The L4n is a nanosecond-kilojoule laser beamline that delivers temporally shapeable nanosecond pulses at a maximum energy of 1.2 kJ. It was recently commissioned at ELI Beamlines and offers unique opportunities for high-pressure, high-energy-density physics, and laser-plasma interaction experiments, particularly due to its high repetition rate of up to 1 shot per minute. Compared to other kJ-class laser systems worldwide, which offer much lower shot rates, the L4n driven experiments will enable significant improvements in collecting data statistics. The results gathered during the first L4n commissioning campaigns, demonstrate the laser capability to deliver hundreds of joules every three minutes with excellent repeatability and clearly show its potential to make significant contributions to the field of high-energy density physics in the coming decades.
The limited aperture and damage threshold of the compressor gratings remains one of the bottlenecks in reaching higher peak powers for the current state-of-the-art laser systems. Object-image-grating self-tiling method provides a way how to double the effective aperture of compressor gratings by phasing them with perpendicularly positioned mirrors. This method is planned to be used in the main compressor for the L4 beamline in ELI Beamlines. A subaperture version of the main compressor was designed to test the feasibility of the objectimage- grating self-tiling method and to measure the temporal profile of the pulse throughout the amplification stages during the operation. The subaperture compressor was successfully implemented and temporal profile of the amplified pulse close to its transform limit was retrieved. The grating-mirror alignment was secured through the online measurement using an in-house developed Fizeau interferometer.
We report on the status of the re-commissioning of a high energy OPCPA laser system with programmable spectrum that serves as a frontend for a 10 PW laser at ELI-Beamlines. The OPCPA chain was developed by a consortium of National Energetics and Ekspla along with scientists of ELI-Beamlines.1 The laser system, consisting of three picosecond OPCPA stages, pulse cleaner, Offner stretcher, and 5 nanosecond OPCPA stages pumped by Nd:YAG lasers with programmable pulse shape (NL944, Ekspla), allows for precise spectral shaping while achieving high nonlinear conversion efficiency. Employing a subsequent Nd:glass power amplifiers (PA), the system was demonstrated to yield>1 kJ of energy, while maintaining broad spectrum of > 13 nm (FWHM). After recommissioning the OPCPA frontend in Dolní Břežany, an output energy of 4.3 J, flat beam-profile and good far-field quality has been demonstrated. The spectral shape has been optimized to support > 15 nm bandwidth and >1.5 kJ, consistent with 10 PW operation of the fully integrated laser system after compression.
State-of-the-art physics experiments are pushing the development of lasers with ultra-high peak power pulses. 4 PW pulses have been produced with TiSa [1] and 10 PW with the same gain medium is scheduled at LULI (Apollon) and at ELI-NP.
The other approach is to use Nd-doped glass as gain medium, whose interest is in its capability of delivering higher energy at the expense of a longer pulse duration. Based on this gain material combined with an OPCPA based front-end, a kJ-10 PW class laser has been designed and built.
The front-end, consisting of picosecond OPCPA, temporal pulse cleaning and nanosecond OPCPA, delivers pulses with excess of 4 Joules at 5 Hz with a shaped spectrum to pre-compensate for gain distortions in Nd:glass power amplifiers. Two liquid-cooled, mixed glass power amplifiers, namely PA1 and PA2, are used for further amplification. Up to now, they have been activated demonstrating 70 J at 1 shot a minute after PA1 and 1 kJ at 1 shot every 7 minutes for PA2. The Fourier limit of the spectrum is 150 fs meaning 6 PW capability after compression.
This energy level has been obtained with only 3 Joules seed energy, from the OPCPA and partial activation of PA2. Scaling of this result suggests that more than 1.7 kJ should be obtained leading to 10 PW after compression while the output spectrum will remain compatible with 150 Fs thanks to the OPCPA spectral tailoring capability.
Overview of progress in construction and testing of the laser systems of ELI-Beamlines, accomplished since 2015, is presented. Good progress has been achieved in construction of all four lasers based largely on the technology of diode-pumped solid state lasers (DPSSL). The first part of the L1 laser, designed to provide 200 mJ <15 fs pulses at 1 kHz repetition rate, is up and running. The L2 is a development line employing a 10 J / 10 Hz cryogenic gas-cooled pump laser which has recently been equipped with an advanced cryogenic engine. Operation of the L3-HAPLS system, using a gas-cooled DPSSL pump laser and a Ti:sapphire broadband amplifier, was recently demonstrated at 16 J / 28 fs, at 3.33 Hz rep rate. Finally, the 5 Hz OPCPA front end of the L4 kJ laser is up running and amplification in the Nd:glass large-aperture power amplifiers was demonstrated.
Tiled-grating compressors of ultra-short pulse multi-petawatt lasers are currently the only viable way how to meet beam size requirements and stay within the damage threshold of the largest available gratings. Recently, a method how to double the effective aperture of compressor gratings by phasing them with perpendicularly positioned mirrors has been proposed, providing simplification to the traditional grating-grating tiling scheme by reducing the number of alignment degrees of freedom. The drawback of the method lies in tighter requirements on adjustment precision and stability of the system making the alignment and monitoring a challenging task. Here we propose and analyze different approaches to precision control of mirror-grating phasing and present a comparative experimental verification of the alignment systems on a small-scale test bench.
A comparison of various pulse stretcher designs accommodating material dispersion for a <; 150 fs 10 PW Nd:glass laser system using low dispersion diffraction gratings is presented. Since the pulse amplification demands a high stretch ratio of the stretcher to suppress non-linear effects and a high temporal contrast of the pulse is required to avoid ionization of the experimental targets, the design of the stretcher is a critical part for dispersion management. Here, we compare several designs using only one diffraction grating based on either a Perry-Banks or an Offner stretcher types, mostly at the Littrow angle. The target spectral phase profile is achieved through the tuning of the grating position, the angle of incidence on the grating, the radii of curvature of curved mirrors and the line density of the grating.
I. Pomerantz, E. McCary, A. Meadows, A. Arefiev, A. Bernstein, C. Chester, J. Cortez, M. Donovan, G. Dyer, E. Gaul, D. Hamilton, D. Kuk, A. Lestrade, C. Wang, T. Ditmire, B. Hegelich
At the Texas Petawatt laser facility we developed a novel ultra-short pulsed laser-driven neutron source generating an unprecedented output peak flux. Our results show a dramatic onset of high-energy electron generation from petawatt laser-irradiated plastic targets for targets thinner than a few microns. In this regime, the copious amounts of multi-MeV electrons emitted from the target are utilized to generate photo-neutrons from a metal converter. The neutrons are generated with a <50 ps pulse duration and a flux of 1018 n/cm2/s, exceeding any other pulsed or CW neutron source. In this paper, we will report on our measurement of the neutron yields produced from high atomic number converters.
B. Rus, P. Bakule, D. Kramer, J. Naylon, J. Thoma, J. Green, R. Antipenkov, M. Fibrich, J. Novák, F. Batysta, T. Mazanec, M. Drouin, K. Kasl, R. Baše, D. Peceli, L. Koubíková, P. Trojek, R. Boge, J. Lagron, Š. Vyhlídka, J. Weiss, J, Cupal, J. Hřebíček, P. Hříbek, M. Durák, J. Polan, M. Košelja, G. Korn, M. Horáček, J. Horáček, B. Himmel, T. Havlíček, A. Honsa, P. Korouš, M. Laub, C. Haefner, A. Bayramian, T. Spinka, C. Marshall, G. Johnson, S. Telford, J. Horner, B. Deri, T. Metzger, M. Schultze, P. Mason, K. Ertel, A. Lintern, J. Greenhalgh, C. Edwards, C. Hernandez-Gomez, J. Collier, T, Ditmire, E. Gaul, M. Martinez, C. Frederickson, D. Hammond, C. Malato, W. White, J. Houžvička
Overview of the laser systems being built for ELI-Beamlines is presented. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition rate pulses, and kilojoule nanosecond pulses for generation of 10 PW peak power. The lasers will extensively employ the emerging technology of diode-pumped solid-state lasers (DPSSL) to pump OPCPA and Ti:sapphire broadband amplifiers. These systems will provide the user community with cutting-edge laser resources for programmatic research in generation and applications of high-intensity X-ray sources, in particle acceleration, and in dense-plasma and high-field physics.
A steady increase of on-target laser intensity with also increasing pulse contrast is leading to light-matter interactions of extreme laser fields with matter in new physics regimes. At the Texas Petawatt laser we have realized interactions in the transparent-overdense regime, which is reached by interacting a highly relativistic, ultra-high contrast laser pulse with a solid density ultrathin target. The extreme fields in the laser focus are turning the overdense, opaque target transparent to the laser by the relativistic mass increase of the electrons. Thus, the interaction becomes volumetric, increasing the energy coupling from laser to plasma. Using plasma mirrors to increase the on-target contrast ratio, we demonstrated generation of over 60 MeV proton beams with pulse energies not exceeding 40 J (on target).
In this paper, we report on current developments aimed at improving the focusability of the Texas Petawatt Laser. Two
major campaigns have been commissioned that address the issue of focusability. First, we implemented a closed loop,
32 actuator bi-moprh deformable mirror (DFM) to compensate for aberrations in the optical train and second, a color
corrector lens assembly was installed that compensates for chromatic errors accumulated in broadband (>15 nm), large
aperture (>20 cm) laser systems.
We will present in detail, pre and post correction results with the DFM and describe challenges faced when one activates
a single shot, high energy closed loop system. Secondly, we will provide modeling and experimental results of our color
correction system. This is a novel approach to a problem only seen in high energy, broadband, large aperture laser
pulses.
By using color correction optics we have demonstrated a 6X increase in focal intensity. With the installation of the
DFM, the rms wavefront error in the system was reduced from 2.4 waves to .131 waves, further increasing intensities
seen at focus by 1 order of magnitude.
D. Javorkova, P. Neumayer, Th. Kühl, S. Borneis, E. Brambrink, C. Bruske, E. Gaul, S. Götte, T. Hahn, H. Heuck, S. Kunzer, T. Merz, D. Reemts, M. Roth, F. Schrader, A. Tauschwitz, R. Thiel, D. Ursescu, P. Wiewior, B. Zielbauer
With PHELIX (Petawatt High Energy Laser for heavy Ion EXperiments) a high energy/ultra-high intensity
laser system is currently under construction at the GSI (Gesellschaft für SchwerIonenforschung, Germany). In
combination with the high current high energy ion accelerator facility this will provide worldwide unique experimental
opportunities in the field of dense plasma physics and inertial fusion research. In the long pulse mode the laser system
will provide laser pulses of up to 5 kJ in 1-10 ns pulses. In the high intensity mode pulse powers in excess of 1 PW will
be achieved. For this the well known technique of chirped pulse amplification (CPA) will be implemented. A new CPA
stretcher-compressor setup for the PHELIX laser was calculated and designed. A 4-pass single-grating stretcher and
a 4-pass single-grating test compressor, both with a full transmission bandwidth of 16 nm, as well as the compact
single-pass compressor for the final pulse compression will be presented. Spatial chirp and spectral phase aberrations of
the stretcher were optimized. We discuss the dependence of critical alignment tolerances on the angle of incidence and
show the effects on the temporal pulse shape.
We report on the design and construction of the Texas Petawatt Laser. This research facility will consist of two, synchronized laser systems that will be used for a wide variety of high intensity laser and high energy density science experiments. The first laser is a novel, high energy (200 J), short pulse (150 fs) petawatt-class laser that is based on hybrid, broadband optical parametric chirped pulse amplification (OPCPA) and mixed silicate and phosphate Nd:glass amplification. The second laser will provide 500 J at 527 nm (>1 kJ @1053 nm) with pulse widths selectable from 2-20 ns. Design and construction began in early 2003 and is scheduled to complete in 2007. In this report we will briefly discuss some of the important applications of this system, present the design of the laser and review some of the technology used to achieve pulse durations approaching 100 fs. Currently, the facility has been renovated for laser construction. The oscillator and stretcher are operational with the first stage of gain measured at 2×106. Output energies of 500μJ have been achieved with good near field image quality. Delivery has been taken for Nova components that will compose the main amplifier chain of the laser system.
We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.
The Gesellschaft fuer Schwerionenforschung (GSI, Society for Heavy Ion Research) is currently the leading facility in the production of radioactive isotopes. Nuclear properties like charge radii, spin, and magnetic moments of exotic nuclei provide important data for testing of nuclear models. These properties are usually accessed by laser spectroscopy, which requires photon energies of around 100 eV in the case of lithium-like ions. We propose to use a transient gain X-ray laser (XRL) at the experimental storage ring (ESR) to perform this kind of spectroscopy. In this article we describe the planned experiments and give an overview of the current construction at GSI.
We have constructed a self-starting Kerr-lens mode-locked Ti:sapphire laser pumped synchronously by a mode-locked, LBO-doubled Nd:YAG laser. Using a home-built beam- pointing stabilizer, beam wander of the 532 nm pump is reduced by a factor of 25, thus enabling long term operation of TEM00 nearly transform limited pulses with amplitude, repetition rate, and pulsewidth fluctuations comparable to or better than those of Ar-pumped Ti3+:Al2O3 lasers. Interferometric autocorrelation using second harmonic in reflection from GaAs yielded a pulse width of 30 fs, limited by the dispersion of wide bandwidth cavity optics that permit tunability from 0.7 to 1.0 micrometers .
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