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.
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.
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.
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.
Mikael Martinez, Kenneth Skulina, Fred Deadrick, John Braucht, Bobby Jones, Steven Hawkins, Ronald Tilley, R. Wing, James Crawford, Donald Browning, John Crane, Frank Penko
We describe recent results and developments in the preamplifier module engineering prototype located in NIF's front end or Optical Pulse Generation system. This prototype uses the general laser design developed on a physics testbed and integrates NIF type packaging as well as controls and diagnostics. We will present laser, mechanical and electrical hardware designed and built to data as well as laser energetics measurements.
We describe the Optical Pulse Generation (OPG) testbed, which is the integration of the MOD and Preamplifier Development Laboratories. We use this OPG testbed to develop and demonstrates the overall capabilities of the NIF laser system front end. We will present the measured energy and power output, temporal and spatial pulse shaping capability, FM bandwidth and dispersion for beam smoothing, and measurements of the pulse-to-pulse power variation o the OPG system and compare these results with the required system performance specifications. We will discus the models that are used to predict the system performance and how the OPG output requirements flowdown to the subordinate subsystems within the OPG system.
The work to improve the energy stability of the regenerative amplifier for the NIF is described. This includes a fast feed-forward system, designed to regulate the output energy of the regen by monitoring how quickly a pulse builds up over many round trips. Shot-to-shot energy fluctuations of all elements prior to the regen may be compensated for in this way, at the expense of a loss of approximately 50 percent. Also included is a detailed study into the alignment sensitivity of the regen cavity, with the goal of quantifying the effect of misalignment on the output energy. This is done by calculating the displacement of the eigenmode by augmenting the cavity ABCD matrix with the misalignment matrix elements, E, F. In this way, cavity misalignment issues due to thermal loading of the gain medium are investigated. Alternative cavity designs, which reduce the alignment sensitivity and therefore the energy drift over periods of continuous operation, are considered. Alterations to the amplifier head design are also considered.
Mikael Martinez, Kenneth Skulina, Fred Deadrick, John Crane, Bryan Moran, John Braucht, Bobby Jones, Steven Hawkins, Ronald Tilley, James Crawford, Donald Browning, Frank Penko
We describe recent, energetics performance results on the engineering preamplifier module (PAM) prototype located in the front end of the 1.8 MJ National Ignition Facility laser system. Three vertically mounted subsystem located in the PAM provide laser gain as well as spatial beam shaping. The first subsystem in the PAM prototype is a diode pumped, Nd:glass, linear, TEM00, 4.5 m long regenerative amplifier cavity. With a single diode pumped head, we amplify a 1 nJ, mode matched, temporally shaped (approximately equals 20 ns) seed pulse by a factor of approximately 107 to 20 mJ. The second subsystem in the PAM is the beam shaping module, which magnifies the gaussian output beam of the regenerative amplifier to provide a 30 mm X 30 mm square beam that is spatially shaped in two dimensions to pre- compensate for radial gain profiles in the main amplifiers. The final subsystem in the PAM is the 4-pass amplifier which relay images the 1 mJ output of the beam shaper through four gain passes in a (phi) 5 cm X 48 cm flashlamp pumped rod amplifier, amplifying the energy to 17 J. The system gain of the PAM is 1010. Each PAM provides 3 J of injected energy to four separate main amplifier chains which in turn delivers 1.8 MJ in 192 frequency converted laser beams to the target for a broad range of laser fusion experiments.
The multi-pass amplifier (MPA) is the last subsystem of the NIF preamplifier, which feeds the main amplification stages of the NIF beamline. The MPA is based on a flashlamp pumped 5-cm diameter by 48 cm long Nd:glass rod amplifier operated at a single pass small signal gain of 15 to 17. The MPA is an off-axis multi-pass image relayed system, which uses two gain isolating image relaying telescopes and passive polarization switching using a Faraday rotator to output the pulse. We describe the MPA system, techniques used to avoid parasitic oscillation at high gain, and suppression of pencil beams. The system is used to generate a well- conditioned 22-joule output from one millijoule input. The output pulse requirements include 22 joules in a square, flat topped beam, and with near field spatial contrast of <5% RMS, square pulse temporal distortion <2.3, and an RMS energy stability of <3%. All of these requirements have been exceeded. The largest impediment to successful operation was overcoming parasitic oscillation. Sources of oscillation could be generally divided into two categories: those due to birefringence, which compromised the polarization contrast of the system; and those due to unwanted reflections from optical surfaces. Baffling in the vacuum spatial filters helps to control the system sensitivity to unwanted stray reflections from flat AR coated surfaces. Stress birefringence in the rather large glass volume of the rod (942 cm3) and the four vacuum loaded lenses are significant, as each of these elements is double passed between each polarizing beam splitter pass. This lowers the polarization contrast of the system, which can prevent the system from operating at sufficient gain. Careful analysis and layout of the MPA architecture has allowed us to address the challenges posed by a system small signal gain of ≈ 33000 and with an output pulse of as high as 27 joules.
The National Ignition Facility (NIF) will house a 2 MJ Nd:glass laser system to be used for a broad range of inertial confinement fusion experiments. This record high energy laser output will be initiated by a single low energy, fiber-based master oscillator which will be appropriately shaped in time and frequency prior to being split into 48 beams for intermediate amplification. These 48 intermediate energy beams will feed the 192 main amplifier chains. We report on the baseline design and test results for an amplifier subsystem in the intermediate amplifiers. The subsystem is based on a diode pumped, Nd:glass regenerative amplifier. The amplifier is comprised of a linear, folded, TEM00, 4.5 m long cavity and represents the highest gain (approximately 107) component in the NIF laser system. Two fundamentally important requirements for this amplifier include output energy of 20 mJ with a square pulse distortion of less than 1.45. With a single 48 bar 4.5 kW peak power diode array and lens duct assembly, we pump a 5 mm diameter X 50 mm long Nd-doped, phosphate glass rod, and amplify the mode-matched, temporally shaped (approximately 20 ns in duration) oscillator seed pulse to 25 mJ of output energy with a very acceptable square pulse distortion of 1.44. This most recent design of the regenerative amplifier has increased the performance and reduced the cost, enabling it to become a solid baseline design for the NIF laser system.
We describe the prototype preamplifier for the NIF laser system and discuss the performance of the regenerative amplifier and 4-pass laser systems that comprise the preamplifier.
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