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Optical Engineering

EUV/FUV response characteristics of photographic films for the Multi-Spectral Solar Telescope Array
Author(s): Richard B. Hoover; Arthur B. C. Walker; Craig Edward DeForest; Maxwell J. Allen; Joakim F. Lindblom
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Paper Abstract

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory designed to produce ultrahigh-resolution full-disk images of the sun. The MSSTA utilizes an array of Ritchey-Chrétien, Cassegrain, and Herschelian normal incidence telescopes operating in the soft x-ray (44- to 100-Å), the extreme ultraviolet (EUV: λλ ~ 100 to 1000 Å), and the far ultraviolet (FUV: λλ ~ 1000 to 2000 Å) portions of the electromagnetic spectrum. These normal incidence multilayer and thin film interference coated optical systems are designed to produce narrow band solar images at selected wavelengths within this very broad spectral regime. The MSSTA mission places extremely strenuous requirements upon the imaging detector. The desire for ultrahigh-resolution (~0.1 to 0.3 arcsec) images of the solar disk and corona out to 1.5 solar radii demands an information storage capacity that at the present time can be met only by the highest quality photographic emulsions. Because a tremendous range exists in the intensity levels and contrast characteristics of solar x-ray/EUV/FUV emission features, the MSSTA photographic films must have a wide latitude to allow extremely bright, high-contrast features associated with flares and active regions to be recorded without saturation, while maintaining the ability to capture the faint, low-contrast structures in coronal holes, polar coronal plumes, network structures, and coronal loops. The MSSTA flight films must have high to ultrahigh-resolution and be sensitive over this very broad and difficult portion of the electromagnetic spectrum. The gelatin overcoat of the film must be maintained at a minimum, while the 70-mm film must retain the ability to be transported through conventional Pentax 645 cameras with minimum degradation due to scratches in the delicate emulsion. Furthermore, because the payload must be evacuated to prevent the delicate EUV and soft x-ray filters from failing due to acoustic vibrational stresses during launch, the MSSTA flight films must also have low-outgassing rates. These films must also be provided with antistatic backing to prevent electrostatic sparks from degrading the images as the dry film is unspooled through the cameras. We describe the performance and characteristics required of the MSSTA photographic films for solar observations in the soft x-ray/EUV and FUV wavelength regimes. We discuss the properties of the important new emulsions selected for flight and present data on the response characteristics of a tabular grain Experimental XUV 100 film and an uncoated Experimental Spectroscopic 649 emulsion.

Paper Details

Date Published: 1 August 1991
PDF: 9 pages
Opt. Eng. 30(8) doi: 10.1117/12.55916
Published in: Optical Engineering Volume 30, Issue 8
Show Author Affiliations
Richard B. Hoover
Arthur B. C. Walker, Stanford Univ. (United States)
Craig Edward DeForest, Stanford Univ. (United States)
Maxwell J. Allen, Stanford Univ. (United States)
Joakim F. Lindblom, Stanford Univ. (United States)

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