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A Stacked Prism Lens Concept for Next-Generation Hard X-Ray Telescopes
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. (Medical Imaging)ORCID iD: 0000-0002-6306-5851
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past half century, the focusing X-ray telescope has played a very prominent role in X-ray astronomy at the frontier of fundamental physics. The finer angular resolution and increased effective area have enabled more and more exciting discoveries and detailed studies of the high-energy universe, including the cosmic X-ray background (CXB) radiation, black holes in active galactic nuclei (AGN), galaxy clusters, supernova remnants, and so on. At present, nearly all the state-of-the-art focusing X-ray telescopes are based on Wolter-I optics or its variations, for which the throughput is severely restricted by the mirror’s surface roughness, figure error, alignment error, and so on.

Within the course of this work, we have developed a novel point-focusing refractive lens, the stacked prism lens (SPL), which is built by stacking disks embedded with various number of prismatic rings. As a Fresnel-like X-ray lens, it could provide a significantly higher efficiency and larger effective aperture than the conventional compound refractive lenses (CRLs). The aim of this thesis is to demonstrate the feasibility of the stacked prism lens and investigate the application to a next-generation hard X-ray telescope.

First, SU-8 prototype lenses are fabricated by focused ultraviolet (UV) lithography, for which a UV lens is used as a photomask to form 3D patterns in the photoresist. The UV lens is homemade by grayscale electron beam lithography (EBL), and a proximity effect correction (PEC) method based on multivariate adaptive regression splines (MARS) ensures accurate control of the desired UV lens profile. The details of the whole fabrication process are described, and the fabrication results are discussed. Following that, the completed stacked prism lenses are characterized in the synchrotron radiation facility, and the results show the expected performance.

Finally, a hard X-ray focusing telescope concept based on the proposed stacked prism lens array is presented. The performance, in terms of angular resolution, effective collecting area, field of view (FOV), mass and so on, is investigated by self-developed simulation software based on ray-tracing method and compared with the current Wolter telescopes. The results suggest that the proposed stacked prism lens is a promising candidate for next-generation hard X-ray telescope with high angular resolution and large effective collecting area.

Abstract [sv]

Under det senaste halvseklet har fokuserande röntgenteleskop spelat en mycket framträdande roll inom röntgenastronomin för att utforska den grundläggande fysikens gränser. Bättre vinkelupplösning och större effektiv area har möjliggjort ett flertal upptäckter och detaljerade studier av universum vid höga energier, inklusive den kosmiska röntgenbakgrundsstrålningen (CXB), svarta hål i aktiva galaktiska kärnor (AGN), galaxkluster, supernovarester och så vidare. För närvarande är nästan alla fokuserande röntgenteleskop baserade på Wolter-I-optik eller variationer på denna teknik, för vilka effektiviteten är starkt begränsad av kvaliteten på spegelns yta och hårda krav på mekaniska toleranser.

Under detta arbete har vi utvecklat en ny punktfokuserande lins, den staplade prisma linsen (SPL), som är uppbyggd av lager med olika antal prismatiska ringar. Som en Fresnel-liknande röntgenlins kan den ge en betydligt högre effektivitet och större effektiv bländare än de konventionella refraktiva linserna (CRLs). Syftet med den här avhandlingen är att demonstrera funktionen för SPL linsen och att diskutera en tillämpning i form av nästa generations röntgenteleskop.

Först tillverkas prototyplinser i SU-8 med fokuserad ultraviolett (UV) litografi, för vilken ett UV-objektiv används som en fotomask för att skapa 3D-mönster i fotoresisten. Vi har själva tillverkat UV-linsen med hjälp av elektronstråle-litografi (EBL). Detaljerna för hela tillverkningsprocessen beskrivs och resultaten diskuteras. Därefter har vi utvärderat den färdiga SPL linsen vid en synkrotronljus anläggning och verifierat att resultaten överensstämmer med simuleringar.

Slutligen presenteras ett koncept för ett röntgenfokuserande teleskop baserat på den föreslagna SPL linsen. Prestandan, i form av vinkelupplösning, effektivt uppsamlingsområde, synfält (FOV), massa och så vidare och jämfört dessa parametrar med nuvarande Wolter-teleskop. Resultaten tyder på att den föreslagna SPL linsen är en lovande kandidat för nästa generations röntgenteleskop med hög vinkelupplösning och möjlighet till stort effektivt uppsamlingsområde.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. , p. 58
Series
TRITA-SCI-FOU ; 2019:41
Keywords [en]
focusing X-ray telescopes, Wolter-I optics, stacked prism lens, focused UV lithography, grayscale e-beam lithography, proximity effect correction, angular resolution, effective collecting area
Keywords [sv]
röntgenteleskop, Wolter-I-optik, staplade prismalinser, fokuserad UV-litografi, elektronstråle-litografi
National Category
Nano Technology Astronomy, Astrophysics and Cosmology Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-257740ISBN: 978-91-7873-286-9 (electronic)OAI: oai:DiVA.org:kth-257740DiVA, id: diva2:1348026
Public defence
2019-09-27, E3, Osquars backe 14, KTH Campus, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Stiftelsen Olle Engkvist Byggmästare, 20111220Available from: 2019-09-06 Created: 2019-09-03 Last updated: 2019-09-06Bibliographically approved
List of papers
1. Efficient proximity effect correction method based on multivariate adaptive regression splines for grayscale e-beam lithography
Open this publication in new window or tab >>Efficient proximity effect correction method based on multivariate adaptive regression splines for grayscale e-beam lithography
2014 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 32, no 3, article id 031602Article in journal, Editorial material (Refereed) Published
Abstract [en]

Grayscale electron beam lithography is an important technique to manufacture three-dimensional (3D) micro- and nano-structures, such as diffractive optical devices and Fresnel lenses. However, the proximity effect due to the scattering of electrons may cause significant error to the desired 3D structure. Conventional proximity correction methods depend on the exposure energy distribution which sometimes is difficult to obtain. In this study, the authors develop a novel proximity effect correction method based on multivariate adaptive regression splines, which takes exposure energy and development into consideration simultaneously. To evaluate the method, a Fresnel lens was fabricated through simulation and experiment. The measurements demonstrate the feasibility and validity of the method.

Place, publisher, year, edition, pages
United States: , 2014
National Category
Physical Sciences Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-147744 (URN)10.1116/1.4875955 (DOI)000337061900046 ()2-s2.0-84900822144 (Scopus ID)
Note

QC 20140704

Available from: 2014-07-04 Created: 2014-07-03 Last updated: 2019-09-17Bibliographically approved
2. Fabrication of circular sawtooth gratings using focused UV lithography
Open this publication in new window or tab >>Fabrication of circular sawtooth gratings using focused UV lithography
Show others...
2016 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 26, no 3, article id 035001Article in journal (Refereed) Published
Abstract [en]

AbstractThis paper presents a novel micro-fabrication method using focused ultraviolet (UV) light to manufacture three-dimensional sawtooth structures in ultra-thick negative photoresist to fabricate a novel multi-prism x-ray lens. The method uses a lens to shape the UV beam instead of the photomask conventionally used in UV lithography. Benefits of this method include the ability to manufacture sawtooth structures in free form, for example in circular shapes as well as arrays of these shapes, and in resist that is up to 76 μm thick.To verify the method, initially a simple simulation based on Fourier optics was done to predict the exposure energy distribution in the photoresist. Furthermore, circular sawtooth gratings were manufactured in a 76 μm SU-8 resist. The UV lens was fabricated using electron beam lithography and then used to expose the SU-8 with UV light. This paper details the complete developed process, including pre-exposure with an e-beam and cold development, which creates stable sawtooth structures. The measured profile was compared to the ideal sawtooth and the simulation. The main discrepancy was in the smallest feature size, the sawtooth tips, which were wider than the desired structures, as would be expected by simulation.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
focused UV lithography, three-dimensional sawtooth structures, SU-8, UV lens, Fourier optics
National Category
Medical Engineering
Research subject
Medical Technology; Physics; Applied Medical Technology
Identifiers
urn:nbn:se:kth:diva-185957 (URN)10.1088/0960-1317/26/3/035001 (DOI)000375230700001 ()2-s2.0-84959432882 (Scopus ID)
Projects
Medical Imaging Project
Funder
Stiftelsen Olle Engkvist Byggmästare, 20111220
Note

QC 20160509

Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2019-09-17Bibliographically approved
3. A stacked prism lens concept for next-generation hard X-ray telescopes
Open this publication in new window or tab >>A stacked prism lens concept for next-generation hard X-ray telescopes
2019 (English)In: Nature Astronomy, E-ISSN 2397-3366Article in journal, Editorial material (Refereed) Published
Abstract [en]

Effective collecting area, angular resolution, field of view and energy response are fundamental attributes of X-ray telescopes. The performance of state-of-the-art telescopes is currently restricted by Wolter optics, especially for hard X-rays. Here we report the development of a stacked prism lens (SPL), which is lightweight and modular and has the potential for a significant improvement in effective area, while retaining high angular resolution. The proposed optics are built by stacking disks embedded with prismatic rings, created with photoresist by focused ultraviolet lithography. We demonstrate the SPL approach using a prototype lens that was manufactured and characterized at a synchrotron radiation facility. The design of a potential satellite-borne X-ray telescope is outlined and the performance is compared with contemporary missions.

Place, publisher, year, edition, pages
United Kingdom: , 2019
National Category
Astronomy, Astrophysics and Cosmology Atom and Molecular Physics and Optics Medical Equipment Engineering
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-256483 (URN)10.1038/s41550-019-0795-y (DOI)2-s2.0-85068069999 (Scopus ID)
Funder
Stiftelsen Olle Engkvist Byggmästare, 20111220Swedish Research Council, 2016-04929
Note

QC 20190826

Available from: 2019-08-26 Created: 2019-08-26 Last updated: 2019-09-17Bibliographically approved

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