High Throughput Soft X-Ray Filters with Enhanced IR-Rejection

To fully realize the advances NASA has made in x-ray microcalorimeter detectors, x-ray filters with enhanced out-of-band performance are needed. Blocking filters are essential components in these cryogenic detectors to minimize thermal load while admitting the soft x-rays of interest. Theoretically, an aluminum coating 15-20 nm thick, on each filter in the stack will provide the necessary IR attenuation. In practice, coatings this thin are less optically dense than predicted, and thickness must be nearly doubled to achieve sufficient thermal blocking. This degrades performance. The proposed innovation is to improve the thin aluminum blocking layer to increase its optical density and thermal rejection performance. Preliminary work suggests it is possible to increase the visible and IR light rejection of aluminized polyimide by a factor of 3 or more. In Phase 1, test samples will be made through altered processes. Film microstructural changes, x-ray, IR, and visible light transmission will be measured to identify process parameters that enhance IR blocking. Once optimized, coatings will provide equivalent IR blocking with thinner layers, enhancing mission throughput for the sounding rockets XQC and Micro-X in the near term and provide needed technology enhancements to make possible future missions such as IXO.

Entrance filters for the GOES solar telescopes Thermal blocking windows for laboratory-based astrophysics using x-ray microcalorimeters Laser entrance windows for targets used in fusion energy experiments. Windows for energy dispersive spectroscopy (EDS) systems used with scanning electron microscopy as well as calorimeter-based EDS systems.

Enhanced filter throughput is needed technology to meet NASA's Astrophysics and Heliophysics goals. The proposed aluminum filter coatings optimized for out-of-band rejection would dramatically enhance stacked filter specifications, such as the blocking filters for x-ray microcalorimeter spectrometers. Blocking filter stacks are needed for ASTRO-H, XQC, MICRO-X , and IXO particularly for observations at lower energies. The technology will also enhance the performance of double-filtered entrance apertures for solar telescopes such as SOLAR-C.

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