or wake field particle acceleration along directed energy applications, and other scientific pursuits. The Computing Directorate partners with NIF&PS on numerous projects and technologies from diagnostic measurements and high performance control systems to data analysis, information technology infrastructure, and scientific simulation code development. "This strong collaboration enables cutting-edge science, particularly with regard to physics-based modeling and simulation," says physicist Jean-Michel Di Nicola. One crucial capability for NIF&PS is the Virtual Beamline (VBL) laser simulation code. It can model all the major laser physics and technology involved in the design optimization, commissioning, and operations of advanced laser architectures from tabletop to NIF-scale. VBL provides researchers with high-fidelity models and high-resolution calculations of laser performance predictions—including for the entire NIF laser system, the Advanced Radiographic Capability, parts of the High Repetition-Rate Advanced Petawatt Laser System laser delivered to the Czech Republic, and the Optical Science Laser. After more than two decades of experimentally verified physics and computing enhancements, this unique workhorse code is wrapping up another major milestone: migration from Java to C++ with a flurry of user interface and optimization features, as well as laser physics and high-resolution enhancements thanks to parallel execution on Livermore Computing platforms.

As the repetition rates of high-intensity, ultrashort laser systems increase, diagnostics with matching data collection speeds must be developed. We have previously developed a spatiotemporal laser diagnostic, STRIPED FISH, which measures the complete laser electric field on a single shot. To provide rapid feedback, we now introduce a high-repetition-rate compatible adaptation of the STRIPED FISH retrieval algorithm which condenses the key electric field quantities into a handful of scalars for rapid assessment of the pulse’s first-order spatiotemporal distortions, and we validate this novel retrieval method with an experimental data trace.

We report recent single-shot spatiotemporal measurements of laser pulses, including pulse-front tilt (PFT) and spatial chirp, taken at the Compact Multipulse Terawatt laser at the Jupiter Laser Facility in Livermore, CA. STRIPED FISH, a device that measures the complete 3D electric field of fs to ps laser pulses on a single shot, was adapted to near infrared for these measurements. We present the design of the instrument used for these experiments, the on-shot measurements of systematic high-order PFT, and shot-to-shot variations in the measurements of spatiotemporal couplings. Finally, we simulate the effect of PFT in target normal sheath acceleration experiments. These simulations showed that pulse front tilt can steer hot electrons, shape the distribution of the accelerating sheath field, and increase the variability of cutoff energy in the resulting proton spectra. While these effects may be detrimental to experimental accuracy if the pulse front tilt is left unmeasured, hot electron steering shows promise for precision manipulation of the particle source for a range of applications, including irradiation of secondary targets for opacity measurements, radiography, or neutron generation.

High-intensity, ultrashort laser sources are a foundational pillar for High-Energy-Density (HED) physics, and as the repetition rates of these systems increase, diagnostics must be developed to match their data collection speed. Characterization of any spatiotemporal distortions in the laser pulse is necessary to standardize results across facilities. We have previously developed a laser diagnostic called spatially and temporally resolved intensity and phase evaluation device: full information from a single hologram, or STRIPED FISH, to measure the full spatiotemporal laser electric field on a single shot. In order to provide rapid feedback, we here adapt the STRIPED FISH retrieval algorithm, which typically has computation times of up to 30 min due to the high spatial resolution of the device and its retrieval of the complete four-dimensional pulse field, to distill the key electric field quantities into a handful of scalars for rapid assessment of the pulse’s 1st-order distortions. Here, our new, rapid non-iterative retrieval algorithm is validated with simulated and experimental data, and it provides, within seconds, the same 1st-order information as given by the full analysis. This algorithm is suitable for on-shot assessment of spatiotemporal distortions and can be adapted to assess high repetition-rate laser quality in HED experiments.

A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps–20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

We demonstrate, for the first time, a single-shot, complete spatiotemporal measurement of pulses from a terawatt-scale, multi-stage-amplified, low repetition-rate laser source. The ultrashort pulse electric field, E(x,y,z,t), is spatiotemporally complex due to distortions that accrue from multiple chirped-pulse amplifiers, which requires a complete characterization. Meanwhile, the instability of the laser source introduces field profiles that vary significantly from pulse to pulse, which, together with the low repetition-rate (15 shots/hour), requires the use of a single-shot measurement technique. To accomplish the measurements, we used a wavelength-multiplexed, digital-holographic technique called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram, specially tailored to measure picosecond pulses at a wavelength of about 1 μm. Specifically, individual pulses from the compact multipulse terawatt laser were measured, with up to 0.3 J per shot of energy and ∼2 ps pulse durations, at 1052 nm. With these measurements, we characterized several major spatiotemporal distortions that affect the peak intensity at the laser focus, as well as the pulse-shape instability on a shot-to-shot basis. Our technique allows detailed diagnosis of laser pulses (especially high-order spatiotemporal distortions) and provides straightforward four-dimensional animations of pulse propagation to a focus.

A single shot, complete spatiotemporal measurement of the complex electric field E(x, y, z, t) emitted by a high power (> 0.1 TW) laser is demonstrated for the first time. We generate movies of the laser's electric field E(x, y, z, t) before and after the chirped pulse amplification chain and examine the temporal, spectral, and spatial field features.

Lawrence Livermore National Laboratory (LLNL) has converted a commercial 200kV transmission electron microscope (TEM) into an ultrafast, nanoscale diagnostic tool for material science studies. The resulting Dynamic Transmission Electron Microscope (DTEM) has provided a unique tool for the study of material phase transitions, reaction front analyses, and other studies in the fields of chemistry, materials science, and biology. The TEM's thermionic electron emission source was replaced with a fast photocathode and a laser beam path was provided for ultraviolet surface illumination. The resulting photoelectron beam gives downstream images of 2 and 20 ns exposure times at 100 and 10 nm spatial resolution. A separate laser, used as a pump pulse, is used to heat, ignite, or shock samples while the photocathode electron pulses, carefully time-synchronized with the pump, function as probe in fast transient studies. The device functions in both imaging and diffraction modes. A laser upgrade is underway to make arbitrary cathode pulse trains of variable pulse width of 10-1000 ns. Along with a fast e-beam deflection scheme, a 'movie mode' capability will be added to this unique diagnostic tool. This talk will review conventional electron microscopy and its limitations, discuss the development and capabilities of DTEM, in particularly more » addressing the prime and pulsed power considerations in the design and fabrication of the DTEM, and conclude with the presentation of a deflector and solid-state pulser design for Movie-Mode DTEM. « less

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Laser-peening surface treatments have demonstrated benefits for improving resistance to stress-corrosion cracking and extension of fatigue lifetimes. The effects of laser peening on hydrogen compatibility of structural metals have not been documented. In this study, annealed and laser-peened alloy 22 (corrosion-resistant nickel-base alloy) is thermally precharged with hydrogen and tested in tension. Laser peening is found to have no significant effect on the solubility of hydrogen in alloy 22 and enhances hydrogen-assisted fracture. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ultrashort pulsed lasers can accurately ablate materials which are refractory, transparent, or are otherwise difficult to machine by other methods. The typical method of machining surfaces with ultrashort laser pulses is by raster scanning, or the machining of sequentially overlapping linear trenches. Experiments in which linear trenches were machined in alumina at various pulse overlaps and incident fluences are presented, and the dependence of groove depth on these parameters established. A model for the machining of trenches based on experimental data in alumina is presented, which predicts and matches observed trench geometry. This model is then used to predict optimal process parameters for the machining of trenches for maximal material removal rate for a given laser.

the material without appreciable heating. It was also found that quenching after solution annealing and shot peening during production of Alloy 22 plate imparts compressive stresses of 35-105 ksi near the surface, a very large buffer against SCC. This means that if seam-welded hollow canisters likewise gain compressive stresses upon post-weld annealing and quenching, and if closure welds are laser peened, all surfaces of the canister would be under compression, thereby precluding SCC of the Alloy 22 canister. Laser peening may plastically deform as much as the top 10% of the metal (about 2 mm out of the 25-mm plate thickness), thereby changing the rate of general corrosion of waste package outer barrier. Long-term corrosion tests of laser peened Alloy 22 welds should be conducted. Present results show that laser peening, currently under development at LLNL using high-energy lasers, induces compressive residual stress on the near surface of the weld. This laser peening process is showing significant retardation of SCC and should be further characterized and assessed to preclude SCC in Alloy 22 canisters.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Abstract A laser processing system has been developed to drill high aspect ratio holes through the impermeable beryllium capsules envisioned for ignition shots on NIF. The drilling system was designed to produce holes with an entrance and exit diameter of approximately 5 μm through the full 175 μm thickness of the capsule. To meet these requirements, a frequency doubled femtosecond-class Ti:Sapphire laser is directed through a high numerical aperture lens to provide the spot geometry needed to drill the hole. The laser pulse is confined by the metallic walls of the hole, thereby maintaining the diameter of the channel well beyond the Rayleigh range of the optical system. Presented is the current state of this work-in-progress, including descriptions of the device and the technique used to produce the holes. The various means of characterizing the laser-drilled channels are also discussed.

Although recent years have seen significant advances in the spatial resolution possible in the transmission electron microscope (TEM), the temporal resolution of most microscopes is limited to video rate at best. This lack of temporal resolution means that our understanding of dynamic processes in materials is extremely limited. High temporal resolution in the TEM can be achieved, however, by replacing the normal thermionic or field emission source with a photoemission source. In this case the temporal resolution is limited only by the ability to create a short pulse of photoexcited electrons in the source, and this can be as short as a few femtoseconds. The operation of the photo-emission source and the control of the subsequent pulse of electrons (containing as many as 5 x 10(7) electrons) create significant challenges for a standard microscope column that is designed to operate with a single electron in the column at any one time. In this paper, the generation and control of electron pulses in the TEM to obtain a temporal resolution <10(-6)s will be described and the effect of the pulse duration and current density on the spatial resolution of the instrument will be examined. The potential of these levels of temporal and spatial resolution for the study of dynamic materials processes will also be discussed.