Laser amplifiers producing high energy (multi-J) nanosecond pulses at high repetition rate (multi-Hz) are required for a wide range of commercial and scientific applications. The DiPOLE concept, developed at the STFC Central Laser Facility (UK), consists in scalable, high-energy DPSSL amplifiers based on cryogenically-cooled, multi-slab ceramic Yb:YAG. In this work we discuss the most recent developments aimed at scaling the pulse repetition of new generation DiPOLE lasers from 10 Hz to 100 Hz. We present the design and current status of a 10 J, 100 Hz DiPOLE laser. We will discuss thermal management approaches adopted for this system.
We present benchmarking of the home-made MATLAB model with the experimental data obtained for the 10 J/10 Hz cryogenically cooled multi-slab laser systems being developed in the Rutherford Appleton Laboratory, STFC, UK. The laser head of each system consists of four, 5 mm thick slabs separated by 2 mm gaps. Each slab is composed of 35 mm diameter Yb:YAG active material surrounded by 10 mm thick absorptive cladding. The slabs are pumped from both sides by diode arrays which in total deliver up to 40 kW of pump power in 1 ms pulses with a central wavelength of 940 nm, bandwidth 6 nm and pump spot 20 mm x 20 mm. The laser head has been modeled to predict gain in the slabs and the amplification of the seed beam for the temperatures of operation ranging from 100 K to 180 K. Output energy for different pump pulse durations has been calculated. It was determined that the maximum output energy obtained after 6 passes for the amplifier operating at the temperature of 120K and repetition rate 1 Hz was 9 J for the seed energy of 20 mJ. For higher temperature of 160 K the output energy was 8 J. The corresponding maximum single pass gain in the amplifier head was 8 for 120 K and 4 for 160 K. Results of the simulations are in a very good agreement with the measured data presented in [1].
An overview of Czech national R&D project HiLASE (High average power pulsed LASEr) is presented. The HiLASE project aims at development of pulsed DPSSL for hi-tech industrial applications. HiLASE will be a user oriented facility with several laser systems with output parameters ranging from a few picosecond pulses with energy of 5 mJ to 0.5 J and repetition rate of 1-100 kHz (based on thin disk technology) to systems with 100 J output energy in nanosecond pulses with repetition rate of 10 Hz (based on multi-slab technology).
We present an adaptive optics system for active wavefront correction of the first stage amplifier of a multi-slab laser system capable of generating 100 W of average output power and transverse dimensions of 20 mm x 20 mm. The results of this experiment are compared with numerical simulations.
Detailed modeling results of 100 J class laser systems with respect to the output energy, beam propagation, nonlinear phase accumulation, wavefront aberrations, and adaptive optics performance obtained in MIRÓ and MATLAB codes are presented here. The laser system is based on a cryogenically cooled Yb 3+ ∶YAG multislab amplifier with two identical amplifier heads and operates at 10 Hz repetition rate with an average power above 1 kW.
Precise values of absorption, emission and gain cross-sections of Yb:YAG, Yb:LuAG, Yb:CaF2 and Yb:FP15-glass at cryogenic temperatures are presented. To obtain the emission cross-sections two theoretical approaches were used. The first is the McCumber or reciprocity method (RM) which is based on the absorption spectra. The second is the Fuchtbauer-Ladenburg (FL) method using fluorescence spectra. From the results of cross-sections one can expect significant impact on laser performance on these materials especially in the case of high energy class diode pumped solid state lasers.
We present the design parameters of a diode-pumped 100J-class multi-slab Yb:YAG laser at 10 Hz scalable to the kJ
regime. Results of detailed energetics and thermo-optical modeling confirm the viability of cryogenic helium-gas cooling approach to drastically reduce thermally-induced distortions in the laser slabs. In addition, a comparison of spectral measurements from laser-diode stacks and Yb:YAG crystals validates the feasibility of highly efficient diode-pumped solid-state lasers at cryogenic temperatures.
We present advanced 3D ray-tracing code for calculation of amplified spontaneous emission (ASE), stored energy and
heat generation in laser active material. New results including spectrally resolved absorption, amplification and super-
Gaussian pump beam profile are obtained for 100 J cryogenically cooled multi-slab amplifier.
We present a comparison of two conceptual layouts of 100 J class laser systems for HiLASE and ELI Beamlines projects
with respect to the output energy, beam propagation and system performance obtained from MIRO code. Both systems
are based on cryogenically cooled Yb:YAG multi-slabs amplifiers technology and operate at 10 Hz repetition rate with
average power above 1 kW. First concept of the laser system consists of separate 10 J preamplifier and 100 J power
amplifiers, while the second consists of a main amplifier with two identical amplifier heads delivering 100 J.
Inertial Confinement Fusion with Shock Ignition relies on a very strong shock created by a laser pulse at an intensity of
the order of 1016W/cm2. In this context, an experimental campaign at the Prague Asterix Laser System (PALS) has been
carried out within the frame of the HiPER project. Two beams have been used, the first to create an extended preformed
plasma (scale length of the order of hundreds of micrometers) on a planar target, the second to generate a strong shock
wave. Different diagnostics were used to study both the shock breakout at the rear surface of the target and the laserplasma
coupling and parametric instabilities. This paper is focused on back-scattering analysis to measure the backreflected
energy and to characterize parametric instabilities such as stimulated Brillouin and Raman scattering. Our
experimental data show that parametric instabilities do not play a strong role in the laser plasma coupling. Moreover,
preliminary analysis of the back reflected light from the interaction region shows that less than 5% of the total incident
laser energy was back-reflected, with only a small fraction of that light was originating from parametric instabilities.
We present the results of an experiment concerning laser-plasma interaction in the regime relevant to shock ignition. The
interaction of high-intensity frequency tripled laser pulse with CH plasma preformed by lower intensity pre-pulse on
fundamental wavelength of the kJ-class iodine laser was investigated in the planar geometry in order to estimate the
coupling of the laser energy to the shock wave or parametric instabilities such as stimulated Raman or Brillouin
scattering, or to the fast electrons. First the complete characterization of the hydrodynamic parameters of preformed
plasma was made using crystal spectrometer to estimate the electron temperature and XUV probe to resolve the electron
density profile close to the critical density region. The other part of the experiment consisted of the shock chronometry,
calorimetry of the back-scattered light and hard X-ray spectrometry to evaluate the coupling to different processes. The
preliminary analysis of the measurements showed rather low energy transfer of the high-intensity pulse to back-scattered
light (< 5%) and no traces of any significant hot electron production were found in the X-ray spectra.
B. Rus, F. Batysta, J. Čáp, M. Divoký, M. Fibrich, M. Griffiths, R. Haley, T. Havlíček, M. Hlavác, J. Hřebíček, P. Homer, P. Hříbek, J. Jand'ourek, L. Juha, G. Korn, P. Korouš, M. Košelja, M. Kozlová, D. Kramer, M. Krůs, J. C. Lagron, J. Limpouch, L. MacFarlane, M. Malý, D. Margarone, P. Matlas, L. Mindl, J. Moravec, T. Mocek, J. Nejdl, J. Novák, V. Olšovcová, M. Palatka, J. P. Perin, M. Pešlo, J. Polan, J. Prokůpek, J. Řídký, K. Rohlena, V. Růžička, M. Sawicka, L. Scholzová, D. Snopek, P. Strkula, L. Švéda
ELI-Beamlines will be a high-energy, repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. It will
be an international facility for both academic and applied research, slated to provide user capability since the beginning
of 2016. The main objective of the ELI-Beamlines Project is delivery of ultra-short high-energy pulses for the
generation and applications of high-brightness X-ray sources and accelerated particles. The laser system will be
delivering pulses with length ranging between 10 and 150 fs and will provide high-energy petawatt and 10-PW peak
powers. For high-field physics experiments it will be able to provide focused intensities attaining 1024 Wcm-2, while this
value can be upgraded in a later phase without the need to upgrade the building infrastructure. In this paper we describe
the overall conception and layout of the designed ELI-Beamlines facility, and review some essential elements of the
design.
A model for calculation of stored energy and heat source assessment in a laser crystal has been developed. We report that
in a pulsed laser amplifier using Yb:YAG slabs at low temperature with ASE suppressing MLD absorptive layer, 58%
of the pump energy is deposited as heat and has to be cooled, while only 11% of the pump energy is converted into heat
inside the pumped part of the Yb:YAG crystal itself.
We demonstrate a novel experimental method for improvement of efficiency of structural surface modification of
various solids (PMMA, amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from high-order
harmonic generation (HHG), and VIS-NIR (410/820 nm) laser pulses. Although the fluence of each individual
pulse was far below the surface ablation threshold, very efficient and specific material modification was observed after
irradiation by a single or a few shots of mixed XUV/VIS-NIR radiation.
We also report results on comprehensive characterization of ultrafast coherent X-ray beamline at Prague Asterix
Laser System (PALS). The beamline is based on 1 kHz, table-top, high-order harmonic generation source capable to
deliver fully coherent beam in the 30 nm spectral range. Ti:sapphire (810 nm, 1 kHz) laser pulses with a duration of 35 fs
and energy 1.2 mJ have been focused into gas cell containing conversion medium (Ar). To achieve highly efficient HHG
we will apply the technique of guided laser pulses. Source parameters were investigated.
In this paper some results of investigations concerning interaction of EUV radiation with inorganic and organic materials
were presented. Samples of different materials were irradiated with a 10 Hz laser - plasma EUV source based on a gas
puff target. The source was equipped with grazing incidence and multilayer collecting mirrors. The grazing incidence
collector was used in experiments concerning surface modification and micromachining of different materials. The
micromachining experiments were performed for different polymers that were irradiated through a fine metal grid as a
contact mask. For fluoropolymers, EUV radiation with fluence of 10 mJ/cm2 was enough for efficient photo-etching. The
photo-etching speed was maximal for polytetrafluoroethylene (PTFE) reaching 30nm per shot. It was shown that using
such a method microstructures with high aspect ratio could be produced. Experiments connected with surface
modification were performed either with organic or inorganic materials. Different kinds of surface structures were
obtained depending on irradiated materials and irradiation parameters. The Mo/Si collector together with argon plasma
was used for obtaining a quasi-monochromatic radiation for EUV microscopy and some metrological applications.
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