Photon Counting Microchannel Plate Research Articles

Multi-channel picosecond photon timing with microchannel plate detectors

Microchannel plate-based detectors have the capability to photon-count at time resolutions which outperform solid-state devices such as the APD or SiPM, and have a geometry that lends itself to pixelated readouts. We describe a multi-channel, photon-counting microchannel plate detector optimised for photon timing in the picosecond regime. The detector was originally developed for application to time-resolved spectroscopy in the life sciences, however its performance characteristics make it suitable for applications where high time resolution and multi-channel photon-counting are required including Cherenkov light detection in nuclear physics, particle physics, and astroparticle astronomy. We describe the prototype detector, a sealed tube device comprising an optical photocathode proximity focussed to a small pore microchannel plate stack. Event charge is collected on a multi-channel readout comprising an 8×8 pixel array, manufactured on a multilayer ceramic, which provides vacuum integrity for the detector enclosure and a multi-way electrical feedthrough for the readout array. Each pixel addresses one channel of a NINO ASIC, a multi-channel preamplifier–discriminator device. The discriminator outputs are timed to 25 ps by the HPTDC time-to-digital converter ASIC, which uses a time-over-threshold technique for amplitude walk correction. We present performance measurements using a pulsed laser of the 64 channel prototype system comprising a 25 mm detector, NINO front-end, and a CAEN V1290A VME module utilising HPTDC. We discuss the next phase in the project—design and manufacture of a 40 mm detector with a 16×16 pixel 2 readout coupled to custom NINO/HPTDC electronics constructed as a series of 64 channel modules, expandable to even larger channel densities.

Reborn quadrant anode image sensor

We describe a position sensitive photon counting microchannel plate based detector with an improved quadrant anode (QA) readout system. The technique relies on a combination of the four planar elements pattern and an additional fifth electrode. The charge cloud induced by single particle detection is split between the electrodes. The measured charge values uniquely define the position of the initial event. QA has been first published in 1976 by Lampton and Malina. This anode configuration was undeservedly forgotten and its potential has been hardly underestimated. The presented approach extends the operating spatial range to the whole sensitive area of the microchannel plate surface and demonstrates good linearity over the field of view. Therefore, the novel image sensor results in spatial resolution better then 50 μ m and count rates up to one million events per second.

TH-C-I-611-06: MTF(f), NPS(f) and DQE(f) of An X-Ray Imaging System Based On a Photon Counting MCP Detector

Purpose: To evaluate inherent MTF(f), NPS(f) and DQE(f) of a prototype x-ray imaging system with photon counting microchannel plate (MCP) detector. Method and Materials: The MCP detector was used in edge illumination mode as a linear array x-ray detector in scanning slit image acquisition geometry. The detector FOV was 60 mm. MCPs with 63 mm length, 25 μm channel diameter and 5 μm channel wall thickness were used. The slit width was 0.25 mm. Delay line position encoding electronics was used. Images were acquired using an x-ray tube with 0.4 mm nominal focal spot size at 40 and 90 kVp using an SID of 50 cm and a magnification 1.1. MTF was measured using edge spread function method. NPS was calculated using flat field corrected flood images. DQE was calculated from MTF, NPS and using both measured and Monte Carlo calculated QE. Results: For 25 μm channel MCP, 50% MTF was achieved at 6 lp/mm and 4 lp/mm for 40 and 90 kVp tube voltages, respectively. The highest visualized frequency was 11 lp/mm at 40 kVp. NPS was shown to be frequency independent. QE measured at 90 kVp was 56% and 70% for 25 μm and 5 μm channel MCPs, respectively. Calculated QE was 64%, 86% and 92% for 25, 5 and 2 μm channel MCPs, at 90 kVp. The above QE values represent the DQE(0). The MTF(f) curves normalized by QE represent DQE(f) due to frequency independent nature of the NPS. Conclusion: MCP detector has shown adequate MTF(f) and DQE(f) for potential application in medical imaging. This is in addition to its inherently high count rate and scatter rejection feature of the scanning slit system. Combination of these capabilities in the photon counting system would allow for significant decrease in patient dose.

Photon counting computed tomography: Concept and initial results

A concept of a photon counting cone beam CT is proposed. The system uses a new Multi Slit Multi Slice (MSMS) cone beam acquisition geometry utilizing a linear array photon counting detectors. The MSMS cone beam acquisition is a direct analogy of the scanning multislit acquisition used in projection x-ray imaging. This geometry provides a CT imaging with dose efficient scatter rejection and allows for using available photon counting detectors. The microchannel plate (MCP) detector is proposed as a linear array photon counting detector for MSMS cone beam CT system. Initial testing of the MCP detector for CT application was performed. The field of view of the prototype MCP detector is 60 mm. A delay line position encoding electronics was used. The electronics has a single channel input for evaluation of events from the entire detector field of view. This limits the system count rate at 2 x 10(5) count/s. The spatial resolution of this detector is 80 microm FWHM at 40 kVp and 200 microm FWHM at 90 kVp tube voltages. The detector noise in CT projections is less than 1 count/pixel for the 80 microm pixel size. The CT projections contain quantum-limited and scatter free signal. Images of a contrast phantom and a small animal were acquired at 50 kVp and 80 kVp tube voltages. The CT numbers for different contrast elements were calculated for a given x-ray spectrum and compared with experimental values. The quantum efficiency of the current detector is 56% at 90 kVp, which is suboptimal because of the large channel diameter (25 microm) of these MCPs. The MCPs with smaller channels and higher efficiencies are being tested. The quantum efficiency was measured to be 70% for a new MCP with 5 microm channel diameter. Design parameters of a clinically applicable photon counting MSMS cone beam CT for breast imaging was evaluated. System uses 20 cm field of view MCP detectors based on 5 microm channel MCPs and high count rate ASIC electronics. It was concluded that the MSMS cone beam CT with a photon counting MCP detector is feasible for volume breast imaging.

2K×2K resolution element photon counting MCP sensor with >200 kHz event rate capability

Siegmund Scientific undertook a NASA Small Business Innovative Research (SBIR) contract to develop a versatile, high-performance photon (or particle) counting detector combining recent technical advances in all aspects of Microchannel Plate (MCP) detector development in a low cost, commercially viable package that can support a variety of applications. The detector concept consists of a set of MCPs whose output electron pulses are read out with a crossed delay line (XDL) anode and associated high-speed event encoding electronics. The delay line anode allows high-resolution photon event centroiding at very high event rates and can be scaled to large formats (>40 mm) while maintaining good linearity and high temporal stability. The optimal sensitivity wavelength range is determined by the choice of opaque photocathodes. Specific achievements included: spatial resolution of <25μm FWHM; formats from 25 to 40 mm with digitized pixel sizes of ∼3μm; total detector rates of >200000 events s−1; local rates of >100 eventss−1 per resolution element; event timing of <1ns; and low background counting rates (<1 event cm−2s−1).

Silicon-anode detector with integrated electronics for microchannel-plate imaging detectors

We describe a silicon anode with integrated electronics for use in photon-counting microchannel-plate (MCP) imaging detectors. Very-large-scale integrated techniques using a 2 μm complementary metal–oxide–semiconductor (CMOS) process allow a passive-anode region, which collects charge from the MCPs, to be surrounded by an active event-processing region. The anode region is made from a rectangular array of pads that are formed using the metal interconnect layers of the CMOS process. Individual pads are electrically connected to form isolated arrays of rows and columns; each row terminates at a well of one charge-coupled device (CCD) register, and each column terminates at a well of a second orthogonal CCD register. The distribution of charge within each register is used to encode the charge-cloud coordinates. A two-dimensional prototype anode was constructed with 128×80 pixels spaced at 50 μm intervals; the anode readout rate is 31 250 Hz. Subpixel centroiding techniques can be employed to reduce the number of pixels that must be read for a given resolution. We envision a rugged, compact, low-power, and low-mass single-substrate imaging anode with a direct (x,y) digital interface. The design offers large array formats with inherent pixel linearity, orthogonality, and stability. An identified upgrade path promises orders-of-magnitude increases in speed (up to 106 photons s−1) and dynamic range, while maintaining large pixel count (&amp;gt;4000×4000) and MCP pore-limited resolution (&amp;lt;8 μm).

Investigations of the small-scale flat field response of microchannel plate detectors in the far and extreme ultraviolet

High signal-to-noise flat field images taken in the extreme and far ultraviolet with photon-counting microchannel plate (MCP) detectors are presented. Small spatial scale (<1 mm) modulations of the flat field, in particular the hexagonal mesh pattern and dead spots, are discussed. It is shown that the hexagonal modulation at the multifiber bundle boundaries of the MCPs is due to a differential nonlinearity in the mapping of input photon position to readout pixel and is caused by the rear plates of the MCP stack. Possible mechanisms for the nonlinearity, including hexagonal gain variations, are presented.

Imaging characteristics of the Extreme Ultraviolet Explorer microchannel plate detectors

The Extreme Ultraviolet Explorer (EUVE) satellite will conduct an all-sky survey over the wavelength range from 70 AA 760 AA using four grazing-incidence telescopes and seven microchannel-plate (MCP) detectors. The imaging photon-counting MCP detectors have active areas of 19.6 cm/sup 2/. Photon arrival position is determined using a wedge-and-strip anode and associated pulse-encoding electronics. The imaging characteristics of the EUVE flight detectors are presented including image distortion, flat-field response and spatial differential nonlinearity. Also included is a detailed discussion of image distortions due to the detector mechanical assembly, the wedge-and-strip anode, and the electronics. Model predictions of these distortions are compared to preflight calibration images which show distortions less than 1.3% RMS of the detector diameter of 50 mm before correction. The plans for correcting these residual detector image distortions to less than 0.1% RMS are also presented. >

Wedge and strip image readout systems for photon-counting detectors in space astronomy

We discuss the application of wedge and strip anodes to photon-counting microchannel plate detector systems for the extreme and far ultraviolet. Performance data, obtained as a result of calibration of the Extreme Ultraviolet Explorer (EUVE) [ Proc. Soc. Photo-Opt. Instrum. Eng.279, 176 ( 1981)] satellite detectors (open face) and the FAUST–Spacelab [ Space Sci. Instrum.5, 21 ( 1979)] far-ultraviolet sensors (sealed tube), are presented. We have achieved CsI quantum detection efficiencies of ~80% at 114 Å and ~40% at 600 and 1300 Å that we believe to be the highest ever obtained. Position sensitivity of &lt;10 μm is demonstrated, and the position resolution, image linearity, background rate, and flat-field characteristics are discussed.

Probing the mechanism of incorporation of fluorescently labeled actin into stress fibers.

The mechanism of actin incorporation into and association with stress fibers of 3T3 and WI38 fibroblasts was examined by fluorescent analog cytochemistry, fluorescence recovery after photobleaching (FRAP), image analysis, and immunoelectron microscopy. Microinjected, fluorescein-labeled actin (AF-actin) became associated with stress fibers as early as 5 min post-injection. There was no detectable cellular polarity in the association of AF-actin with pre-existing stress fibers relative to perinuclear or peripheral regions. The rate of incorporation was quantified by image analysis of images generated with a two-dimensional photon counting microchannel plate camera. After equilibration of up to 2 h post-injection, FRAP demonstrated that actin subunits exchanged rapidly between filaments in stress fibers and the surrounding cytoplasm. When co-injected with rhodamine-labeled bovine serum albumin as a control, only actin was detected in the phase-dense stress fibers. The control protein was excluded from fibers and any linear fluorescence of the control was demonstrated as a pathlength artifact. The incorporation of AF-actin into stress fibers was studied by immunoelectron microscopy using anti-fluorescein as the primary antibody and goat anti-rabbit IgG coupled to peroxidase as the secondary antibody. At 5 min post-injection, reaction product was localized periodically in some fibers with a periodicity of approximately 0.75 microns. In large diameter fibers at 5 min post-injection, the analog was seen first on the surface of fibers, with individual filaments resolvable within the core. In the same cell, thinner diameter fibers were labeled uniformly throughout the diameter. By 20 min post-injection, most fibers were uniformly labeled. We conclude that the rate of actin subunit exchange in vivo is extremely rapid with molecular incorporation into actin filaments of stress fibers occurring as early as a few minutes post-injection. Exchange appears to first occur in filaments along the surface of stress fibers and then into more central regions in a periodic manner. We suggest that the periodic localization of actin at very early time points is due to a local microheterogeneity in which microdomains of fast vs. slower incorporation result from the periodic localization of actin-binding protein, such as alpha-actinin, along the length of the fiber.

Rocket-borne instrument with a high-resolution microchannel plate detector for planetary UV spectroscopy

A telescope-spectrograph employing a photon-counting microchannel plate (MCP)-CODACON detector has been built, tested, and flown on a sounding rocket. The detector uses a curved-channel MCP proximity focused onto a coded anode array of 1024 channels spaced 25.4-mm center to center. High quantum efficiency is obtained by depositing a cesium iodide photocathode on the front surface of the MCP. The instrument has obtained an ultraviolet (1500-1800-A) spectrum of Jupiter with a spectral resolution of 8 A, which is higher than that of any previously reported observation in this wavelength range.

Ralicon anodes fabricated by electron beam lithography for image photon counting detectors

The Anger wedge and strip anode event location system developed for microchannel plate image photon detectors at the Space Sciences Laboratory of the University of California, Berkeley, has been extended in the present work by the use of electron beam lithography (EBL). Computer-aided design methods have been used to develop several types of RALICON (Readout Anodes of Lithographic Construction) for use in photon counting microchannel plate imaging detectors. These anodes are suitable for linear, two dimensional or radial position measurements and they incorporate novel design features made possible by the EBL fabrication technique which significantly extend their application relative to published wedge-strip anode designs.

Rocket instrument for far-UV spectrophotometry of faint astronomical objects

A sensitive sounding rocket instrument for moderate (~10-A) resolution far-UV (lambda1160-lambda1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employs a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.