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Computer simulation of heat transfer in zone plate optics exposed to X-ray FEL 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.ORCID iD: 0000-0003-2745-6289
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.ORCID iD: 0000-0002-4394-0591
2011 (English)In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, Vol. 8077Article in journal (Refereed) Published
Abstract [en]

Zone plates are circular diffraction gratings that can provide diffraction-limited nano-focusing of x-ray radiation. When designing zone plates for X-ray Free Electron Laser (XFEL) sources special attention has to be made concerning the high intensity of the sources. Absorption of x-rays in the zone material can lead to significant temperature increases in a single pulse and potentially destroy the zone plate. The zone plate might also be damaged as a result of temperature build up and/or temperature fluctuations on longer time scales. In this work we simulate the heat transfer in a zone plate on a substrate as it is exposed to XFEL radiation. This is done in a Finite Element Method model where each new x-ray pulse is treated as an instantaneous heat source and the temperature evolution between pulses is calculated by solving the heat equation. We use this model to simulate different zone plate and substrate designs and source parameters. Results for both the 8 keV source at LCLS and the 12.4 keV source at the European XFEL are presented. We simulate zone plates made of high Z metals such as gold, tungsten and iridium as well as zone plates made of low Z materials such as diamond. In the case of metal zone plates we investigate the influence of substrate material by comparing silicon and diamond substrates. We also study the effect of different cooling temperatures and cooling schemes. The results give valuable indications on the temperature behavior to expect and can serve as a basis for future experimental investigations of zone plates exposed to XFEL radiation.

Place, publisher, year, edition, pages
2011. Vol. 8077
Keyword [en]
X-ray optics, Zone plate, XFEL, Heat transfer
National Category
Other Physics Topics
URN: urn:nbn:se:kth:diva-41021DOI: 10.1117/12.887566ISI: 000293212000005ScopusID: 2-s2.0-79960518222OAI: diva2:444350
QC 20110928Available from: 2011-09-28 Created: 2011-09-23 Last updated: 2013-05-14Bibliographically 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.
Trita-FYS, ISSN 0280-316X ; 2013:14
X-ray optics, Zone plates, XFEL, x-rays, free-electron laser, heat transfer
National Category
Physical Sciences
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)

QC 20130514

Available from: 2013-05-14 Created: 2013-05-13 Last updated: 2013-05-14Bibliographically approved

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Nilsson, DanielAnders, HolmbergVogt, Ulrich
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