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Lobster-eye optics

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Schematic diagram of lobster eye lens. The green arrow represents the incident light and the red arrow represents the normal of the channel wall.[1]

Lobster-eye optics is an X-ray optics design that mimic the structure of the lobster's eyes and has an ultra wide field of view. It was proposed in 1970s, and first used in the Chinese technology demonstrator Lobster Eye Imager for Astronomy launched in 2022. Currently several space telescopes that uses lobster-eye optics are under constuction, including Chinese Einstein Probe.

Description

Lobster

Lobster-eye optics mimic the structure of the lobster's eyes, that are made up of long, narrow cells that each reflect a tiny amount of light from a given direction. This allows the light from a wide viewing area to be focused into a single image. The optics is made of microchannel plates (or micropores) — thin, curved slabs of material dotted with tiny tubes across the surface. X-ray light can enter these tubes from multiple angles and is focused through grazing-incidence reflection that gives a wide field of view necessary for finding and imaging transient events that cannot be predicted in advance.[2]

The field of view of a lobster-eye optic, which is the solid angle subtended by the optic plate to the curvature center, is limited only by the optic size for a given curvature radius. Since the micropore optics is spherically symmetric in essentially all directions, theoretically, an idealized LE optic is almost free from vignetting except near the edge of the FoV.[3]

History

The lobster-eye X-ray optics principle was first proposed for X-rays in the 1979 by Roger Angel.[4][5][6] In 1989, physicists Keith Nugent and Stephen W. Wilkins collaborated to develop a lobster-eye optics, independently of Angel. Nugent and Wilkins' key contribution was to open up an approach to manufacturing these devices using microchannel plate technology. The lobster-eye approach opened the way for X-ray telescopes with a 360 degree view of the sky. "The reason it's got such a high profile is that other X-ray telescopes see a tiny, tiny part of the sky. Although normal telescopes see a small part of the sky, X-ray telescopes see an even smaller part. The beauty (of the new telescope) is that it actually expands that field of view hundreds of times," Nugent said.[7]

Usage

Configuration of the focusing mirror system, focal detector array, and FoV of LEIA. The mirror assembly is divided into four individual quadrants, each consisting of 3 × 3 MPO plates and associated with one of the four detectors. The overall FoV of the telescope module is 18fdg6 × 18fdg6.[3]

Lobster-eye optics can be used for backscattering imaging that is a single-sided access technology for homeland security, detection of improvised explosive devices, non-destructive testing, and medical imaging.[1]

LEIA instrument undergoing on-ground X-ray calibration at IHEP before being assembled onto the SATech satellite.[3]

A lobster-eye X-ray satellite was successfully launched on 25 July 2020 from the Taiyuan Satellite Launch Center in China. It was the first in-orbit space exploration satellite equipped with such imaging technology.[8]

Chinese Lobster Eye Imager for Astronomy (LEIA) is a wide-field X-ray imaging space telescope built by Chinese Academy of Sciences (CAS) and launched on July 27, 2022 onboard of SATech-01 satellite. LEIA has a sensor module giving it a field of view of 340 square degrees. It is a preliminary mission testing the sensor design for the future Einstein Probe which will use a 12 sensor module Wide-field X-ray Telescope for a 3600 square degree field of view.[9] In 2022 August and September, LEIA carried out a series of test observations for several days as part of its performance verification phase. A number of preselected sky regions and targets were observed, including the Galactic Center, the Magellanic Clouds, Sco X-1, Cas A, Cyg Loop, and a few extragalactic sources. The observations were performed in Earth's shadow to eliminate the effects of the Sun, starting 2 minutes after the satellite entering the shadow and ending 10 minutes before leaving it, resulting in an observational duration of ∼23 minutes in each orbit. The CMOS detectors were operating in the event mode.[3]

Einstein Probe is expected to be launched in January 2024.[10]

  • First-light X-ray image of the Galactic center region obtained by LEIA in a one-shot observation of 798 s in 0.5–4 keV, covering a field of view of 18fdg6 × 18fdg6 (left). Colors represent counts per pixel.[3]
    First-light X-ray image of the Galactic center region obtained by LEIA in a one-shot observation of 798 s in 0.5–4 keV, covering a field of view of 18fdg6 × 18fdg6 (left). Colors represent counts per pixel.[3]
  • Left: X-ray image of Sco X-1 in 0.5–4 keV observed by LEIA with 673 s exposure. Right: X-ray image of the Cygnus Loop nebula with a diameter of ∼2fdg5 obtained with a 604 s observation (colors represent photon energies).[3]
    Left: X-ray image of Sco X-1 in 0.5–4 keV observed by LEIA with 673 s exposure. Right: X-ray image of the Cygnus Loop nebula with a diameter of ∼2fdg5 obtained with a 604 s observation (colors represent photon energies).[3]

NASA's Goddard Space Center proposed an instrument that uses lobster-eye design for the ISS-TAO mission (Transient Astrophysics Observatory on the International Space Station), called X-ray Wide-Field Imager (WFI).[2]

SMILE, a space telescope project by European Space Agency and the Chinese Academy of Sciences, is planned to be launched in 2025. Its Soft X-ray Imager will use lobster-eye optics. THESEUS, ESA's proposed space telescope, also includes Soft X-ray Imager.

Further reading

  • Hudec, Rene; Feldman, Charly (2022). "Lobster Eye X-ray Optics". Handbook of X-ray and Gamma-ray Astrophysics. Springer Nature. pp. 1–39. ISBN 978-981-16-4544-0.

References

  1. ^ a b Ma, Shizhang; Ouyang, Mingzhao; Fu, Yuegang; Hu, Yuan; Zhang, Yuhui; Yang, Yuxiang; Wang, Shengyu (September 2023). "Analysis of Imaging Characteristics of Wide-field Lobster Eye Lens". Journal of Physics: Conference Series. 2597 (1): 012010. doi:10.1088/1742-6596/2597/1/012010. ISSN 1742-6596. Retrieved 29 December 2023. Material was copied from this source, which is available under a Creative Commons Attribution 3.0
  2. ^ a b "Proposed NASA Mission Employs "Lobster-Eye" Optics to Locate Source of Cosmic Ripples - NASA". NASA. 26 October 2017. Retrieved 29 December 2023. Public Domain This article incorporates text from this source, which is in the public domain.
  3. ^ a b c d e f Zhang, C.; et al. (1 December 2022). "First Wide Field-of-view X-Ray Observations by a Lobster-eye Focusing Telescope in Orbit". The Astrophysical Journal Letters. 941 (1): L2. doi:10.3847/2041-8213/aca32f. ISSN 2041-8205. Retrieved 29 December 2023.{{cite journal}}: CS1 maint: unflagged free DOI (link) Material was copied from this source, which is available under a Creative Commons Attribution 4.0
  4. ^ Bugos, Claire (23 June 2021). "How lobster eyes can help astronomers get a wider view of the cosmos". Astronomy Magazine. Retrieved 29 December 2023.
  5. ^ Angel, J. R. P. (Oct 1, 1979). "Lobster eyes as X-ray telescopes". Astrophysical Journal. 233 (Part 1): 364-373. Retrieved 29 December 2023.
  6. ^ Hartline, Beverly Karplus (4 January 1980). "Lobster-Eye X-ray Telescope Envisioned". Science. 207 (4426): 47–47. doi:10.1126/science.207.4426.47. ISSN 0036-8075. Retrieved 29 December 2023.
  7. ^ "Scientist has an all-seeing eye on the future". The Age. 2004-08-19. Retrieved 2021-12-17.
  8. ^ Kong, The University of Hong. "Launch of the world's first soft X-ray satellite with 'Lobster-Eye' imaging technology". phys.org. Retrieved 2021-12-17.
  9. ^ "Einstein Probe Time Domain Astronomical Information Center". ep.bao.ac.cn. Retrieved 28 December 2023.
  10. ^ "Einstein Probe factsheet". www.esa.int. Retrieved 28 December 2023.
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