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 1979, and first used in the Chinese technology demonstrator spacecraft Lobster Eye Imager for Astronomy, launched in 2022. First major space telescope that uses lobster-eye optics is Chinese Einstein Probe, launched in 2024. Several space telescopes that use lobster-eye optics are under development or consideration.

Description

Mantis shrimp's eyes

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

Only three geometries that use grazing incidence reflection of X-rays to produce X-ray images are known: Wolter system, Kirkpatrick-Baez system, and lobster-eye geometry.[4]

The lobster-eye X-ray optics design was first proposed in the 1979 by Roger Angel.[5][6] His design is based in Kirkpatrick-Baez optics, but requires pores with square cross-section. Alternative arrangement was proposed by Shmidt in 1975: a one-dimensional arrangement consisted of a set of flat reflecting surfaces.[7][8] 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.[9]

Two designs are usually called the "Schmidt focusing collimator objective" and "Angel multi-channel lens".[4]

Multipores required for the lobster-eye optics is very hard to manufacture. Requirements are desribed in The WSPC Handbook of Astronomical Instrumentation:[4]

The pores must be square with width, 0.01 <d< 0.5 mm, and length L such that L/d is in the range 20–200, depending on the X-ray energy range you hope to cover and the angular resolution you hope to achieve. All the inner walls of the pores must be flat, very smooth with a surface roughness ≤ 1 nm, and made from or coated with a high-Z (dense) material to give a high X-ray reflection efficiency. The pores must be integrated into an array using a simple square, waffle, or similar packing scheme with a wall thickness that gives an open fraction of > 50% so that the optic has a reasonable efficiency. Finally, the pores must be packed on a spherical surface with radius of curvature 2F and with the axis of every pore aligned to point towards the common center of curvature with an accuracy in the range 0.1–5 arc minutes, commensurate with the angular resolution required.

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.[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 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.[10]

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.[11] In August and September of 2022, 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, Cygnus 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]

LEIA a preliminary mission testing the sensor design for the future Einstein Probe (EP) which uses a 12 sensor module Wide-field X-ray Telescope for a 3600 square degree field of view.[11] EP, a joint mission by Chinese Academy of Sciences (CAS) in partnership with ESA, was launched on 9 January 2024.[12]

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.

References

  1. 1 2 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. Bibcode:2023JPhCS2597a2010M. 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. 1 2 "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. 1 2 3 4 5 6 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. arXiv:2211.10007. Bibcode:2022ApJ...941L...2Z. doi:10.3847/2041-8213/aca32f. ISSN 2041-8205. Material was copied from this source, which is available under a Creative Commons Attribution 4.0
  4. 1 2 3 Richard Willingale (July 2021). "Lobster Eye Optics". In Sternberg, Amiel; Burrows, David N (eds.). The WSPC Handbook of Astronomical Instrumentation: Volume 4: X-Ray Astronomical Instrumentation. World Scientific Publishing Co. Pte. Ltd. pp. 33–47, 85–106. ISBN 978-981-4644-38-9. Retrieved 1 January 2024.
  5. ↑ Angel, J. R. P. (Oct 1, 1979). "Lobster eyes as X-ray telescopes". Astrophysical Journal. 233 (Part 1): 364–373. Bibcode:1979ApJ...233..364A. doi:10.1086/157397. Retrieved 29 December 2023.
  6. ↑ Hartline, Beverly Karplus (4 January 1980). "Lobster-Eye X-ray Telescope Envisioned". Science. 207 (4426): 47. Bibcode:1980Sci...207...47K. doi:10.1126/science.207.4426.47. ISSN 0036-8075. Retrieved 29 December 2023.
  7. ↑ Hudec, Rene; Feldman, Charly (2022). "Lobster Eye X-ray Optics". Handbook of X-ray and Gamma-ray Astrophysics. Springer Nature. pp. 1–39. arXiv:2208.07149. doi:10.1007/978-981-16-4544-0_3-1. ISBN 978-981-16-4544-0. S2CID 260481363.
  8. ↑ Schmidt, W. K. H. (August 1, 1975). "A proposed X-ray focusing device with wide field of view for use in X-ray astronomy". Nuclear Instruments and Methods. 127 (2): 285–292. doi:10.1016/0029-554X(75)90501-7 – via ScienceDirect.
  9. ↑ "Scientist has an all-seeing eye on the future". The Age. 2004-08-19. Retrieved 2021-12-17.
  10. ↑ "Launch of the world's first soft X-ray satellite with 'Lobster-Eye' imaging technology". phys.org. Retrieved 2021-12-17.
  11. 1 2 "Einstein Probe Time Domain Astronomical Information Center". ep.bao.ac.cn. Retrieved 28 December 2023.
  12. ↑ "Einstein Probe lifts off on a mission to monitor the X-ray sky". www.esa.int.
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