Photon-counting Microchannel Plate Detector 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.

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.

Chemical method to increase extreme ultraviolet microchannel-plate quantum efficiency

The quantum detection efficiency of photon-counting microchannel-plate detector channels can be increased by a factor of 2 in the extreme ultraviolet bandpass, from 256 A to 1024 A, by subjecting the input channel plate to a chemical solution treatment. The efficiency increase has proven to be insensitive to the exposure of laboratory atmosphere and is stable over the extracted charge lifetime equivalent of multiyear astrophysical observations. Chemically treated microchannel plates that are overcoated with opaque photocathodes of KBr and CsI show a factor of 2 quantum detection efficiency increase from 834 A to 1100 A in comparison with previous measurements using conventional untreated microchannel plates.

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 <10 μm is demonstrated, and the position resolution, image linearity, background rate, and flat-field characteristics are discussed.