Laser-based X-ray sources like laser-induced plasma (LIP) established as laboratory scale EUV- and soft X-radiation
sources in many scientific fields. Concerning the relative low conversion efficiencies of about 0.5% to 1% one has to
avoid scattered laser light reaching the X-ray optical setup. For this, thin metal filters with a thickness of a few hundred
nanometres are used. Another purpose of the filter is to block high-speed ions, clusters and particles (debris) originating
from the plasma, thus protecting the X-ray optics against damage. This is especially true when solid targets are used for
Concerning the application of LIP sources, one needs to collect as much radiation as possible. Therefore X-ray optics
with a high numerical aperture are required and the shielding filter has to be large and far-off the source or vice versa.
Since large thin filters are very fragile, one has to find a compromise between these two parameters to achieve
appropriate filter lifetime.
In this work we describe the stage of experiments to learn more about the process of debris emission characteristics and
the risk of damage to sensitive filters and X-ray optics. The experiments were carried out at a LIP source using a liquid
nitrogen jet or an ethanol jet as target. Several types of metal foils are investigated at different distances to the source.
Each filter is imaged onto a CMOS-Camera to examine the leakage of scattered laser light by debris-generated pinholes.
The analysis of the experiments is carried out particularly with regard to the theoretical X-ray throughput versus lifetime
of the different filter types.
EUV- and X-ray sources with laser like properties, e.g. free electron lasers, offer possibilities for many new experiments. In
order to successfully plan and perform experiments at these high flux sources, it is necessary to know which kind of optics,
exposed to the full beam, can be used. Due to the high intensities, it is not clear, whether transmissive diffractive optics are
applicable, because these optics are usually fabricated on thin membranes, thus introducing additional absorption in the
desired energy range. Since diffractive optics, especially zone plates, offer the possibility to achieve small spots when used
as a focussing element and can also achieve good image quality in microscopic setups, their usage would facilitate many
experiments, especially for their easy handling. As a proof of concept, we set up a zone plate based scanning transmission
microscope at the unfocussed beamline BL3 at FLASH (DESY/Hamburg). The operating wavelength was 32 nm and
13.8 nm, respectively. While the first attempt, utilizing a zone plate composed of PMMA on silicon substrate failed due to
ablation of the PMMA, a second zone plate (chromium on silicon nitride) was successfully used to focus the beam onto
different samples (e.g. nickel-mesh and a silicon nitride structured sample). The resulting focal spot size was estimated
from the acquired images to be in the range of 1 μm - 3μm in diameter. After several hours of exposure, no damage was
visible to the optics. Beside the optics, different filters (Silicon/Zirconium, Zirconium and Aluminum) have been placed
in the beam to evaluate possibilities to further reduce intensity which may be necessary if sensitive detectors are involved.
All of the filters withstood the irradiation during the whole experiment.
We report on a compact full-field transmission microscope (CTXM) and a scanning transmission microscope (CSTXM) developed for imaging at laboratory scale X-ray sources. The microscopes are based on zone plates for imaging in the EUV and water window region (wavelength 2.3 nm to 4.4 nm).
The radiation for the full-field microscope is generated by focusing short laser pulses with an energy of 100 mJ on a 20 μm cryogenic liquid nitrogen jet. A condenser zone plate in conjunction with an aperture is used to provide monochromatic sample illumination. This allows for easy wavelength selection within the N<sub>2</sub>-Emission spectrum. Thus, the presented setup offers the possibility of spectral imaging. A micro zone plate generates a magnified image detected by a back illuminated TE-cooled CCD camera (1,340 x 1,300 pixel). The actual configuration provides magnifications up to 1,000x at exposure times in a range of a few ten minutes with sub-100 nm resolution.
Our compact scanning microscope (CSTXM) operates with a zone plate, focusing the radiation onto a sample which is placed on a piezo driven xy-stage with 1 nm lateral resolution. Using high-harmonic radiation at 13 nm wavelength sub-micron resolution is achieved. With light at 17 nm wavelength originating from the O-VI emission line of a laser plasma source based on an ethanol jet, 500 nm structures were imaged in less than 20 minutes resulting in an 100 x 40 pixel image.
A wavefront sensing and beam monitoring system applicable to various kinds of X-ray and EUV sources like synchrotron radiation from undulators, X-ray lasers and laser induced plasma sources in the spectral range from 40 eV up to 40 keV is presented. One of the main applications will be the feedback for adaptive optical elements, e.g. deformable mirrors, for X-rays above 10 keV. It also provides the possibility to estimate the source dimension and distance. The wavefront sensor is based on a modified Hartmann setup; the beam is sampled by a rectangular grid and generates a distorted image on the detector. Comparison of this image with a known reference yields the wavefront's local slope at an extensive number of points. However, the Hartmann pattern is not directly imaged but is converted to the visible spectral range by a scintillator. This offers the possibility to use off the shelf cameras for image acquisition. First measurements, performed at the VUV-FEL (DESY, Hamburg) and at ELETTRA (Trieste), show the feasibility of this approach. The Hartmann principle offers the advantage to measure both, intensity and phase, thus allowing to reconstruct not only the wavefront but also the beam profile. Wavefront resolution of up to λ/100 (λ = 1 nm) can be achieved. The intensity profile and the beam shape can be measured with a spatial resolution better than 10 μm. With the current setup it is also possible to analyze the temporal and spatial stability of the source.