Joseph M. Stock

High-resolution cross delay line detectors for the GALEX mission

The GALEX instrument consists of a 50cm normal incidence mirror telescope in combination with a grism, and a dichroic beamsplitter system projecting images onto two detectors simultaneously. The objective of this instrument is to provide sensitive high resolution imaging of galaxies in two bandpasses, with the option of the modest resolution spectroscopy. We are currently developing the microchannel plate, delay line, sealed tube detectors for the Galaxy Evolution Explorer mission to be launched in 2001.

Performance of the double delay line microchannel plate detectors for the Far-Ultraviolet Spectroscopic Explorer

The microchannel plate, delay line, detectors developed for the far ultraviolet spectroscopic explorer mission to be launched in 1998 are described. The two FUSE detectors have a large format (approximately equals 184 mm by 10 mm split into two 88.5 by 10 mm segments), with high spatial resolution (less than 20 micrometers by 50 micrometers FWHM, greater than 9000 by 200 resolution elements) and good linearity (plus or minus 25 micrometers), high image stability, and counting rates in excess of 4 by 104 events sec-1. KBr opaque photocathodes have been employed to provide quantum detection efficiencies of 30 - 40% in the 900 - 1200 angstrom range. Microchannel plates with 10 micrometer pores and an 80:1 pore length to diameter ratio, with a 95 mm by 20 mm format have been used in a Z stack configuration to provide the photon amplification (gain approximately equals 2 by 107). These show narrow pulse height distributions (less than 35% FWHM) even with uniform flood illumination, and good background levels (less than 0.3 event cm-2sec-1). Flat field images are demanded by the microchannel plate multifiber boundary fixed pattern noise and are stable.

The galaxy evolution explorer

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit mAB~20-21) to an ultra-deep survey of 4 square degrees (limit mAB~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (mAB~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

Delay-line detectors for the UVCS and SUMER instruments on the SOHO Satellite

Microchannel plate based detectors with cross delay line image readout have been rapidly implemented for the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in July 1995. In October 1993 a fast track program to build and characterize detectors and detector control electronics was initiated. We present the detector system design for the SOHO UVCS and SUMER detector programs, and results from the detector test program. Two deliverable detectors have been built at this point, a demonstration model for UVCS, and the flight Ly (alpha) detector for UVCS, both of which are to be delivered in the next few weeks. Test results have also been obtained with one other demonstration detector system. The detector format is 26mm x 9mm, with 1024 x 360 digitized pixels,using a low resistance Z stack of microchannel plates (MCPs) and a multilayer cross delay line anode (XDL). This configuration provides gains of approximately equals 2 X 107 with good pulse height distributions (<50% FWHM) under uniform flood illumination, and background levels typical for this configuration (approximately equals 0.6 event cm-2 sec-1). Local counting rates up to approximately equals 400 event/pixel/sec have been achieved with no degradation of the MCP gain. The detector and event encoding electronics achieves approximately equals 25 micrometers FWHM with good linearity (+/- approximately equals 1 pixel) and is stable to high global counting rates (>4 X 105 events sec-1). Flat field images are dominated by MCP fixed pattern noise and are stable, but the MCP multifiber modulation usually expected is uncharacteristically absent. The detector and electronics have also successfully passed both thermal vacuum and vibration tests.

Microchannel plates for the UVCS and SUMER instruments on the SOHO satellite

The microchannel plates for the detectors in the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCPs) is employed in a detector format of 27 mm multiplied by 10 mm using a multilayer cross delay line anode (XDL) with 1024 by 360 digitized pixels. The MCP stacks provide gains of greater than 2 multiplied by 107 with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approximately equals 0.6 event cm-2 sec-1 are obtained for this configuration. Local counting rates up to approximately equals 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (approximately equals 10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown.

Cross-delay-line microchannel plate detectors for the Spectrographic Imager on the IMAGE satellite

We have developed compact microchannel plate detectors utilizing a cross delay line readout system for the IMAGE- FUV Spectrographic Imager. We present a description of the detector head assembly and performance data typical for both detectors. Both detectors are nearly identical, the only different being the position of the input window on the front cover. Each detector, optimized for operation in the far UV with a KBr photocathode, provides high spatial resolution and good linearity over a 20 mm square format.

High-resolution monolithic delay-line readout techniques for two-dimensional microchannel plate detectors

Developments in high resolution double delay line (DDL) and cross delay line image readouts for applications in UV and soft X-ray imaging and spectroscopy are described. Our current DDLs achieve approximately equals 15 micrometers X 25 micrometers FWHM over 65 X 15 mm (> 4000 X 500 resolution elements) with counting rates of > 105 (10% dead time), good linearity (+/- approximately equals 1 resolution element) and high stability. We have also developed 65 mm X 15 mm multilayer cross delay line anodes with external serpentine delay lines which currently give approximately equals 20 micrometers FWHM resolution in both axes, with good linearity (approximately equals 30 micrometers ) and flat field performance. State of the art analog to digital converter and digital signal processor technology have been employed to develop novel event position encoding electronics with high count rate capability (2 X 105 events sec-1).

Delay line microchannel plate detectors for the far-ultraviolet spectroscopic explorer satellite

Delay line detectors have been chosen for the Far Ultraviolet Spectroscopic Explorer1 mission to be launched in 2000. The demands of the FUSE detectors include large format (220mm x 10mm format), high spatial resolution (15im x 35im FWHM) and linearity, high image stability, low power consumption and weight, and counting rates in excess of 3 x i0 events sec1. The FUSE program builds on the previous work, which includes two delay line detectors (95mm x 27mm double delay line format) that have already been successfully employed in the ORFEUSASTROSPAS2 ultraviolet spectrometer launched by shuttle in September 1993. We present the plans for the FUSE detector program, and results from double delay line (DDL) detectors that are under investigation to meet the requirements of the FUSE program. Our current detector achieves 15im x 25p,m FWHM (<4000 x 500 resolution elements) over the 65 x 15mm format used for the FUSE demonstration detector (90% of the flight detector segment format length), with good linearity (±1 resolution element) and high stability. State of the art analog to digital converter (ADC), gated integrator, and digital signal processor (DSP) technology have been employed to develop novel event position encoding electronics with high count rate capability (<5 x104 events sec). Microchannel plates with lOj.tm pores and an 80: 1 pore length to diameter ratio, with a 70mm x 20mm format have been used in a Z stack configuration to provide the photon amplification (gain 2 x 10). These show good pulse height distributions (<35% FWHM) even with uniform flood illumination, and background levels typical for this configuration (<1 event cm 2 sec 1). Flat field images are dominated by the microchannel plate fixed pattern noise due to the multifiber boundaries, and are stable. High efficiency photocathodes, such as KBr have been extensively studied, and provide quantum detection efficiencies of 40-50% in the 900 - 1200A range for FUSE.

Optical metrology of the JWST Integrated Science Instrument Module test platform

The James Webb Space Telescope is a large infrared observatory with a segmented primary mirror, part of the Optical Telescope Element (OTE), and four science instruments supported by the Integrated Science Instrument Module (ISIM). We present the calibration plan for the ISIM Test Platform (ITP) which replicates the ISIM-to-OTE interface: to calibrate the location and orientation of metrology features at ambient and cryogenic environmental conditions, to verify that ITP behavior (deflection under load, warm-to-cold alignment shift) can be modeled, predicted, and tested, to prove that the ITP is stable (upon repeated cryogenic cycles, and after loading and handling), and to calibrate the relationship between the Master Alignment Target Fixture and the ITP at ambient and cryogenic conditions.

Progress on high-efficiency photocathodes for soft x-ray, EUV, and FUV photon detection

We report on progress in the development of high quantum detection efficiency photocathodes for microchannel plate based photon detectors to increase soft X-ray, EUV and FUV response. Initial investigations of NaBr, KI and CsBr opaque photocathodes are discussed. All show QDEs of approximately 40% in the 300 - 1000 angstroms regime, and QDE > 60% at approximately 100 angstroms. KI also shows high QDE, approximately 60%, for soft X-rays (approximately 11 angstroms). Photoelectron energy and number distributions are also presented. Lifetest measurements on KBr and CsBr photocathodes show good long term stability for storage in dry nitrogen. A co-evaporated photocathode is also evaluated.