Southwest Research Institute intensified detector development capability

The research on key techniques of wide field extreme ultraviolet( EUV) spherical micro-channel plate( MCP) photon-counting imaging detector which will be used in space probe in China have been done.Firstly,the secondary electron yield model of photocathode material was built,and the secondary yield of alkali halide and MCP in soft X-ray and EUV band were calculated using the model. The measurement equipment of MCP's quantum detection efficiency also was set up. The calculated fomula of MCP' s quantum efficiency was introduced,and MCP's quantum efficiency vs. wavelength and incidence angle in soft X-ray and EUV region were measured. secondly,the instrument of solid core spherical MCP fabrication was established,a set ofspherical MCP with 150 mm radius were made using the instrument. The 48 mm induced charge wedge and strip anode in effective diameter was made by the use of traditional UV lithography,and the photon-counting imaging detector was integrated based on the anode and spherical MCP stack in Z configuration. Thirdly,the position readout electronics including analog frent-end and digital processing circuit and the software with image distortion rectification and real-time collection were developed. Finally,the measurement instrument of spherical MCP detector's spatial resolution and image linearity was built,and the specifications of the detector were measured using the instrument,showing that all technical specificaions of the detector satisfy the design requirements.

The EUV grating spectrograph (EGS) as part of the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) solar EUV experiment (SEE) presents a number of performance challenges for its microchannel plate (MCP)- based detector. The EGS measures the solar spectral irradiance from 25 to 200 nm. The intensities of the line and continuum emissions over this spectral range vary by up to five orders of magnitude. While a variety of transmission filters are strategically used to bring the signal over the entire spectrum into the dynamic range of a single chevron pair of MCPs, a number of concerns regarding the characteristic behavior of MCPs remain. The nominal TIMED mission is two years while the extended mission potentially doubles to four years. Over this period, the MCP response is expected to change to some extent. Detailed changes in MCP performance are notoriously application dependent,however. In order to better anticipate and accommodate these changes over the duration of the mission as well as to potentially enhance detector performance, we are performing a series of life-tests on a variety of MCPs. In these tests we characterize MCP gain, pulse height distribution, quantum detection efficiency, and linearity as function of accumulated charge and exposure to atmosphere. Here we report on the result of these test.s

We present investigations on the improvements in quantum detection efficiency (QDE) of microchannel plate (MCP) detectors resulting from the application of various photocathode materials. Nine different photocathode materials were deposited and their QDE measured in the soft x-ray and UV region from 12 angstrom to 1850 angstrom. Four of these materials (CsCl, RbCl, RbI, BaCl) significantly enhance the QDE performance of bare MCPs, and five materials were proven unsatisfactory (AgCl, LiCl, LiI, LiF, MgBr). CsCl has very high (greater than 90%) short wavelength QDE and both CsCl and RbI have UV QDE in the region of 40%. Our studies also include life testing of a KBr photocathode for a period of over 5 years. This shows good stability, and the angular response and photoemissive characteristics over time are described. The effects of long wavelength QDE activation of KBr by exposure to 2537 angstrom photons are discussed.

A photon-counting detector for determination of the ion temperature in magnetically confined plasmas has been developed.1 The detector is based around an image intensifier tube which is fiber optically coupled to a self-scanning linear photodiode array. The image intensifier incorporates three high strip current (∼280 μA) microchannel plates in a ‘‘Z’’ configuration. Frame times of 10 μs are possible through the use of pixel selection, resulting in a time resolution on the order of 5 ms. The detector system will be mounted on a 1-M Ebert–Fastie spectrometer and used to study the Alcator C plasma. Laboratory evaluation of the detector and associated electronics has been completed. The results of this evaluation, and progress toward integration of the detector and spectrometer systems, will be presented. This work, and additional information, will be published in greater detail in the near future.

We have designed, fabricated, and tested a modular CCD area detector system for macromolecular crystallography at synchrotron x-ray sources, code-named the `gold' detector system. The sensitive area of the detector is 150 mm X 150 mm, with 3,072 X 3,072 pixel sampling, resulting in roughly a 50 micrometers pixel raster. The x-ray image formed on the face of the detector is converted to visible light by a thin phosphor layer. This image is transferred optically to nine CCD sensors by nine square fiberoptic tapers (one for each CCD), arranged in a 3 X 3 array. Each taper demagnifies the image by a factor of approximately 2. Each CCD has a 1,024 X 1,024 pixel raster and is read out through two independent data channels. After each x-ray exposure period the x-ray shutter is closed and the electronic image is digitized (16-bit) and read out in 1.8s. Alteratively, the image may be binned 2 X 2 during readout, resulting in a 1,536 X 1,536 raster of 100 micrometers pixels; this image can be read out in 0.4s. The CCD sensors are operated at -40 degree(s)C to reduce electronic noise. The detector is operated under full computer control: all operational parameters (readout rates, CCD temperature, etc.) can be adjusted from the console. The image data (18 MByte/image) are transferred via a fast VME system to a control processor and ultimately to disk storage. During April 1994 we carried out a complete set of measurements at the Stanford Synchrotron Radiation Laboratory (SSRL) for a full characterization of the gold detector. Characterization includes quantitative evaluation of the instrument's conversion gain (signal level/x-ray photon); detective quantum efficiency (DQE); point-spread function; sensitivity as a function of x-ray energy; geometrical distortion of images; spatial uniformity; read noise; and dark image and dark image noise. Characterization parameters derived from these measurements show that this detector will be extraordinarily valuable for macromolecular crystallography.

The image linearity of a charge division position readout anode, for instance, a Wedge and Strip Anode (WSA), is controlled by several factors. In addition to the drift field uniformity and pattern geometry requirements, linearity can be affected by the surface characteristics of the anode itself. We have undertaken experiments to establish the mechanisms which lead to non-linear response and suggest ways to avoid it. We present measured image non linearity of image intensifier tubes using two different types of charge division position readout anode; the Wedge and Strip anode (WSA) and the Spiral Anode (SPAN) devices. Both intensifier tubes were manufactured by DEP bv., Holland and utilize S20 or Caesium Telluride semi- transparent photocathodes on Magnesium Fluoride, Fused Silica or Calcium fluoride windows, proximity focused to a microchannel plate (MCP) stack. All detector variants built thus far use a stack of three MCPs in a Z configuration. We have undertaken experiments using a de- mountable detector of similar design but without window or photocathode. The role of secondary electrons produced on the anode in charge redistribution was investigated by using an intermediate conductive grid of high open area between the MCP and anode. The grid was used to define the electric field in a region just above the anode in order to either suppress the range of the anode secondary electrons, or prevent them from returning to the anode by collecting them on the grid. We present some preliminary results from these experiments and suggest modifications to the intensifier design to maximize the detector performance.

The emergence of Silicon based microchannel plates (MCP's) has been awaited for a number of years, with many proposed advantages over standard glass MCPs for space-based detectors. Si should have a very low inherent background ( -1 cm -2 ), as well as being a low Z element with low stopping power for x, gamma and cosmic rays. The surface is oxidized and can be baked to very high temperatures (> 800 degrees Celsius), and will not react with photocathodes deposited on the surface. This could potentially allow opaque photocathodes, with their higher resolution and efficiency, to be used in the near UV/optical bands. Since the microchannel positions are determined photolithographically, the pattern will be uniform and coherent, resulting in more uniform flat fields and less differential non-linearity in the spatial response. Microchannel spacing could decrease to the micron regime, while size formats could increase. The potential advantages of Si MCPs encompass increased gain, stability, longevity, event rate, and QE. However, glass MCPs have a strong and successful heritage in space-based detector systems and the advantages of Si MCP's must be demonstrated in the laboratory before being considered for flight applications. We have tested some newly developed silicon (Si) MCP's provided by Nanosciences Corp. Although these are still in the developmental stage we have achieved a number of significant results. The gain, pulse height, response and gain uniformity, and quantum detection efficiency are very similar to glass MCP's. However the Si MCP background is approximately 0.02 events sec -1 cm -2 without shielding, a significant improvement over even low noise MCP's. The small samples we have tested are 25 mm format with 8 micrometer pore spacing, but they are taken from a 75 mm substrate, which offers the possibility of large MCP's in the near future. More testing and process development are underway to probe other operational parameters and optimize the manufacturing process.

With the introduction of the night-vision goggle (NVG) into vehicle cockpits, the transfer of visual information to the observer became more complex. The problem emanated from the image intensifier tube photocathode spectral response. NVGs were capable of sensing and amplifying visible cockpit light, making observation of the scene outside of the cockpit, the primary use for NVGs, difficult. Over the years, several documents were published outlining night vision imaging system (NVIS) compatible lighting performance. These documents limited the permissible amount of light visible to image intensifier tubes that cockpit displays could emit, enhancing pilot visual performance. Recent advances in short wave infrared (SWIR) sensor technology make it a possible alternative to image intensifiers for night imaging application. However, while popular SWIR cameras are not particularly sensitive to visible light, they may be sensitive to other display emissions not attenuated by state-of-the-art NVIS filters. This paper examines the possibility of expanding the traditional treatment of vehicle cockpit compatibility to include new, novel vision enhancement devices yet to be designed and vehicle cockpit geometry.

The European Space Agency’s (ESA’s) Rosetta mission to comet 67P/Churyumov-Gerasimenko, launched 2004, carried the first in the Southwest Research Institute’s (SwRI’s) Alice series of ultraviolet imaging spectrographs. Subsequent iterations of the instrument are currently operational on NASA’s New Horizons, Lunar Reconnaissance Orbiter (LRO) and Juno missions, launched 2006, 2009 and 2011, respectively, and two further versions of the spectrograph are in development at SwRI for flight on ESA’s JUICE mission to the Jovian system (Phase C) and NASA’s Europa Clipper mission (Phase B). While the basic optical design is similar for all versions of the instrument, developments in microchannel plate (MCP) detector and electronics technology have enhanced the scientific return of the more recent Alice spectrographs, with some corresponding increase in the mass and power of the system. Here, we describe a reevaluation of the Rosetta-Alice (R-Alice) instrument design based on updated technology, lessons learned from subsequent Alice-type instrument development, and a “wish list” of suggested improvements in instrument performance provided by the R-Alice Science Team. The resulting instrument design, which we designate R-Alice II, would form the baseline concept for an ultraviolet instrument proposed by the SwRI UVS/Alice team for future Rosetta-type missions.

We report upon our continued investigation of a chemical treatment method for improving the quantum detection efficiency and gain of photon counting microchannel plate detectors for vacuum UV and soft x-radiation. The process improved MCP quantum detection efficiency for approximately 100-1200 angstrom radiation by a factor of 1.5-2. The performance results of DIP treated microchannel plates are summarized.

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.

Current Generation II Gallium Arsenide (GaAs) image intensifier tube technology requires that the tube microchannel plate (MCP) component have a thin dielectric coating on the side facing the tube's photocathode component. This protective coating substantially reduces the release from the MCP of ions and neutral species, particularly when the image intensifier is operated. The prevention of MCP outgassing is necessary in order ot prevent the poisoning of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. Such experiments have consistently led to an intensifier with a significantly reduced lifetime, due to contamination of the Cs:O layer on the photocathode. Unfortunately the MCP film acts as a scattering cneter to electron transport within the intensifier and effectively reduces the photoelectron detection efficiency. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. Removal of the MCP film promises to simplify MCP fabrication and enhance the intensifier parameters related to Electro-Optical performance and image quality. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single unfilmed MCP and achieve improved imaging and performance characteristics.

Evaluation of Photon-event-counting Intensifiers

The concept of spatial frequency depending DQE and its application to a comparison of two detectors used in transvenous coronary angiography

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is designed to make high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 Angstrom). Its high effective area, low background and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. The FUSE instrument includes two large format microchannel plate detectors. Each detector system consists of two microchannel plate segments in a Z-stack configuration with double delay line anodes and associated electronics. High detector spatial resolution was required in order to obtain scientific data with high spectral resolving power, and low detector background was necessary in order to observe faint objects. We describe the performance of the FUSE detectors during their first year on orbit, including the mechanical and thermal stability, throughput, background, and flat field of the detector system. We will also discuss the regular single event upsets of the detector electronics, and the strategy adopted in order to minimize their impact on mission efficiency.