X-ray light capture for a much lighter space
Before (top) and after 150 hours of annealing (bottom) on different length scales (left to right). It can be seen that the surface roughness measured using Atomic Force Microscopy is significantly reduced over a wide range of length scales. Credit: Tokyo Metropolitan University
A team led by scientists from Tokyo Metropolitan University has created an unprecedented lightweight optic for an X-ray space telescope, breaking the traditional trade-off between angular resolution and weight. They used Micro Electro-Mechanical System (MEMS) technology, creating intricate patterns in silicon wafers that can direct and collect X-rays. By annealing and polishing, they realized ultra-sharp features that could rival the performance of existing telescopes for a fraction of their weight, at significantly lower launch costs.
X-ray astronomy is a vital tool that helps scientists study and classify various celestial bodies that emit and interact with X-rays, including our planet. But there’s one thing that’s interesting: most of the X-ray radiation is absorbed in our atmosphere, which means that telescopes and detectors have to be launched into space. With this comes various limitations, in particular, how heavy the device can be.
One of the main features of all astronomical observation optics is their angular resolution, or the angle that two light sources can create with a detector and still be identified individually. The problem with conventional X-ray optics is that in order to achieve higher resolutions, devices become increasingly heavy. This makes their launch into space very expensive. Even for the Hitomi telescope launched in 2016, it is considered very light, its effective weight is 600 kg per square meter of effective area.
The arrangement of the concentric slits allows the X-rays to enter and bounce off the inner walls, pushing them so that they are directed to a single point. Credit: Tokyo Metropolitan University
Now, a team led by Associate Professors Yuichiro Ezoe and Aoto Fukushima have solved this trade-off by engineering a high-performance unit weighing only 10 kg per square meter. They used Micro Electro-Mechanical Systems (MEMS) technology, a technique designed to fabricate microscopic mechanical actuators, to create sharp and intricate design patterns into silicon wafers that can direct and collect X-rays. The design itself follows the Wolter I geometry of existing X-ray telescopes, a concentric arrangement of tree ring-like slits that can push X-rays through a narrow range of angles and collect them to a point.
In particular, the team perfected the pattern itself. After etching the gap using a technique called deep reactive ion etching (DRIE), they found that there is surface roughness in the pattern that can smear the X-ray collection, effectively lowering the resolution. They annealed the pattern, applying heat in a special device for an unprecedented time. With a longer annealing, the silicon atoms on the surface of the pattern can move more, rounding out any roughness and increasing the angular resolution of the telescope. This is followed by grinding and chemical polishing to straighten the rounded edges of the gap itself.
The GEO-X mission aims to observe Earth’s magnetosphere using cosmic X-rays. It weighs only 50kg. Credit: Tokyo Metropolitan University
Importantly, the performance reported by the team matches that of telescopes already in action. Its weight makes it particularly suitable for the mission of GEO-X, a satellite designed to visualize Earth’s magnetosphere. The team targeted a very low total weight of 50 kg, a technological breakthrough that could see future missions sent into orbit at a much lower cost.
The results of their research were published in Express Optics.
The telescope’s radically different design offers a deeper view into space
Aoto Fukushima et al, Improved optical imaging performance of microporous silicon X-rays by ultra long-term annealing, Express Optics (2022). DOI: 10.1364/OE.459774
Provided by Tokyo Metropolitan University
Quote: X-ray light catcher for space gets much brighter (2022, 18 July) retrieved 18 July 2022 from https://phys.org/news/2022-07-x-ray-catchers-space-lot-lighter . html
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