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 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.
We present experimental demonstrations of the energy density storage and extraction capabilities of Tm:YLF using a table-top diode-pumped system. Here, a Tm:YLF-based oscillator, producing mJ-class pulse energies within both short (nanosecond) and long (millisecond) duration pulses, seeds a single far-field multiplexed power amplifier. The amplifier produced pulse energies up to 21.7 J in 20 ns (>1 GW peak power) using a 4-pass configuration, and 108.3 J in a long duration pulse using a 6-pass configuration. Additionally, the system was reconfigured and operated in a burst mode, amplifying a 6.8 kHz few-ms duration burst of 36 pulses up to 3.6 kW average power. An optical-to-optical efficiency of 19% was achieved during the quasi-steady-state amplification, with an individual pulse fluence over an order of magnitude lower than the saturation fluence.
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.
We present the first demonstration of a multi-joule diode-pumped Tm:YLF amplifier. The compact demonstrator setup, consisting of a Tm:YLF-based oscillator producing ~20mJ, 20ns pulses at 1880nm wavelength that seeds a diode pumped four-pass Tm:YLF power amplifier, generated pulse energies up to 3.9J with a maximum net gain exceeding 200. No saturation effects were observed within this amplifier, as the output pulse energies increased exponentially with the input pump power. When the amplifier was seeded with the free-running oscillator, with pulse durations still significantly shorter than the 15ms radiative lifetime of Tm:YLF, energies of up to 38J were achieved. To the best of our knowledge, this represents over a 100-fold improvement in the highest reported pulse energy from a Tm:YLF amplifier, and nearly an order of magnitude higher energy than any laser operating near 2μm. These results show that Tm:YLF, when operated in an efficient high repetition rate extraction regime and combined with a high-capacity heat removal technique, has the potential to enable a new class of efficient, high peak and average power laser systems to meet the demands of next generation scientific and industrial applications.
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 present a study of the temporal pre-pulse contrast degradation of high focused intensity pulses produced in CPA laser systems due to imperfections in amplifier design, alignment of amplifier components, and crystal inhomogenity. Using a measurement technique we have developed, we demonstrate the presence of multiple crystal domains inside Ti:sapphire slabs with ≈10 cm diameter. The results of our numeric calculations show that crystalline c-axis orientation inhomogenity caused by these crystal domains can lead to generation of pre-pulses with relative contrast >10-10 within several picoseconds before the main pulse. In a multiple-slab amplifier head configuration sometimes used in high repetition rate systems, the misalignment of the amplifier slabs crystalline c-axes with respect to each other can lead to the generation of pre-pulses with relative contrast as high as 10-6, depending on the magnitude of misalignment.
Petawatt laser applications, such as laser plasma acceleration, EUV generation, neutron generation, and materials processing are average-power limited. However, the highest average-power petawatt-class laser to date has an average power of less than 1 kW. Scaling Petawatt-class lasers beyond 10 kW of average power requires a paradigm shift in laser design. To date, average power scaling has been accomplished by increasing the repetition rate of single-shot lasers, in which each shot represents a complete pump/extraction cycle. We propose an alternative scheme, multipulse extraction, in which the gain medium is pumped continuously and the upper state population is extracted over many pulses. This method has two primary benefits: First, because efficient extraction is not necessary in a single pulse, the extraction fluence (and hence the B-integral) can be much lower than in a single pulse design. Second, there isn’t a need to pump within a single inverse lifetime, and therefore less expensive, less complex, and more efficient CW pump sources can be used. Multipulse extraction requires that the gain material have an inverse lifetime significantly less than the desired repetition rate. The design and optimization two multipulse extraction amplifiers, a 10 kHz-100 fs-30J amplifier and a 200 Hz-240 fs-240 J amplifier, will be presented. These point designs have applications in laser plasma acceleration and neutron generation, respectively
New control techniques are required to utilize the full potential of next generation high-energy high-repetition-rate pulses lasers while ensuring their safe operation. During automated optimization of an experiment, the control system is required to identify and reject unsafe laser configurations proposed by the optimizer. Using conventional physics codes render impossible when applied to a high energy laser system with 1ms or less time between shots, and also including laser fluctuations and drift. To mitigate this, we are using a deep Bayesian neural network to map the laser’s input power spectrum to its output power spectrum and demonstrate the speed of this approach. The Bayesian neural network can provide an estimate of its own uncertainty as a function of wavelength. A recently developed algorithm enables the uncertainty to be calculated inexpensively using multiple dropout layers inserted into the model. The uncertainty estimates are used by an active learning algorithm to improve the accuracy of the model and intelligently explore the input domain.
C. Haefner, A. Bayramian, S. Betts, R. Bopp, S. Buck, J. Cupal, M. Drouin, A. Erlandson, J. Horáček, J. Horner, J. Jarboe, K. Kasl, D. Kim, E. Koh, L. Koubíková, W. Maranville, C. Marshall, D. Mason, J. Menapace, P. Miller, P. Mazurek, A. Naylon, J. Novák, D. Peceli, P. Rosso, K. Schaffers, E. Sistrunk, D. Smith, T. Spinka, J. Stanley, R. Steele, C. Stolz, T. Suratwala, S. Telford, J. Thoma, D. VanBlarcom, J. Weiss, P. Wegner
Large laser systems that deliver optical pulses with peak powers exceeding one Petawatt (PW) have been constructed at dozens of research facilities worldwide and have fostered research in High-Energy-Density (HED) Science, High-Field and nonlinear physics [1]. Furthermore, the high intensities exceeding 1018W/cm2 allow for efficiently driving secondary sources that inherit some of the properties of the laser pulse, e.g. pulse duration, spatial and/or divergence characteristics. In the intervening decades since that first PW laser, single-shot proof-of-principle experiments have been successful in demonstrating new high-intensity laser-matter interactions and subsequent secondary particle and photon sources. These secondary sources include generation and acceleration of charged-particle (electron, proton, ion) and neutron beams, and x-ray and gamma-ray sources, generation of radioisotopes for positron emission tomography (PET), targeted cancer therapy, medical imaging, and the transmutation of radioactive waste [2, 3]. Each of these promising applications requires lasers with peak power of hundreds of terawatt (TW) to petawatt (PW) and with average power of tens to hundreds of kW to achieve the required secondary source flux.
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.
G. Doumy, C. Blaga, F. Catoire, R. Chirla, P. Colosimo, I. Lachko, A.-M. March, C. Roedig, E. Sistrunk, J. Tate, J. Wheeler, H. Muller, P. Agostini, L. DiMauro
This document reports recent theoretical and experimental investigations of strong field ionization and high
harmonic generation from mid-infrared lasers at 2 and 4 microns. Numerical solution of the time-dependent
Schrodinger equation as well as Strong Field approximation calculations are reported. Photoelectron and high
harmonic spectra are discussed. Preliminary experimental results are compared to the theoretical predictions.
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