Optical module HEW simulations for the X-ray telescopes SIMBOL-X, EDGE and XEUS

Cusumano²,

Pareschi

2007

SPIE Proceedings

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Future X-ray telescopes like SIMBOL-X will operate in a wide band of the X-ray spectrum (from 0.1 to 80 keV); these telescopes will extend the optical performances of the existing soft X-ray telescopes to the hard X-ray band, and in particular they will be characterized by a angular resolution (conveniently expressed in terms of HEW, Half-EnergyWidth) less than 20 arcsec. However, it is well known that the microroughness of the reflecting surfaces of the optics causes the scattering of X-rays. As a consequence, the imaging quality can be severely degraded. Moreover, the X-ray scattering can be the dominant problem in hard X-rays because its relevance is an increasing function of the photon energy. In this work we consistently apply a numerical method and an analytical one to evaluate the X-ray scattering impact on the HEW of an X-ray optic, as a function of the photon energy: both methods can also include the effects of figure errors in determining the final HEW. A comparison of the results obtained with the two methods for the particular case of the SIMBOL-X X-ray telescope will be presented.

Section: Comparison Of the Two Methods For The Simbol-x Optical Modulementioning

confidence: 57%

HEW simulations and quantification of the microroughness requirements for x-ray telescopes by means of numerical and analytical methods

Cusumano²,

Pareschi

2007

SPIE Proceedings

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“…where we omitted the explicit dependence on λ to simplify the notation. Indeed, we demonstrated [17] that such an average would lead to an overestimate of HEW T . A more detailed approach, based on a first-order expansion of the k th PSF normalized to 1, S k , around the k th half-energy radius, Ω k , suggests that the formula to be used is [17] !…”

Section: The Hew Of the Entire Optical Modulementioning

confidence: 82%

“…This correction was not accounted for in previous simulations [17] of the XEUS mirror module. This, in turn, caused an overestimate of the previously simulated HEW for XEUS.…”

Section: The Hew Of the Entire Optical Modulementioning

confidence: 99%

Surface smoothness requirements for the mirrors of the IXO x-ray telescope

Pareschi

2009

SPIE Proceedings

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The International X-ray Observatory (IXO) is a very ambitious mission, aimed at the X-ray observation of the early Universe. This makes IXO extremely demanding in terms of effective area and angular resolution. In particular, the HEW requirement below 10 keV is 5 arcsec Half-Energy Width (HEW). At higher photon energies, the HEW is expected to increase, and the angular resolution to be correspondingly degraded, due to the increasing relevance of the X-ray scattering off the reflecting surfaces. Therefore, the HEW up to 40 keV is required to be better than 30 arcsec, even though the IXO goal is to achieve an angular resolution as close as possible to 5 arcsec also at this energy. To this end, the roughness of the reflecting surfaces has to not exceed a tolerance, expressed in terms of a surface roughness PSD (Power-Spectral-Density). In this work we provide such tolerances by simulating the HEW scattering term for IXO, assuming a specific configuration for the optical module and different hypotheses on the PSD of mirrors.

“…For example, in Fig. 8 we can see the comparison of two mandrel surface PSD with the roughness tolerance as derived from the HEW requirements for SIMBOL-X (HEW < 20 arcsec at 30 keV), following the approach proposed in a previous SPIE volume [6] . The PSD of the mandrel 291 is very close to the mirror roughness PSD tolerance.…”

Section: Conclusion and Final Remarksmentioning

confidence: 99%

“…A degradation of the smoothness level has become apparent from the PSD comparison after 2 and 4 replicae, especially in the spectral regime 100 -1 µm, which turns out to be crucial in determining the HEW degradation due to X-ray scattering [6] . We have then measured the change of surface roughness introduced by the replication of an Au-coated X-ray mirror shell prototype.…”

Section: Conclusion and Final Remarksmentioning

confidence: 99%

Surface roughness evaluation on mandrels and mirror shells for future X-ray telescopes

Sironi

Space Telescopes and Instrumentation 2008: Ultraviolet to Gamma Ray

2008

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More X-ray missions that will be operating in near future, like particular SIMBOL-X, e-Rosita, Con-X/HXT, SVOM/XIAO and Polar-X, will be based on focusing optics manufactured by means of the Ni electroforming replication technique. This production method has already been successfully exploited for SAX, XMM and Swift-XRT. Optical surfaces for X-ray reflection have to be as smooth as possible also at high spatial frequencies. Hence it will be crucial to take under control microroughness in order to reduce the scattering effects. A high rms microroughness would cause the degradation of the angular resolution and loss of effective area. Stringent requirements have therefore to be fixed for mirror shells surface roughness depending on the specific energy range investigated, and roughness evolution has to be carefully monitored during the subsequent steps of the mirror-shells realization. This means to study the roughness evolution in the chain mandrel, mirror shells, multilayer deposition and also the degradation of mandrel roughness following iterated replicas. Such a study allows inferring which phases of production are the major responsible of the roughness growth and could help to find solutions optimizing the involved processes. The exposed study is carried out in the context of the technological consolidation related to SIMBOL-X, along with a systematic metrological study of mandrels and mirror shells. To monitor the roughness increase following each replica, a multiinstrumental approach was adopted: microprofiles were analysed by means of their Power Spectral Density (PSD) in the spatial frequency range 1000-0.01 µm. This enables the direct comparison of roughness data taken with instruments characterized by different operative ranges of frequencies, and in particular optical interferometers and Atomic Force Microscopes. The performed analysis allowed us to set realistic specifications on the mandrel roughness to be achieved, and to suggest a limit for the maximum number of a replica a mandrel can undergo before being refurbished.