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Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.ORCID iD: 0000-0002-4394-0591
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.
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2005 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 15, 2167- p.Article in journal (Refereed) Published
Abstract [en]

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda = 2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.

Place, publisher, year, edition, pages
2005. Vol. 30, no 15, 2167- p.
Keyword [en]
Diffraction; Imaging techniques; Interferometers; Light propagation; Plasmas; X rays; Compact interferometer; Focal spots; Laser-plasma source; Liquid nitrogen; Interferometry
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-7017DOI: 10.1364/OL.30.002167ISI: 000231072700039Scopus ID: 2-s2.0-24344492433OAI: oai:DiVA.org:kth-7017DiVA: diva2:11892
Note
QC 20100616Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2012-03-21Bibliographically 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. Nanofabrication of Zone Plate Optics for Compact Soft X-Ray Microscopy
Open this publication in new window or tab >>Nanofabrication of Zone Plate Optics for Compact Soft X-Ray Microscopy
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This Thesis describes the development of the KTH/Stockholm nanofabrication process for diffractive soft x-ray optics. The effort is motivated by the need for and requirement of specially designed diffractive optics and test objects for compact x-ray microscopy as well as optics for other applications such as phase imaging. The optics have been fabricated in-house, in the KTH Nanofabrication Laboratory.

The nanofabrication process is based on electron-beam lithography in combination with reactive ion etching (RIE) and nickel electroplating. This process has successfully been used for the fabrication of micro zone plates, condenser zone plates, diffractive optical elements for differential-interference microscopy, and different test structures. Optics with electroplated feature sizes down to 25 nm have been fabricated with high aspect-ratios. Special consideration has been given the reproducibility and optimization of the process parameters. This is essential for improving the yield and quality of the fabricated optics. The work includes, e.g., improved e-beam writing strategies and controlled electroplating. Furthermore, a high diffraction efficiency is necessary for our applications, which are based on compact low-power sources. This requires the fabrication of optics with a high and uniform aspect ratio. For this purpose the electroplating process step has been improved with an in-situ light-transmission-based thickness control method for optimum mold filling, and pulse and pulse-reverse techniques for uniform plating.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006
Series
Trita-FYS, ISSN 0280-316X ; 2006:41
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4045 (URN)91-7178-390-3 (ISBN)
Public defence
2006-06-16, Sal FD5, AlbaNova univ centrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100616Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-06-16Bibliographically approved
3. Nanofabrication of Diffractive Soft X-ray Optics
Open this publication in new window or tab >>Nanofabrication of Diffractive Soft X-ray Optics
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis summarizes the present status of the nanofabrication of diffractive optics, i.e. zone plates, and test objects for soft x-ray microscopy at KTH. The emphasis is on new and improved fabrication processes for nickel and germanium zone plates. A new concept in which nickel and germanium are combined in a zone plate is also presented. The main techniques used in the fabrication are electron beam lithography for the patterning, followed by plasma etching and electroplating for the structuring of the optical materials. The process for fabricating nickel zone plates has been significantly improved. The reproducibility of the electroplating step has been increased by the implementation of an in-situ rate measurement and an end-point detection method. We have also shown that pulse plating can be used to obtain zone plates with a uniform height profile. New plating mold materials have been introduced and electron-beam curing of the molds has been investigated and implemented to increase their mechanical stability so that pattern collapse in the electroplating step can be avoided. The introduction of cold development has improved the achievable resolution of the process. This has enabled the fabrication of zone plates with outermost zone widths down to 16 nm. The nickel process has also recently been adapted to fabrication of gold structures intended for test objects and hard x-ray zone plates. For the fabrication of germanium zone plates we developed a highly anisotropic plasma-etch process using Cl2 feed and sidewall passivation. Germanium zone plates have been fabricated with zone widths down to 30 nm. The diffraction efficiency is comparable to that of nickel zone plates, but the process does not involve electroplating and thus has for potential for highyield fabrication. The combination of nickel and germanium is a new fabrication concept that provides a means to achieve high diffraction efficiency even for thin nickel. The idea is to fabricate a nickel zone plate on a germanium film. The nickel zone plate itself is then used as etch mask for a highly selective CHF3- plasma etch into the germanium layer. Proof of principle experiments showed an efficiency increase of about a factor of two for nickel zone plates with a 50- nm nickel thickness.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. vii, 71 p.
Series
Trita-FYS, ISSN 0280-316X ; 2008:57
Keyword
Nanofabrication, Zone plate, x-ray, diffractive x-ray optics, x-ray microscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-9800 (URN)978-91-7415-205-0 (ISBN)
Public defence
2009-02-06, FR4, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100728Available from: 2009-01-13 Created: 2009-01-07 Last updated: 2011-10-20Bibliographically approved

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Vogt, UlrichHolmberg, AndersHertz, Hans

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