Highly transparent CaF₂ has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF₂ single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb³⁺ doped CaF₂ crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb³⁺ /Yb²⁺ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

For laser performance simulations, optical properties of applied active materials have to be exactly known. Here we report on temperature dependent emission and absorption cross section measurements for Yb:YAG, Yb:CaF₂ and Yb:FP15-glass. The temperature of the samples was aligned in steps of 20 K between 100 K and room temperature with a liquid nitrogen driven cryostat. Absorption spectra were obtained with a fiber coupled white light source and fluorescence spectra by excitation with a fiber coupled 10W laser diode at 970 nm. All spectral measurements were performed with a scanning spectrum analyzer, providing a spectral resolution down to 0.05 nm. By applying the McCumber relation in combination with the Fuchtbauer-Ladenburg method, we were able to obtain a valid emission cross section over the whole range of interest from the measured data.

Bonding-induced mechanical stress in GaAs-based laser diodes is studied by numerical and experimental techniques. This stress, induced by the soldering processes, appears when cooling down the assembly because of Coefficient of Thermal Expansion (CTE) mismatch, and dimensional disparities. Detailed mechanisms taking place are not fully understood. Residual stress is also known to influence device reliability. Composite submounts studied are composed of a CuW heat spreader on an AlN bottom plate in standard and optimized designs to lower mechanical stress levels. CuW shows a high thermal conductivity and a matched CTE with GaAs. Plain AlN submounts are studied as a reference. The numerical technique is a Finite Element Method calculation to compute the stress tensor induced in GaAs-based laser diodes during the soldering process on submounts with 80-20 AuSn eutectic solder pads. Starting with 31 MPa on the plain AlN submount, the standard composite submount gives 23.5 MPa while the optimized version is as low as 12 MPa. The experimental technique consists of Degree of Polarization (DoP) measurements of the photoluminescence emitted by a planarized diode bonded to a submount. From the DoP, relative stress variations induced by the submount are estimated. Starting with DoP referenced at 100% on plain AlN submounts, the standard composite submount gives 46% DoP reduction while the optimized version is expected to exhibit a reduction larger than 65%. Composite submounts with reduced mechanical stress and preserved thermal properties were studied experimentally and theoretically. An optimized design allows reducing the mechanical stress by a factor 2.5 at least.

We report on a novel 10 mJ-level diode-pumped Yb:KYW amplifier at 1040 nm, which generates picosecond pulses at a repetition rate of 10 Hz. It will be used in the front end of a petawatt laser system for pumping an optical parametric amplifier (OPA) for contrast enhancement. For synchronization purposes the amplifier is seeded by pulses that are derived from the femtosecond oscillator. After stretching by a volume Bragg grating and amplification in a double stage fiber amplifier the pulses are injected into the Yb:KYW regenerative cavity. Finally, the pulses are compressed to 1 ps before preparing pump pulses for the OPA by second harmonic conversion.

We propose a simple physical mechanism to explain observed instabilities in the dynamics of passively phased fiber amplifier arrays that arises from two properties: First that a weak phase disturbance of the output field of the array is converted into a strong intensity disturbance through the mode-selective feedback mechanism. Second, that this intensity fluctuation regenerates a phase fluctuation due to the nonlinear properties of the amplifying media. At sufficiently high operating power levels this cyclic disturbance continues to grow upon each cavity round trip, creating instability. This simple picture is supported by the results of a linear stability analysis of the set of propagation and population rate equations, which are in good agreement with observed critical power levels. A third level of quantitative confirmation was obtained by comparison to the results of numerical integration of the original set of nonlinear equations. This predicted instability is entirely a property of passively phased arrays of more than one element.

Laser properties of Yb:YAG crystal are investigated at 80-300K temperature range. On cooling we obtained amplification cross-section increase (5 times), maximum amplification cross-section wavelength shift (from 1030.1 nm to 1029.3 nm) and amplification cross-section bandwidth narrowing (from ~ 10 nm to 1.3 nm). Thermooptical constants P and Q and a parameter of photoelastic anisotropy, that determine thermal distortions in the active element are measured. Significant influence of the ASE on the storied energy in disk active elements is shown. It is necessary to use Yb:YAG/YAG "sandwich" active element geometry to reduce ASE. The current status of the laser system development with 0.5 J output energy at 1 kHz repetition rate is presented. 0.1 J in 50 ns pulse at 200 Hz repetition rate are achieved at the output of the laser system. Projected results will be achieved by changing disk active elements to Yb:YAG/YAG "sandwiches".

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 present temperature dependent gain measurements with different Ytterbium doped laser media, such as Yb:YAG, Yb:FP15-glass and Yb:CaF₂ in a multi-pass amplifier setup. The temperature of these materials was adjusted arbitrarily between 100K and 300K, while heat removal was realized by transverse cooling. In order to obtain a good beam profile throughout the amplification process, we used an all-mirror based relay imaging setup consisting of a telescope accomplishing a 4f-imaging with a plane mirror in each image plane. The amplification beam is then coupled into the cavity and doing several round trips wandering over the surface of the spherical mirrors. Hence the laser material is placed in one of the image planes, the beam quality of the amplifier was ruled by the intensity profile of the pumping laser diodes consisting of two stacks with 2.5kW peak output power each. Due to the given damage threshold fluence, the output energy of the amplifier was limited to about 1J at a beam diameter of 4.5 mm (FWHM). The seed pulses with a duration of 6 ns were generated in a Yb:FP15-glass cavity dumped oscillator with further amplification up to the 100mJ level by a room temperature Yb:YAG multi pass amplifier. The 1 Hz repetition rate of the system was limited by the repetition rate of the front-end. With Yb:YAG for instance an output energy of 1.1 J with an record high optical to optical efficiency of more than 35% was achieved, which was further increased to 45% for 500 mJ output energy.

We discuss upgrades and development currently underway at the Z-Backlighter facility. Among them are a new optical parametric chirped pulse amplier (OPCPA) front end, 94 cm 42 cm multi layer dielectric (MLD) gratings, dichroic laser beam transport studies, 25 keV x-ray source development, and a major target area expansion. These upgrades will pave the way for short/long pulse, multi-frame, multi-color x-ray backlighting at the Z-Accelerator.

We introduce a method to suppress prepulses of pulse picking systems due to the limited extinction ratio of polarization gating systems. By matching the round trip times of the oscillator and the subsequent regenerative amplifiers, leaking pulses are hidden below the temporal intensity pedestal of the main pulse. With this method, prepulses at the temporal position equal to the time difference of the round trip times of the cavities could be suppressed completely.

Single crystal photo-elastic modulators (SCPEM) are based on a single piezo-electric crystal which is electrically excited on a resonance frequency such that the resulting resonant oscillation causes a modulated artificial birefringence due to the photo-elastic effect. Polarized light experience in such a crystal a strong modulation of polarization, which, in connection with a polarizer, can be used for Q-switching of lasers with pulse repetition frequencies in the range of 100- 1000 kHz. A particularly advantageous configuration is possible with crystals from the symmetry class 3m. Besides LiTaO₃ and LiNbO₃, both already well explored as SCPEM-materials, we introduce now BBO, which offers a very low absorption in the near infrared region and is therefore particularly suited for Q-switching of solid state lasers. We demonstrate first results of such a BBO-modulator with the dimensions 8.6 x 4.05 x 4.5mm in x-, y-, z- direction, which offers a useful resonance and polarization modulation at 131.9 kHz. Since the piezo-electric effect is small, the voltage amplitude for achieving Q-switching for an Nd:YAG-laser is expected to be in the range of 100V. Nevertheless it is a simple and robust device to achieve Q-switching with a high fixed repetition rate for high power solid state lasers.

In this contribution we present a technology for deposition of interference coatings for optical components designed to operate as active media in power pulsed lasers. The aim of the technology is to prepare crystals for lasers for the HiPER project (High Power laser Energy Research) which should demonstrate the feasibility of laser driven fusion as a future energy source. Diode pumped solid state lasers (DPSSL) are the most likely option for fusion ignition. The choice of material for the lasers active medium is critical. Some of the most important properties include the ability to be antireflection coated to reduce the energy losses and increase the overall efficiency. This contribution deals with some of the materials considered to be candidates for slabs serving as the active medium of the DPSSLs. We tested Yb:YAG, Yb:CaF2 and Yb:KGW samples. As large amounts of heat need to be dissipated during laser operation, cryogenic cooling is necessary. Appropriate coating materials and techniques need to be chosen. Therefore differences between available coating techniques are investigated in terms of adhesion, enduring of stress resulting from temperature shocks, etc. Coated samples were placed in a specially designed cryogenic apparatus in order to simulate conditions similar to those in real life operation. Optical microscopy and spectrophotometer measurements were used for coating investigation after the conducted experiments.

The aims of paper were theoretical analysis of thermo-optic effects occurring inside laser elements under high heat load and its experimental verification for two particular cases: dichroic window and Nd:YAG ceramics disk. Transient thermal effects in dichroic mirrors and ceramic gain media were modeled applying COMSOL Multiphysics software and verified experimentally. Moreover, thermally induced distortions, thermally induced stresses and birefringence were calculated for gain elements of rod and disk shapes applying analytical, stationary model based on linear thermoelasticity theory. The 100-mm diameter dichroic mirrors made of BK7 and fused silica and gain disks made of Nd:YAG ceramics of 15-mm diameter and 3-mm thickness were prepared for experimental verification of the theoretical models. The special laboratory set-up enabling simultaneous registration of thermally induced birefringence and wavefront distortions was worked out. We have investigated the thermo-optical effects for different heat densities in range of 0.1 kW/cm² up to 50 kW/cm² changing the pump power , beam diameter or duty cycle. The experiments were carried out in lasing and non lasing conditions. The new method of measurement of heat conversion efficiency and absorption in mirrors based on threshold shearing interferometry was proposed and verified for dichroic mirror and ceramic Nd:YAG disk.

More than 10 Joules at 2 Hz were recently obtained from the LUCIA laser system based on diode-pumped Yb:YAG active mirrors. This achievement is the result of careful management of both Amplified Spontaneous Emission and thermal effects in laser amplifiers. Future developments including a cryogenically-cooled active mirror are also presented.

This study drafts simulation code to model the optical filed oscillation of end-pumped solid-state lasers, and proposed a kind of axicon-based stable laser resonator. Using numerical explorations, we find a systematic method to the selective excitation of nearly non-diffraction Mathieu-Gauss beams in end-pumped solid-state lasers with the proposed resonator.

The energy storage in the Cr⁴⁺,Yb:YAG crystal amplifier was stimulated under the conditions of concentration thickness product 15at.%mm and pumping power density 20kW/cm² for different aperture and doped Cr⁴⁺ and Yb³⁺density, using the pumping dynamic model for Cr4+,Yb:YAG crystal amplifier. The results indicated that, the density of energy storage decreases with the increasing of Yb³⁺ and amplifier aperture in absence of Cr⁴⁺; but the co-doped Cr⁴⁺ in Yb:YAG crystal would suppress the ASE in amplifier and affect on the energy storage in the amplifier, the ASE decreases with the increasing of co-doped Cr⁴⁺. But the maximum energy storage in amplifier increases firstly, and then decreases with the increasing of Cr⁴⁺ density. The reason is that, the Cr⁴⁺ in amplifier absorb not only the ASE but also the pumping energy. When less co-doped Cr⁴⁺, the ASE in amplifier would be serious, but when more co-doped Cr⁴⁺, the co-doped Cr⁴⁺ would absorb more pumping energy. Namely, in order to obtain maximum energy storage there is an optimized Cr⁴⁺ density, which was determined by the Yb³⁺ density and aperture of amplifier.

We present an overview of the Ti:sapphire laser chain recently commissioned at the PALS laboratory. The laser is based on commercial laser units and of an in-house-designed-and-built compressor. The system provides peak power of 25 TW in <40-fs pulses and delivers up to 0.9 J on the target in the main beam, at a repetition rate of 10 Hz. The laser chain employs conventional CPA amplification technique consisting of oscillator, stretcher, regenerative amplifier, pulse picker, and multipass amplifier, followed by compressor. The compressor is designed to use residual zero diffraction orders to produce two additional 50-mJ beams. One of these beams is compressed by an additional small-size compressor. All three beams can be delayed with respect to each other in the range of about 0-20 ns. The beams are delivered by vacuum distribution system into a target room serving to development of sources of X-rays and accelerated particles. In the near future the system will be synchronized with the PALS kJ laser and will serve as an ultrafast diagnostic probe beam.

In this article we analyze a broadband noncollinear optical parametric amplification. A general model, which allows us to find an optimal configuration of the OPA, was created. This model was applied to study amplification of supercontinuum, which was generated in sapphire crystal. Finally, we discuse a possibility of a contrast improvement by shaping supercontiuum seed spectra.

The spectacular progress of electron and heavy-ions acceleration driven by ultra-short high-power laser has opened the way for new methods of investigations in nuclear physics and related fields. On the other hand, upshifting the photon energies of a high repetition TW-class laser through inverse Compton scattering on electron bunches classically accelerated, a high-flux narrow bandwidth gamma beam can be produced. With such a gamma beam in the 1-20 MeV energy range and a two-arms 10-PW class laser system, the pillar of "Extreme Light Infrastructure" to be built in Bucharest will focus on nuclear phenomena and their practical applications. Nuclear structure, nuclear astrophysics, fundamental QED aspects as well as applications in material and life sciences, radioactive waste management and homeland security will be studied using the high-power laser, the gamma beam or combining the two. The article includes a general description of ELI-Nuclear Physics (ELI-NP) facility, an overview of the Physics Case and some details on the few, most representative proposed experiments.

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.

In this paper we report the perspectives of the development of the XUV laser sources and applications using High-power laser facilities. We focus our paper on the present status of the French LASERIX facility and more especially about its role in the development of the XUV laser sources considering the French "Institut de la Lumière Extrême " (ILE) and the potential European project Extreme Light Infrastructure (ELI). Finally, we present the scientific perspectives of X-ray laser sources developments using these laser facilities.

The generation of attosecond pulses with an amplitude greatly exceeding the driving field of an ultrarelativistic laser pulse at oblique irradiation of a solid target is investigated. We develop a universal model of the process, the so-called relativistic electronic spring, which is different from the conventional concept of an oscillating mirror. It follows from the model that there exists a parameter region where the energy conversion from the femto- to the attosecond regime is maximal. Based on the study we propose a new concept of laser pulse interaction with a target having a groove-shaped surface, which opens up the potential to exceed an intensity level of 10²⁶ W/cm² and observe effects due to nonlinear quantum electrodynamics with upcoming laser sources.

Seeding plasma-based soft x-ray laser (SXRL) demonstrated diffraction-limited, fully coherent in space and in time beam but with energy not exceeding 1 μJ per pulse. Quasi-steady-state (QSS) plasmas demonstrated to be able to store high amount of energy and then amplify incoherent SXRL up to several mJ. Using 1D time-dependant Bloch-Maxwell model including amplification of noise, we demonstrated that femtosecond HHG cannot be efficiently amplified in QSS plasmas. However, using Chirped Pulse Amplification concept on HHG seed allows to extract most of the stored energy, reaching up to 5 mJ in fully coherent 130 fs pulses. Original pump-probe experiments will be proposed thanks to the high laser energy available in ELI facilities.

Fast ignition of inertial fusion targets is one of the promising ways for future energy production. Recent studies of ignition with fast electrons have shown only little progress - mainly caused by the unresolved problem of controlled electron transport in dense plasmas. Ion-assisted ignition schemes are less sensitive in this regard and laser energies in the range of 50 - 100 kJ are required for fuel ignition. Picosecond laser pulses with intensities exceeding 10²² Wcm^-2 and a high intensity contrast of better than 10^-10 are needed thereby. The cone-guided target proves to be the most efficient scheme, although targets without a cone are more appropriate for high repetition rate operation.

Current high-intensity laser sources offer a multitude of research, experiment and application possibilities, ranging from e.g. ionisation studies of atomic and molecular systems to particle acceleration for medical purposes. Planned upgrades of existing laser sources will further increase the deliverable intensities and make certain lowintensity (as compared to the Schwinger field) tests of quantum electrodynamics viable. Moreover, secondary sources of radiation, and planned future facilities, offer several-orders-of-magnitude increases in intensities. Thus, it is highly relevant to ask what kind of physics that may be probed using future light sources.

This is a preliminary version of a conceptional study how to employ the unique ELI Beamlines facility to start the work in a novel research area - laser-based positron science. The main aim of the presentation is to initiate discussion to the topic as a basis for potential broad cooperation in this branch of new physics. Three potential specific research themes will be outlined: (1) Laser-driven positron sources. (2) Positron beam interactions. (3) Pair systems and mirror matter.

The critical electric field of quantum electrodynamics, called also the Schwinger field, is so strong that it produces electron-positron pairs from vacuum, converting the energy of light into matter. Since the dawn of quantum electrodynamics, there has been a dream on how to reach it on Earth. With the rise of laser technology this field has become feasible through the construction of extremely high power lasers or/and with the sophisticated use of nonlinear processes in relativistic plasmas. This is one of the most attractive motivations for extremely high power laser development, i.e. producing matter from vacuum by pure light in fundamental process of quantum electrodynamics in the nonperturbative regime. Recently it has been realized that a laser with intensity well below the Schwinger limit can create an avalanche of electron-positron pairs similar to a discharge before attaining the Schwinger field. It has also been realized that the Schwinger limit can be reached using an appropriate configuration of laser beams. In experiments on the collision of laser light and high intensity electromagnetic pulses generated by relativistic flying mirrors, with electron bunches produced by a conventional accelerator and with laser wake field accelerated electrons the studying of extreme field limits in the nonlinear interaction of electromagnetic waves is proposed. The regimes of dominant radiation reaction, which completely changes the electromagnetic wave-matter interaction, will be revealed. This will result in a new powerful source of high brightness gamma-rays. A possibility of the demonstration of the electronpositron pair creation in vacuum via multi-photon processes can be realized. This will allow modeling under terrestrial laboratory conditions neutron star magnetospheres, cosmological gamma ray bursts and the Leptonic Era of the Universe.

The Extreme Light Infrastructure project ELI¹ is aiming at laser intensities up to 10²⁶ W/cm². At such high intensities novel aspects of laser-matter and laser-vacuum interaction have to be considered.² In particular, cascades of electrons, positrons, and photons may arise that are capable of absorbing the laser energy efficiently. In the present paper we report about first simulations of cascading in strong laser fields.

We show that a strong laser pulse combined with a strong x-ray pulse can be employed in a detection scheme for characterizing high-energy γ-ray pulses down to the zeptosecond timescale. The scheme employs streak imaging technique built upon the high-energy process of electron-positron pair production in vacuum through the collision of a test pulse with intense laser pulses. The role of quantum radiation reaction in multiphoton Compton scattering process and limitations imposed by it on the detection scheme are examined.

HiPER (High Power laser Energy Research) is the first European plan for international cooperation in developing inertial fusion energy. ICF activities are ongoing in a number of nations and the first ignition experiments are underway at the National Ignition Facility (NIF) in the USA. Although HiPER is still in the preparatory phase, it is appropriate for Europe to commence planning for future inertial fusion activities that leverage the demonstration of ignition. In this paper we shall detail some of the key points of the laser design. Some of the main topics of the laser architecture are presented and discussed.

A major challenge the HiPER project is facing is to derive laser architectures satisfying simultaneously all HiPER requirements; among them, high wall-plug efficiency (~ 10%) and repetition rate (5 to 10 Hz) are the most challenging constraints. The active mirror Yb:YAG amplifier proposal from LULI is described.

A conceptual design for a kJ-class diode-pumped solid-state laser (DPSSL) system based on cryogenic gas-cooled multislab ceramic Yb:YAG amplifier technology has been developed at the STFC as a building block towards a MJ-class source for inertial fusion energy (IFE) projects such as HiPER. In this paper, we present an overview of an amplifier design optimised for efficient generation of 1 kJ nanosecond pulses at 10 Hz repetition rate. In order to confirm the viability of this technology, a prototype version of this amplifier scaled to deliver 10 J at 10 Hz, DiPOLE, is under development at the Central Laser Facility. A progress update on the status of this system is also presented.

HiPER is the European Project for Laser Fusion that has been able to join 26 institutions and signed under formal government agreement by 6 countries inside the ESFRI Program of the European Union (EU). The project is already extended by EU for two years more (until 2013) after its first preparatory phase from 2008. A large work has been developed in different areas to arrive to a design of repetitive operation of Laser Fusion Reactor, and decisions are envisioned in the next phase of Technology Development or Risk Reduction for Engineering or Power Plant facilities (or both). Chamber design has been very much completed for Engineering phase and starting of preliminary options for Reactor Power Plant have been established and review here.

We review development in the repetition-rate target area systems and technologies within the Work Package 15 of the HiPER Preparatory Phase project. The activities carried out in 2009-2010 have been involving analysis of solutions and baseline design of major elements of the repetition-rated fusion chamber, analysis of prospective injector technologies, numerical modelling of target survival during acceleration phase and during flight in the environment of fusion chamber, analysis of options of remote handling, systems of mitigation of fusion debris, and others. The suggested solutions assume operation at the repetition rate of 10 Hz and fusion yield between 20 and 100 MJ. Shock ignition is assumed as the baseline ignition scenario, although some technologies are applicable in the fast ignition; a number of the technologies identified are exploitable as well in the indirect drive. The operation of the HiPER repetition-rate chamber will contribute to technology development for the Demonstration Reactor HiPER facility.

Current status of recently proposed novel approach to inertial fusion energy technology, where phase conjugating mirrors generated by stimulated Brillouin scattering are employed to take care of automatic self-navigation of every individual laser beam on injected pellets, has been reviewed. This new technology is of a particular importance to the direct drive schemes of pellets irradiation as assumed, e.g., in HiPER project. If successful also in its full scale realization, such an aiming scheme would greatly reduce the technical challenges of adjusting large and heavy optical elements on each shot in a system with a repetition rate of at least several Hertz. In the gradual step-by-step tuning of this technology, in this paper a close attention has been payed to the unconverted basic harmonic issue with a special Faraday isolator design proposed.

An essential element of the HiPER project is the design of high gain targets, compatible with high repetition-rate operation and that can be mass produced at low cost. HiPER WP9 (Work Package 9 Requirements analysis for the fusion programme) studied schemes based on direct laser irradiation and advanced ignition (fast ignition and shock ignition), which have potentials for gain in excess of 100 at laser energy of about 1 MJ. To begin with, a very simple target was designed, which could allow for ignition demonstration with a few hundred kJ laser, and can be scaled at higher energy and gain. The ignition requirements have been determined, and crucial issues have been identified. This led to select shock ignition as the main option, since it turns out that all the relevant issues could be tested experimentally at existing facilities in the present decade. WP9 investigated irradiation schemes, target symmetry and stability issues, sensitivity to parameter changes, requirements for beam delivery and focusing and target positioning. Current work is directed towards increasing target robustness, scaling to greater energy, and designing targets for full scale demonstration.

The HiPER project is moving into an R&D phase with an increasingly clear vision of the stages required to demonstrate inertial fusion energy (IFE) as a power source. One of the major technical challenges will be to demonstrate the production and delivery to chamber of microtargets. The project baseline targets and Targetry-relevant system requirements are reviewed. An update is given of the current status of the HiPER Targetry workpackage summarising the coordinated range of progress which has been made within the project's Preparatory phase. A forward strategy is then presented in the context of the Targetry technology development plan. The full delivery plan is complex and only its essential structure will be presented in this paper focussing primarily on mass production issues and risk reduction. General technical issues of significance for Targetry are also discussed.

HiPER will include a Tritium target factory. This presentation is an overview. We start from process ideas to go to first sketch passing through safety principles. We will follow the Tritium management process. We need first a gas factory producing the right gas mixture from hydrogen, Deuterium and Tritium storage. Then we could pass through the target factory. It is based on our LMJ single shot experiment and some new development like the injector. Then comes pellet burst and vapour recovery. The Tritium factory has to include the waste recovery, recycling process with gas purification before storage. At least, a nuclear plant is not a classical building. Tritium is also very special... All the design ideas have to be adapted. Many facilities are necessary, some with redundancy. We all have to well known these constraints. Tritium budget will be a major contributor for a material point of view as for a financial one.

HiPER laser will need several large cooling systems. We will start from a thermal budget. We will consider different solutions (Liquefaction vs Refrigeration cycles). We will set some key elements such as thermodynamic optimization and economic approach As for the tritium item, the cooling budget will be a major contributor for a material point of view as for a financial aspect.

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to "Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future reactors, and making fusion possible with smaller facilities. In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France) Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling in the 10¹⁶ W/cm² intensity regime of interest for Shock Ignition.

Comparison of computer simulations applied to the experiments at RAL(UK), LULI(France), PALS(Czech Republic), and ILE(Japan) is given. Temporal evolution of densities, electron temperatures, compression/implosion velocities, are discussed using one dimensional hydrodynamic code (HYADES).

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.

The HiPER infrastructure reprsents a uniquely valuable tool for scientific discovery because it will be able to generate extreme matter conditions similar to those existing in our sun and the universe. The existence of long and short laser pulses in one infrastructure is fascinating and will allow for the study of new branches of physics suck as the properties of matter under extremer conditions in the laboratory. HiPER is therefore being designed to enable a broad area of new science studies including warm dense matter studies, astrophysics in the laboratory, extreme mater studies (under extreme magnetic and electric fields), highly nonlinear laser plasma interactions etc. The scope of this presentation is to present the progress of work on: a) the fundamental science target area design and b) the shielding requirements for the fundamental science programme.

A new diagnostic tool has recently been developed, which allows to get 2D images of X-ray sources with simultaneous energy encoded information. This is achieved by using a pinhole camera scheme in which a CCD camera, forced to operate in the single-photon regime, is used as a detector. The use of this method, initially limited to a single pinhole, multi-shot basis, has recently been extended to single-shot experiments typical of large scale installations using custom pinhole arrays of sub-10μm diameter. Preliminary tests have been carried out at the PALS facility and the diagnostics has been successfully employed in a PW environment in a recent experiment at RAL. The details of the method as well as some results from such recent experiments will be given.

A detailed knowledge of the physical phenomena underlying the generation and the transport of fast electrons generated in high-intensity laser-matter interactions is of fundamental importance for the fast ignition scheme for inertial confinement fusion. Here we report on an experiment carried out with the VULCAN Petawatt beam and aimed at investigating the role of collisional return currents in the dynamics of the fast electron beam. To that scope, in the experiment counter-propagating electron beams were generated by double-sided irradiation of layered target foils containing a Ti layer. The experimental results were obtained for different time delays between the two laser beams as well as for single-sided irradiation of the target foils. The main diagnostics consisted of two bent mica crystal spectrometers placed at either side of the target foil. High-resolution X-ray spectra of the Ti emission lines in the range from the Lyα to the Kα line were recorded. In addition, 2D X-ray images with spectral resolution were obtained by means of a novel diagnostic technique, the energy-encoded pin-hole camera, based on the use of a pin-hole array equipped with a CCD detector working in single-photon regime. The spectroscopic measurements suggest a higher target temperature for well-aligned laser beams and a precise timing between the two beams. The experimental results are presented and compared to simulation results.

Generation of high intensity and well collimated multi energetic proton beams from laser-matter interaction extend the possibility to use protons as a diagnostic to image imploding target in Inertial Confinement Fusion experiments. An experiment was done at the Rutherford Appleton Laboratory (Vulcan Laser Petawatt laser) to study fast electron propagation in cylindrically compressed targets, a subject of interest for fast ignition. This was performed in the framework of the experimental road map of HiPER (the European High Power laser Energy Research facility Project). In the experiment, protons accelerated by a ps-laser pulse were used to radiograph a 220 m diameter cylinder (20 m wall, filled with low density foam), imploded with 200 J of green laser light in 4 symmetrically incident beams of pulse length 1 ns. Point projection proton backlighting was used to get the compression history and the stagnation time. Detailed comparison with 2D numerical hydro simulations has been done using a Monte Carlo code adapted to describe multiple scattering and plasma effects and with those from hard X-ray radiography. These analysis shows that due to the very large mass densities reached during implosion processes, protons traveling through the target undergo a very large number of collisions which deviate protons from their original trajectory reducing proton radiography resolution. Here we present a simple analytical model to study the proton radiography diagnostic performance as a function of the main experimental parameters such as proton beam energy and target areal density. This approach leads to define two different criteria for PR resolution (called "strong" and "weak" condition) describing different experimental conditions. Finally numerical simulations using both hydrodynamic and Monte Carlo codes are presented to validate analytical predictions.

The target factory of an Inertial Fusion Energy (IFE) power plant (or reactor) must supply the targets with a rate of 1-10 Hz including their injection and transport through the chamber. HiPER is a proposed European High Power laser Energy Research facility dedicated to demonstrate the feasibility of laser driven fusion for IFE reactor. The work of HiPER facility requires formation & delivery of cryogenic free-standing targets with a rate of more than 1 Hz. To meet these requirements, an approach to fuel layering based on conduction cooling of a batch of moving spherical targets has been developed at the Lebedev Physical Institute (LPI). The approach demands to use free-standing targets in each production step: fuel filling, fuel layering, target characterization and injection. In this report, the expert results on the development of a specialized layering module prototype for a high reprate FST formation of HiPER cryogenic targets are presented.

This paper presents a short analysis of possible techniques for fusion targets tracking in rep-rate regime. Target tracking solution is limited with necessity of high speed, high precise and long-distance measurement combined with a harsh environment of the vacuum fusion chamber. The only optical measurement seems to be usable to meet required conditions to measurement system. Few standards and less traditional methods are presented in this paper. Its possibility to meet the target goal resolution is discussed. Preparation of experimental techniques for verification of measurement conditions of suggested methods is shown too.