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Zone Plates for Hard X-Ray Free-Electron Lasers
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
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 [en]
X-ray optics, Zone plates, XFEL, x-rays, free-electron laser, heat transfer
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-122161ISBN: 978-91-7501-769-3 (print)OAI: oai:DiVA.org:kth-122161DiVA: diva2:621137
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
List of papers
1. Simulation of heat transfer in zone plate optics irradiated by X-ray free electron laser radiation
Open this publication in new window or tab >>Simulation of heat transfer in zone plate optics irradiated by X-ray free electron laser radiation
2010 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 621, no 1-3, 620-626 p.Article in journal (Refereed) Published
Abstract [en]

Zone plates are high quality optics that have the potential to provide diffraction-limited nano-focusing of hard X-ray free electron laser radiation. The present publication investigates theoretically the temperature behavior of metal zone plates on a diamond substrate irradiated by 0.1 nm X-rays from the European X-ray Free Electron Laser. The heat transfer in the optic is simulated by solving the transient heat equation with the finite element method. Two different zone plate designs are considered, one small zone plate placed in the direct beam and one larger zone plate after the monochromator. The main result is that for all investigated cases the maximum temperature in the metal zone plate layer is at least a factor 2 below the melting point of the respective material, proving the efficiency of the proposed cooling scheme. However, zone plates in the direct beam experience large and rapid temperature fluctuations of several hundred Kelvin that might prove fatal to the optic. The situation is different for optics behind the monochromator with fluctuations in the 20 K range and maximum temperatures well below room temperature. The simulation results give valuable indications on the temperature behavior to be expected and are a basis for future experimental heat transfer and mechanical stability investigations of fabricated nanostructures.

Keyword
X-ray optics, Zone plate, XFEL, Heat transfer
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-26821 (URN)10.1016/j.nima.2010.03.115 (DOI)000281109100092 ()2-s2.0-77957924973 (Scopus ID)
Note
QC 20101208Available from: 2010-12-08 Created: 2010-11-29 Last updated: 2017-12-11Bibliographically approved
2. Computer simulation of heat transfer in zone plate optics exposed to X-ray FEL radiation
Open this publication in new window or tab >>Computer simulation of heat transfer in zone plate optics exposed to X-ray FEL radiation
2011 (English)In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, 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.

Keyword
X-ray optics, Zone plate, XFEL, Heat transfer
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-41021 (URN)10.1117/12.887566 (DOI)000293212000005 ()2-s2.0-79960518222 (Scopus ID)
Note
QC 20110928Available from: 2011-09-28 Created: 2011-09-23 Last updated: 2017-12-08Bibliographically approved
3. Thermal stability of tungsten zone plates for focusing hard x-ray free-electron laser radiation
Open this publication in new window or tab >>Thermal stability of tungsten zone plates for focusing hard x-ray free-electron laser radiation
Show others...
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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-96447 (URN)10.1088/1367-2630/14/4/043010 (DOI)000303673100003 ()2-s2.0-84860151594 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20120605Available from: 2012-06-05 Created: 2012-06-04 Last updated: 2017-12-07Bibliographically approved
4. Damage investigation on tungsten and diamond diffractive optics at a hard x-ray free-electron laser
Open this publication in new window or tab >>Damage investigation on tungsten and diamond diffractive optics at a hard x-ray free-electron laser
Show others...
2013 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 7, 8051-8061 p.Article in journal (Refereed) Published
Abstract [en]

Focusing hard x-ray free-electron laser radiation with extremely high fluence sets stringent demands on the x-ray optics. Any material placed in an intense x-ray beam is at risk of being damaged. Therefore, it is crucial to find the damage thresholds for focusing optics. In this paper we report experimental results of exposing tungsten and diamond diffractive optics to a prefocused 8.2 keV free-electron laser beam in order to find damage threshold fluence levels. Tungsten nanostructures were damaged at fluence levels above 500 mJ/cm(2). The damage was of mechanical character, caused by thermal stress variations. Diamond nanostructures were affected at a fluence of 59 000 mJ/cm(2). For fluence levels above this, a significant graphitization process was initiated. Scanning Electron Microscopy (SEM) and mu-Raman analysis were used to analyze exposed nanostructures.

Keyword
X-ray optics, Zone plate, XFEL
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-122159 (URN)10.1364/OE.21.008051 (DOI)000317659300021 ()2-s2.0-84875987203 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130514

Available from: 2013-05-13 Created: 2013-05-13 Last updated: 2017-12-06Bibliographically approved
5. Ronchi test for characterization of nanofocusing optics at a hard x-ray free-electron laser
Open this publication in new window or tab >>Ronchi test for characterization of nanofocusing optics at a hard x-ray free-electron laser
Show others...
2012 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 24, 5046-5048 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate the use of the classical Ronchi test to characterize aberrations in focusing optics at a hard x-ray free-electron laser. A grating is placed close to the focus and the interference between the different orders after the grating is observed in the far field. Any aberrations in the beam or the optics will distort the interference fringes. The methodis simple to implement and can provide single-shot information about the focusing quality. We used the Ronchi test to measure the aberrations in a nanofocusing Fresnel zone plate at the Linac Coherent Light Source at 8.194 keV.

Keyword
Different order, Far field, Focusing optics, Fresnel zone plate, Hard X ray, Interference fringe, Linac Coherent Light Source, Nano-focusing, Ronchi test, Single-shot, Lasers, Light sources, Optics
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-116618 (URN)10.1364/OL.37.005046 (DOI)000312707600008 ()2-s2.0-84871311756 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130125

Available from: 2013-01-25 Created: 2013-01-22 Last updated: 2017-12-06Bibliographically approved

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