An open question in the measurement of X-ray optics for telescopes in space is what the point spread function (PSF) looks like in orbit and what is the focal length for an infinite source distance. In order to measure such a PSF, a parallel X-ray beam with a diameter of several centimeters to meters is needed.
For this purpose it is studied of how to collimate the X-rays using a zone plate. Furthermore, a configuration study is presented to characterize X-ray optics with such a collimated beam at the PANTER X-ray test facility. In particular, estimations for segmented optics for future X-ray missions such as ATHENA+ with a focal length of 10m to 20m are presented.
We present a diffractive-refractive x-ray telescope for simultaneous imaging in multiple energy bands. Based on segmented achromatic lenses, the system yields an angular resolution around 1 mas between 5 and 10 keV for a focal distance of a few
. The total sensitivity, measured via the bandwidth-integrated effective area, reaches at least
. Our arrangement exploits Fresnel lenses used in higher phase shift orders for orderly protection from scattered radiation as well as reduced refractive profiles for an enhanced throughput. The telescope, which has its focal plane detector on a separated spacecraft, may be reoriented to new astrophysical targets on short timescales. Scientific applications are briefly discussed for active galactic nuclei.
We report on recent theoretical and experimental results on diffractive-refractive transmission lenses as promising
candidates for next-generation X-ray telescopes with an ultra-high angular resolution. This feature is especially
analyzed for elementary refractive, diffractive and dispersion-corrected hybrid lenses and a fundamental limit to
the angular resolution for optics of the latter type is identified. An inherent flexibility in adjusting the image
sharpness is obtained from the segmentation of an aperture into small partitions, whose degree of coherence can
be controlled continuously. Successfully realized monolithic phase zone plates from a spin-coated polymer show
the way to the practical implementation of large-scale objectives. Based on these concepts, an arrangement for
enhanced and variable high-throughput imaging around the Fe-Kα line at 6.4 keV is finally proposed.
We report on a theoretical study of free-standing phase transmission gratings for high-resolution extreme ultraviolet (EUV) and soft x-ray spectroscopy and investigate their properties. Designed for wavelengths between about 2 and 40 nm, the devices may provide a first order diffraction efficiency beyond 30%. We use rigorous coupled wave analysis methods in order to optimize the grating design parameters and discuss features of segmented grating arrays. Elemental, as well as compound, materials such as Be, Mo, LiF, and poly-(methylmethacrylate) are considered with respect to their potential and practical limitations in terms of feasibility and sensitivity to radiation damage. Simulations are performed for several samples on the radiation produced by a table-top EUV plasma source and applications to astrophysical problems are considered.
Arrays of achromatic Fresnel lenses are investigated for future high-resolution X-ray imaging missions. Unlike
single-focus instruments, parallel arrangements of numerous tiny telescopes provide an easy and natural approach
to spectroscopic observations in several energy bands, at an unprecedented short focal length of few 103 m. We
suggest an optimized design with an angular resolution around 1 mas between 5 and 10 keV and analyze its
optical capabilities as well as issues like the background problem which affects the achievable signal-to-noise
ratio. An astronomical simulation is performed on the sun-like star Capella.
We report on a theoretical study of binary phase transmission gratings for high-resolution EUV and soft X-ray
spectroscopy and investigate their optical properties. Designed for wavelengths between about 2 and 40 nm, the
devices may provide a first order diffraction efficiency beyond 30%. We use RCWA methods in order to optimize
the grating design parameters and discuss special features of segmented grating arrays. Several elemental as
well as compound materials like Be, Mo, LiF and PMMA are considered with respect to their potential and
practical limitations in terms of feasibility and sensitivity to radiation damage. Simulations are performed for
several samples on the radiation produced by a table-top EUV plasma source and applications to astrophysical
problems are considered.
We discuss various astrophysical science drivers for upcoming high-resolution X-ray instruments on the mas
scale. Even more than current missions like Chandra and XMM-Newton, planned diffraction-limited telescopes
would provide unprecedented insights into hottest-ever physical processes in the universe. We apply an efficient
and simple Fresnel lens design to samples of well-known targets like stellar coronae, X-ray binaries, AGN, ultraluminous
X-ray sources and supernova remnants. The cosmological impact of deep observations is discussed as
well as potential applications to low-mass gravitational lenses.
We present a diffractive-refractive X-ray telescope for simultaneous imaging in multiple energy bands. Based on
segmented dispersion corrected hybrid lenses, the system yields an angular resolution around 1 mas for photon
energies between 5 and 10 keV. The total sensitivity, measured in terms of effective area times spectral bandwidth,
reaches several 103 cm2 keV. The suggested arrangement exploits Fresnel lenses used in higher diffraction orders
for orderly protection from scattered radiation as well as reduced refractive profiles for an enhanced throughput.
With a focal distance of a few 102 km, the telescope having its focal plane detector on a separated spacecraft,
may be re-oriented to new astrophysical targets on short timescales. Scientific applications are briefly discussed
for active galactic nuclei (AGN).
We present an innovative X-ray telescope design for diffraction-limited imaging on the mas scale. The long focal
distance scheme is based on dispersion-corrected Fresnel lenses made of Li and Be. Annular apertures with an outer
diameter of 3.5 m permit simultaneously focused X-rays in two energy bands around 5 and 10 keV. Concentrated to
focal spot sizes of ~ 1 mm, a photon throughput of ~ 1400 cm2 keV is achieved in the soft and hard band as well. With
its partial spectroscopic capability, the device might be preferably suited for measurements of hardness ratios in X-ray
emitting coronae of nearby stars and even disc-to-jet conversion mechanisms within AGN.
In our ongoing studies of high precision glass slumping we have successfully formed the first Wolter-I X-ray mirror
segments with parabola and hyperbola in one piece. It could be demonstrated that the excellent surface roughness of the
0.55 mm thick display glass chosen is conserved during the slumping process. The influence of several parameters of the
process, such as maximum temperature, heating and cooling rates etc. have to be measured and controlled with adequate
metrology. Currently, we are optimizing the process to reduce the figure errors down to 1 micrometer what will be the
starting point for further, final figure error corrections. We point out that metrology plays an important role in achieving a
high precision optics, i.e. an angular resolution of a few arcsec. In this paper we report on the results of our studies and
discuss them in the context of the requirements for future X-ray telescopes with large apertures.
We present new schemes for a next-generation X-ray telescope for the energy range between approximately 1 and 10 keV providing an angular resolution of at least 1 milli-arcsec. Its technology will be based on diffractive transmission optics, e.g. Fresnel zone plates and their derivatives. Beside near-diffraction limited imaging, these devices hold the potential of a large collecting area well beyond 10 square meters at a simple and lightweight construction, compared to conventional mirror telescopes. However, there are drawbacks. Firstly the intrinsically long focal lengths do require separation and precise
formation flight of lens and detector spacecraft. Accordingly, techniques will be discussed for relative stabilization on the one hand and possibilities to reduce focal length and thus lever arm on the other hand. For this purpose, large arrays of small, independent lenses might offer a notable perspective. Secondly, diffractive optics
feature severe focal length dispersion which has to be accepted using narrow-band spectral selection or-better-should be corrected over a practicable wide energy range. In the hard X-ray regime, hybrid lens devices made of beryllium, lithium or plastics like polycarbonate will be an appropriate solution for a fixed energy, while tunable systems with variable correction lenses possess-in principle-the capability for dispersion compensation in the soft X-ray region, too. An overview on the science case of milli-arcsec X-ray imaging will conclude the contribution. We show that significant new insights in astrophysical processes are expected just at and beyond this angular scale and give examples from X-ray binaries over AGN's up to gamma-ray bursts.