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Abstracts, Meeting of WG4, April 18-20, 2016, Belgrade, Serbia

<Presentation of the new laser facilities in Magurele, Romania ELINP and CETAL> Carmen Ristoscu; National Institute for Laser, Plasma and Radiation Physics, Romania;; The project Center for Advanced Laser Technologies (CETAL in INFLPR started in 2007 in the framework of National Plan for Research, Development and Innovation 2007-2013, PNII program, coordinated by National Authority for Scientific Research. The project was aimed to develop an infrastructure dedicated to research and innovation in the field of advanced photonic technologies. The main R&D directions are: High-field laser interactions with matter; Laser material processing; and Photonic investigations. At present, CETAL is a research infrastructure providing access and research services to any academic and industrial entities. It is focused of development new laser based technologies for microfabrications and nanostructuring, development new applications of nanomaterials and micronano-structures on optics, electronics, medicine, chemistry etc. CETAL is ready to join the EU efforts to develop regional R&D activities. Extreme Light Infrastructure (ELI) Pan-European project represents a major step forward in scientific research with extreme high electromagnetic fields. Extreme Light Infrastructure – Nuclear Physics (ELINP), one of the three pillars of ELI, will be located in Bucharest-Magurele, Romania. The ELI-NP Project,worth 300 million euro, is co-financed by the European Regional Development Fund. The project implementation started in 2013 and the facility will be operational in 2018. At ELI-NP, a high power laser system (2x10 PW) together with a very brilliant gamma beam system are the two main research equipment. ELI-NP will be a research center for ultra-high intensity lasers and nuclear physics. This multidisciplinary facility will provide completely new opportunities to study fundamental processes that occur in ultraintense laser fields during light-matter interaction. Basic and applied physics research as well will be present in the scientific program of the new Center. The status of the project implementation, the planned high power laser system and the gamma beam system will be presented, together with the main directions of the scientific program ( <Solid Hydrogen target for laser driven proton acceleration> J.P.Perin, D.Chatain;Low temperature laboratory, CEA, 17 rue des Martyrs, Grenoble, 38054, France; There is a great interest for fundamental research but also for applied research, in producing energetic protons. These protons can be used for example in the field of thermonuclear inertial confinement fusion research or in medical domains as proton therapy. One mean to obtain a beam of energetic protons consists in focusing a high intensity laser on a target. Various physical mechanisms of laser-driven ion acceleration have been investigated to date. The mechanism most investigated experimentally is the Target Normal Sheath Acceleration (TNSA) hen ions are accelerated at the rear side of thin target in a quasielectrostatic sheath formed by fast electrons propagating from the target front side 3,4 . A suitable target for this application is a thin ribbon of solid H2. In this context, the low temperature laboratory of the CEA developed a cryostat able to produce a continuous film of solid H2 of some tens of microns in thickness and one millimeter in width. A new extrusion technique is used, without any mobile part. Thermodynamic properties of the fluid are used to achieve this goal. The principle is as follow: Once the experimental cell is totally filled with solid H2, the inlet valve is closed and the top of the cell is heated up. The pressure increases and pushes the solid H2 placed at the bottom of the cell through a calibrated hole. The construction of new high power laser facilities (e.g. high repetition rate petawatt-class lasers at ELI-Beamlines5) will clearly enable numerous prospective applications based on secondary sources of energetic particles. In particular the use of the proposed solid hydrogen cryogenic target along with these emerging laser technologies will allow demonstrating future medical applications such as hadron therapy 6,7. In fact, in recent years pilot experiments of cancer cell irradiation have already been realized 8. The possibility to use other gases than hydrogen (e.g. deuteron) suitable for different applications is also envisioned in the future; References: 3 S.P. Hatchett et al., Phys. Plasmas 7, 2076 (2000). 4 A. Maksimchuk et al., Phys. Rev. Lett. 84, 4108 (2000). 5 6 K.W.D. Ledingham et al., British J. Radiology 80, 855 (2007). 7 D. Margarone, P. Cirrone , G. Cuttone, G. Korn, 2nd ELIMED Workshop and Panel, Vol. 1546, AIP Proceedings (2013) ISBN: 978-0-7354-1171-5. 8 A. Yogo, T. Maeda, T.Hori et al., Appl. Phys. Lett. 98, 053701 (2011). Contact: <Investigations at the IPPLM on laserproduced ions and applications>   M. Rosinskia , P. Parysa, A. Zaras-Szydlowskaa, J. Badziaka, L. Ryca, P. Gasiora,L. Andoc, L. Giuffrridac, L. Torrisib, A. Szydlowskia,d, A. Malinowskad, J. Wolowskia; a) Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland b) Dipartimento di Fisica, Università di Messina, Messina, Italy c) INFN- Laboratori Nazionali del Sud, Catania, Italy d) National Centre for Nuclear Research, Otwock, Poland; High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion(IPPLM) offers the possibility of investigation of laser plasma generated by pulses of Ti:Sa Femtosecond Laser (~0.5 J ~40 fs pulses) by the means of advanced diagnostic systems including ion collectors, SiC detectors, fast semiconductors detectors of hard  and soft X-rays,Radiochromic Films and Track detectors. With the use of these diagnostic systems extensive studies of ultra-intense laser interactions with plasma can be conducted including generation of ultra-short X-ray pulses, laser acceleration of particles, studies of physical phenomena related to inertial confinement fusion, investigation of photo-induced material modifications due to ultrashort pulses, and research for potential applications. Besides of applications for investigation in physics of high energy particles, the systems at the IPPLM can be used for technological research, for example in laser modification of physical, mechanical and chemical properties of the laser treated samples or laser techniques in semiconductor technology, namely ion implantation. In comparison to many other solutions which are based on especially  designed lasers, the unique ion implantation source developed at the IPPLM offers the advantage of application of standard industrial lasers. It has been achieved by the application of the precisely shaped electrostatic field which not only accelerated the ions but also due to deflection removes contamination from the ion and allows to adjust their implantation energy. The system has been simulated and designed with the use of OPERA 3D code and its efficiency was confirmed by the set-up based on the commercial Nd:YAG laser system. The scope of the presentation will be at the research opportunities of the HPLL and the advanced system for the ion implantation; e-mail: <Particle production using high power high intensity lasers>P.Raczka; Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland; One of the important features of laser interaction with a solid target at ultra-high intensities is the phenomenon of particle production at the expense of the kinetic energy of laser-accelerated electrons and/or ions. In particular, the interaction of a high energy and high intensity laser pulse with a thick solid target leads to the formation of a population of fast electrons, which in turn generate high energy bremsstrahlung radiation. Fast electrons have typically an exponential energy distribution, with the so called temperature that is an increasing function of the laser intensity. The exact form of this dependence is, however, a subject of some debate; for example, it is clearly sensitive to the presence of a preplasma and to the structure of the target. Sufficiently energetic fast electrons and high energy gamma rays may in turn initiate production of secondary particles through electromagnetic and/or nuclear interactions, a simplest example being the production of electron-positron pairs. The phenomenon of particle production under such circumstances is studied using a model for fast electron propagation and gamma ray generation in a solid target. Using an optimistic assumption about the scaling of the fast electron temperature, the possibility of producing pions and muons at laser intensities not exceeding by much 1021 W/cm2 is assessed. <Fluid modeling of laser interaction with micro-structure targets>Jiri Limpouch; Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering,Czech Republic; The physics of laser interaction with low average density porous materials is of major importance for many applications, in particular for the high energy density physics and Inertial Confinement Fusion (ICF). The numerical modeling of interactions of high power laser beams with low density foams and aerogels presents a serious challenges originating from extremely different spatial scales. Analytical and numerical models of laser-supported heating and ionization wave will be reviewed. Our novel method is presented here in which a simplified model of pore filling is coupled in real time to the macroscopic hydrodynamics in our fluid code. <Sub-Micrometres and Nanometres Low Density Polymeric Foams and Full Density Polymers for Laser Targets – present and future>Wigen Nazarov Ph.D.; Polymer and materials Chemist, Production of materials for laser targets; Low density polymeric foams and full density polymers have been used as components of laser targets for many years in some high energy laser experiments. The main challenges in synthesising low density porous materials is that they must have the required composition, pore size (morphology) and have reasonable mechanical strength so it could be utilised in a laser target. The rapid progress in high energy laser physics determines the specifications of the porous materials required in this field. In recent years, promising experimental results involving interaction of high energy lasers and porous material, has been the driving force behind new and more stringent specifications for these materials for future experiments. One of the major achievements reported here is using chemical and hysical methods for controlling the pore morphology and diameter in the porous materials of same composition. In this presentation, some of the earlier successes that paved the path to current capabilities and the future requirements for mesoporous and macroporous materials used in high energy laser experiments will be presented. Challenges and successes in production of very low density materials (below 3 mg/cm-3), together with production of divinyl benzene aerogels and an innovative prototype rapid filling technique for the manufacture of foam-filled fast repetition rate targets will be presented.Porous materials that will be presented are: Photo-initiated acrylate foams, polyHIPE foams, polyimide aerogels, Silica aerogels, Polymethyl pentene (TPX). Additionally, techniques such as in-situ polymerisation, temperature controlled synthesis, fast repetition rate target production will be  reported. Email: <Nanostructured materials for nuclear fusion research and laser-driven ion acceleration>    A. Maffini1, D. Dellasega1,2, V. Russo1, L. Fedeli1, L. Cialfi1, M. Passoni1,2; 1Dipartimento di Energia, Politecnico di Milano, Via Ponzio 34/3, 20133 Milano, Italy, 2Istituto di Fisica del Plasma "P. Caldirola", CNR, via R. Cozzi 53, 20125 Milano, Italy; The Micro- and Nanostructured Materials Lab (NanoLab) at the Politecnico di Milano works on the nanoscale design, production, processing and investigation of advanced materials for different scientific and technological purposes, including nuclear fusion research and ultraintense laser-matter interaction experiments.The capability of controlling material characteristics down to the nanoscale has opened new frontiers in many fields of science and technology [1]. Nanometric structures can show peculiar properties not shared with their bulk counterpart. At Nanolab, bottom-up growth techniques such as Pulsed Laser Deposition (PLD) are exploited to produce nanoscale-engineered materials with tailored chemical, electrical, optical, and mechanical properties, also suitable to exhibit a radically different response to electromagnetic and particle radiation.Different kinds of nanostructured films have been studied in the frame of plasma-wall interaction research in magnetic confinement fusion machines. Highly reflective rhodium films with a controlled response to plasma erosion have been developed as functional coatings for diagnostic first mirrors in fusion reactors like ITER [2,3]. Tungsten coatings with different degree of structural disorder, designed to mimic the effect of particle bombardment and plasma interaction on a plasma facing component, have been produced and characterized, also with respect to their deuterium retention properties [4,5]. The versatility of PLD technique was also exploited to reproduce in the laboratory materials similar to those expected to be re-deposited on the first wall of fusion reactors, like mixed co-deposits [6,7]. Although these activities have been carried out in the context of magnetic fusion research, the developed methods, tools and results can be of interest also for the research on inertial fusion. In the frame of laser-driven ion acceleration experiments, where an ultraintense, ultrashort laser pulse is focused on a target to obtain high energy ions, non-conventional nano-engineered target concepts have been investigated. According to particle–in–cell simulations, a near critical plasma layer (initial density in the order of few mg/cm3, hundreds times lower than solid density) in front of the target should enhance the laser–target coupling and, as consequence, the energy conversion from laser to ions [8]. Such low densities have been achieved at Nanolab thanks to the deposition of a nanostructured carbon foam with tuneable properties and optimal adhesion to a solid substrate [9, 10]. A recent experiment on a PW class laser facility (GIST, Gwangju, Korea) has shown that foam-attached target can ensure a marked increase in both cut-off energy and total number of ions with respect to bare foils [10]. References: [1] E. Roduner, Chem. Soc. Rev., 2006, 35, 583–592. [2] A. Uccello et al., Jour. Nucl. Mater. 432 (2013) 261–265. [3] A. Uccello et al., Jour. Nucl. Mater. 446 (2014) 106–112. [4] D. Dellasega et al., J. Appl. Phys. 112, 084328 (2012). [5] M.H.J. ‘t Hoen et al. Jour. Nucl. Mater. 463 (2015) 989–992. [6] A. Maffini et al., Jour. Nucl. Mater. 463 (2015) 944–947. [7] A. Maffini et al., Laser cleaning of diagnostic mirrors from tungsten-oxygen tokamak-like contaminants, submitted to Nuclear Fusion (2016). [8] A. Sgattoni et al., Phys. Rev. E 85, 036405 (2012).[9] A. Zani et al., Carbon 56 (2013) 358–365. [10] I. Prencipe et al., Plasma Phys. Control. Fusion 58 (2016) 034019 (8pp).<Laser-Plasma Sources Enabling Sub-Threshold Spectro-Radiography>Davide Bleiner, Francesco Barbato, Yunieski Arbelo, Leili Masoudnia, Claudio Cirelli, Bruce Patterson; Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, CH-8600, Dübendorf, Switzerland.E-mail:; X-ray absorption spectroscopy (XAS) is a powerful method to study compositional and geometric characteristics of matter. High-brightness, short pulses X-ray sources have opened the possibility to perform time-resolved XAS studies of photo-active species. However the need to scan the incident beam energy across the investigated absorption edge puts severe constraints in combination with transient signals. Moreover, the need to perform on-site spectroscopy requires small portable sources, besides the advanced accelerator-based light sources. Recently it has been demonstrated with the new high energy resolution off-resonance spectroscopy (HEROS) technique [1] that a high resolution XAS spectrum can be reconstructed by collecting a X-ray fluorescence (XES) spectrum at a single excitation energy far below the absorption threshold. To date, these measurements have been performed solely at advanced radiation sources, e.g. synchrotron and XFEL. Plasmas with electron temperatures ranging from several tens to hundreds eV and electron densities in the range from 1017 cm-3 to 1019 cm-3 can be exploited as alternative effective emitters of XUV-radiation [2, 3] at well-defined wavelengths. These plasma-driven XUV sources feature excellent brightness and their compactness makes them particularly appealing for the realization of table-top X-ray spectroscopic experiments. Here, we present the characteristics of a table-top XUV-source based on pseudospark plasma emission aimed to the implementation of soft X-ray absorption and emission spectroscopy as well as imaging experiments in a lab-scale system. The source performances are tested with different working gases (argon, nitrogen and oxygen), pressures and input voltages and the dependence of these parameters on the source repetition rate and XUV flux is analyzed. For the measurements a photodiode and a concave-grating spectrometer operating in the soft X-rays energy region between 12 and 30 nm) are used. Our results demonstrate that an increase of working gas pressure or input voltage from the power supply induce an increment of the repetition rate up to about 30 Hz and a decrement of the emitted XUV flux (λ between 7 nm and 16 nm) by about one order of magnitude. However, a total flux of 1013 photons/(2πsr pulse) can be recovered when the working gas is mixed with helium. Stability measurements and determination of optimal sample position for XUV-irradiation are also presented. Fluctuations lower than 6% are observed, demonstrating the feasibility of the experiments. References: [1] J. Szlachetko et al., “High resolution off-resonant spectroscopy at sub-second time resolution: (Pt(acac)2) decomposition”, Chem. Commun. 48, 10898 (2012). [2] K. Bergmann, et al., “Soft x-ray emission from a pulsed gas discharge in a pseudosparklike electrode geometry,” J. Appl. Phys.,103, 123304 ( 2008). [3] K. Bergmann et al., “Highly repetitive, extreme-ultraviolet radiation source based on a gasdischarge plasma”, Appl. Opt.,38, 5413-5417 (1999). <Generate and control giant nanoscale acoustic strains in Silicon using chirped femtosecond laser pulses>M. Bakarezos1, G.D. Tsibidis2, I. Tzianaki1,3, S. Petrakis1, P.A. Loukakos2, K. Kosmidis3,M. Tatarakis1, and N.A. Papadogiannis1; 1Centre for Plasma Physics & Lasers (CPPL), T.E.I. of Crete, Tria Monastiria, 74100 Rethymno, Crete, Greece, 2Institute of Electronic Structure and Laser (IESL), FORTH, N. Plastira 100, Vassilika Vouton, 70013 Heraklion, Crete, Greece 3Department of Physics, University of Ioannina, Ioannina, 45110, Greece. ; Laser-generated nanoacoustical strain waves in materials are localized, short-lived lattice vibrations that are becoming increasing appealing to many applications. Of particular interest is the use of these waves for the non-destructive haracterization of materials under harsh environments, for example under electromagnetic and particle irradiation produced in fusion reaction chambers. Therefore, the generation of high-amplitude strain waves and their control on ultrafast time scales via shaped laser pulses is of significant importance. Here we use femtosecond pulses to generate longitudinal acoustic strains in Si (100) monocrystal substrates and we employ a degenerate femtosecond pump-probe transient reflectivity technique for the detection of these waves and to study the influence of the rearrangement in time of the spectral content of the generating laser pulses, i.e. the laser pulse chirp, on the induced strain waves. The Si substrates are covered by thin Ti films that facilitate both the efficient conversion of the laser pulse energy into mechanical strain and the efficient transfer of the generated mechanical strain into the Si substrate, while at the same time allowing for a part of the femtosecond probe laser pulses to reach the Si crystal in order to probe the strain that travels inside it. Our xperimental results reveal the generation of giant nanoscale acoustic strains, manifested as strong Brillouin oscillations, and that they are more effectively induced when negatively chirped femtosecond laser pulses are used. These results are theoretically supported by a modified thermo-mechanical model based on the combination of a revised two-temperature model and elasticity theory which takes into account the instantaneous frequency of the chirped femtosecond laser pump pulses. <Optimization of nanostructured targets for efficient laser-driven ion acceleration>  J.Psikal1,2, D. Margarone2, T. M. Jeong2,3, I. J. Kim3, J. Kaufman2, O. Klimo1,2,J. Proska1, L. Stolcova1,2, J. Limpouch1, A. Choukorov2,4, J. Grym5; 1FNSPE, Czech Technical University in Prague, Czech Republic, 2ELI-Beamlines project, IoP ASCR, Prague, Czech Republic, 3Advanced Photonics Research Institute, GIST, Gwangju, Republic of Korea, 4Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic, 5Institute of Photonics and Electronics, ASCR, Prague, Czech Republic; Recent experiments have shown increased efficiency of ion acceleration from the targets with deposited layer of closely-packed nanospheres on the laser-irradiated side. Moreover, last experimental results also demonstrated a homogeneous spatial profile observed with the nanosphere dielectric target. Particle-in-cell simulations reveal that the homogeneous beam profile is related with a broad angular distribution of hot electrons, which is initiated by the nanosphere structure. The nanosphere target is relatively simple for optimization due to only single free parameter (diameter of the spheres). However, we also propose different targets with even higher absorption of laser pulse energy and higher efficiency of laser-driven ion acceleration. In our numerical 2D and 3D simulations, we will demonstrate that hollow targets and targets with non-closely packed structures are very promising for forthcoming experiments. Optimal sizes of such microstructured targets as well as the possibility of manufacturing them will be also discussed. This research has been partially supported by the Czech Science Foundation, project No. 15-02964S.<Material surface modification by ns-, ps- and fs-laser pulses> Milan.S. Trtica, VINCA Institute of Nuclear Sciences, University of Belgrade, P.O. BOX 522, 11001 Belgrade, Serbia, E-mail:; The studies of surface modifications of various materials such as metals, alloys, semiconductors, etc. by ns-, ps- and fs-laser pulses are of fundamental, as well as practical significance. These studies are important for applications in: (i) micro- and nano-structuring technologies; (ii) industry; (iii) nuclear complex; (iv) bio-medicine; etc. A review of the research carried out in the last years at the VINCA Institute on various bulk and coating/thin film materials, using ns-, ps- and fs-lasers, will be presented. Special attention will be given to laser surface modification of Ti6Al4V and double layer a-CN/TiAlN/ASP 30 steel target. Surface modifications of materials by ultra-short lasers induce a range of effects: (i) appearance of crater-like features at the surface; (ii) appearance of hydrodynamic characteristics; (iii) creation of periodic surface structures; (iv) production of plasma in front of the target, etc. Generally, pico- and femto-second laser pulses produce better defined changes at the surfaces than nano-second pulses. It is therefore believed that efficient surface modification at micro- and nano-level by ultra-short laser pulses can be of interest in numerous applications. <Laser beam effects on protective coatings>Suzana Petrović, Biljana Gaković, Davor Peruško, *Carmen Ristocu, *Ion Mihailescu; Institute of Nuclear Science—Vinča, University of Belgrade, POB 522, 11001 Belgrade, Serbia, *National Institute for Laser, Plasma and Radiation Physics, Romania; Laser-induced structural and chemical composition changes of nanolayered thin films (Al/Ti, Ni/Ti ,CrN/(Cr,V)N) after femtosecond (fs) and nanosecond (ns) laser pulses action were studied. In the case of processing with fs pulses, on the surface of Ni/Ti and Al/Ti multilayer were formed laser-induced periodic surface structures (LIPSSs). The low spatial frequency LIPSS (LSFL), oriented perpendicular to the laser polarization with periods slightly lower than the irradiation wavelength, was typically formed at elevated laser fluences. On the contrary,  high spatial frequency LIPSS (HSFL) with uniform period of 155 nm, parallel to the laser light polarization, appeared at low laser fluences, as well as in the wings of the Gaussian laser beam distribution for higher used fluence. LSFL formation was associated with the material ablation process and accompanied by the intense formation of nanoparticles, especially in the Ni/Ti system. The composition changes at the surface of multilayer systems in the LSFL area indicated the intermixing between layers and the substrate. Concentration and distribution of all constitutive elements in the irradiated area with formed HSFLs were almost unchanged. The evolution of the surface composition and microstructure after laser irradiation at different number of ns pulses was systematically analysed depending on initial content of vanadium in the as- deposited CrN/(Cr,V)N coatings. Most of the absorbed laser energy was rapidly transformed into heat, producing intensive modifications of composition and morphology on the surface CrN/(Cr,V)N coatings. The concentration of metallic components were fairly homogeneous distributed through the sample, only at surface and in sub-surface region, the contents of Cr and V are reduced due to the surface oxidation. The composition and thickness of formed oxide mixture Cr2O3 and V2O5 are conditioned by the number of applied laser pulses and the initial vanadium content. The  symmetric progress of surface morphology is included the formation grain structures on peripheries and the appearance of cracks created by irregular closed shapes in the centre of the irradiation area. The special morphology of the laser-induced formation of mixture of Cr2O3 and V2O5 in the form of an ultra-thin oxide layer can improve their characteristics for functional applications. <Cleaning ultrashort KrF laser pulses with plasma mirrors>Zsolt Kovács1, István B. Földes1, Barnabás Gilicze2 and Sándor Szatmári2; 1Wigner Research Centre of the Hungarian Academy of Sciences, H-1525 Budapest, P.O.B. 49., Hungary, 2University of Szeged, Department of Experimental Physics, H-6720 Szeged, Dóm tér 9. Hungary; It is demonstrated that efficiency as high as 70% can be obtained from plasma mirrors even in the ultraviolet, i.e. for KrF lasers. Clearly, plasma mirrors are the ultimate cleaning tools of ultrashort laser pulses from pedestals. Plasma mirrors are reliable in the visible/IR spectral range [1] but their applicability for UV lasers were limited because of the large penetration depth and higher absorption of the 248 nm laser beam. Short pulse KrF lasers generally use direct amplification, i.e. prepulses are coming from the ASE of the amplifiers. Even if the contrast is high, a prepulse with 107 W/cm2 intensity of 15 ns duration may cause photoablation and ionization of the solid target. Until now plasma mirrors for KrF lasers had less than 50% efficiency [2]. It is shown that efficiency up to 70% can be obtained resulting in 2 orders of magnitude contrast improvement, thus extending the applicability of plasma mirrors to the ultraviolet. The observation of the good focusability of the reflected beam - and that despite the Doppler shift of the reflected beam its spectrum remains within the range of the gain bandwidth of the KrF amplifier - allows different possibilities for application. References: [1] I.J. Kim et al.; Appl. Phys. B 104, 81 (2011). [2] I.B. Földes, D. Csáti, F.L. Szűcs, S. Szatmári; Rad. Effects and Defects in Solids 165, 429 (2010). [3] I. B. Földes, A. Barna, D. Csáti, F. L. Szűcs, S. Szatmári; J. Phys. Conf. Ser. 244, 032004 (2010).<Degradation of transmissive KrF laser optics under intensive UV, x/gamma irradiation> V.D. Zvorykin1,2* S.V. Arlantsev3, and V.I. Shvedunov4; 1 Lebedev Physical Institute of RAS, Leninsky Pr. 53, Moscow, 119991 Russia, 2 National Research Nuclear University “MEPhI”, Kashirskoe Sh. 31, Moscow, 115409 Russia, 3 Moscow Institute of Physics and Technology (State University), Institutskii Per. 9,Dolgoprudnyi, Moscow Region, 141700 Russia, 4 Skobel’tsyn Institute of Nuclear Physics, Moscow State University, Vorob’evy Gory 1, Moscow,119992 Russia; *E-mail:; A repetition-rate operation, high wall-plug efficiency, short radiation wavelength, and a broad bandwidth, being the inherent properties of Krypton Fluoride laser, are attractive for the directdrive Inertial Confinement Fusion (S. Obenschain, et al., 2015, Applied Optics, 54, F103), and especially for a Shock Ignition approach. A challenge to using KrF lasers for  the SI ICF is radiation stability of UV optics. A considerable quantity of large-size, high laser strength and radiation resistant optics is required to overcome the mismatch between a long-time e-beam amplifier pumping (>100 ns) and a short gain lifetime (~2 ns). Commonly used angular multiplexing optical scheme with propagation of multiple beams along extended air paths provides target irradiation pulses of tens ns duration and of a required pulse-form. In the SI ICF a powerful final spike of hundred ps duration with peak power ten times higher than the main pulse is the most critical in respect of the nonlinear interactions along air paths and in a transmissive optics. Another challenge is KrF laser windows degradation under simultaneous action of the UV laser light, scattered electrons and x/gamma bremsstrahlung caused by e-beams deceleration during laser pumping. Experiments performed at 100-J KrF amplifier of GARPUN-MTW laser facility in conjunction with 3D Monte-Carlo numerical simulation gave a complete characterization of bremsstrahlung yield in the real laser geometry (V.D. Zvorykin and S.V. Arlantsev in Short Wavelength Laboratory Sources: Principles and Practices, RSC Publishing, 2015, p 207). The predicted absorbed dose ~1 MG in the laser windows of 100-kJ ICF driver over 108 shots, i.e. for one-year & 5 Hz operation cycle would produce a significant optics darkening (V.D. Zvorykin, et al., 2013, Plasma Fusion Res., 2405000). Linac-based powerful quasi-CW bremsstrahlung gamma source used for optical samples testing allowed dose rate ~40 Gy/s with total amassed doses equivalent to the ICF driver operation. A very fast recovery time of the KrF laser gain anables us to realize a simultaneous amplification of a train of short (~1 ps) pulses against a background of the long (~ 100 ns) pulse (V.D. Zvorykin et al., Quantum Electron., 2013, 43, 332) that might have a strong impact on a simpler architecture of the SI ICF KrF driver. Propagation of high-power ps UV pulses along an extended air path was shown to deteriorate laser beam quality due to radiation self-focusing and filamentation while nonlinear losses in the transmissive optics and multi-photon ionization and stimulated Raman scattering in air reduces laser energy delivered to a target. Thus, vacuum beamlines or filled with a gas with low nonlinear refraction index are needed to eliminate this effect; This work is performed under the auspices of  RSF Project No. 14-12-00194 and is partially supported by RFBR Project No. 15-02-09410 and IAEA Research Contract No. 19273 in the part of optics degradation studies.<Optically induced ultrafast photocurrents and high harmonic generation in bulk diamond>T. Apostolova1,2 and B. Obreshkov1; 1Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria, 2Institute for Advanced Physical Studies.New Bulgarian University, 1618 Sofia, Bulgaria; The generation of ultrafast currents in bulk diamond induced by intense femtosecond laser pulses is theoretically investigated. Calculations based on the time-dependent Schrodinger equation1 predict transition from nonlinear polarization currents during the laser pulse at low  intensities to Zener tunneling into the conduction band at higher intensities. The DC current generated after the end of the pulse at high intensities is considered to be the precursor of optical breakdown on a femtosecond scale2. The Fourier transform of the ultrafast current is analyzed in terms of highharmonic generation (HHG) in bulk diamond3 and the non-linear laser-intensity dependence of individual harmonics (HHG spectrum) is presented. References:1. B.Obreshkov, T. Apostolova, Bulg. J. Phys, 42, 304 (2015), 2. S. Lagomarsino,…T.Apostolova.., Phys. Rev. B 93, 085128, 3. T. Otobe, J. Appl. Phys. 111 093112 (2012).<Simulation of captured electrons from dense plasmas inducing nuclear excitations. A bridge between atomic and nuclear physics> Stoyan Mishev1,3 and T. Apostolova2,3;1Joint Institute for Nuclear Research, Dubna, Russia, 2INRNE, Bulgarian Academy of Sciences,3Institute for Advanced Physical Studies, New Bulgarian University; Nuclear excitations triggered by the exchange of a virtual photon between a captured electron in a bound atomic state and the nucleus are considered. The calculation of the rate of such excitations depends on the correct description of the dynamics of the nuclear, atomic and in our case plasma systems involved in the process. Applying a set of criteria a selection of states in nuclei from diferent parts of the nuclear chart are discussed as candidates for high reaction rates for this excitation mechanism. An overview for describing these states is given along the lines of the collective and a microscopic model. Practical and astrophysical aspects of this process are  outlined. <Valorization of X-Ray Beams from Laser Plasma Accelerator>F. Sylla, A. Ricci and G. Bouchon; SourceLAB SAS, 86 rue de Paris, 91400 Orsay, France and A. Lifschitz, K. Ta Phuoc, A. Rousse and V. Malka Laboratoire d’Optique Appliquée, ENSTA, CNRS, Ecole Polytechnique, UMR 7639, 91761 Palaiseau, France; Valorization depicts here the activities driving the creation of new processes and products based on results generated by public research organizations. Contrary to academic efforts, the emergence of novelty through valorization is oriented mainly towards societal and economic impacts. As such, valorization is a privileged tool for innovation, and one of the most supported activities by national and European research policies. With the example of an innovative platform for material Non-Destructive Testing implementing a Laser Plasma Accelerator, it is shown how a valorization effort has been carried out at LOA over the last decade. In particular, this presentation emphasizes the different phases of the project, from the laboratory proof-of-concept to a dedicated French industrial consortium, passing by the creation of the spin-off SourceLAB. This tangible example might shed light on upcoming challenges, timeline and resources to be expected regarding the valorization of revolutionary results from laser plasma accelerators for medical applications. Capitalizing on this experience, a recent initiative was launched at LOA/SourceLAB to explore the potentialities of laser-based X-ray phase contrast imaging for preclinical and clinical markets. <Modification of bismuth germanium oxide characteristics by femtosecond irradiation> Aleksander Kovačević1,*, Jasna L. Ristić-Djurović1, Marina Lekić1, Branka Hadžić1,    Giuma Saleh Isa Abudagel2, Slobodan Petričević2, Pedja Mihailović2, Branko Matović3, Dragan Dramlić1, Ljiljana M. Brajović4, Nebojša Romčević1 ; 1 Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia, 2 School of Electrical Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11000 Belgrade, Serbia, 3 Vinča Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia, 4 Faculty of Civil Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11000 Belgrade, Serbia, * Corresponding author e-mail:; Abstract. Bismuth germanium oxide, having the cubic I23 space group, shares the structure with similar compounds, like bismuth titanium oxide and bismuth silicon oxide, sillenite. With the formula of Bi12GeO20, it is abbreviated as BGO. The suitability of BGO for applications like holography, optical phase conjugation, Pockels cells, spatial light modulation, fiber optic sensors, is enabled by its support of magneto-optic and electro-optic effects as well as by its characteristics [1, 2]. Single crystals of Bi12GeO20 with diameters of 12–13 mm and length of 70–80 mm were grown by the Czochralski technique in the air using the crystal puller MSR 2 combined with the Eurotherm temperature controller. Crystal samples were exposed to a femtosecond laser beam of 800 nm wavelength produced by the Coherent Mira 900F system, and the Ocean Optics  HR2000CG UV-NIR spectrometer was used to determine the wavelength. The beam power, measured by an Ophir powermeter, was adjusted from 50 mW to 950 mW, corresponding to the fluence range on the sample of 75 to 1425 nJ/ cm2. Sample transmittance was determined by the Beckman Coulter DU 720 General Purpose UV/VIS spectrometer and the spectra were used to obtain the sample color. The Rigaku Ultima IV Multipurpose X-ray diffraction system was used to obtain the X-ray diffraction patterns. The micro-Raman spectra of crystal samples were obtained with the Jobin Yvon T64000 spectrometer with the backscattering configuration and the 532 nm line as an excitation source. Femtosecond irradiation caused significant permanent changes in optical properties of Bi12GeO20 single crystals. The transmittance dependence on the applied irradiation shows maximum for 455 mW. The anisotropy, detected in the transmission spectra of unirradiated sample, disappeared and the transmission increased. The XRD measurements confirmed mechanical imperfections as well as femtosecond laser induced structural changes. The Raman spectra peaks became somewhat stronger, except for the E type peaks at 234, 454, and 619.6 cm–1, which disappeared. Irradiation also caused significant change of the crystal color. The magneto-optical quality was improved, the Verdet constant increased and the absorption coefficient decreased by the irradiation. Optical properties of Bi12GeO20 single crystals can be improved by irradiation with the femtosecond pulsed laser beam. This work is financially supported by the Serbian Ministry of Education, Science, and Technological Development through the projects III45003 and III45016. We thank Z. Velikić for his assistance with transmission spectra measurements and A. Valčić for his help with sample preparation. References: [1] Skorikov VM, Kargin YuF, Egorysheva AV, Volkov VV, Gospodinov M. Growth of sillenite-structure single crystals. Inorg Mater 2005;41:S24–46. [2] Ganeev RA, Ryasnyansky AI, Palpant B, Debrus S. Third-order nonlinearities of Bi12GeO20 crystal measured by nanosecond radiation. J Appl Phys 2005;97:104303, <Cluster diagnostics with Rayleigh scattering and high harmonics generation> R. Bolla, M. Aladi and I. B. Földes; Wigner Research Centre for Physics of the Hungarian Academy of Sciences, H-1525 Budapest, P.O.B. 49. Hungary; The efficiency of high harmonics generation (HHG) may be increased by applying cluster targets [1]. Clusters can be generated using supersonic valves due to the fast expansion of noble gases streaming into the vacuum from the valve. The properties of the clusters (size, size distribution) affect the efficiency and the wavelength of the generated harmonics. In order to understand the interaction between the gas target and the high intensity laser it is necessary to characterise the target and especially the clusters in the target. Although – besides the Hagena-scaling - cluster sizes can be estimated from the HHG spectrum [2], it is important to compare it with independent diagnostics. An easy and efficient way to investigate the gas clusters is with Rayleigh scattering. The main principle behind this diagnostics is that the Rayleigh-scattered intensity is proportional to the 6th power of particle size. Examining the scattered light with CCD camera and photomultiplier (besides different background pressure and time delay) provides information about the average cluster radius, time evolution and spatial distribution of the cluster size. We compared the results for different nozzles in different gases as He, Ar and Xe. The results for – the optimal - Laval nozzles are compared with earlier diagnostics with interferometry, too [3]. References: [1] T. D. Donnelly et al., Phys. Rev. Lett. 76, 2472 (1996). [2] M. Aladi, R. Bolla, P. Rácz and I.B. Földes, Nucl. Instrum. and Methods in Physics Research B 369, 68 (2016). [3] K. Schmid and L. Veisz, Rev. Sci. Instrum. 83, 053304 (2012). <Laser induced transition from a dielectric solid to a dense plasma by femtosecond pulses> The understanding of the laser induced transition from the dielectric solid state to plasma is crucial for various applications going from optical material structuration (wave guides, nano-gratings, cutting, welding, etc) to simulation of the very beginning of the interaction in conditions relative to inertial confinement fusion. The physical mechanisms responsible for this phase transition are as follows for femtosecond laser pulses in the visible range with intensities going from a few to hundreds of TW/cm2. A laser pulse may first promotes the valence electrons to the conduction band, and then heats the conduction electrons which can then transfer their energy to the lattice. That leads to a local increase in the material temperature together with heat diffusion and hydrodynamic response. Since the laser pulse is partially absorbed, the electron dynamics and the pulse propagation are closely coupled. Ultimately, the solid material may transform into a dense plasma depending on laser pulse characteristics as energy and duration. In order to progress in the understanding of such mechanisms, experimental and associated theoretical studies have been performed. First, a time-dependent model describing  the coupled electron dynamics and laser pulse propagation has been developed to predict the laser energy deposition in the material. It includes both photo- and impact ionization, and a full 3D Maxwell solver is used to describe the pulse propagation. The calculations shows that the  electronic excitation affects in turn the spatial and temporal properties of the laser pulse. Based on this knowledge, the evolution of a glass is studied by using a train of laser pulses. Such an approach allows us to very well control the energy deposition in the nJ range by adjusting the number of pulses. Due to the low heat diffusion coefficient of dielectric materials, the laser energy may be accumulated in the absorbing region, leading to high temperatures and subsequent significant material modifications. In order to shed light on the underlying cumulative effects taking place on relatively large spatial scales of the order of tens of micrometers, the energy deposition is obtained here by simulating the laser pulse propagation through a Forward Maxwell code under the paraxial approximation which also includes the electron dynamics. The thermal effects are modeled by solving a heat diffusion equation with the deposited laser energy as initial condition. The softening temperature is considered as the threshold for a permanent index modification of the matter. The obtained theoretical evolutions of the characteristic lengths of material modifications with respect to the laser repetition rate are in a good agreement with the experimental data. It demonstrates that the material modifications originate from heat accumulation and subsequent.