Lobster-eye optics

File:Odontodactylus scyllarus eyes.jpg's) eyes]]

While most animals have refractive eyes, lobsters and other crustaceans have reflective eyes.{{cite book |doi=10.1201/9781351255479-3 |chapter=X-Ray and γ Ray Regions |title=Remote and Robotic Investigations of the Solar System |date=2017 |last1=Kitchin |first1=C. R. |pages=95–136 |isbn=978-1-351-25547-9 }} 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.{{cite web |title=Proposed NASA Mission Employs "Lobster-Eye" Optics to Locate Source of Cosmic Ripples - NASA |url=https://www.nasa.gov/missions/station/proposed-nasa-mission-employs-lobster-eye-optics-to-locate-source-of-cosmic-ripples/ |publisher=NASA |access-date=29 December 2023 |date=26 October 2017 |archive-date=29 December 2023 |archive-url=https://web.archive.org/web/20231229113457/https://www.nasa.gov/missions/station/proposed-nasa-mission-employs-lobster-eye-optics-to-locate-source-of-cosmic-ripples/ |url-status=live }} {{PD-notice}}

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.{{cite journal |last1=Zhang |first1=C. |last2=Ling |first2=Z. X. |last3=Sun |first3=X. J. |display-authors=1 |title=First Wide Field-of-view X-Ray Observations by a Lobster-eye Focusing Telescope in Orbit |journal=The Astrophysical Journal Letters |date=December 2022 |volume=941 |issue=1 |pages=L2 |doi=10.3847/2041-8213/aca32f |doi-access=free |arxiv=2211.10007 |bibcode=2022ApJ...941L...2Z |issn=2041-8205}} 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }} Micropore imagers are created from several layers of lobster-eye optics that creates an approximation of Wolter type-I optical design.

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.

The lobster-eye X-ray optics design was first proposed in 1979 by Roger Angel.{{cite journal |last1=Angel |first1=J. R. P. |title=Lobster eyes as X-ray telescopes |journal=Astrophysical Journal |date=Oct 1, 1979 |volume=233 |issue=Part 1 |pages=364–373 |doi=10.1086/157397 |bibcode=1979ApJ...233..364A |doi-access=free }}{{cite journal |last1=Hartline |first1=Beverly Karplus |title=Lobster-Eye X-ray Telescope Envisioned |journal=Science |date=4 January 1980 |volume=207 |issue=4426 |pages=47 |doi=10.1126/science.207.4426.47 |pmid=17730799 |bibcode=1980Sci...207...47K }} 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".{{cite book |doi=10.1142/9789811203800_0005 |title=Lobster Eye Optics |date=2021 |last1=Willingale |first1=Richard |volume=4 |pages=85–106 |bibcode=2021hai4.book...85W |isbn=978-981-4644-38-9 }} This design was inspired directly by the reflective properties of lobster eyes. 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".{{cite book |doi=10.1007/978-981-16-4544-0_3-1 |chapter=Lobster Eye X-ray Optics |title=Handbook of X-ray and Gamma-ray Astrophysics |date=2022 |last1=Hudec |first1=Rene |last2=Feldman |first2=Charly |pages=1–39 |isbn=978-981-16-4544-0 }}{{cite journal |last1=Schmidt |first1=W.K.H. |title=A proposed X-ray focusing device with wide field of view for use in X-ray astronomy |journal=Nuclear Instruments and Methods |date=August 1975 |volume=127 |issue=2 |pages=285–292 |doi=10.1016/0029-554X(75)90501-7 |bibcode=1975NucIM.127..285S }} 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.{{cite news |title=Scientist has an all-seeing eye on the future |url=https://www.theage.com.au/national/scientist-has-an-all-seeing-eye-on-the-future-20040819-gdyhdr.html |work=The Age |date=19 August 2004 }}

In 1992, Philip E. Kaaret and Phillip Geissbuehler proposed a new method for creating lobster-eye optics with microchannel plates.{{cite book |doi=10.1117/12.51261 |chapter=Lobster-eye x-ray optics using microchannel plates |title=Multilayer and Grazing Incidence X-Ray/EUV Optics |date=1992 |editor-last1=Hoover |editor-first1=Richard B. |last1=Kaaret |first1=Philip E. |last2=Geissbuehler |first2=Phillip |volume=1546 |page=82 }} 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.

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).

File:Configuration of the focusing mirror system of LEIA.jpg plates and associated with one of the four detectors.]]

File:LEIA instrument.jpg

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.{{cite journal |last1=Collier |first1=Michael R. |last2=Porter |first2=F. Scott |last3=Sibeck |first3=David G. |last4=Carter |first4=Jenny A. |last5=Chiao |first5=Meng P. |last6=Chornay |first6=Dennis J. |last7=Cravens |first7=Thomas E. |last8=Galeazzi |first8=Massimiliano |last9=Keller |first9=John W. |last10=Koutroumpa |first10=Dimitra |last11=Kujawski |first11=Joseph |last12=Kuntz |first12=Kip |last13=Read |first13=Andy M. |last14=Robertson |first14=Ina P. |last15=Sembay |first15=Steve |last16=Snowden |first16=Steven L. |last17=Thomas |first17=Nicholas |last18=Uprety |first18=Youaraj |last19=Walsh |first19=Brian M. |title=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 |display-authors=1 |journal=Review of Scientific Instruments |date=July 2015 |volume=86 |issue=7 |doi=10.1063/1.4927259 |pmid=26233339 |bibcode=2015RScI...86g1301C |hdl=1808/22116 |hdl-access=free }}{{cite press release |last1=Keesey |first1=Lori |title=NASA scientists build first-ever wide-field X-ray imager |url=https://phys.org/news/2013-02-nasa-scientists-first-ever-wide-field-x-ray.html |work=phys.org |publisher=NASA's Goddard Space Flight Center |date=7 February 2013 }} 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.{{cite web |title=MIXS: mercury imaging x-ray spectrometer |url=https://www.cosmos.esa.int/web/bepicolombo/mixs |website=BepiColombo |publisher=European Space Agency }}

CNSA launched the Lobster-Eye X-ray Satellite in 2020, the first in-orbit lobster-eye telescope.{{cite press release |title=Launch of the world's first soft X-ray satellite with 'Lobster-Eye' imaging technology |url=https://phys.org/news/2020-07-world-soft-x-ray-satellite-lobster-eye.html |work=phys.org |publisher=The University of Hong Kong |date=27 July 2020 }} 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. LEIA has a sensor module that gives it a field of view of 340 square degrees.{{cite web |title=LEIA: Introduction |url=https://ep.bao.ac.cn/leia/cms/article/view?id=91 |website=Einstein Probe Time Domain Astronomical Information Center }} 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.

File:First-light X-ray image of the Galactic center region obtained by LEIA.jpg|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.

File:X-ray image of Sco X-1 and Cygnus Loop nebula.jpg|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.

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.{{Cite web|date=January 9, 2024|url=https://www.esa.int/ESA_Multimedia/Images/2024/01/Einstein_Probe_lifts_off_on_a_mission_to_monitor_the_X-ray_sky|title=Einstein Probe lifts off on a mission to monitor the X-ray sky|author=The European Space Agency|website=www.esa.int|access-date=February 6, 2024|archive-date=January 9, 2024|archive-url=https://web.archive.org/web/20240109092739/https://www.esa.int/ESA_Multimedia/Images/2024/01/Einstein_Probe_lifts_off_on_a_mission_to_monitor_the_X-ray_sky|url-status=live}} 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.

The joint French-Chinese SVOM was launched on 22 June 2024.{{Cite web|url=https://www.svom.eu/en/mxt-langouste-en//|title=The MXT and the lobster eye - Svom|publisher=China National Space Administration (CNSA); Chinese Academy of Sciences (CAS); French Space Agency (CNES)|access-date=2024-02-06|archive-date=2023-10-04|archive-url=https://web.archive.org/web/20231004194123/https://www.svom.eu/en/mxt-langouste-en/|url-status=live}}

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. ISS-Lobster is a similar concept by ESA.{{cite book |doi=10.1117/12.2176745 |chapter=ISS-Lobster: A low-cost wide-field x-ray transient detector on the ISS |title=EUV and X-ray Optics: Synergy between Laboratory and Space IV |date=2015 |editor-last1=Hudec |editor-last2=Pina |editor-first1=René |editor-first2=Ladislav |last1=Camp |first1=Jordan |last2=Barthelmy |first2=Scott |last3=Petre |first3=Rob |last4=Gehrels |first4=Neil |last5=Marshall |first5=Francis |last6=Ptak |first6=Andy |last7=Racusin |first7=Judith |volume=9510 }}

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.{{cite tech report

| last1 = Branduardi-Raymont

| first1 = G.

| last2 = Wang

| first2 = C.

| last3 = Escoubet

| first3 = C.P.

| display-authors = etal

| title = ESA SMILE definition study report

| year = 2018

| publisher = European Space Agency

| doi = 10.5270/esa.smile.definition_study_report-2018-12

| id = ESA/SCI(2018)1

| pages = 1–84

| url = https://sci.esa.int/documents/35028/36141/1567260374869-SMILE_RedBook_ESA_SCI_2018_1.pdf

}} ESA's THESEUS is now under consideration.{{cite book |doi=10.1142/9789813226609_0421 |chapter=The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) |title=The Fourteenth Marcel Grossmann Meeting |date=2017 |last1=Amati |first1=Lorenzo |pages=3295–3300 |arxiv=1907.00616 |isbn=978-981-322-659-3 }}

Lobster-eye optics can also be used for backscattering imaging for homeland security, detection of improvised explosive devices, nondestructive testing, and medical imaging.{{cite journal |last1=Ma |first1=Shizhang |last2=Ouyang |first2=Mingzhao |last3=Fu |first3=Yuegang |last4=Hu |first4=Yuan |last5=Zhang |first5=Yuhui |last6=Yang |first6=Yuxiang |last7=Wang |first7=Shengyu |title=Analysis of Imaging Characteristics of Wide-field Lobster Eye Lens |journal=Journal of Physics: Conference Series |date=September 2023 |volume=2597 |issue=1 |pages=012010 |doi=10.1088/1742-6596/2597/1/012010 |bibcode=2023JPhCS2597a2010M |doi-access=free }} 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0] {{Webarchive|url=https://web.archive.org/web/20110223101209/http://creativecommons.org//licenses//by//3.0// |date=2011-02-23 }}

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