We report new, near-normal-incidence, transmission grating efficiency results at selected extreme-ultraviolet wavelengths between 4.5 and 30.5 nm for two transmission gratings, one with a period of 200 nm and the other with a period of 400 nm. These gratings consist of opaque gold bars separated by open spaces that have been produced by photolithography techniques commonly used to produce electronic components. The gold bars and the open spaces are nominally of the same width. Both gratings have a thickness of 470 nm. The transmission efficiency at the central, first, and, when possible, second order of diffraction was measured. In addition, guided-wave phenomena at nonnormal angles of incidence, as well as transmission differences depending on which side of the grating was illuminated, were investigated. The observed guided-wave effects allow one to selectively enhance the transmission of the grating at desired wavelengths, as is realized with a blazed reflection grating.
A solar ultraviolet detector prototype for the GOES spacecraft has been calibrated using the X24C beamline at the Brookhaven NSLS. Similar in design to the 3-channel 50110 CELIAS SEM, the GOES EUV uses a combination of transmission gratings and silicon photodiodes with thin-film metal overcoats to provide the required bandpasses. Four of the channels position the photodiodes at the first to fourth orders of 2500 and 5000 L/mm transmission gratings to provide spectral information over four wavelength bands from approximately 5-80 nm. The fifth channel positions the photodiode at first order of a 1667 L/mm transmission grating in combination with a bandpass filter centered at approximately 120 nm to provide coverage in the Lyman alpha region of the solar spectrum. The GOES EUV will provide continuous monitoring of solar EUV in bandpasses that are known to have a large variability in the amount of energy deposition in the earth's ionosphere over a solar cycle. Prototype detector design and calibration procedure are discussed. Absolute responses of the design model and synchrotron beamline properties relevant to calibration are presented.
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