Bedrich Rus

The Prague Asterix Laser System

The Prague Asterix Laser System (PALS) is a new international laboratory where research teams are invited to compete for the beam time. The PALS Center runs an iodine photodissociation high-power laser system delivering up to 1.2 kJ of energy in ∼400 ps pulses at the wavelength of 1.315 μm. Optional doubling and tripling of the frequency is assured by large-diameter nonlinear crystals. The ASTERIX IV laser [H. Baumhacker et al., Appl. Phys. B 61, 325 (1995)], transferred from Garching into a new laser hall in Prague, was updated and put into operation on 8 June 2000. These upgrades include new beam delivery options and a twin interaction chamber, which is designed flexibly for a broad spectrum of applications. Results of the first series of experiments are presented and some planned upgrades are briefly described. These include implementation of adaptive optics, replacement of the iodine master oscillator by a more flexible solid state oscillator based on fiber optics, and a femtosecond extension of the l...

Recent experiments on the hydrodynamics of laser-produced plasmas conducted at the PALS laboratory

We present a series of experimental results, and their interpretation, connected to various aspects of the hydrodynamics of laser produced plasmas. Experiments were performed using the Prague PALS iodine laser working at 0.44 μm wavelength and irradiances up to a few 10 14 W/cm 2 . By adopting large focal spots and smoothed laser beams, the lateral energy transport and lateral expansion have been avoided. Therefore we could reach a quasi one-dimensional regime for which experimental results can be more easily and properly compared to available analytical models.

Astrophysical radiative shocks: From modeling to laboratory experiments

Radiative shock waves are observed around astronomical objects in a wide variety of environments, for example, they herald the birth of stars and sometimes their death. Such shocks can also be created in the laboratory, for example, by using energetic lasers. In the astronomical case, each observation is unique and almost fixed in time, while shocks produced in the laboratory and by numerical simulations can be reproduced, and investigated in greater detail. The combined study of experimental and computational results, as presented here, becomes a unique and powerful probe to understanding radiative shock physics. Here we show the first experiment on radiative shock performed at the PALS laser facility.The shock is driven by a piston made from plastic and gold in a cell filled with xenon at 0.2 bar. During the first 40 ns of the experiment, we have traced the radiative precursor velocity, that is showing a strong decrease at that stage.Three-dimensional ~3D! numerical simulations, including state-of-art opacities, seem to indicate that the slowing down of the precursor is consistent with a radiative loss, induced by a transmission coefficient of about 60% at the walls of the cell. We infer that such 3D radiative effects are governed by the lateral extension of the shock wave, by the value of the opacity, and by the reflection on the walls. Further investigations will be required to quantify the relative importance of each component on the shock properties.

Modeling of amplified spontaneous emission, heat deposition, and energy extraction in cryogenically cooled multislab Yb 3+ :YAG laser amplifier for the HiLASE Project

A three-dimensional ray-tracing code for determination of amplified spontaneous emission in a multislab laser amplifier is presented. In addition to energy stored in the amplifier, the code also calculates the heat distribution and the amplification of the signal beam. For cryogenically cooled multislab amplifiers with Yb3+:YAG and absorptive Cr4+:YAG cladding, energy storage efficiency greater than 52% and small signal gain of 22  m−1 were obtained. The pump energy converted to heat was found to be 11% in the active volume and 50% in the Cr4+:YAG cladding.

Experimental study of radiative shocks at PALS facility

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.

Measurements of the highest acceleration gradient for ions produced with a long laser pulse

Ultrafast plasma light ion streams have been produced using the 300 ps, kJ-class iodine laser, operating at PALS Centre in Prague. Ion detection was performed through standard ion collectors (IC) in time-of-flight configuration (TOF), shielded by thin metallic absorbers. This new diagnostics technique has been theoretically studied and experimentally tested in order to cut the long photopeak contribution and to analyze the ultrafast particle signal. Processing the obtained experimental IC-TOF data, including deconvolution processes of the TOF signals, UV/soft-x-ray photopeak absorption, and ion transmission calculations for different metallic filters, is shown. Mainly amorphous carbon (graphite) targets have been irradiated in order to limit the maximum number of ion charge states and to focus our study on demonstrating the validity of the proposed investigation technique. Maximum ion energy and acceleration gradient estimations as a function of the laser energy and focal spot diameter are reported.

Investigation of XUV amplification with Ni-like xenon ions using laser-produced gas puff plasmas

Abstract This paper presents results of a study of a gas-puff plasma soft-X-ray amplifier using Ni-like xenon. The target was created by pulsed injection of xenon from a high-pressure solenoid valve through a nozzle in the form of a 2 cm long slit. The plasma was produced by irradiating the gas puff plume with six line-focused laser beams. The uniformity of the plasma column was monitored using a crossed-slit X-ray pinhole camera while the ionisation balance was assessed with the help of keV resonance spectra obtained by a crystal spectrometer. A modest amplification was seen at two J =0–1 lasing lines allowing however the first precise measurement of their wavelengths. Comparison of the results with a previously reported amplification in the gas-puff system is made, indicating issues essential to the performance of these systems.

ELI-beamlines: extreme light infrastructure science and technology with ultra-intense lasers

We present the current status of ELI-Beamlines that will be the Czech pillar of the ELI (Extreme Light Infrastructure) project. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, 10 Hz repetition rate laser pulses at the petawatt level together with kilojoule nanosecond laser pulses that will be used for generation of 10 PW. These beamlines will be combined to generate X-ray secondary sources, to accelerate electrons, protons and ions and to study dense plasma and high-field frontier physics. These programs will be introduced together with the engineering program necessary for building a users’ facility.

New methods for high current fast ion beam production by laser-driven acceleration.

An overview of the last experimental campaigns on laser-driven ion acceleration performed at the PALS facility in Prague is given. Both the 2 TW, sub-nanosecond iodine laser system and the 20 TW, femtosecond Ti:sapphire laser, recently installed at PALS, are used along our experiments performed in the intensity range 10(16)-10(19) W∕cm(2). The main goal of our studies was to generate high energy, high current ion streams at relatively low laser intensities. The discussed experimental investigations show promising results in terms of maximum ion energy and current density, which make the laser-accelerated ion beams a candidate for new-generation ion sources to be employed in medicine, nuclear physics, matter physics, and industry.

Investigations of collisionally pumped optical field ionization soft-x-ray lasers

We report recent investigations of optical field ionization soft-x-ray lasers. We generated the amplifying medium by focusing a circularly polarized 760-mJ, 30-fs 10-Hz Ti:sapphire laser system into a gas cell a few millimeters long filled with xenon or krypton gas. 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 ∼5×109 photons per pulse. More recently we demonstrated lasing at 32.8 nm in Ni-like krypton. The influence of the pumping energy and the laser polarization on the lasing output as well as on the far-field pattern of the x-ray laser beam are reported and discussed.