Development of grazing-incidence multilayer mirrors by direct Ni electroforming replication: a status report

Abstract

The Ni electroforming replication process has been used successfully by Beppo-SAX, JET-X/SWIFT, and XMMNewton, to produce their gold-coated X-ray mirrors. The important feature of the technique is that, also with thin substrates, it is possible to achieve a good angular resolution, which is important for obtaining high signal-to-noise ratios in deep observations and imaging extended sources, while the assembly and integration of the monolithic shells is a relatively easy task. Two approaches can be used for the up grade of this technique also to the case of mirrors with multilayer coating, to be used in future hard X-ray missions: i) the direct replication of the mirror shell, after the deposition of the multilayer film on the master (mandrel) surface followed by the electroforming of the Ni walls, ii) the application of the multilayer film to the internal surface of Ni mirror shells, previously realized by replication. In this paper the last results achieved in Italy in the context of an activity aiming at the development of the former of the two methods will be presented and discussed.

The MPE X-ray test facility PANTER: Calibration of hard X-ray (15–50 kev) optics

“…We have shown that the PANTER X-ray Test Facility is not only well-suited for the calibration and characterisation of short focal length X-ray mirror performance parameters like effective Reflectivity R(parabola) × R(hyperbola) as function of energy for a Pt/C multilayer shell, with model (solid line) for incidence angles of 0.257 • and 0.129 • , respectively [8] area and half-energy width in the "classical" soft X-ray range (up to 15 keV). It can very well also be used for longer focal lengths (here: 10 m) where the mirror sample will be put into the vacuum tube.…”

“…photons are reflected at the paraboloid but do not hit the hyperboloid anymore and thus do not reach the focal point. These effects, however, can be calculated and taken into account when analysing the calibration data [8]. Figure 4 shows a NiCo replicated shell with W/Si multilayer coating (MSFC+SAO) mounted on a spider, just at the entry of the PANTER vacuum tube to the instrument chamber.…”

“…For a parallel input beam the grazing incidence angles at paraboloid (α p ) and hyperboloid (α h ) are identical; for a finite source distance (divergent beam) α p increases while α h decreases, leading to an image distance greater than the focal length coatings. With numerous stacks of alternating layers of low and high atomic number (e.g., W/Si, Pt/C) with different thicknesses (from about 1 nm to 10 nm) a significant increase of reflectivity at high energies (10-80 keV) on the basis of Bragg reflection (constructive interference) can be achieved [8,9].…”

Progress Toward Light Weight High Angular Resolution Multilayer Coated Optics

“…Our group is the only one that uses CN x to coat and smooth the mandrel (see Ulmer et al (2003) and references therein), but the multilayer coating process we developed has been copied by at least one other group (i.e. Pareschi et al, 2005). This process is to coat a mandrel with multilayer, electroform over these layers, and then remove the electroformed multilayers with layers intact on the inside of the mirror.…”

Analytical evaluation of the X-ray scattering contribution to imaging degradation in grazing-incidence X-ray telescopes

“…The PANTER X-ray facility now allows testing in soft (0.2 ÷ 10 keV) and hard (15 ÷ 50 keV) X-rays multilayer-coated optics prototypes for future X-ray telescopes (Pareschi et al 2005;Romaine et al 2005). The source distance finiteness causes some departures of the optic performances, with respect to the case with the source at astronomical distance: effective area loss, different incidence angles on paraboloid and hyperboloid, focal length displacement, a slight focal spot blurring (Van Speybroeck & Chase 1972).…”