The advent of high energy, high peak power laser systems through chirped pulse amplification (CPA) in broadband solid-state gain media has opened new avenues into High Energy Density, High Field and Material Science research. There are ongoing efforts at numerous institutions in Europe, USA, and China that are striving to achieve output powers up to 200 PW. One main limitation of total laser energy output is the damage threshold and physical size of diffraction gratings. For the 10 PW (1.5 kJ, 150 fs) ELI-Beamline L4 Aton laser, we have developed a new class of meter-sized, multilayer dielectric (MLD) gratings based a low-dispersion design of 1136 lines/mm for a Littrow out-of-plane compressor design operating at 1060 nm. This new class of MLD gratings allows for approximately 4X more total energy on grating compared to the present state of the art. Fabrication of a 850 mm wide x 700 mm tall grating resulted in 98.7% efficiency with 0.3% uniformity at 1060 nm.
We present experimental results that show how diode-pumped Tm:YLF can be used to develop the next generation of lasers with high peak and high average power. We demonstrate the production of broad bandwidth, λ≈ 1.9 μm wavelength, high energy pulses with up to 1.6 J output energy and subsequent compression to sub-300 fs duration. This was achieved using a single 8-pass amplifier to boost stretched approximately 50 μJ pulses to the Joule-level. Furthermore, we show the average power capability of this material in a helium gas-cooled amplifier head, achieving a heat removal rate almost ten times higher than the state-of-the-art, surpassing 20 W/cm2. These demonstrations illustrate the capabilities of directly diode-pumped Tm:YLF to support TW to PW-class lasers at kW average power.
The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a 192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to 351nm light or 3w. It was built to access the extreme high energy density conditions needed to support the nation’s nuclear stockpile in the absence of further underground nuclear tests, including studying Inertial Confinement Fusion (ICF) and ignition in the laboratory.
Over the last year, important results have been obtained demonstrated a fusion yield of 1.35MJ with 1.9MJ of laser energy (and 440 TW power) injected in the target, bringing the NIF to the threshold of ignition [2-3]. As the yield curve near ignition is steep, the laser performance team has focused on providing improved power accuracy and precision (better shot-to-shot reproducibility) with a high-fidelity pulse shaping system (HiFiPS), and also on extending the NIF operating power and energy space by 15% to 2.2MJ and 500TW.
The Matter in Extreme Conditions Upgrade (MEC-U) project is a major upgrade to the MEC instrument on the Linac Coherent Light Source (LCLS) X-ray free electron laser (XFEL) user facility at SLAC National Accelerator Laboratory. The MEC instrument combines the XFEL with a high-power, short-pulse laser and high energy shock driver laser to produce and study high energy density plasmas and materials found in extreme environments such as the interior of stars and fusion reactors, providing the fundamental understanding needed for applications ranging from astronomy to fusion energy. When completed, this project will significantly increase the power and repetition rate of the MEC high intensity laser system to the petawatt level at up to 10 Hz, increase the energy of the shock-driver laser to the kilojoule level, and expand the capabilities of the MEC instrument to support groundbreaking experiments enabled by the combination of high-power lasers with the world’s brightest X-ray source. Lawrence Livermore National Laboratory (LLNL) is developing a directly diode-pumped, 10 Hz repetition rate, 150 J, 150 fs, 1 PW laser system to be installed in the upgraded MEC facility. This laser system is an implementation of LLNL’s Scalable High power Advanced Radiographic Capability (SHARC) concept and is based on chirped pulse amplification in the diode-pumped, gas-cooled slab architecture developed for the Mercury and HAPLS laser systems. The conceptual design and capabilities of this laser system will be presented.
In this work, we will review and evaluate the laser-induced optics damage observed on the final compressor gratings of the Advanced Radiographic Capability (ARC) laser. Damage initiation and growth rules are derived from online inspections and both measured and modeled laser performance are compared to a laser damage performance assessment of compressor grating witness samples performed offline. In addition, we will report the result of adapting these damage and growth rules to conditions relevant for the Scalable High-average-power Advanced Radiographic Capability (SHARC) 10 Hz Petawatt laser concept.
The high-average-power petawatt-class Big Aperture Thulium (BAT) laser concept was proposed to meet the requirements for the next-generation compact particle accelerators. Our previous work reported the laser damage test and modeling of pulse compression gratings designed for the BAT laser and operating at 2 micron wavelength. Notably, we observed blister formation of the underlying layers at low fluences and ablation of the grating pillars at higher fluences. Here we present the measurement and analysis of these bulging damage precursors on the MLD gratings and mirrors using the cross-sectional transmission electron microscopy combined with focused ion beam processing.
The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a
192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to
351nm light or 3w. It has been designed to support the study of Inertial Confinement Fusion (ICF)
and High Energy Density Physics (HEDP). The NIF Precision Diagnostic System (PDS) was reactivated and new
diagnostic packages were designed and fielded that offer a more comprehensive suite
of high-resolution measurements. The current NIF laser performance will be presented as well as the preliminary results obtained with the various laser experimental campaigns using the new diagnostic tool suites.
Novel architectures of Petawatt-class, high peak power laser systems that allow operating at high repetition rates are opening a new arena of commercial applications of secondary sources and discovery science. The natural path to higher average power is the reduction of the total heat load induced and generated in the laser gain medium and eliminating other inefficiencies with the goal to turn more energy into laser photons while maintaining good beam quality. However, the laser architecture must be tailored to the specific application and laser parameters such as wavelength, peak power and intensity, pulse length, and shot rate must be optimized. We have developed a number of different concepts tailored to secondary source generation that minimize inefficiencies and maximize the average power. The Scalable Highaverage- power Advanced Radiographic Capability (SHARC) and the Big Aperture Thulium (BAT) laser are examples of two such high average power laser concepts; SHARC is designed for production of ion beams and x-rays, and exploration of high energy density physics at 1.5 kW average power, and BAT is envisioned for driving laser-based electron accelerators at 300 kW average power.
We investigate the optical damage performance of multi-layer dielectric (MLD) coatings suitable for use in high energy, large-aperture petawatt-class lasers. We employ small-area damage test methodologies to evaluate the damage resistance of various coatings as a function of deposition methods and coating materials under simulated use conditions. In addition, we demonstrate that damage initiation by raster scanning at lower fluences and growth threshold testing are required to estimate large-aperture optics’ performance.
We investigate the laser damage resistance of multilayer dielectric (MLD) diffraction gratings used in the pulse compressors for high energy, high peak power laser systems such as the Advanced Radiographic Capability (ARC) Petawatt laser on the National Ignition Facility (NIF). Our study includes measurements of damage threshold and damage density (ρ(Φ)) with picosecond laser pulses at 1053 nm under relevant operational conditions. Initial results indicate that sparse defects present on the optic surface from the manufacturing processes are responsible for damage initiation at laser fluences below the damage threshold indicated by the standard R-on-1 test methods, as is the case for laser damage with nanosecond pulse durations. As such, this study supports the development of damage density measurements for more accurate predictions on the damage performance of large area optics.
Betatron x-rays with multi-keV photon energies have been observed from a GeV-class laser-plasma accelerator. The experiment was performed using the 200 TW Callisto laser system at LLNL to produce and simultaneously observe GeV-class electron beams and keV Betatron x-rays. The laser was focused with two different optics (f/8 and f/20), and into various gas cells with sizes ranging from 3 to 10 mm, and containing mixed gases (He, N, CO2, Ar, Ne) to accelerate large amounts of charge in the ionization induced trapping regime. KeV betatron x-rays were observed for various concentrations of gases. Electron spectra were measured on large image plates with the two-screen method after being deflected by a large 0.42 Tesla magnet spectrometer. Betatron oscillations observed on the electron spectra can be benchmarked against a simple analytical model (Runge-Kutta algorithm solving the equation of motion of an electron in the wakefield), in order to retrieve the electron injection conditions into the wake.
We discuss recent advances in the development of high repetition rate table-soft soft x-ray lasers resulting from
research conducted at Colorado State University. Advancing saturated table-top lasers to shorter wavelengths we report
the operation of gain-saturated sub-10 nm table-top lasers at 1 Hz repetition rate. We also present experimental results
that show that injection-seeding of solid-target soft x-ray plasma amplifiers reduces the far field divergence by an order
of magnitude and to allow for control of the far-field beam characteristics by tailoring the divergence of the seed. We
finally discuss progress towards the development of high repetition rate compact all-diode-pumped soft x-ray lasers. We
have operated the front end of the diode-pumped soft-ray laser driver at 100Hz repetition rate, obtaining sub-5 ps optical
laser pulses of 100 mJ energy.
We describe our recent progress in the investigation of the spectral properties of collisional XUV lasers, including both
experimental measurements and numerical calculations. Using a wavefront-division, variable path-difference
interferometer, we have characterized the temporal coherence and the spectral width of an injection-seeded transient
XUV laser emitted at 18.9 nm from a Ni-like Mo plasma. Our results show that the temporal coherence of the beam is
significantly increased by the injection-seeded operation, compared to the standard ASE mode, in agreement with
detailed numerical simulations. Using the PPP code we have calculated the intrinsic linewidth of the same lasing line
over a range of electron density and at temperatures that are relevant to transient collisional pumping. We discuss the
relative contributions of homogeneous and inhomogeneous broadening to the overall profile.
We report new advances in the development of high repetition rate table-top soft x-ray lasers. We have extended the gain-saturated operation of these lasers to 10.9 nm demonstrating a 1 Hz repetition rate laser operation in Ni-like tellurium with an average power of 1 microwatt. In a separate development we have demonstrated the first all-diodepumped soft x-ray laser. Lasing was achieved in the 18.9 nm line of Ni-like molybdenum in a plasma heated by a compact all-diode-pumped Yb:YAG laser. The solid state pump laser produces 8.5 ps pulses with up to 1 J energy at 10 Hz repetition rate. This diode-pumped laser has the potential to greatly increase the repetition rate and average power of soft x-ray lasers on a significantly smaller footprint. These compact soft X-ray lasers offer new scientific opportunities in small laboratory environments.
We have recently demonstrated high repetition rate tabletop lasers operating at wavelengths as short as 10.9 nm
based on collisional transient excitation of ions in plasmas created by laser heating of solid targets. As a further step in
the development of these lasers into very high brightness and fully coherent soft x-ray sources, we have demonstrated
injection seeding of the amplifiers with high harmonic seed pulses. We report results of an experiment in which a 32.6
nm Ne-like Ti amplifier was used to amplify a seed pulse from the 25th harmonic of Ti:Sapphire into the gain saturation
regime. Simultaneous amplification of the 27th harmonic at 30.1 nm was also observed. The seeded soft x-ray laser beam
was measured to approach full spatial coherence. We have demonstrated that this scheme is scalable to shorter
wavelengths and that is capable of producing extremely bright soft x-ray laser pulse with essentially full coherence.
We have demonstrated gain-saturated operation of high repetition rate table-top soft x-ray lasers producing microwatt average powers at wavelengths ranging from 13.2 to 32.6 nm in transitions of Ni-like and Ne-like ions. Lasing was also observed for shorter wavelength transitions of the 4d1S0→4p1P1 Ni-like isoelectronic sequence, with amplification approaching gain saturation in the 11.9 nm line of Ni-like Sn and progressively reduced gain for wavelengths as low as 10.9 nm in Ni-like Te. The results were obtained heating a pre-created plasma with a picosecond optical laser pulse with an energy of only 1 J impinging at optimized grazing angles of incidence for maximum pump energy deposition efficiency. This pumping geometry takes advantage of the refraction of the pump beam to increase the energy deposition efficiency of the pump beam into the gain region, making it possible to operate soft x-ray lasers in this wavelength range at significantly increased repetition rates. The results demonstrate the feasibility of producing high average powers of coherent radiation in the 100 eV spectral region for applications using a table-top source.
We report the generation and characterization of plasma waveguides in a highly ionized Ar plasma created by a fast capillary discharge. Their results are of interest for the efficient longitudinal laser excitation of collisional soft x-ray lasers. A discharge-driven hydrodynamic compression guides progressively lower order modes through a plasma with increasing density and degree of ionization. The mode structure and guiding properties were investigated using near and far field imaging, and transmission measurements. The lowest order mode (FWHM diameter ~ 50 um) is guided with an energy transmission of ~ 75% over a 5.5 cm long plasma a fraction of a ns before the discharge plasma column reaches the conditions for lasing in Ne-like Ar. The rapid expansion of the highly ionized plasma column after the pinch forms a significantly more leaky and absorbent waveguide.
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