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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 arrows represent the normal of the channel wall.[1]

Lobster-eye optics are a biomimetic design, based on the structure of the eyes of a lobster with an ultra wide field of view, used in X-ray optics. This configuration allows X-ray light to enter from multiple angles, capturing more X-rays from a larger area than other X-ray telescopes. The idea was originally proposed for use in X-ray astronomy by Roger Angel in 1979, with a similar idea presented earlier by W. K. H. Schmidt in 1975. It was first used by NASA on a sub-orbital sounding rocket experiment in 2012. The Lobster Eye Imager for Astronomy, a Chinese technology demonstrator satellite, was launched in 2022. The Chinese Einstein Probe, launched in 2024, is the first major space telescope to use lobster-eye optics. Several other such space telescopes are currently under development or consideration.

Description

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Close-up view of crustacean's (mantis shrimp's) eyes

While most animals have refractive eyes, lobsters and other crustaceans have reflective eyes.[2] The eyes of a crustacean contain clusters of cells, each reflecting a small amount of light from a particular direction. Lobster-eye optics technology mimics this reflective structure. This arrangement allows the light from a wide viewing area to be focused into a single image. The optics are made of microchannel plates. X-ray light can enter small tubes within these plates from multiple angles, and is focused through grazing-incidence reflection that gives a wide field of view. That, in turn, makes it possible to locate and image transient astronomical events that could not have been predicted in advance.[3]

The field of view (FoV) 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 are spherically symmetric in essentially all directions, theoretically, an idealized lobster-eye optic is almost free from vignetting except near the edge of the FoV.[4] Micropore imagers are created from several layers of lobster-eye optics that creates an approximation of Wolter type-I optical design.[2]

History

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Only three geometries that use grazing incidence reflection of X-rays to produce X-ray images are known: the Wolter system, the Kirkpatrick-Baez system, and the lobster-eye geometry.[5]

The lobster-eye X-ray optics design was first proposed in 1979 by Roger Angel.[6][7] His design is based on Kirkpatrick-Baez optics, but requires pores with a square cross-section, and is referred to as the "Angel multi-channel lens".[5] This design was inspired directly by the reflective properties of lobster eyes.[1][4] Before Angel, an alternative design involving a one-dimensional arrangement consisting of a set of flat reflecting surfaces had been proposed by W. K. H. Schmidt in 1975, known as the "Schmidt focusing collimator objective".[5][8][9] In 1989, physicists Keith Nugent and Stephen W. Wilkins collaborated to develop lobster-eye optics independently of Angel. Their key contribution was to open up an approach to manufacturing these devices using microchannel plate technology. This lobster-eye approach paved the way for X-ray telescopes with a 360-degree view of the sky.[10]

In 1992, Philip E. Kaaret and Phillip Geissbuehler proposed a new method for creating lobster-eye optics with microchannel plates.[11] Micropores required for lobster-eye optics are difficult to manufacture and have strict requirements. The pores must have widths between 0.01 and 0.5 mm and should have a length-to-width ratio of 20–200 (depends on the X-ray energy range); they need to be coated with a dense material for optimal X-ray reflection. The pore's inner walls must be flat and they should be organized in a dense array on a spherical surface with a radius of curvature of 2F, ensuring an open fraction greater than 50% and pore alignment accuracy between 0.1 and 5 arc minutes towards a common center.[5]

Similar optics designs include honeycomb collimators (used in NEAR Shoemaker's XGRS detectors and MESSENGER's XRS) and silicon pore imagers (developed by ESA for its planned ATHENA mission).[2]

Uses

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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.[4]
The LEIA instrument undergoing on-ground X-ray calibration before being assembled onto the SATech satellite.[4]

NASA launched the first lobster-eye imager on a Black Brant IX sub-orbital sounding rocket in 2012. The STORM/DXL instrument (Sheath Transport Observer for the Redistribution of Mass/Diffuse X-ray emission from the Local galaxy) had micropore reflectors arranged in an array to form a Kirkpatrick-Baez system.[12][13] BepiColombo, a joint ESA and JAXA Mercury mission launched in 2018, has a non-imaging collimator MIXS-C, with a microchannel geometry similar to the lobster-eye micropore design.[8][14]

CNSA launched the Lobster-Eye X-ray Satellite in 2020, the first in-orbit lobster-eye telescope.[15] In 2022, the Chinese Academy of Sciences built and launched the Lobster Eye Imager for Astronomy (LEIA), a wide-field X-ray imaging space telescope. It is a technology demonstrator mission that tests the sensor design for the Einstein Probe.[16] LEIA has a sensor module that gives it a field of view of 340 square degrees.[16] In August and September of 2022, LEIA conducted measurements to verify its functionality. 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. To eliminate interference from sunlight, the observations were obtained in Earth's shadow, starting 2 minutes after the satellite entered 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.[4]

  • 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 18° × 18° (left). Colors represent counts per pixel.[4]
    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 18° × 18° (left). Colors represent counts per pixel.[4]
  • 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.[4]
    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.[4]

Current and future space telescopes

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The Einstein Probe, a joint mission by the Chinese Academy of Sciences (CAS) in partnership with the European Space Agency (ESA) and the Max Planck Institute for Extraterrestrial Physics, was launched on 9 January 2024.[17] It uses a 12-sensor module wide-field X-ray telescope for a 3600 square degree field of view, first tested by the Lobster Eye Imager for Astronomy mission.[16]

The joint French-Chinese SVOM was launched on 22 June 2024.[18]

NASA's Goddard Space Center proposed an instrument that uses the lobster-eye design for the ISS-TAO mission (Transient Astrophysics Observatory on the International Space Station), called the X-ray Wide-Field Imager.[3] ISS-Lobster is a similar concept by ESA.[19]

Several space telescopes that use lobster-eye optics are under construction. SMILE, a space telescope project by ESA and CAS, is planned to be launched in 2025.[20] ESA's THESEUS is now under consideration.[21]

Other uses

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Lobster-eye optics can also be used for backscattering imaging for homeland security, detection of improvised explosive devices, nondestructive testing, and medical imaging.[1]

References

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  1. ^ a b c 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. Material was copied from this source, which is available under a Creative Commons Attribution 3.0 Archived 2011-02-23 at the Wayback Machine
  2. ^ a b c Kitchin, C. R. (2017). "X-Ray and γ Ray Regions". Remote and Robotic Investigations of the Solar System. pp. 95–136. doi:10.1201/9781351255479-3. ISBN 978-1-351-25547-9.
  3. ^ a b "Proposed NASA Mission Employs "Lobster-Eye" Optics to Locate Source of Cosmic Ripples - NASA". NASA. 26 October 2017. Archived from the original on 29 December 2023. Retrieved 29 December 2023. Public Domain This article incorporates text from this source, which is in the public domain.
  4. ^ a b c d e f g Zhang, C.; et al. (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 Archived 2017-10-16 at the Wayback Machine
  5. ^ a b c d Willingale, Richard (2021). Lobster Eye Optics. Vol. 4. pp. 85–106. Bibcode:2021hai4.book...85W. doi:10.1142/9789811203800_0005. ISBN 978-981-4644-38-9.
  6. ^ 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.
  7. ^ 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. PMID 17730799.
  8. ^ a b Hudec, Rene; Feldman, Charly (2022). "Lobster Eye X-ray Optics". Handbook of X-ray and Gamma-ray Astrophysics. pp. 1–39. doi:10.1007/978-981-16-4544-0_3-1. ISBN 978-981-16-4544-0.
  9. ^ Schmidt, W.K.H. (August 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. Bibcode:1975NucIM.127..285S. doi:10.1016/0029-554X(75)90501-7.
  10. ^ "Scientist has an all-seeing eye on the future". The Age. 19 August 2004.
  11. ^ Kaaret, Philip E.; Geissbuehler, Phillip (1992). "Lobster-eye x-ray optics using microchannel plates". In Hoover, Richard B. (ed.). Multilayer and Grazing Incidence X-Ray/EUV Optics. Vol. 1546. p. 82. doi:10.1117/12.51261.
  12. ^ Collier, Michael R.; et al. (July 2015). "Invited Article: First flight in space of a wide-field-of-view soft x-ray imager using lobster-eye optics: Instrument description and initial flight results". Review of Scientific Instruments. 86 (7). Bibcode:2015RScI...86g1301C. doi:10.1063/1.4927259. hdl:1808/22116. PMID 26233339.
  13. ^ Keesey, Lori (7 February 2013). "NASA scientists build first-ever wide-field X-ray imager". phys.org (Press release). NASA's Goddard Space Flight Center.
  14. ^ "MIXS: mercury imaging x-ray spectrometer". BepiColombo. European Space Agency.
  15. ^ "Launch of the world's first soft X-ray satellite with 'Lobster-Eye' imaging technology". phys.org (Press release). The University of Hong Kong. 27 July 2020.
  16. ^ a b c "LEIA: Introduction". Einstein Probe Time Domain Astronomical Information Center.
  17. ^ The European Space Agency (January 9, 2024). "Einstein Probe lifts off on a mission to monitor the X-ray sky". www.esa.int. Archived from the original on January 9, 2024. Retrieved February 6, 2024.
  18. ^ "The MXT and the lobster eye - Svom". China National Space Administration (CNSA); Chinese Academy of Sciences (CAS); French Space Agency (CNES). Archived from the original on 2023-10-04. Retrieved 2024-02-06.
  19. ^ Camp, Jordan; Barthelmy, Scott; Petre, Rob; Gehrels, Neil; Marshall, Francis; Ptak, Andy; Racusin, Judith (2015). "ISS-Lobster: A low-cost wide-field x-ray transient detector on the ISS". In Hudec, René; Pina, Ladislav (eds.). EUV and X-ray Optics: Synergy between Laboratory and Space IV. Vol. 9510. doi:10.1117/12.2176745.
  20. ^ Branduardi-Raymont, G.; Wang, C.; Escoubet, C.P.; et al. (2018). ESA SMILE definition study report (PDF) (Technical report). European Space Agency. pp. 1–84. doi:10.5270/esa.smile.definition_study_report-2018-12. ESA/SCI(2018)1.
  21. ^ Amati, Lorenzo (2017). "The Transient High-Energy Sky and Early Universe Surveyor (THESEUS)". The Fourteenth Marcel Grossmann Meeting. pp. 3295–3300. arXiv:1907.00616. doi:10.1142/9789813226609_0421. ISBN 978-981-322-659-3.
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