Tomas Mocek

Prague Asterix Laser System (PALS) - results and upgrades

The PALS multi-user laser facility has been offering the beam time to the groups of both domestic and foreign rsearchers since September 2000. During the past two years of operation of its terawatt iodine laser system, a number of technical innovations and new diagnostic options were implemented, the most important of which are described in the paper. A brief survey of the current PALS research program is also given. Laser plasma sources of x-radiation and of highly stripped ions represent the two main lines followed. Recent highlights include the development and application of a highly coherent double-pass XUV laser based on Ne-like zinc. The reported studies of material response to the XUV pulses are mainly motivated by a potential use of the observed ablation phenomena e.g. in nanotechnology, while the x-ray contact microscopy permitted to image living biological objects with a resolution comparable to that of the electron microscopy. The PALS laser system is now in a routine operation, which opens the way to its new upgrades. The progress reached with the key ones -- application of elements of adaptive optics, replacement the original iodine oscillator by a solid-state based one, and, most important, implementation of the optical parametric chirped pulse amplification (OPCPA) technique -- is also reported.

Development and applications of X‐ray lasers at LSAI/LIXAM

We present an overview of our research activity achieved since the last X‐ray laser Conference in Saint‐Malo. Our research program involves the development of laser‐pumped collisional X‐ray lasers under different regimes of irradiation, and the use of these sources for applications. The work presented involves a number of French and international collaborations and was carried out at different pump laser facilities: LULI (Ecole Polytechnique), LOA (ESNTA) in France; Rutherford Laboratory in U.K; PALS in Czech Republic.

Collisional optical-field ionization soft x-ray lasers

We report recent investigations on collisional Optical-Field Ionization soft x-ray lasers. The amplifying medium is generated by focusing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filled with gas (xenon or krypton). Using xenon, a gain of 67 cm-1 on the 4d95p-4d95d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 109 photons per pulse. Using krypton, a large amplification of the 3d94d-3d94p line at 32.8 nm has been observed for the first time. The influence of the pumping energy and the laser polarization on the lasing output are also presented.

Influence of laser-beam focusing on the production of highly charged ions from laser plasma

Laser beam focus position was varied with respect to the target surface to obtain the maximum current of highly charged Ta ions from laser-produced plasma in the far expansion zone. The experiments prove that the optimum position must be settled with the accuracy plus or minus 125 micrometers.

Development of ultrafast soft X-ray beamline based on high-order harmonic generation at PALS

We report on the development of ultrafast coherent soft X-ray beamline at the Prague Asterix Laser System (PALS) Research Center intended for interdisciplinary applications such as ablation and controlled surface modification of solid materials for a micro/nano-patterning, soft X-ray interferometry and holography for surface probing with nanometric resolution, and improvement of focusing optics for soft X-ray beams. The beamline is based on 1 kHz, table-top, highorder harmonic generation (HHG) source capable of delivering fully coherent beam, tunable in the 13 - 40 nm spectral range. The Ti:sapphire (810 nm) laser pulses with a duration of 35 fs and energy 1.1 mJ are focused into a static gas cell containing conversion medium (Ar). To achieve highly efficient HHG at 30 nm we apply the technique of guided laser pulses. Experimental results on HHG source characterization, optimization, and spectral tunability are presented. Achievements on the implementation of so called two-color HHG using gas cell have been reported for the first time. The complete beamline will consist of a tandem of two vacuum chambers: one for the HHG source and its diagnostics, and second intended for the application experiments. The access to this new soft X-ray installation will be opened to external users since 2009.

X-ray microscopy and imaging of Caenorhabditis elegans nematode using a laser-plasma-pulsed x-ray source

An experiment on Soft X-ray Contact Microscopy (SXCM) performed on Caenorhabditis elegans nematodes is discussed. This sample has been selected since it is a well studied case used as model in many biological contexts. The experiment has been performed using the iodine PALS laser source to generate pulsed soft X-rays from laser-plasma interaction, using molybdenum and gold as targets. Typical intensities on the targets exceeded 1014 W/cm2. The SXCM imprints have been recorded on Polymethilmetacrylate (PMMA) photo resists which have been chemically developed and analyzed with an Atomic Force Microscope (AFM) operating in constant force mode. The use of error signal AFM images together with topography AFM images, did allow an easier recognition of biological patterns, and the identification of observed structures with internal organs. Several organs were identified in the SXCM images, including cuticle annuli, alae, pharynx, and three different types of cell nuclei. These are the first SXCM images of multi-cellular complex organisms.

X-ray laser progress for applications

We present a review of new progress performed in several laboratories (Laboratoire pour lUtilisation des lasers Intenses, Rutherford Appleton Laboratory, Prague Asterix Laser System, Institute of Laser Engineering, Laboratoire dOptique Appliquee). Concerning the realization of x-ray lasers sources, using different laser pumping techniques (600 ps, 100 ps, ns/ps, OFI) and the optimization of their optical properties, using curved and plane half-cavity mirrors. In parallel of these developments, we present the main results obtained with x-ray laser in interferometry applications. These studies concern on the one hand the Michelson interferometry with an x-ray laser emitting at 13.9 nm (recently realized at LULI), and on the other hand the Fresnel bi-mirror with an x-ray laser emitting at 21.2 nm (recently realized at PALS).

Intensity distribution of the focal lines of the prepulse and mainpulse at the solid target surface

At the Prague Asterix Laser System (PALS) of the Academy of Sciences of Czech Republic the former Asterix IV iodine laser of the Max-Planck-Institut fur Quantenoptik is currently re-installed. For the soft x-ray laser experiments that will be performed in the near future a well defined focal line at the position of the target surface is important. Applying the prepulse technique there are two possibilities, either the main beam a d the prepulse beam are focused by the same focusing optics or the two different beams are focused by two optical systems separately. It is important to characterize the physical properties of the both line foci, i.e. their intensity distribution in two dimensions, since their energy ratio is giving only a mean value and not the actually existing non-uniformities along or across the focal line. By using two different focusing optics it is possible that the two lien foci do not have exactly the same width at full-width-half-maximum. In order to realize a well defined prepulse line focus it is important to measure the exact intensity distribution in two dimensions. We concept a method to obtain quantified 2D focal images and we present preliminary experimental results using a cylindrical lens array as well as using only a single cylindrical lens in combination with a spherical focusing lens.

Electron density profile measurements of line plasmas by interferometric technique

Interferometry measurements of zinc, copper and iron line plasmas created by the iodin laser PERUN ((lambda) equals 1.315 micrometer, (tau) approximately equals 400 ps FWHM) with intensities equivalent to those generated by low-level prepulses in the collisional excitation soft x-ray lasers (5 times 109 minus 1.3 times 1011 Wcm-2) are presented. The interferograms were taken with 4 and 10 ns delays with respect to the peak of the drive laser pulse using the third harmonic of the iodine laser ((lambda) equals 438 nm). Preliminary results of electron density profile reconstructions in the plane perpendicular to the line plasma axis are reported.