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Simulation of partially coherent image formation in a compact soft x-ray microscope
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: 0000-0002-4394-0591
2007 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 107, no 8, 604-609 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we describe a numerical method of simulating two-dimensional images in a compact soft X-ray microscope using partially coherent illumination considerations. The work was motivated by recent test object images obtained by the latest generation inhouse compact soft X-ray microscope, which showed diffraction-like artifacts not observed previously. The numerical model approximates the condenser zone plate as a secondary incoherent source represented by individually coherent but mutually incoherent source points, each giving rise to a separate image. A final image is obtained by adding up all the individual source point contributions. The results are compared with the microscope images and show qualitative agreement, indicating that the observed effects are caused by partially coherent illumination.

Place, publisher, year, edition, pages
2007. Vol. 107, no 8, 604-609 p.
Keyword [en]
Image formation; Partial coherence; X-ray microscopy; Zone plates; Computer simulation; Light sources; Mathematical models; X ray diffraction; X ray microscopes; Incoherent sources; Partial coherence; X ray microscopy; Zone plates; Image processing; article; diffraction; illumination; image analysis; mathematical model; microscopy; qualitative analysis; separation technique; simulation; X ray analysis
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-7020DOI: 10.1016/j.ultramic.2006.12.001ISI: 000246937000006Scopus ID: 2-s2.0-34247139671OAI: oai:DiVA.org:kth-7020DiVA: diva2:11895
Note
QC 20100820. Uppdaterad från In press till Published 20100820.Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Compact Soft X-Ray Microscopy: Sources, Optics and Instrumentation
Open this publication in new window or tab >>Compact Soft X-Ray Microscopy: Sources, Optics and Instrumentation
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis describes the development of a sub-60-nm full-period resolution compact soft x-ray microscope operating in the water-window region (2.3-4.4 nm). Soft x-ray water-window microscopy is a powerful technique for high-resolution imaging of organic materials exploiting the natural contrast mechanism between carbon and oxygen, cf. Sect. 4.1. The thesis discusses the components of, as well as the integration of the microscope, including liquid-jet laser-plasma x-ray sources, optics, simulations, and image-processing tools.

Liquid-jet-target laser-plasma sources for generation of soft x-rays and extreme-ultraviolet radiation are compact sources with high brightness. The work focused on improved target stability, decreased debris, and accurate source characterization. For x ray microscopy applications a liquid-jet target delivery system allowing cryogenic liquids was developed. Source characterization was performed for two different liquid-jet targets: Methanol and liquid nitrogen. For extreme-ultraviolet lithography applications, the potential use of a liquid-tin-jet laser-plasma source was explored including conversion efficiency and debris measurements.

High quality optics are essential in the development of compact x-ray microscopes. For soft x-ray wavelengths, zone plates and multilayer mirrors are used to focus or redirect radiation. This thesis describes the development and characterization of a condenser zone plate suitable for use in a compact soft x-ray microscope operating at λ = 2.478 nm. It also investigates the possibility to perform differential interference contrast microscopy in the water window using a single diffractive optical element. An arrangement for rapid and accurate determination of absolute and local diffraction efficiency of soft x-ray zone plates using a compact laser-plasma source has been developed. The instrument is used to characterize the zone plates fabricated at the Biomedical & X-Ray Physics division at KTH. Through a collaboration with the Fraunhofer-Institut in Jena, Germany, a large diameter spherical Cr/Sc multilayer mirror, suitable as condenser in the compact x-ray microscope, was developed and characterized. The mirror is designed for λ = 3.374 nm and shows a high, and uniform reflectivity of 3%. This increases the photon flux by an order of magnitude compared to the W/B4C mirrors previously used.

The thesis describes the development of a compact soft x-ray microscope with sub-60-nm full-period resolution. It can operate at two different wavelengths in the water window using the soft x-ray laser-plasma sources combined with the condenser optics described above. Imaging is performed by zone plate objectives. The microscope is capable of imaging hydrated biological samples with thicknesses up to ~10 μm. Improvements made to the mechanical design has turned it into a user friendly instrument allowing daily operation. A numerical method was developed to study the effects of partially coherent illumination on 2D imaging. To stimulate experiments on functional imaging in x-ray microscopy an image-analysis algorithm for identifying colloidal-gold particles was developed. Size selective identification and localization of single gold particles down to a diameter of 50 nm was demonstrated.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. x, 59 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:25
Keyword
soft x-ray microscopy, water window, compact, laser plasma, liquid jet, zone plate optics
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4342 (URN)978-91-7178-613-5 (ISBN)
Public defence
2007-05-04, FD 5, Albanova, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100819Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-20Bibliographically approved
2. Phase-Contrast and High-Resolution Optics for X-Ray Microscopy
Open this publication in new window or tab >>Phase-Contrast and High-Resolution Optics for X-Ray Microscopy
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray microscopy is a well-established technique for nanoscale imaging. Zone plates are used as microscope objectives and provide high resolution, approaching 10 nm, currently limited by fabrication issues. This Thesis presents zone plate optics that achieve either high resolution or phase contrast in x-ray microscopy. The high-resolution optics use high orders of the zone plate, which alleviates the demands on fabrication, and the phase-contrast optics are single-element diffractive optical elements that produce contrast by Zernike or differential-interference contrast methods. The advantage of phase contrast in x-ray microscopy is shorter exposure times, and is crucial in the hard x-ray regime. Microscopy in the absorption‑contrast region of the water-window (2.34 - 4.37 nm) also benefits from these optics. The development of the optics for a laboratory soft x-ray microscope spans from theoretical and numerical analysis of coherence and stray light to experimental implementation and testing. The laboratory microscope uses laser-produced plasma-sources in the water-window and is unique in its design and performance. It will be shown that the laboratory microscope in its current form is a user-oriented and stable instrument, and has been used in a number of applications. The implementation of a cryogenic sample stage for tomographic imaging of biological samples in their natural environment has enabled applications in biology, and 3D x-ray microscopy of cells was performed for the first time with a laboratory instrument.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. x, 61 p.
Series
Trita-FYS, ISSN 0280-316X ; 72
Keyword
Microscopy, X-ray optics, X-ray microscopy, Soft X-ray physics
National Category
Atom and Molecular Physics and Optics Physical Sciences
Identifiers
urn:nbn:se:kth:diva-26781 (URN)978-91-7415-834-2 (ISBN)
Public defence
2010-12-17, FD5, Roslagstullsbacken 21, Stockholm, 15:42 (English)
Opponent
Supervisors
Note
QC 20101130Available from: 2010-11-30 Created: 2010-11-26 Last updated: 2010-11-30Bibliographically approved

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