Laser- Plasma- Source

Scheme of the laser-plasma-source for the 1 keV region.

© AG Kanngießer

The concept of hitting a target with a focused, short-pulse, high average power laser beam in order to obtain tailored X-ray pulses has been introduced during the last two decades. Due to recent improvements in high average power solid state lasers producing short pulses in the ns or sub-ns range, laser induced plasmas covering a broad range of photon energies in the soft and hard x-ray region are nowadays used as laboratory X-ray sources. Up until now the main focus in the soft X-ray region has been laid on X-ray sources for extreme ultraviolet (EUV)-lithography at 13.5 nm and X-ray sources in the water window (2.3 – 4.4 nm) for the analysis of biological samples.

We propose the concept of a laser-plasma-source (LPS) for the 1 keV region. A stable laser-plasma-source in the 1 keV region is especially interesting for the investigation of L-edges of transition metals, thus, enabling analysis of technological samples with a depth resolution in the nm-regime. The lack of suitable X-ray tubes in this energetic region and factors like beam time restrictions at synchrotron sources will render this new instrument into a valuable tool for X-ray fluorescence spectroscopy, X-ray emission spectroscopy as well as for example X-ray photoelectron spectroscopy or Auger spectroscopy.

The spectral and temporal properties of X-rays generated by a laser-plasma are mainly dependent on the used laser as well as target parameters.

Laser System

The concept of our LPS is based on a high average power commercial Yb:YAG – disk laser system (TRUMPF Laser Technology) which is modified with a 1 ns seed-diode in order to obtain optimal pulse parameters.

The seed-diode is developed in a cooperation with the Ferdinand-Braun-Institut für Höchstfrequenztechnik and PicoLas GmbH. First experiments show, that the Trumpf laser system can be seeded by a 1 ns laser pulse. The performance is stable and further changes in repetition rate and pump power will be evaluated.

Target System

One of the main difficulties in the design of laser-plasma-sources is the choice of target system due to the necessity of new target material for each laser pulse. Different systems are used (solid state cylinders, solid state tapes, liquid jets, etc.). First experiments are currently performed at the MBI with different target materials and target types in order to evaluate the optimal parameters for the design of the BLiX laser-plasma-source.

Cu-cylinder as target for the LPS, the optical emission of the plasma can be observed as well as the crater lines created by the rotation of the cylinder.

© AG Kanngießer

Contact: Ioanna Mantouvalou, Katharina Witte

© MBI