Fyzikální ústav Akademie věd ČR

High power lasers and the laser produced plasma

The main task of the Laser plasma department is the operation, maintenance and upgrade of high power iodine photodissociation laser Asterix, including the interaction chamber for the users. Organizationally, the system is a part of the Research Centre PALS (joint laboratory between the Institute of Physics of Academy of Sciences of the Czech Republic – IOP and of the Institute of Plasma Physics of ASCR – IPP) and it is located in a dedicated building of IPP finished in 1999. The Astreix system was originally developed and operated in the Max-Planck-Institute for Quantum Optics – MPQ at Garching near Munich and it was transferred to the Czech Republic on the basis of a 1996 Contract. Besides the laser operation the division runs a scientific programme of its own.

Fundamental aspects of laser interaction with a plasma.

This comprises the properties of the plasma generated by a focused laser beam in the IR and VIS range on various targets and its use as a source of x-ray radiation and multiply charged ions. The diagnostic methods developed in the division have been successfully applied to other plasma sources of similar properties such as pinch or plasma focus experiments.

Studies and applications of point-like sources of a soft incoherent x-ray raditation (XUV).

At our disposal are unique sources of highly energetic (~ 10 J) pulses of XUV radiation, which can under optimized condition deposit a high dose of such a radiation in single a sub-nanosecond pulse in any system under illumination. Such XUV sources are used for x-ray microscopy of biological objects and for studies of the radiation with surfaces, including the x-ray ablation. In this case all the other emission from the source such as corpuscular, VIS and NIR radiation is eliminated. The physical interest represents mainly the correlation between various radiation components, such XUV with multiply charged ions contained in the expanding plasma and hard x-rays directly from the laser focus.

Realization and use of laser driven sources of multiply charged ions.

In a cooperation with IPPLM Warsaw and INFN Catania the development of laser driven ion sources is directed towards their potential use for an ion implantation or like injectors for large ion accelerators. The ion injector programme was taken to a commercially viable stage and it could be considered as an alternative ion source of the just starting collider LHC at CERN. Generation and acceleration of highly charged ions takes place due to the electron ionizing collisions and by the electron gas dynamics within the plasma corona of the plasma plume generated on a target. The electron kinetics is thus vital for the properties of the ion groups observed during the plasma expansion.

The properties of the weekly collisional electron gas undergoing an evolution in its phase space are inaccessible for direct measurements. For that reason a copmputational model has been developed based on a simultaneous solution of the Vlasov equation and of the Maxwell equation in 1D. The model yielded a number of features of the electron gas phase space evolution, especially those connected with the onset and growth of the Raman instability and el;ectron acceleration. The implications for other physical situation such as phenomena at the entrance holes in the hohlraum of the indirectly driven fusion experiments are obvious.

In our department based on a detailed analysis of measured signals from the ion detectors a notion of crucial role played by the non-linearities in the process of ion production. For the first time it was proven that the surprising efficiency of laser ion sources even at low power densities delivered by the laser driver is due to self-focusing or filamentation of the driving laser beam in the corona. The same model helped interpret the complex structure of the charge-energy spectra of ions in the form of fast and slow ion groups arriving during the plasma expension on particle sensors. The important practical consequence is the fact that even smaller lasers may be used as efficient drivers of ion sources.

A surprising outcome during these studies came in the form of plasma jets surviving many ns after the switching off the driving laser beam mainly on targets of heavier elements. These jets have a number of hydrodynamic similarity parameters very close to the jets observed by astrophysicists in planetary nebulas and other interesting celestial objects within our Galaxy. The detailed studies of jet behaviour thus cover the field of laboratory astrophysics.

Detection and spectroscopy of x-ray radiation.

The main contribution in this field is the design and the manufacture of a unique Johann type x-ray spectrometer with a cylindrically bent crystal and the vertical dispersion. Which is now in a number of leading laser laboratories utilized for the exploration of x-ray spectra with a ultra high special and spectral resolution. This pioneering approach came from our division, where a prototype was constructed and the design is now widely used also elsewhere.

Other diagnostics development seeks new detectors of XUV on the principle of radiation thermoluminiscence dosimetry and the corresponding calibration. Similar detectors are now in use for a detection of neutrons on large facilities such as the giant plasma focus PF1000 in Warsaw.

XUV is also an instrument for the atomic holography, a unique atom imaging method, which is pursued in co-operation with the Italian Sinchrotrone Trieste. This method can in principle visualize the atoms of a crystal elementary cell independent of its periodicity.