G. A. Johansson

Design and performance of a laser-plasma-based compact soft x-ray microscope

We describe the design of a user-friendly compact water-window x-ray microscope. The microscope is based on a λ=3.37 nm liquid-jet-target laser-plasma source in combination with a normal-incidence multilayer condenser mirror and high-resolution diffractive optics for the imaging. With its high mechanical and thermal stability, the instrument demonstrates enhanced resolution and potential for compact x-ray imaging with the quality of synchrotron-based microscopes. Furthermore, a new sample handling system, computer control, and other improvements facilitate application-oriented x-ray microscopy outside the synchrotron laboratory.

Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition

Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. ...

Normal-incidence condenser mirror arrangement for compact water-window x-ray microscopy

We demonstrate a water-window condenser arrangement for transmission x-ray microscopy based on table-top sources. A spherical normal-incidence multilayer mirror is used to focus and monochromatize water-window x-ray emission from a high-brightness droplet-target laser-plasma source. The condenser arrangement is compact, has high collection efficiency, and is easy to align. The maximum normal- incidence reflectivity at the desired wavelength, (lambda) equals 3.37 nm, was determined to be up to 3 percent. The potential for compact water-window transmission x-ray microscopy using the condenser arrangement is discussed.

Compact soft x-ray reflectometer based on a line-emitting laser-plasma source

We describe a compact soft x-ray reflectometer for in-house characterization of water-window multilayer optics. The instrument is based on a line-emitting, liquid-jet, laser-plasma source in combination with angular scanning of the studied multilayer optics. With a proper choice of target liquid and thin-film filters, one or a few lines of well-defined wavelength dominate the spectrum and multilayer periods are measured with an accuracy of 0.003 nm using a multi-line calibration procedure. Absolute reflectivity may also be estimated with the instrument. The typical measurement time is currently 10 min. Although the principles of the reflectometer may be used in the entire soft x-ray and extreme ultraviolet range, the current instrument is primarily directed towards normal-incidence multilayer optics for water-window x-ray microscopy, and is thus demonstrated on W/B4C multilayers for this wavelength range.

Capillary nozzles for liquid-jet laser-plasma x-ray sources

We describe a method to fabricate tapered glass nozzles suitable for liquid-jet-target generation in laser-plasma soft x-ray and extreme ultraviolet sources. In the method, a tapered nozzle is formed as an integral part of a flexible capillary glass tubing. The method makes use of inert materials, extending the possible choice of target liquids compared to current nozzles. It also provides flexibility as regards nozzle diameter and pressure, thereby allowing optimization of the target size and extending the range of applicability for the liquid-jet-target laser plasmas.

Compact water-window x-ray microscopy with a droplet laser-plasma source

We summarize the development of the Stockholm compact water-window x-ray microscope (CXM-1) and show the first image of a biological object. The microscope is based on a liquid-droplet laser-plasma source, which is combined with normal-incidence water-window condenser optics for the object illumination. High-resolution imaging is performed with zone-plate optics and CCD detection. We demonstrate sub-100-nm resolution imaging with good signal-to-noise ratio and exposure times of minutes for dry diatoms and fixed cells.

Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion assisted sputter deposition

Cr/Sc multilayers have been grown on Si substrates using DC magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second order with multilayer periods of 1.692 nm and 3.381 nm, and layer thickness ratios of 0.471 and 0.237, respectively. At-wavelength soft x-ray reflectivity measurements were carried out using a reflectometer with a compact soft x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9-113 eV) and flux, in order to stimulate the ad-atom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required. Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low energy (9 eV) Ar ions founded the most favorable growth condition in order to limit the intermixing with a subsistent surface flatness.

Characterization of normal-incidence water-window multilayer optics

Spherical normal-incidence multilayer mirrors are attractive alternatives as condensers in compact water-window x-ray microscopes. In this paper we discuss the properties of such multilayer mirrors and the requirements when they are combined with a line-emitting soft x-ray source.

Accurate multilayer period determination with laser plasma water-window reflectometer

This paper describes a new method for improved determination of multilayer period using a soft x-ray reflectometer based on a line-emitting high-brightness water-window liquid-jet laser- plasma source. The use of line emission with well-known wavelengths allows accurate measurements of multilayer period without source monochromatization and calibration. By using a new multi-line data analysis procedure the multilayer period of W/B4C mirrors can be determined with an accuracy of 0.001 nm.