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ABSTRACT: Imaging microchannel plate (MCP) detectors with cross strip (XS) readout anodes require centroiding algorithms to determine the location of the amplified charge cloud from the incident radiation, be it photon or particle. We have developed a massively parallel XS readout electronic system that employs an amplifier and ADC for each strip and uses this digital data to calculate the centroid of each event in real time using a field programmable gate array (FPGA). Doing the calculations in real time in the front end electronics using an FPGA enables a much higher input event rate, nearly two orders of magnitude faster, by avoiding the bandwidth limitations of the raw data transfer to a computer. We report on our detailed efforts to optimize the algorithms used on both an 18 mm and 40 mm diameter XS MCP detector with strip pitch of 640 microns and read out with multiple 32 channel "Preshape32" ASIC amplifiers (developed at Rutherford Appleton Laboratory). Each strip electrode is continuously digitized to 12 bits at 50 MHz with all 64 digital channels (128 for the 40 mm detector) transferred to a Xilinx Virtex 5 FPGA. We describe how events are detected in the continuous data stream and then multiplexed into firmware modules that spatially and temporally filter and weight the input after applying offset and gain corrections. We will contrast a windowed "center of gravity" algorithm to a convolution with a special centroiding kernel in terms of resolution and distortion and show results with < 20 microns FWHM resolution at input rates > 1 MHz.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2011; 633(S1):S255-S258. · 1.21 Impact Factor
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ABSTRACT: At the heart of future space-based astronomical UV instruments will be a sensitive UV detector. Though there has been a death
of new UV mission opportunities, detector development has continued. Improvements have been made in spatial resolution, dynamic
range, detector size, quantum efficiency and background. At the same time the power and mass required to achieve these goals
have decreased. We review the current capabilities of microchannel plate based detectors at Berkeley, both in the laboratory
and aboard current on-orbit spacecraft. We also discuss what can be expected from the next generation of UV detectors over
the next decade.
Astrophysics and Space Science 03/2009; 320(1):247-250. · 1.69 Impact Factor
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ABSTRACT: A new hybrid optical detector is described that has many of the attributes desired for the next generation adaptive optics (AO) wavefront sensors. The detector consists of a proximity focused microchannel plate (MCP) read out by multi-pixel application specific integrated circuit (ASIC) chips developed at CERN (“Medipix2”) with individual pixels that amplify, discriminate and count input events. The detector has 256×256 pixels, zero readout noise (photon counting), can be read out at 1 kHz frame rates and is abutable on 3 sides. The Medipix2 readout chips can be electronically shuttered down to a temporal window of a few microseconds with an accuracy of 10 ns. When used in a Shack–Hartmann style wavefront sensor, a detector with 4 Medipix chips should be able to centroid approximately 5000 spots using 7×7 pixel sub-apertures resulting in very linear, off-null error correction terms. The quantum efficiency depends on the optical photocathode chosen for the bandpass of interest.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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ABSTRACT: A CMOS application-specific integrated circuit (ASIC) called the “Timepix” has been used to readout the pulsed charge signal from various microchannel plate (MCP) stacks. The Timepix 256×256 array is a newer version of the Medipix2 ASIC with added features and modes. One of these modes is the “time over threshold” (TOT) mode where the amplitude of a single charge event can be determined per pixel. With a properly sized input charge cloud from an MCP stack, the centroid of the charge cloud can be determined to sub-pixel accuracy, allowing much higher spatial resolution than the 55 μm pixel size. Using this technique, we demonstrate a spatial resolution better than 57 lp/mm for UV photons, limited by the MCP pore spacing. Also, by changing the top MCP in the stack to a neutron-sensitive MCP, we show a spatial resolution to thermal neutrons of less than 35 μm FWHM. This technique can also be applied to alpha particle imaging using silicon diode arrays bump bonded to a Timepix. Allowing the large conversion charge generated by the alpha particle to diffuse over many pixels, we can centroid 5.5 MeV alphas from 241Am to 18 μm FWHM.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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ABSTRACT: We describe the development of an imaging photon counting detector based on microchannel plates (MCPs) with specialized readout integrated circuits (ROICs). The detector consists of a photocathode, MCPs that amplify the photoelectron, and a ROIC that has event counters on every pixel. In this detector, it is the event counts that are integrated, not the charge, and there is no associated readout noise. Also, the integrated signal per pixel is already digital and the frame can therefore be readout very fast without noise penalty. The quantum efficiency is dependent on the photocathode chosen and can be tailored to the application (e.g. FUV solar blind to the near infrared). Both the electronic counters and the MCPs can be gated to nanosecond accuracy for ranging applications. The first application for this detector concept is a 256x256 optical wavefront sensor using the Medipix2 ROIC funded by the NSF Adaptive Optics Development Program. This detector can achieve a frame rate of 1 kHz with zero readout noise and 37% QE at 600 nm. We have demonstrated the spatial resolution and event rate (~1 GHz) of this detector with a laboratory vacuum test detector in the UV and are in the process of integrating this detector into a vacuum tube with a GaAs photocathode. We will also present possible future ROICs to be used with MCP technology to achieve faster frame rates or more pixels or both and discuss the possibility of using avalanche photodiodes (APDs) as the input photoconverter/amplifier rather than MCPs to increase the optical QE.
