We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and scientific applications for our technology includes: a monochromatic X-ray collimater for medical diagnostics, a relay optic to transport an X-ray beam from the target in a scanning electron microscop0e to a lithium-drifted silicon and microcalorimeter detectors and a satellite mounted telescope to collect celestial X-rays. A wide variety of mono- and multilayer coatings allow X-rays up to ~100 keV to be reflected. Our paper presents data from a variety of diagnostic measurements on the properties of the PET foil and imaging results form single- and multi-shell lenses.
A number of X-ray astronomical missions of near future will make use of hard X-ray optics with broad-band multilayer coatings. However multilayer mirrors can be also useful to enhance the effective area of a given X-ray telescope in the "classical" low energy X-ray band (0.1 - 10 keV), the window where X-ray spectroscopy provides very useful plasma diagnostics) with a consistent gain with respect to usual single-layer reflectors. Multilayers for soft X-rays are based on stacks with constant d-spacing (in order to minimize the loss due to the photoelectric effect). A further gain in reflectivity (however only restricted to the energy range between 0.5 and 4 keV) can be achieved by using a low density material as a first external layer of the film, with the role of reducing the photoelectric absorption effect when the mirror acts in total external reflection regime (Carbon is the most performing material for this specific scope). In this paper the impact of using soft X-ray multilayer mirrors in future X-ray telescopes is discussed, and soft X-ray reflectivity tests performed on prototype samples presented.
The X-Ray Telescope (XRT) experiment on-board the Japanese satellite
SOLAR-B (launch in 2006) aimed at providing full Sun field of view at
~ 1.5" angular resolution, will be equipped with two wheels of focal-plane filters to select spectral features of X-ray emission from the Solar corona, and a front-end filter to significantly reduce the visible light contamination. We present the results of the X-ray calibrations of the XRT flight filters performed at the X-ray Astronomy Calibration and Testing (XACT) facility of INAF-OAPA. We describe the instrumental set-up, the adopted measurement technique, and present the transmission vs. energy and position measurements.
The X-Ray Telescope (XRT) experiment on-board the Japanese satellite SOLAR-B (launch in 2006) is equipped with a modified Wolter I grazing incidence X-ray telescope (focal length 2700 mm) to image the full Sun at ~ 1.5" angular resolution onto a 2048 x 2048 back illuminated CCD focal plane detector. The X-ray telescope consisting of one single reflecting shell is coated with ion beam sputtered Iridium over a binding layer of Chromium to provide nearly 5 square centimetres effective area at 60 Å. We present preliminary results of X-ray calibrations of the XRT flat mirror samples performed at the X-ray Astronomy Calibration and Testing (XACT) facility of INAF-OAPA. We describe the instrumental set-up, the adopted measurement technique, and present the measured reflectivity vs. angle of incidence at few energies.
A single stage Adiabatic Demagnetization Refrigerator (ADR), has been
set-up at the X-ray Astronomy Calibration and Testing (XACT) facility
of INAF - Osservatorio Astronomico di Palermo G.S. Vaiana, for the
development and testing of cryogenic X-ray detectors for laboratory and astrophysical applications. The ADR allows to cool detectors at
temperatures below 40 mK and to maintain them at constant operating
temperature for many hours. We describe the design and construction of
the ADR and present test results and performances.
We are conducting a measurement program on back-up filters of the
XMM-Newton EPIC camera aimed at monitoring possible aging effects
during the mission lifetime. One thin and one medium EPIC back-up
filters have been stored since 1997 in an environment similar to that
one of the flight filters (dry nitrogen box before launch, high vacuum
after launch). The transmission of the two filters has been measured
periodically in the 1900-10000 angstrom wavelength range where effects of aging would be clearly evident. The preliminary results, after 5 years of monitoring, show that a slight aging effect has occurred on both filters which, however, has no significant impact onto the EPIC calibration for the correct analysis of the X-ray astrophysical observations.
We present preliminary results on a program aimed at characterizing the optical properties of materials of potential usage in filters for soft x-ray detectors. In particular, we discuss a method that we have used to derive and model the refractive index n and the extinction coefficient k of thin plastic film materials. The method is based on best fit estimates of the parameters of a quanto- mechanical model describing k. The value of n is then evaluated using the Kramers-Kronig relationship. This method has provided accurate values of previously unknown optical constants of polyimide and lexan allowing to model the transmission of multilayer filters such as the aluminized polyimide filters of the HRC on board Chandra X-ray Observatory.
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