillating plastic fibers. In this paper, fiber tracking for the CDF and D0 upgrades and a possible usage of the VLPC readout for the experiment E803 at Fermilab will be discussed.

The upgrade of the D/spl phi/ detector at Fermilab is scheduled to run in 1999. One component of the upgrade is a cylindrically shaped preshower detector, placed on the outside of a solenoidal magnet that will surround the tracking volume. The technology for this detector will be plastic scintillating strips, with axial wavelength shifting (WLS) fiber and Visible Light Photon Counter (VLPC) readout. The VLPCs, with their quantum efficiency of /spl sim/70%, perform much better than traditional photomultipliers. We have performed extensive tests on different detector variations; investigating different scintillators, WLS fibers, and construction techniques. Prototype modules were placed in a cosmic ray test stand and over 120000 clean events per detector variant were collected. The large event sample and superior performance afforded by the VLPCs allow precise characterisation of the detector response. In this paper, we present results of our test programs, including uniformity of response, yields and interchannel crosstalk. We have achieved effective attenuation lengths exceeding 11 meters and yields of 4.5 photoelectrons per millimeter of scintillator traversed. An additional factor of 2 increase in yield seems achievable.

The low signal to noise ratio produced by the VLPC (Visible Light Photon Counter) chip in the detection of a single photon necessitates the use of a filtering capacitor. Maximum performance of the filtering capabilities dictate the placement of the capacitor be as close to the VLPC chip as possible. However, the chip operates at extremely low temperatures (7K). In addition, available space within the VLPC cassette is limited. Therefore it is desired to find a capacitor which provides good temperature stability at cryogenic temperatures within a minimal space (e.g. surface mounted). This engineering note presents the results from a test of the effect of low temperature on surface mounted capacitors. Preliminary testing suggested that capacitors of the tantalum type would provide the best te mperature stability at cryogenic temperatures, therefore two different tantalum capacitors were tested. A ceramic capacitor was also included in the results as a comparison, even though preliminary results suggested the ceramic type would not provide sufficient temperature stability.

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 first investigate single photon generation, using a modified Hanbury-Brown Twiss (HBT) intensity interferometer to verify the single photon nature of the light. We then use a second VLPC to experimentally demonstrate generation of 2,3 and 4 photons with high fidelity. We investigate the effect of the detection efficiency of the VLPC on the generation rate and fidelity of the created states.

In photonic quantum computing and quantum information processing, photon number resolution is crucial for generating highly non-classical quantum states. Superconducting transition-edge sensors (TESs) are considered one of the most effective photon number-resolving detectors for this purpose. However, the current timing properties of TESs, such as timing jitter (a few ns) and recovery time (several hundred ns), are insufficient, limiting the operational speed of quantum applications. To address the potential for improving TES timing performance, we have proposed an improved calculation to derive TES timing jitter. Our calculations including the effect of the SQUID noise indicate that expanding the electrical bandwidth of the external voltage amplifier and optimizing the inductance to match that bandwidth, can significantly improve timing jitter. According to our model, timing jitter 1 ns FWHM is achievable with an input inductance of 0.35 nH and an electrical bandwidth of 1 GHz. Additionally, we have shown that with our TES and SQUID parameters, the lowest achievable timing jitter is approximately 0.71 ns FWHM. Achieving an even lower jitter would require a redesign aimed at further reducing the SQUID noise.

Non-repeatable positioning of transitions in the media (jitter) is one of the primary limiting factors in achieving higher linear density in magnetic recording. In a typical magnetic recording system, the primary sources of jitter are due to the finite grain size and the switching field distribution of the grains in the media. These contributions to jitter are generally referred to as the "written-in" contributions [1] . However, if the system that delivers the write field to the media itself has jitter, as all real-world systems will, then this "timing jitter" will also contribute to the total written-in jitter.

This engineering note documents the design of the control dewar and vacuum pump platform that is to be installed on the D-Zero detector. It's purpose is twofold. Firstly it is a summary and repository of the final design calculations of the structure. Secondly, it documents that design follows the American Institute of Steel Construction (AISC) manual and applicable OSHA requirements with respect to walking working surfaces. The information contained in the main body of this note is supported by raw calculations included as the appendix. The platform is a truss type frame strucrure constructed primarily of rectangular steel tubing. The upper platform is for support of the control dewar (cryogenic/electrical interface for the solenoid), visible light photon counter (VLPC) cryogenic bayonet can, and infrequently, personnel during the connection and disconnection of the detector to building services. Figure 1 shows a layout of the structure as mounted on the detector and with the installed equipment. The connection of the platform to the detector is not conventional. Two main booms cantilever the structure to a location outside of the detector. The mounting location and support booms allow for the uninhibited motion of the detector components.

With the demise of the Superconducting Supercollider (SSC) Project, there was great concern that the technological developments for that accelerator and its associated detectors might well be lost in the aftermath. In the case of scintillating fiber tracking, such as not been the case. During the period 1990--1993, several tracking technologies were under development for SDC, including Scintillating Fiber Tracking, Straw-tubes, and Microstrip Gas Chambers. In summer 1990, several members of the Fiber Tracking Group (FTG) proposed the use of Scintillating Fiber Tracking to the D0 experiment at Fermilab. This proposal was accepted, and D0 now is building a 75,000 fiber channel tracking detector with readout via Visible Light Photon Counters (VLPC) which were devices pioneered by the SDC Fiber Tracking Group. In addition, all the preshower detectors for D0 also make use of fiber readout (in this case waveshifting fibers) and VLPC for photosensing. In February 1993, a full 7 months prior to cancellation of the SSC project by Congress, the SDC experiment rejected scintillating fiber tracking for further development. Fortunately for all concerned, the D0 experiment had already embraced this technology, so this important detector concept could be further developed, refined, and utilized for physics experimentation. In early 2000, data will be taken with the D0 fiber tracker to study Top Quarks, Beauty Particles, Electroweak Physics, QCD phenomena, and to search for new phenomena. The University of Notre Dame has played a fundamental and seminal role in the development and implementation of this detector technology. R. Ruchti has served as cospokesman of the Fiber Tracking Group since its inception in 1989, and has been a pioneer of fiber tracking technology since 1980. In addition, at least one other experiment at Fermilab, E835, has utilized scintillating fibers with VLPC readout to study Charmonium in proton-antiproton collisions using a gas-jet target in the Tevatron antiproton accumulator ring. This fiber detector has been operated successfully for over 1 year of actual beam conditions.

The multi-photon counting capability of the Visible Light Photon Counter (VLPC), along with the process of parametric downconversion, is used to experimentally generate photon number states containing 1,2,3 and 4 photons with high fidelity.

Precise control and measurement of Laser–RF synchronization for Thomson-scattering X-ray source

Solar blind Al0.5Ga0.5N/AlN metal-semiconductor-metal photodetectors (MSM PDs) are characterized by means of photocurrent spectroscopy. In order to enhance the external quantum efficiency (EQE) at low bias voltages several strategies have been adopted including absorber layer thicknesses, electrode layout and metallization scheme. Analysis of experimental EQE-bias characteristics under top and bottom illumination conditions reveals (1) a correlation between EQE and electrode pair density for symmetric electrode designs and (2) a slight asymmetry of the EQE with respect to bias polarity for bottom-illuminated MSM PD consisting of electrode pairs with different electrode widths (asymmetric design) and (3) zero-bias operation for a-MSM PD consisting of electrode pairs with different metallization schemes. In addition, the combination of thin absorber layer and asymmetric electrode design leads to high EQE values under bottom illumination at very low voltages and zero-bias operation is achieved for the a-MSM detector. The zero-bias EQE of the a-MSM is further enhanced by combining the symmetric detector design with a high electrode pair density.

An investigation of the optimal relaxation oscillation damping for high-speed 850-nm vertical-cavity surface-emitting laser (VCSEL) under large signal operation is presented, using devices with K -factors ranging from 0.1 to 0.4 ns. Time-domain measurements of turn-on transients are used to quantify damping dependent rise times, overshoots, and signal amplitudes. Optical eye diagrams together with timing jitter and bit error rate measurements reveal a tradeoff between the rise time and the duration of the relaxation oscillations. To produce a high-quality eye at a specific data rate, a proper amount of damping is needed to simultaneously obtain sufficiently high bandwidth and low timing jitter. We found that for error-free transmission, a VCSEL with a 0.3 ns K-factor achieved the best receiver sensitivity at 10 and 25 Gb/s, whereas a less damped VCSEL with a 0.2 ns K-factor achieved the best sensitivity at 40 Gb/s.

We present recent progress in development of low-jitter all-normal dispersion (ANDi) Yb-doped fiber laser. We developed a timing jitter measurement scheme employing a broadband lock-in amplifier working up to 600 MHz operational frequency which allowed us to measure single side band (SSB) phase noise and long-term drift in laser repetition rate. Following the measurement, we were able to determine timing jitter of our oscillator in the most critical frequency range (10 Hz – 10 kHz) to 1.6 ps. Long-term drift has been successfully suppressed by applying a piezo motor-based active feedback in the cavity.

The SLC (Stanford Linear Collider) thermionic gun and electron source provide a beam of up to 15*10/sup 10/ e/sup -/ in a single S-band bunch. A 170-keV, 2-ns FWHM (full width at half maximum) pulse out of the gun is compressed by means of two subharmonic buncher cavities followed by an S-band buncher and a standard SLAC (Stanford Linear Accelerator Center) accelerating section. Ceramic gaps in the beam pipe at the output of the gun allow measurement of the beam intensity and timing. A measurement at these gaps of the timing jitter, with a resolution of >