This PDF file contains the front matter associated with SPIE Proceedings Volume 8780 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The Orion Laser Facility at AWE in the UK consists of ten nanosecond beamlines and two sub-picosecond beamlines. The nanosecond beamlines each nominally deliver 500 J at 351 nm in a 1 ns square temporal profile, but can also deliver a user-definable temporal profile with durations between 0.1 ns and 5 ns. The sub-picosecond beamlines each nominally deliver 500 J at 1053 nm in a 500 fs pulse, with a peak irradiance of greater than 10²¹ W/cm². One of the sub-picosecond beamlines can also be frequency-converted to deliver 100 J at 527 nm in a 500 fs pulse, although this is at half the aperture of the 1053 nm beam. Commissioning of all twelve beamlines has been completed, including the 527 nm sub-picosecond option. An overview of the design of the Orion beamlines will be presented, along with a summary of the commissioning and subsequent performance data. The design of Orion was underwritten by running various computer simulations of the beamlines. Work is now underway to validate these simulations against real system data, with the aim of creating predictive models of beamline performance. These predictive models will enable the user’s experimental requirements to be critically assessed ahead of time, and will ultimately be used to determine key system settings and parameters. The facility is now conducting high energy density physics experiments. A capability experiment has already been conducted that demonstrates that Orion can generate plasmas at several million Kelvin and several times solid density. From March 2013 15% of the facility operating time will be given over to external academic users in addition to collaborative experiments with AWE scientists.

We present details of a refurbishment and development programme that we have undertaken on the Vulcan Nd:Glass laser system to improve delivery to its two target areas. For target area petawatt in addition to replacing the gratings in the compressor chamber we have installed a new diagnostic line for improved pulse length measurement and commissioned a high energy seed system to improve contrast. In target area west we have replaced a grating on the high energy short pulse line and improved the focal spot quality. Both areas have been re-commissioned and their laser parameters measured showing that the pulse in petawatt has been measured below 500fs and focused to a spot size of 4μm the two short pulse beam lines in target area west have been measured as short as 1ps and have been focused to 5μm.

We introduce the directly diode-pumped PEnELOPE laser-system which is designed for a pulse energy of 150 J, a repetition rate of 1Hz and a pulse duration of 120 fs. The principle setup of amplifier and stretcher-compressor system as well as the pumping, energy extraction and cooling scheme of the power amplifiers will be reported. In this paper we focus on numerical modeling as well as design studies.

The Diode Pumped Optical Laser Experiments (DiPOLE) project at Central Laser Facility (CLF) is aimed at the development of scalable diode pumped, cryogenic gas cooled, multi-slab Yb:YAG amplifiers. Optimized designs for amplifiers capable of generating kJ pulse energies at multi-Hz repetition rate have been finalised and development of a scaled-down 10J, 10Hz prototype is currently underway at the CLF. We report on the recent results obtained on a 4-pass bowtie as well as 6-pass image relaying multi-pass setup for the DiPOLE amplifier. Additionally, Preliminary results for the amplifier performance with uniform doping (3 × 2at%) compared to gradient doping (2 × 1at% + 2 × 2at%) at cryogenic temperatures, confirms the multi-slab gradient doped design adopted for DiPOLE amplifier.

We present a novel approach for the construction of a high energy, high power burst mode laser system, based on diode pumped cryogenically cooled Yb:CaF₂. The system consists of a frontend producing pulses of 300 fs duration with 1 MHz. Bursts of 1000 subsequent pulses are cut from the continuous train by an electro optical modulator. Afterwards the duration of the individual pulses is stretched to 50 ps. The amplifier system consists of two amplifiers. Both amplifiers utilize mirror based relay imaging schemes to allow for a sufficient number of extraction passes for achieving efficient energy extraction. The goal parameters of the system are to achieve a total energy of 5J per burst with a repetition rate of 10Hz. Amplification results for the first of two amplifiers are demonstrated. A total output energy of 480 mJ was achieved corresponding to an optical to optical efficiency from absorbed pump energy to extracted energy of more than 17%. Single pulse energies of up to 7.5mJ are generated when changing to less pulses per burst. To achieve a constant energy from pulse to pulse during the burst we present a technique based on the modulation of the laser diode current during one pulse. With this technique the gain variation during the burst was than 5% peak to peak.

Development of high-power, picosecond laser sources is a desirable venture for both industry and research. Within the Hilase project, we are conducting research on both 500-mJ, 1-kHz and 5-mJ, 100-kHz picosecond laser sources based on the Yb:YAG thin-disk technology. We have developed a prototype thin-disk regenerative amplifier operating up to 10- kHz repetition rate pumped by the 940-nm fiber-coupled laser diodes. We achieved 5-mJ pulse energy at 10-kHz operation and 29.5-mJ at 1-kHz. Afterwards, we developed the high-energy regenerative amplifier operating at fixed repetition rate of 1-kHz and the pulse energy was achieved up to 40-mJ. Simultaneously, we elaborated the highrepetition rate regenerative amplifier operating at 100-kHz with pulse energy of 220-μJ. The amplified pulse was compressed with the efficiency of 88% using chirped volume Bragg grating.

In this paper, we report the measurements of the specific heat, the density and the thermal diffusivity at room and cryogenic temperatures of Ytterbium doped cubic sesquioxides (Sc₂O₃, Y₂O₃, Lu₂O₃) ceramics and of Ytterbium doped crystals (YAG, CaF₂). These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers.

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.

Results of laser induced damage threshold (LIDT) of fused silica, sapphire and Ti:Sa crystals in single shot mode in the femtosecond regime down to few optical cycles (< 10 fs) are presented. Different approaches to determine LIDT are described and compared. Our methodology yields accurate determination of damage/ablation threshold of any material (or component) irradiated by pulsed laser, as well as complementary physical results characterizing laser–matter interaction and/or concerning the deterministic character of femtosecond damage. It is shown that the abrupt decrease of both damage and ablation thresholds observed with ultra-short pulses (< 30 fs) is related to the significance of tunnel ionization in the ultrashort regime. Moreover, the results indicate that the laser damage occurrence is more deterministic below 30 fs.

Advanced high intensity laser matter interaction experiments always call for optimized laser performance. In order to further enhance the POLARIS laser system, operational at the University of Jena and the Helmholtz-Institute Jena, in particular its energy, bandwidth and focusability, new amplifier technologies have been developed and are reported here. Additionally, existing sections were considerably improved. A new multi-pass amplification stage, which is able to replace two currently used ones, was developed in close collaboration with the MPQ (Garching). The new basic elements of this amplifier are well homogenized pump modules and the application of a successive imaging principle. By operating the amplifier under vacuum conditions a top hat beam profile with an output energy of up to 1.5 J per pulse is foreseen. The already implemented POLARIS amplifier A4 was further improved by adapting an advanced method for the homogenization of the multi-spot composed pump profile. The new method comprises a computer-based evolutionary algorithm which optimizes the position of the different spots regarding its individual size, shape and intensity. The latter allowed a better homogenization of the POLARIS near field profile.

Slabs with non-uniform doping distribution are studied with the aim of reducing thermal deformations in high-energy high-average-power Yb:YAG slab systems. We present a numerical analysis based on Finite Element Mesh (FEM) methods suitable to model non-uniform devices. The thermal variation of the refractive index, the end-faces deformations and the photo-elastic effect have been calculated in order to estimate the total thermal-lens effect. The stress distributions are also obtained. Some results of this numerical approach are compared to experimental thermal lens measurements in a simple geometry for both uniform and structured samples, in order to validate the numerical procedures. Finally we compare numerical simulations for different single- or double-sided pumping and cooling geometries. They show that structured slabs can reduce thermal gradients with respect to uniformly doped means with comparable absorption and geometry. This means a reduction of thermal lens effect and thus an increase of maximum allowed pump power loading. Previous literature reports some work made with structured slabs where higher doping was located in layers with lower pump radiation levels, in order to get a more uniform absorption. Interestingly our modeling indicates that reduced thermal effects are instead obtained when a higher doping is located close to the cooled surfaces.

Physical and fabrication peculiarities which provide the high output energy and beam quality for the diode pumped erbium glass and Nd:YAG lasers are considered. Developed design approach allow to make passively Q-switched erbium glass eye-safe portable laser sources with output energy 8 − 12 mJ (output pulse duration is less than 25 ns, pulse repetition rate up to 5 Hz) and beam quality M² less than 1.3. To reach these values the erbium laser pump unit parameters were optimized also. Namely, for the powerful laser diode arrays the optimal near-field fill-factor, output mirror reflectivity and heterostructure properties were determined. Construction of advanced diode and solid–state lasers as well as the optical properties of the active element and the pump unit make possible the lasing within a rather wide temperature interval (e.g. from minus forty till plus sixty Celsius degree) without application of water–based chillers. The transversally pumped Nd:YAG laser output beam uniformity was investigated depending on the active element (AE) pump conditions. In particular, to enhance the pump uniformity within AE volume, a special layer which practically doesn’t absorb the pump radiation but effectively scatters the pump and lasing beams, was used. Application of such layer results in amplified spontaneous emission suppression and improvement of the laser output beam uniformity. The carried out investigations allow us to fabricate the solid-state Nd:YAG lasers (1064 nm) with the output energy up to 420 mJ at the pulse repetition rate up to 30 Hz and the output energy up to 100 mJ at the pulse repetition rate of of 100 Hz. Also the laser sources with following characteristics: 35 mJ, 30 Hz (266 nm); 60 mJ, 30 Hz (355 nm); 100 mJ, 30 Hz (532 nm) were manufactured on the base of the developed Nd:YAG quantrons.

AOA Xinetics (AOX) has been at the forefront of Deformable Mirror (DM) technology development for over two decades. In this paper the current state of that technology is reviewed and the particular strengths and weaknesses of the various DM architectures are presented. Emphasis is placed on the requirements for DMs applied to the correction of high-energy and high average power lasers. Mirror designs optimized for the correction of typical thermal lensing effects in diode pumped solid-state lasers will be detailed and their capabilities summarized. Passive thermal management techniques that allow long laser run times to be supported will also be discussed.

With increasing energy densities of laser pulses the laser induced damage threshold (LIDT) testing becomes an important characterization of optical components. The emission wavelength of several laser materials is in the 2 − 3 μm wavelength-range. We propose a wavelength conversion system generating tunable sub-ns pulses for LIDT measurements in this IR spectral range. The pump beam of the conversion system will be based on the thin-disk laser technology. The Yb-fiber-laser seeded CPA system with high-energy Yb:YAG thin-disk regenerative amplifier will produce uncompressed pulses of 0.5 ns width, 130 mJ energy, at wavelength of 1030 nm with 1 kHz repetition rate giving 130 W of average power. Output of the thin-disk regenerative amplifier will pump an optical parametric generator (OPG) and subsequent optical parametric amplifiers (OPA). The tunable output wavelength of the OPG will be between 1.5 μm - 2.1 μm for the signal beam and between 2.1 μm - 3 μm for the idler beam. The signal will be amplified in the OPAs because the optics and diagnostics is more easily available below 2 μm wavelength. The tunable multi-millijoule source above 2.1 μm will be the idler beam taken from the last amplification stage. High-average output power of 10 W at 1 kHz repetition rate will be unique among 2 − 3 μm tunable systems. Operation of the amplifiers at high-intensities and high-average powers limits the system performance. The thermal load of crystals caused by the partial beam absorption will be studied. Further, the damage threshold of optical components, transmission range of nonlinear crystals, and amplifiers bandwidths will be addressed.

We present preliminary simulation and experimental results obtained in the frame of QOMA project funded by the European Space Agency (ESA), involving the design and development of a diode-pumped solid state (DPSS) Nd:YAG laser. The simulation results were obtained using the LASCAD software code, while the experimental results were obtained at the Laboratoire Charles Fabry (France) and the National Technical University of Athens (NTUA).

We analyzed the transient response characteristics of Yb:YAG thin disk in to clarify the experimentally obtained advantages of pulsed pumping in 1-kHz repetition rate reported in ref. 2. We applied commercial 2D FEA software which can calculate transient response of thermal effects. The temperature distributions of thin disk in both the CW power of 125-W and the average power of pulsed 125-W have been calculated. Even the net heat power were same in both CW and pulsed pumping, the temperature distribution was lower in pulsed pumping which can provide higher O-O efficiency and smaller beam distortion. The time evolution of OPD in the pulsed pumping has been analyzed, too.

Two Yb:LuAG (Yb:Lu₃Al₅O₁₂) plates (thickness 1.05 mm, diameter 3 mm, AR/AR @ 0.9 − 1.1 μm, Yb-doping c = 15% and 20 %) were prepared for laser experiments. For Yb:LuAG pumping, fibre coupled laser diode operating in pulsed regime was used (fibre core diameter 100 μm, emission wavelength 968 nm, pulse length 2 ms, repetition rate 10 Hz, maximum energy 40 mJ). The longitudinally pumped Yb:LuAG was placed inside the 148mm long resonator formed by a flat pumping mirror (HR @ 1.0 − 1.1 μm, HT @ 0.97 μm) and by a curved output coupler (radius of curvature 150 mm). Set of output couplers with reflectivity R = 70 − 97% @ 1.0−1.1 μm was used and the output power amplitude was measured in dependence on absorbed pumping power amplitude. It was found that for both samples the output coupler reflectivity had only minor influence on laser output parameters expect emission wavelength (1048nm for R < 90% and otherwise 1031 nm). The sample with lower concentration had a lower threshold (∼ 2.5W for c = 15% and ∼ 3.0W for c = 20%) and higher slope efficiency (∼ 61% for c = 15% and ∼ 50% for c = 20 %). The maximum output power amplitude 6.7W was obtained using Yb:LuAG with c = 20% and R = 92% for pumping power amplitude 14W. Obtained results confirmed the good quality of newly grown highly doped Yb:LuAG crystals.

This paper has been withdrawn by the publisher because it was not presented at the conference.

We present calculation of aberration compensation in high average power multi-slab laser by a deformable mirror. The calculations were compared with a simple experiment. For the calculations we have developed a code that works with a square-shaped piston driven push/pull deformable mirror with continuous facesheet and allows optimization of mirror parameters and actuator array geometry. We have corrected the calculated output wavefront of Hilase 10 J multi-slab laser system in MIRÓ by using several actuator array geometries. The numerical results were benchmarked on an experimental model of multi-slab chamber using a membrane deformable mirror.

Several simple single-beam non-interferometric measuring techniques for ultrashort laser pulse analysis have been proposed lately (e.g. MIIPS, dispersoscopy). They are based on a compensation of the pulse spectral phase by an acousto-optic pulse shaper followed by a SHG crystal, for example . The output signal is detected by a nonlinear optical medium. Dispersoscopy was originally verified by broadband pulses of Ti:sapphire oscillator and has never been tested in different spectral range or on narrow band subpicosecond pulses. We modified such a dispersoscope for measurement of sub picosecond pulses of an Yb:YAG renerative amplifier generating at wavelength of 1030nm. We also modified the device for measurement of picosecond pulses having their mid-IR wavelength in the range between 2 and 3 microns.

We discuss the key important regimes of electromagnetic field interaction with charged particles. Main attention is paid to the nonlinear Thomson/Compton scattering regime with the radiation friction and quantum electrodynamics effects taken into account. This process opens a channel of high efficiency electromagnetic energy conversion into hard electromagnetic radiation in the form of ultra short high power gamma ray flashes.

Radiation energy losses of electrons in ultra-intense laser fields constitute a process of major importance when considering laser-matter interaction at intensities of the order of and above 10²² W/cm². Radiation losses can strongly modify the electron (and ion) dynamics, and are associated with intense and directional emission of high energy photons. Accounting for such effects is therefore necessary for modeling of, electron and ion acceleration and creation of secondary photon on the forthcoming ultra-high power laser facilities. To account for radiation losses in the particle-in-cell code PICLS, we have introduced the radiation friction force using a renormalized Lorentz-Abraham-Dirac model.¹⁰ Here, we present a study of the effect of radiation friction on the electron and photon energy distribution in a semi-infinite and overdense plasma. A possibillity to create a collisonless shock using an ultra intense laser field, in the context of laboratory astrophysics is discussed. The influence of the radiation reaction on the plasma dynamics is demonstrated.

We have developed a 0.1-Hz-repetition-rate, 30-fs, 1.5-PW Ti:sapphire laser system for the research on high field physics. In this paper, we describe the design and output performance of the PW Ti:sapphire laser and its applications in the generation of relativistic high order harmonic generation and the acceleration of charged particles (protons and electrons). In the experiment on relativistic harmonic generation, the harmonic order dramatically extended up to 164^th that corresponds to 4.9 nm in wavelength, and the dramatic extension was explained by the oscillatory flying mirror model. Recently, we could accelerate protons up to 45 MeV from a 10-nm polymer target and show the change in the acceleration mechanism from target normal sheath acceleration to radiation pressure acceleration. The femtosecond high power laser system is a good candidate for developing a compact electron accelerator as well. The generation of multi-GeV electron beam was observed from an injection scheme when a PW laser pulse was focused by a long focal length spherical mirror.

Extreme Light Infrastructure (ELI) Pan-European facility initiative represents a major step forward in quest for extreme electromagnetic fields. Extreme Light Infrastructure – Nuclear Physics (ELI-NP) is one of the three pillars of the ELI facility, that aims to use extreme electromagnetic fields for nuclear physics and quantum electrodynamics research. At ELI-NP, high power laser systems together with a very brilliant gamma beam are the main research tools. Their targeted operational parameters are described. The related experimental areas are presented, together with the main directions of the research envisioned.

Electron-positron plasmas are a prominent feature of the high energy Universe. In the relativistic winds from pulsars and black holes it is thought that non-linear quantum electrodynamics (QED) processes cause electromagnetic energy to cascade into an e-e+ plasma. We show that next-generation 10PW lasers, available in the next few years, will generate such a high density of pairs that they create a micro-laboratory for the first experimental study of a similarly generated e-e+ plasma. In the first simulations of a 10PW laser striking a solid we demonstrate the production of a pure electron-positron plasma of density 10²⁶m^-3. This is seven orders of magnitude denser than currently achievable in the laboratory and is comparable to the critical density for commonly used lasers, marking a step change to collective e-e+ plasma behaviour. Furthermore, a new ultraefficient laser-absorption mechanism converts 35% of the laser energy to a burst of gamma-rays of intensity 10²²Wcm^-2, potentially the most intense gamma-ray source available in the laboratory. This absorption results in a strong feedback between both pair and gamma-ray production and classical plasma physics leading to a new physical regime of QED-plasma physics. In this new regime the standard particle-in-cell (PIC) simulation approach, which has been the dominant kinetic simulation tool in plasma physics for 50 years, is inadequate. We have developed a new approach (QED-PIC) which will provide a powerful new modelling tool essential to the future advancement of the field of high intensity laser-plasma interactions.

Research with lasers of extremely high intensity has been proposed in terms of tunneling and the “Schwinger Limit”, which refers to breakdown of the vacuum into electron-positron pairs caused by a static or quasistatic electric field. The difficulty is that lasers produce transverse fields, wherein the electric and magnetic fields form a mutually orthogonal triad with the direction of propagation. Tunneling, including the Schwinger Limit, relates to longitudinal fields, in which the direction of the electric field vector is the only preferred direction. Transverse fields propagate indefinitely without inputs from source or current distributions. By contrast, longitudinal fields require continuing contributions from external source or current distributions. Failure to distinguish between longitudinal and transverse fields is consequential in that some proposed applications of very high intensity lasers pertain only to tunneling processes, but not to laser fields. A related difficulty is the flawed notion that tunneling constitutes a low-frequency limit of laser-induced processes. A counter-indication is that the ponderomotive potential of a charged particle in a laser field is proportional to the inverse square of the field frequency. Thus there is no possible approach to a zero-frequency laser field. The Göppert-Mayer gauge transformation of atomic physics makes possible a limited correspondence between transverse and longitudinal fields. The correspondence fails at both high and, most importantly, at low field frequencies. Vacuum pair production does not require the Schwinger Limit, but can be achieved at much lower intensities.

When crossing an electron beam in vacuum with an optical (laser) beam with standing waves, an interaction was redicted known as Kapitz-Dirac effect where the electrons are diffracted at the nodes of the optical field. After the final success of an experiment was reported (Freimund et al. 2001) confirming this classical kind of laser interaction with free electrons, the generalization of this effect (Schwarz-Hora effect) in the presence of a target or medium in the crossing area of the beams is re-considered as a basic non-resonance nonlinear quantum interaction process. The proof is based on a discovery of Peierls and of repeated later measurements agreeing with a quantum threshold for which the theory was elaborated initially. This is confirmed also in connectnion with the quantum theory of 1/f noise. Other aspects for electron acceleration of electrons by lasers may be interesting up to PeV energy using laser pulses of femtosecond (fs) duration and powers from Petawatt (PW) to Exawatt and Zetawatt.

Since the radiation reaction effect on electron propagation is very small in most cases, it can be usually neglected and the Lorentz force equation can be applied. However, ultra-intense lasers with normalized vector potential of the order of 100 can accelerate electrons to relativistic velocities with very high gamma factor. When the electron is accelerated to such high velocities the amount of emitted radiation may become large and radiation damping and emission of energetic photons should be considered. This work studies the influence of the radiation reaction force on laser interaction with solid foil targets. It compares different approaches adopted in PIC simulations to take into account the radiation reaction. The simulations of a counter-propagating relativistic electron and an ultra-intense laser beam demonstrate a strong energy loss of electrons due to non-linear Compton scattering. The interaction of ultra-intense laser pulse with solid foil is studied using PIC simulations. It is shown that the effect of radiation reaction strongly depends on the recirculation of high-energy electrons. When the recirculation is efficient, the radiation coming from the target is much more intense and it shows different spectral and angular characteristics.

Computational methods are indispensable to study the quantum dynamics of relativistic light-matter interactions in parameter regimes where analytical methods become inapplicable. We present numerical methods for solving the time-dependent Dirac equation and the time-dependent Klein-Gordon equation and their implementation on high performance graphics cards. These methods allow us to study tunneling from hydrogen-like highly charged ions in strong laser fields and Kapitza-Dirac scattering in the relativistic regime.

We consider interaction of two counter-propagating homogeneous sub-relativistic plasma beams with no external magnetic field applied. In numerical simulations performed with a particle-in-cell code three stages of evolution can be identified. The shock formation is initiated with development of the electron two stream and Weibel-like micro-instabilities, followed by fast electron heating and ion deceleration and heating. We present a theoretical analysis of the instabilities development and the nonlinear saturation to explore the origins of the heating and the magnetic field generation. From the dispersion relation, the instabilities are characterized and the dependence on the electron temperature and ion velocity is studied. The growth rate and the characteristic scales of instability are compared to simulation results.

We present an overview of the projected and/or implemented laser systems for ELI-Beamlines. The ELI-Beamlines facility will be a high-energy, high repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition rate laser pulses, and kilojoule nanosecond laser pulses that will be used for generation of 10 PW, and potentially higher, peak power. These systems will allow meeting user requirements for cutting-edge laser resources for programmatic research in generation and applications of high-intensity X-ray sources, in electron and proton/ion acceleration, and in dense plasma and high-field frontier physics.

We present a design of a high average power vacuum compressor unit for 1 kHz repetition rate pump laser operating at 1030 nm. The unit comprises two compressors and two SHG units located in a common vacuum vessel. Both compressors are designed with GDD of -270.5 ps² for compressing high energy, 1J, 500 ps pulses to 1.5 ps duration with efficiency that exceeds 88.5%. We also considered the feasibility of high efficiency, average power conversion to 515 nm in a range of nonlinear crystals in vacuum. The calculated temperature profiles in large aperture crystals are compared with temperature acceptance bandwidths for the second harmonic generation. It is concluded that in LBO and YCOB crystals the conversion efficiency can exceed 60%, thus allowing generation of 1 kHz train of 1.5 ps pulses at 515 nm with energy exceeding 0.5 J that will be used for pumping the high energy amplifier stages of a femtosecond OPCPA system.

DiPOLE is a concept for a large aperture gas-cooled cryogenic multislab DPSSL amplifier based on ceramic Yb:YAG. It is designed to amplify ns-pulses at multi-Hz repetition rates and is scalable up the kJ-level. The concept was first tested on a small scale prototype which has so far produced 7.4 J at 10 Hz, with the aim of reaching 10 J at an optical-to-optical efficiency of 25 %. The design of an additional amplifier stage producing 100 J at 10 Hz is underway. When used to pump short-pulse Ti:S or OPCPA systems, PW peak power levels can be produced at repetition rates and efficiencies that lie orders of magnitude above what is achievable today.

The ELI-beamlines project is expected to reach state of the art parameters in its laser systems. The Laser Induced Damage Threshold of the corresponding optical systems will have to sustain the expected fluences and repetition rates. The LIDT requirements for the ultrafast pulse compressors, vacuum transport mirrors and high average power optics are presented together with the current and planned capabilities for LIDT testing with a 25TW laser system at 800 and 1060nm.

We report on the initial performance of the first ELI-Beamlines high repetition rate, thin disk-based OPCPA pump laser. The laser is designed to produce a pulse train with pulse energies of 10-30 mJ at a 1 kHz repetition rate and is intended to be used as a pump source for an OPCPA amplifier. While the preliminary tests and analysis show that these target energies are well within the capabilities of the equipment available, the output energies of the current design are limited by self-phase modulation. We discuss the sources of this modulation and a new amplifier design to reduce these nonlinear effects. The efficiency of the second harmonic conversion of the thin disk amplifier output is measured to be higher than 65% and scaling to higher energies is discussed.

The enhancement of laser-driven proton acceleration mechanism in TNSA regime has been demonstrated through the use of advanced nanostructured thin foils. The presence of a monolayer of polystyrene nanospheres on the target frontside has drastically enhanced the absorption of the incident laser beam, leading to a consequent increase in the maximum proton beam energy and total laser conversion efficiency. The experimental measurements have been carried out at the 100 TW and 1 PW laser systems available at the APRI-GIST facility. Experimental results and comparison with particle-in-cell numerical simulations are presented and discussed.

A fundamental difference between interaction of laser pulses of less than picosecond duration and power in the range of and above Petawatt appears in contrast to pulses of nanosecond duration. This is due to the basic property that the long pulse interaction is based on thermal effects with inefficient delays of chaotic microscopic thermal motion while the short pulses avoid these complications and the interacting plasma reacts as a macroscopic collective known from atomic physics. Optical energy is converted into mechanical motion with high efficiency and nearly no thermal losses. These developments cover a long history of laser developments leading now into a new era of nonlinear physics combined with quantum properties. One of the applications is laser driven fusion energy

Simulation studies of laser-induced ion acceleration are extended from the present intensities up to ~10²² W/cm² that will be achieved soon at the ELI-Beamlines facility in Prague. Numerical simulations of target normal sheath acceleration (TNSA) enhancement by micro-structures on the front and rear sides of thin foils will be extended to higher laser intensities together with a brief description of target preparation techniques. Computational study of the impact of laser polarization, laser incidence angle, foil thickness and material is presented for PW laser beam of intensity of the order 10²² W/cm². Acceleration regime that combines TNSA with radiation pressure acceleration (RPA) is identified.

An energetic study of focused ultrashort Gaussian beams was carried out using the Fresnel diffraction formulae in the frequency domain. Analysis of the encircled energy at the focused plane shows that diffraction spreading of a focused pulsed beam occurs in the limiting case of a ultrashort pulse by comparing it to a cw beam whose frequency is ω_m which strongly contributes to the diffracted intensity rather than the carrier frequency ω₀.

Laser ignition of fusion (LIF) of light nuclei for fusion reactions for producing energy (LIFE) by using very powerful laser pulses with duration in the range of picoseconds is the aim of fast ignition where HiPER is one of the options. Special attention is given to the ultrahigh acceleration of plasma blocks about which option results are reported including an alternative scheme for avoiding lateral energy losses. Examples of relativistic accelerations are evaluated for HiPER and LIFE applications.