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Thermal stability of tungsten zone plates for focusing hard x-ray free-electron laser radiation
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.ORCID iD: 0000-0003-2723-6622
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2012 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, 043010- p.Article in journal (Refereed) Published
Abstract [en]

Diffractive Fresnel zone plates made of tungsten show great promise for focusing hard x-ray free-electron laser (XFEL) radiation to very small spot sizes. However, they have to withstand the high-intensity pulses of the beam without being damaged. This might be problematic since each XFEL pulse will create a significant temperature increase in the zone plate nanostructures and it is therefore crucial that the optics are thermally stable, even for a large number of pulses. Here we have studied the thermal stability of tungsten zone-platelike nanostructures on diamond substrates using a pulsed Nd:YAG laser which creates temperature profiles similar to those expected from XFEL pulses. We found that the structures remained intact up to a laser fluence of 100 mJ cm(-2), corresponding to a 6 keV x-ray fluence of 590 mJ cm-2, which is above typical fluence levels in an unfocused XFEL beam. We have also performed an initial damage experiment at the LCLS hard XFEL facility at SLAC National Accelerator Laboratory, where a tungsten zone plate on a diamond substrate was exposed to 105 pulses of 6 keV x-rays with a pulse fluence of 350 mJ cm-2 without any damage occurring.

Place, publisher, year, edition, pages
2012. Vol. 14, 043010- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-96447DOI: 10.1088/1367-2630/14/4/043010ISI: 000303673100003Scopus ID: 2-s2.0-84860151594OAI: oai:DiVA.org:kth-96447DiVA: diva2:530931
Funder
Swedish Research Council
Note
QC 20120605Available from: 2012-06-05 Created: 2012-06-04 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Zone Plates for Hard X-Ray Free-Electron Lasers
Open this publication in new window or tab >>Zone Plates for Hard X-Ray Free-Electron Lasers
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hard x-ray free-electron lasers are novel sources of coherent x-rays with unprecedented brightness and very short pulses. The radiation from these sources enables a wide range of new experiments that were not possible with previous x-ray sources. Many of these experiments require the possibility to focus the intense x-ray beam onto small samples. This Thesis investigates the possibility to use diffractive zone plate optics to focus the radiation from hard x-ray free-electron lasers.

The challenge for any optical element at free-electron laser sources is that the intensity in a single short pulses is high enough to potentially damage the optics. This is especially troublesome for zone plates, which are typically made of high Z elements that absorb a large part of the incident radiation. The first part of the Thesis is dedicated to simulations, where the temperature behavior of zone plates exposed to hard x-ray free-electron laser radiation is investigated. It is found that the temperature increase in a single pulse is several hundred Kelvin but still below the melting point of classical zone plate materials, such as gold, tungsten, and iridium.

Even though the temperature increases are not high enough to melt a zone plate it is possible that stresses and strains caused by thermal expansion can damage the zone plate. This is first investigated in an experiment where tungsten gratings on diamond substrates are heated to high temperatures by a pulsed visible laser. It is found that the gratings are not damaged by the expected temperature fluctuations at free-electron lasers. Finally, a set of tungsten zone plates are tested at the Linac Coherent Light Source where they are exposed to a large number of pulses at varying fluence levels in a prefocused beam. Damage is only observed at fluence levels above those typically found in an unfocused x-ray free-electron laser beam. At higher fluences an alternative is to use a diamond zone plate, which has significantly less absorption and should be able to survive much higher fluence. Damage in diamond structures is investigated during the same experiment, but due to a remaining tungsten etch mask on top of the diamond the results are difficult to interpret.

Additionally, we also demonstrate how the classical Ronchi test can be used to measure aberrations in focusing optics at an x-ray free-electron laser in a single pulse.

The main result of this Thesis is that tungsten zone plates on diamond substrates can be used at hard x-ray free-electron laser sources.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiii, 60 p.
Series
Trita-FYS, ISSN 0280-316X ; 2013:14
Keyword
X-ray optics, Zone plates, XFEL, x-rays, free-electron laser, heat transfer
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-122161 (URN)978-91-7501-769-3 (ISBN)
Public defence
2013-05-31, FB 42, Albanova, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130514

Available from: 2013-05-14 Created: 2013-05-13 Last updated: 2013-05-14Bibliographically approved
2. Nanofabrication of Zone Plates for Hard X-Ray Free-Electron Lasers
Open this publication in new window or tab >>Nanofabrication of Zone Plates for Hard X-Ray Free-Electron Lasers
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis describes the development of hard X-ray zone plates intended for focusing radiation at X-ray free-electron lasers (XFELs). XFELs provide unprecedented brightness and zone plates which are put in the intense X-ray beam are at risk of being damaged. Therefore, it is crucial to perform damage tests in order to design zone plates which can survive the XFEL beam.

Zone plates are diffractive nanofocusing optics and are regularly used at high brightness synchrotron beamlines in the soft and hard X-ray regime. The resolution of a zone plate is proportional to its outermost zonewidth and thus depends on the smallest feature that can be fabricated. State-of-the-art nanofabrication processes developed for zone plates are able to produce zonewidths down to 10 nm. However, for hard X-rays, the zone plates need to be of sufficient thickness to efficiently focus the radiation. Thus, the limit in the fabrication of hard X-ray zone plates lies in the high aspect-ratios. This Thesis describes two processes developed for high aspect-ratio nanostructuring. The first process uses tungsten as diffractive material. Aspect-ratios up to 1:15 have been accomplished. Furthermore, a mounting method of a central stop directly on the zone plate is also presented. The other fabrication process uses diamond, in which aspect-ratios of 1:30 have been demonstrated. Both processes rely on thin-film deposition techniques, electron-beam lithography, and reactive ion etching. Thanks to the materials’ excellent thermal properties these types of zone plates should be suitable for XFEL applications. Tungsten and diamond diffractive optics have been tested at an XFEL at Stanford (LCLS), and damage investigations were performed in order to determine the maximum fluence that could be imposed on the optics before degradation occured. The conclusion of these damage tests is that tungsten and diamond diffractive optics can survive the XFEL beam and could potentially be used in beamline experiments relying on nanofocused X-ray beams. Finally in this Thesis, characterization of two zone plates using an interferometer is presented, where it is also shown that the interferometric method can be used to pin-point beamline instabilities.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xiii, 69 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2014:77
Keyword
X-ray optics, Zone plates, Nanofabrication, X-ray free-electron lasers
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-158121 (URN)978-91-7595-406-6 (ISBN)
Public defence
2015-01-23, FA31, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20150112

Available from: 2015-01-12 Created: 2014-12-22 Last updated: 2015-01-12Bibliographically approved

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