First X-ray imaging with a micromachined Wolter type-I telescope

Abstract

be a new probe to investigate chemical compositions of planetary atmospheres, surfaces of planets, moons or asteroids and high energy particles in planetary magnetospheres. A potential future Japanese exploration to Jupiter needs a light-weight (<10 kg) X-ray imager in order to capture X-ray auroras from Jupiter . However, limited resources, i.e., mass, power, size, have hindered exploration satellites from carrying a good angular resolution and large effective area X-ray telescope.Wolter type-I telescopes have been widely used in X-ray astronomy. X-rays are doubly reflected upon paraboloid and hyperboloid mirrors, to minimize aberrations (Wolter 1952). A few to hundreds of mirrors are conically nested to increase the effective area. Each mirror is fabricated individually with either polishing of thick mirror substrates, replication of precisely fabricated mandrels, or thermal forming of thin aluminum foils. However, these mirrors have to be heavy when a high angular resolution is sought for Bavdaz et al. (2004). Furthermore, the lightest aluminum foil mirror approximates ideal mirror surfaces with cones, which degrades the angular resolution to 10 arcmin under a short focal length less than 1 m. Therefore, a new mirror fabrication technology is needed for future X-ray astronomy missions as well as planetary explorations.A possible solution is micropore optics (Frazer 1997). Sidewalls of micro pores whose width is typically of the order of 10 to 100 µm are used for X-ray mirrors. The mirror thickness can be extremely thin, of the order of 100 µm to 10 mm. The micropore optics can thus be ultralight weight. Three types of micropore optics are proposed and being developed.The first type is silicon pore optics (SPO) (Bavdaz et al. 2004(Bavdaz et al. , 2010 which is composed of flat silicon wafers with groove structures as mirrors. The wafers are stacked and elastically bent into a conical shape. This type is being developed aiming at an angular resolution of ∼10 arcsec for the future gigantic X-ray astronomy satellite Athena. 1 1 http://www.the-athena-x-ray-observatory.eu.Abstract A light-weight Wolter type-I telescope for future space X-ray observations is prototyped by using micromachining technologies. Curvilinear micro pores with a width of 20 µ m are fabricated with deep reactive ion etching. Sidewalls of the pores are smoothed with high temperature annealing. Then, two wafers are deformed to different curvature radii, 1000 and 333 mm. The two wafers are aligned using parallel X-ray beams which are dominated by Al-K α line at 1.49 keV. High angular and positional accuracies of the order of arcsec and µm are achieved using movable stages. The first clear X-ray focusing is confirmed. Its angular resolution is 4.1 arcmin in full width half maximum while it is at least 92 arcmin in half power width. The effective area is 19.0 mm 2 which is ∼5 times smaller than a model calculation. We discuss causes of the degraded angular resolution and effective area and also future improvements.

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

“…47). To date, X-ray imaging with the Wolter type-I sample has been demonstrated, while the angular resolution was of the order of 10 (Ogawa et al 2017). Efforts are being made to increase resolution by improving the fabrication processes.…”

“…Although it has a conically approximated Wolter type-I geometry, the thinness of the wafer makes the effect negligible. The theoretical (Ogawa et al 2017) limit on the angular resolution comes from X-ray diffraction due to the narrow pores, which is estimated as 13 at 1 keV and 20 µm pore width (Fig. 47).…”

Development of Binary Black Hole Observation Satellite “ORBIS”

“…We developed the mission equipment for ORBIS, which consisted of the MEMS X-ray optics 4,5) and a charge-coupled device (CCD) image sensor. The MEMS X-ray optics are much less expensive and much lighter than the X-ray concentrators in the conventional telescopes on satellites are.…”

Enhanced X-ray reflectivity from Pt-coated silicon micropore optics prepared by plasma atomic layer deposition

“…We have been developing silicon micropore X-ray optics based on micro-electromechanical systems (MEMS) technologies. [5][6][7][8][9][10][11][12] Micropores with widths of the order of tens of micrometers are fabricated by deep reactive ion etching (DRIE) through silicon wafers with thicknesses of hundreds of micrometers. The sidewalls are smoothed at a high temperature to obtain a surface with sub-nanometer root mean square (rms) roughness over a length scale of several tens of micrometers.…”

“…Two wafers are precisely stacked and bent with different curvature radii to form a conical approximation to a Wolter type-I telescope. We previously demonstrated X-ray reflection and imaging with sample optics, 6,10) for use in future astronomical and planetary exploration missions. 13) Silicon is relatively easy to process with MEMS technologies, while heavier materials or those with a higher atomic number can achieve a higher reflectivity.…”