ABSTRACT
We have measured and compared the spatial fidelity of two types of microchannel plates over roughly half of their active area. Measurements of the spatial fidelity of curved-channel microchannel plates confirm earlier reports of large (>25 microm), irregular position offsets between the front and the back of the microchannel plates. Straight-pore microchannel plates used in a chevron configuration, on the other hand, showed almost no such position offsets (<4 microm).
ABSTRACT
We report here a technique for determining the quantum throughput of a high-resolution, extreme-UV spectrometer by use of the National Institute of Standards and Technology's Synchroton Ultraviolet Radiation Facility at Gaithersburg, Md. (SURF-II). Observations were obtained at three different synchrotron operating energies with and without a magnesium fluoride filter and a tin-germanium filter. This calibration permits us to extract system efficiencies for three overlapping spectroscopic orders with uncertainties of 10-30%. The uncertainties quoted in this preliminary experiment were limited by the available time, and we propose that with minor refinements a significant improvement could be realized.
ABSTRACT
One of the many calibrations performed for a scientific-quality spectrometer is the characterization of its scattered-light properties. The scattered light can arise from any optical surface, and light leaks or scattering from baffles can also contribute to the instrumental stray-light level. For a diffraction-grating spectrometer the primary contribution to instrumental scattered light has been found to be the scattered light from the grating. The results from measuring the scattered-light properties of 10 diffraction gratings are discussed along with the application of these results in analyzing the total scattered light measured for three spectrometers. It has been found from these measurements that there are two components of the grating scattered light: a Lorentzian-type component and a constant background component. The Lorentzian component is predicted from the diffraction theory for a grating, and the constant background component is consistent with Rayleigh scattering from the microscopic surface im erfections. It was also discovered that multiple replicas of gratings from the same master grating exhibit significantly more scattered light than the preceding replica by factors of 1.1-2.
ABSTRACT
Microchannel plate detectors are widely used for ultraviolet (UV) and extreme-ultraviolet (EUV) observations. Curved-channel microchannel plates, or C plates, provide an electron gain of approximately 10(6) in a single plate because the curved channels prevent ion feedback. However, offsets between input and output in curved-channel microchannel plates produce slight distortions in the spatial or spectral scale of thedetector, complicating the use of such detectors for high-resolution imaging and spectroscopy. We have examined the image distortion caused by nonconstant curvature of the channels by (a) observing spectral nonlinearities in an EUV spectrometer, (b) measuring the positions of several plugged channels of a typical plate and comparing the positions of the channels on both the input and the output sides, and (c) mapping input versus output of typical plates, using a mechanically scanned spot of UV light. We find that a typical C plate with 25-microm-diameter pores exhibits +/-25-microm image distortion across the plate. Calibration of this image distortion as reflected in the spectral nonlinearity of our EUV spectrograph improves the spectral line positions by a factor of 4, permitting solar-emission-line Doppler shift determination of +/- 2 microm (+/- 1 km/s).