Timothy J. Norton

Line spread function degradation in photon-counting detectors

An investigation of the degradation of the line spread function due to electron scattering in a micro-channel plate intensifier employing a semi-transparent photocathode and proximity focusing is reported. Data obtained using the Anglo-Australian Telescope (AAT) are used to measure emission line broadening and infilling of absorption features in astronomical spectra, due to scattering in the micro-channel plate intensifier. A comparison with a magnetically focused four-stage cascade intensifier is made. Values are obtained with the two intensifiers for equivalent width and residual infilling of a totally saturated absorption feature. The micro-channel plate intensifier is found to scatter into the wings of emission lines a larger fraction of the input signal than the cascade intensifier, amounting to 6.5% of the total signal. A model of the line spread function degradation observed in the micro-channel plate intensifier, based on electron scattering in the input proximity focused lens, is also presented. The modified line spread function obtained from this model is found to be a remarkably good fit to the data obtained at the AAT, and the values for infilling of absorption line features calculated from the model are close to those observed in the spectra. Finally, suggestions are made as to how the design of future micro-channel plate intensifiers can be modified to reduce scattering from the input micro-channel plate.

DQE enhancement of MCP intensifiers for astronomy results of the MIC II program

The microchannel plate intensified CCD (MIC) photon counting detector system was developed to replace a common user photon counting detector, the image photon counting system (IPCS), at the Anglo Australian Telescope and at the William Herschel Telescope and the Isaac Newton Telescope at La Palma Observatory. The IPCS incorporated magnetically-focused four-stage cascade image intensifiers. This paper discusses technological aspects of the design and optimization of very high gain microchannel plate image intensifiers for such photon counting systems and particularly the optimization of device detective quantum efficiency.

MCP image intensifier with improved DQE

The Microchannel-plate Intensified CCD (MIC) photon-counting detector system has been developed as a future replacement for a common user photon counting detector, the IPCS (Image Photon Counting System) on both the Isaac Newton and William Herschel telescopes at the La Palma Observatory and at the Anglo-Australian Observatory. These detectors previously incorporated EMI 4-stage cascade image intensifiers. This paper addresses the technological aspects of the design and optimization of very high gain MCP image intensifiers for such photon counting systems, and particularly the optimization of device detective quantum efficiency.

Evaluation of Photon-event-counting Intensifiers

Publisher Summary This chapter discusses the evaluation of photon-event-counting intensifiers. It is proposed to consider some of the measurements that have been carried out to evaluate the performance of the detector for photon-event counting. Measurements carried out on the prototype 40 mm microchannel plate (MCP) image intensifiers that have been produced as part of a programme to develop an improved front-end detector for photon-event-counting systems indicate that the tubes have several desirable characteristics for use in this application. Device operating parameters such as gain, resolution, pulse height distribution, noise, and detective quantum efficiency can be measured. Light entering the device may suffer several reflections in the intensifier input faceplate or inside the vacuum envelope. Measurements have been made of a number of critical parameters that are of particular importance for photon-event-counting systems and that are often not quoted by commercial manufacturers. MCP counting efficiency can be improved by modifications to the manufacturing procedures.

Performance of a large-area microchannel plate photon-counting intensifier

A 75 mm diameter microchannel plate (MCP) intensifier has been developed for astronomical applications. The intensifier incorporates a semi-transparent photocathode, three MCPs in a Z- stack configuration, and a P20 phosphor screen in a dual proximity focused arrangement. The input MCP is a thin 40:1 channel plate which is conditioned to run at low gain and hence act as an ion barrier for the succeeding 80:1 chevron pair. The intensifier has been incorporated into a CCD readout system and has undergone extensive laboratory testing. The preconditioning of these 75 mm diameter channel plates required a large area, highly uniform electron scrub beam, this has led to the development of a novel electron gun. The design of the 75 mm intensifier and the novel electron gun are described. Results from the laboratory evaluation of the intensifier are presented. Flat field illumination showed the existence of self- exciting channels in a hexagonal pattern. Finally, a future UV or x-ray detector based on this design and incorporating large area MCPs is discussed.

Development of the BIGMIC photon-counting detector for astronmomical applications

University College London and The Imperial College of Science, Technology & Medicine are together developing a new large area imaging photon counting system, BIGMIC, for use primarily on very large telescopes. This detector is designed for applications requiring the highest sensitivity and resolution such as, high dispersion Echelle spectroscopy. The system incorporates a specially designed 75mm active diameter image intensifier fibre- optically coupled to a fast scanning 770 x 576 pixel frame transfer CCD. Photon events at the intensifier output screen are centroided to 1/8 of a CCD pixel in both X and Y in order to sample adequately the point spread function of the intensifier, giving a data acquisition format of 6160 x 4608 sub-pixles. The area imaged onto the CCD is 61mm x 46mm with a data acquisition pixel size of 10 micrometers . A hardware windowing facility, built into the detector system, enables the astronomer to select a subset of the imaging area for data acquisition. This permits the user to match the system to specific applications; for example in a number of spectroscopic applications an essentially one dimensional image is required and a detector format of perhaps 6160 x 100 pixels could be utilized.

Development of the MIC photon-counting detector for astronomical applications

The MIC, a 40-mm intensified microchannel-plate photo-counting detector being developed for the Anglo-Australian, Isaac Newton, and William Herschel telescopes, is described and illustrated with diagrams and sample spectra. The MIC is linked by optical fibers to a fast-scanning CCD detector, and an accurate centroiding technique is applied to yield an effective maximum of 3104 x 2304 10.6-micron pixels, for field-averaged resolution 27 microns FWHM. Applications include high-resolution spectroscopy, especially in the blue, and Fabry-Perot and speckle interferometry.

Properties of a 40-mm Microchannel Plate Intensifier

A 40mm, proximity-focussed, micro channel— plate intensifier using dual double-thickness plates has been developed for use in image photon counting applications. Some of the more important manufacturing techniques are described, along with the results of initial tests of the performance characteristics of the tube.

A 40 mm MCP Intensifier for Photon Counting

Publisher Summary This chapter presents an introduction of microchannel plate (MCP) intensifier for photon counting. The chapter describes the construction and manufacturing techniques required to produce an intensifier of the specification. A 40 mm dual microchannel plate intensifier has been developed for use in high-resolution, centroiding, photon-counting systems for astronomy. The device incorporates an S.20 photocathode using proximity focus to a dual, double-length microchannel plate stack in the chevron configuration. The resulting electron cloud is proximity-focused onto an aluminized P. 20 phosphor screen deposited on a fiber-optic window. The intensifier body is of metal and ceramic construction, metal rings providing the relevant electrode feedthroughs into the vacuum envelope for the microchannel plates, phosphor screen and tube getter. Two, double-length (length-to-diameter ratio of 80: 1), “long life” microchannel plates are used in the “chevron” configuration. An extremely compact, very high-gain, photon-counting image intensifier has been manufactured for use in high-resolution astronomical photoncounting systems.

Performance of a 40-mm unfilmed microchannel plate intensifier

A prototype 40-mm-diameter proximity-focused microchannel-plate intensifier intended for photon-counting applications in both ground-based and space astronomy is described. The intensifier described is a sealed-window device and is also well suited to open-window ultraviolet applications in space astronomy. The tube makes use of a combination of an unfilmed curved-channel plate (C-plate), to prevent ion feedback, and a single straight-channel plate, aligned to prevent optical feedback. The tube has excellent cosmetic quality and shows a counting efficiency superior to that of filmed plate devices reported previously, giving an overall detective quantum efficiency at least equal to that of the best four-stage magnetically focussed intensifiers.