Showing papers by "Anton S. Tremsin published in 1999"
22 Oct 1999
TL;DR: The GALEX instrument as discussed by the authors consists of a 50cm normal incidence mirror telescope in combination with a grism, and a dichroic beamsplitter system projecting images onto two detectors simultaneously.
Abstract: 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.
82 citations
TL;DR: In this article, the authors measured the electron cloud footprints produced by a stack of microchannel plates (MCPs) as a function of gain, MCP-to-readout distance and accelerating electric field.
Abstract: The measurements of the electron cloud footprints produced by a stack of microchannel plates (MCPs) as a function of gain, MCP-to-readout distance and accelerating electric field are presented. To investigate the charge footprint variation, we introduce a ballistic model of the charge cloud propagation based on the energy and angular distribution at the MCP output. We also simulate the Coulomb repulsion in the electron cloud, which is likely to cause the experimentally observed increase in the cloud size with increasing MCP gain. Calculation results for both models are compared to the charge footprint sizes measured both in our experiments with high rear-field values (∼200–900 V/mm) and in the experiments of Edgar et al. [Rev. Sci. Instrum. 60, 3673 (1989)] (accelerating electric field ∼30–130 V/mm).
56 citations
22 Oct 1999
TL;DR: In this article, the authors studied variation efficiencies of CsI, KBr and KI- evaporated reflective planar phototcathodes with the angle of radiation incidence in the spectral range of 25-115 nm.
Abstract: We studied variation efficiencies of CsI, KBr and KI- evaporated reflective planar phototcathodes with the angle of radiation incidence in the spectral range of 25-115 nm. The photocurrent increases with the photon incidence angle for short wavelengths, while it changes only approximately 5 percent at wavelengths approximately 90-115 nm. The theoretical calculations of the photocathode angular response based on the absorption length of the photons and the escape length of the photoelectronics are in a relatively good agreement with the measured data. A detailed study of the detection efficiency angular variation for the microchannel plates with CsI, KI and KBr photocathodes in the spectral range of 25-191 nm is also presented. Heat annealing of the planar photocathodes did not result in any significant variation in their angular response.
23 citations
TL;DR: It is shown that the flat-field detector response can have moiré beat pattern modulations of as great as approximately 27% with periods from as small as a few channel diameters to as great of a MCP multifiber, which may be used for the development of MCP x-ray optics.
Abstract: The spatial resolution of position-sensitive detectors that use
stacks of microchannel plates (MCP’s) with high-resolution anodes
can be better than 20-µm FWHM [Proc. SPIE3114, 283–294 (1997)]. At this level of accuracy, channel
misalignments of the MCP’s in the stack can cause observable
moire interference patterns. We show that the flat-field
detector response can have moire beat pattern modulations of as
great as ∼27% with periods from as small as a few channel diameters
to as great as the size of a MCP multifiber. These modulations,
however, may be essentially eliminated by rotation of the MCP’s or by
a mismatch of the channel sizes. We also discuss how the modulation
phenomena can be a useful tool for mapping the metric nonlinearities of
MCP detector readout systems. Employing the optical moire
effect, we demonstrate a simple, but effective, technique for
evaluation of geometrical deformations simultaneously over a large MCP
area. For a typical MCP, with a 60-channel-wide multifiber, we can
obtain accuracies of 1.2 mrad for multifiber rotations and twists and
35/(L/
p) mrad for channel-long axis distortions
(where L/
p is MCP thickness to interchannel distance
ratio). This technique may be used for the development of MCP
x-ray optics, which impose tight limitations on geometrical
distortions, which in turn are not otherwise easily measurable with
high accuracy.
20 citations
22 Oct 1999
TL;DR: The optical constants of thin films of CsI, KI, and KBr in the spectral range of 53.6-174.4 nm were obtained from the measurements of reflectivity as a function of the incidence angle as discussed by the authors.
Abstract: The optical constants of thin films of CsI, KI, and KBr in the spectral range of 53.6-174.4 nm were obtained from the measurements of reflectivity as a function of the incidence angle. The effect of film heating to 420 K and exposure to UV radiation on the optical constants of the three materials was also investigated. The quantum efficiencies of the planar photocathodes made with the three alkalihalides, as well as the changes in these QEs after the photocathode treatment similar to that applied to the thin films was measured. KBr was found to be the most stable to heating and irradiation. KI appeared to be close to temperature-stable, while UV exposure affected its optical constants. CsI optical constants were changed after 420-K heating, as well as after UV exposure. The changes in the optical constants were related to the QE changes and the correlation between these variations was determined.
6 citations