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The advanced radiographic capability (ARC) laser system, part of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, is a short-pulse laser capability integrated into the NIF. The ARC is designed to provide adjustable pulse lengths of ∼ 1 − 38 p s in four independent beamlets, each with energies up to 1 kJ (depending on pulse duration). A detailed model of the ARC lasers has been developed that predicts the time- and space-resolved focal spots on target for each shot. Measurements made to characterize static and dynamic wavefront characteristics of the ARC are important inputs to the code. Modeling has been validated with measurements of the time-integrated focal spot at the target chamber center (TCC) at low power, and the space-integrated pulse duration at high power, using currently available diagnostics. These simulations indicate that each of the four ARC beamlets achieves a peak intensity on target of up to a few 10 18 W / c m 2 .

ARC is a kilojoule petawatt-class laser system which generates high energy x-ray and particle sources for radiography of experiments on the National Ignition Facility. We present recent progress on laser performance measurements and system modeling.

Entov and Hinch [J. Non-Newtonian Fluid Mech. 72,31-53 (1997)] predicted a Weissenberg number of 2/3 during capillary thinning of slender filaments of polymer solutions. Data from the experiments of Clasen et al. [J. Rheol. 50, 849-881 (2006)] however show that that is not the case. The Weissenberg number is observed to systematically decrease with concentration in nominally dilute solutions to values well below the critical value of 1/2 for the coil-to-stretch transition to reach a minimum around the critical-overlap concentration c*, and thereafter increase in semidilute solutions. Conformation dependence of the polymeric friction coefficient and the phenomenon of coil-stretch hysteresis are shown to play vital roles in determining capillary thinning dynamics. A key result is that when steady-state coil-stretch hysteresis exists, transient polymer conformations during capillary thinning evolve quasistatically along the unstable manifold of the hysteresis window. It is further found necessary to account for changes in polymeric friction due to intermolecular interactions as chains stretch in the flow. A new constitutive model for unentangled polymer solutions is proposed combining blob concepts to account for the effect of hydrodynamic screening on the average friction coefficient of partially stretched chains. It is shown that stretching causes intermolecular interactions to become stronger in the dilute regime and weaker in semidilute solutions. Predictions with this constitutive model agree well with the experimental data in capillary thinning. (C) 2016 The Society of Rheology.

We investigate the formation and diffraction efficiency of plasma gratings generated by the interference of two laser beams crossing at a small angle on the surface of a planar aluminum target. Such gratings were observed during National Ignition Facility experiments with the ratio of energy in the first-order to zeroth order of ≈60%. Recently, additional experiments were performed on the Optical Sciences Laser. These experiments with only two interfering beams showed high normalized energy (ratio of energy in diffracted order to zeroth order) of approximately 10% and 3% at the first and second diffracted order locations, respectively, for intensities less than 1012 W/cm2. The existence of the higher-orders is the characteristic of diffraction from gratings in the Raman-Nath as opposed to the Bragg regime. In addition, we show conical diffraction from the generated plasma grating. Using numerical simulations, we explore the large difference in diffraction efficiency observed in these two experiments and highlight the role of plasma temperature and density scale length. The simulations suggest a modulation depth of the plasma grating refractive index ranging from 1.77 × 10−4 to 3.5 × 10−2. These results are relevant to Inertial Confinement Fusion experiments or plasma photonics applications of gratings in high-field laser-physics and high-energy density science, specifically in the nanosecond regime.We investigate the formation and diffraction efficiency of plasma gratings generated by the interference of two laser beams crossing at a small angle on the surface of a planar aluminum target. Such gratings were observed during National Ignition Facility experiments with the ratio of energy in the first-order to zeroth order of ≈60%. Recently, additional experiments were performed on the Optical Sciences Laser. These experiments with only two interfering beams showed high normalized energy (ratio of energy in diffracted order to zeroth order) of approximately 10% and 3% at the first and second diffracted order locations, respectively, for intensities less than 1012 W/cm2. The existence of the higher-orders is the characteristic of diffraction from gratings in the Raman-Nath as opposed to the Bragg regime. In addition, we show conical diffraction from the generated plasma grating. Using numerical simulations, we explore the large difference in diffraction efficiency observed in these two experiments and h...

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, is the first of its kind megajoule-class laser facility with 192 beams capable of delivering over 1.8 MJ and 500TW of 351 nm light for high accuracy laser-matter interaction experiments. It has been commissioned and operated since 2009 to support a wide range of missions including the study of inertial confinement fusion, high energy density physics, material science, and laboratory astrophysics. In the first section of this paper we discuss the current status of laser performance obtained during the 408 target experiments completed in 2017. The performance spanned a wide range of laser energies, powers and pulse durations as requested for these target experiments. A special emphasis is given on energy delivery and cone power accuracy in the UV, as these are key parameters for successful experiments. In the second section of the paper, the results obtained during the 2017 performance quad campaign are briefly described. During this campaign a series of laser-only shots were taken to perform tests at elevated energies on a single NIF quad. These tests were designed to assess laser performance limits and operational costs against predictive models. This campaign culminated with the delivery of ~54 kJ of UV on a single quad of NIF, and 14 kJ on a single beam aperture, which are both to our knowledge the largest energies achieved to date for a neodymium-glass, frequency tripled architecture.

Titania is the latest series of ultraviolet laser systems developed with the highest laser beam brightness. It can be configured in two alternative modes which can deliver a brightness of

The absorption spectrum of brown diamond is broad and featureless, in both natural type IIa and CVD-grown material. It is argued that such an absorption is due to an extended, rather than a point, defect. Ab-initio modelling studies have been conducted on dislocations and extended vacancy-related defects. While certain dislocations could potentially explain the origin of colour, their density is too low to account for experimentally observed absorption magnitudes. It is demonstrated that a vacancy disk lying in the {111} plane has an absorption spectrum similar to that seen in natural and CVD brown diamond. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is the first of a kind megajoule-class laser with 192 beams capable of delivering over 1.8 MJ and 500TW of 351nm light [1], [2]. It has been commissioned and operated since 2009 to support a wide range of missions including the study of inertial confinement fusion, high energy density physics, material science, and laboratory astrophysics. In order to advance our understanding, and enable short-pulse multi-frame radiographic experiments of dense cores of cold material, the generation of very hard x-rays above 50 keV is necessary. X-rays with such characteristics can be efficiently generated with high intensity laser pulses above 1017 W/cm² [3]. The Advanced Radiographic Capability (ARC) [4] which is currently being commissioned on the NIF will provide eight, 1 ps to 50 ps, adjustable pulses with up to 1.7 kJ each to create x-ray point sources enabling dynamic, multi-frame x-ray backlighting. This paper will provide an overview of the ARC system and report on the laser performance tests conducted with a stretched-pulse up to the main laser output and their comparison with the results of our laser propagation codes.

The National Ignition Facility (NIF) is a stadium-sized facility containing a 192-beam, 1.8 MJ, 500-TW, 351-nm laser system together with a 10-m diameter target chamber with room for many target diagnostics. NIF is the world’s largest laser experimental system, providing a national center to study inertial confinement fusion and the physics of matter at extreme energy densities and pressures. A computational system, the Laser Performance Operations Model (LPOM) has been developed that automates the laser setup process, and accurately predict laser energetics. LPOM uses diagnostic feedback from previous NIF shots to maintain accurate energetics models (gains and losses), as well as links to operational databases to provide ‘as currently installed’ optical layouts for each of the 192 NIF beamlines. LPOM deploys a fully integrated laser physics model, the Virtual Beamline (VBL), in its predictive calculations in order to meet the accuracy requirements of NIF experiments, and to provide the ability to determine the damage risk to optical elements throughout the laser chain. LPOM determines the settings of the injection laser system required to achieve the desired laser output, provides equipment protection, and determines the diagnostic setup. Additionally, LPOM provides real-time post shot data analysis and reporting for each NIF shot. The LPOM computation system is designed as a multi-host computational cluster (with 200 compute nodes, providing the capability to run full NIF simulations fully parallel) to meet the demands of both the controls systems within a shot cycle, and the NIF user community outside of a shot cycle.

The achievement of shoulder balance is an important measure of successful scoliosis surgery. No previously described classification system has taken shoulder balance into account. We propose a simple classification system for AIS based on two components which include the curve type and shoulder level. Altogether, three curve types have been defined according to the size and location of the curves, each curve pattern is subdivided into type A or B depending on the shoulder level. This classification was tested for interobserver reproducibility and intraobserver reliability. A retrospective analysis of the radiographs of 232 consecutive cases of AIS patients treated surgically between 2005 and 2009 was also performed. Three major types and six subtypes were identified. Type I accounted for 30 %, type II 28 % and type III 42 %. The retrospective analysis showed three patients developed a decompensation that required extension of the fusion. One case developed worsening of shoulder balance requiring further surgery. This classification was tested for interobserver and intraobserver reliability. The mean kappa coefficients for interobserver reproducibility ranged from 0.89 to 0.952, while the mean kappa value for intraobserver reliability was 0.964 indicating a good-to-excellent reliability. The treatment algorithm guides the spinal surgeon to achieve optimal curve correction and postoperative shoulder balance whilst fusing the smallest number of spinal segments. The high interobserver reproducibility and intraobserver reliability makes it an invaluable tool to describe scoliosis curves in everyday clinical practice.

Ab Initio calculations, using density functional theory within the AIMPRO code, have been performed on bulk diamond and silicon in order to calculate the change in the dielectric constant due to strain, and hence the values of the photoelastic tensors. A combination of compressive and tensile strain has been applied to two atom unit cells of Si and diamond and the tensors relating to p 11 + 2p 12 , p 12 - 2p 11 and p 44 extracted. Good agreement is found with experimental results for absolute values and frequency dependence of the constants for silicon. Results are also given for diamond where experimental data is much more limited and scattered.

The small or near-zero band gap of germanium found by supercell local density functional treatments causes difficulties in the study of the properties of charged defects in Ge. Here, we use large H-terminated Ge clusters together with a non-linear core corrected (NLCC) Ge pseudopotential to explore the structure, vibrational and electrical properties of the vacancy–oxygen complex (VO). The cluster possesses a gap sufficiently wide to contain defect related energy levels, thus allowing us to model the three charge states of the defect. The local vibrational modes (LVM) calculated for the neutral ( VO 0 ), negatively charged ( VO - ) and double negative ( VO = ) defect are 602, 684 and 694 cm - 1 , and can be favourably compared with experimental values of 621, 669 and 716 cm - 1 , respectively [Markevich VP, et al. Physica B 2003; 340–2, 844–8]. Using substitutional gold ( Au s ) as a marker defect, electric levels of VO are found at E ( -/ 0 ) = E v + 0.30 eV and E ( = /- ) = E c - 0.29 eV , in excellent agreement with the respective experimental enthalpies for hole and electron emission Δ H h ( -/ 0 ) ≃ 0.32 eV and Δ H e ( = /- ) = 0.26 eV , respectively. Finally, the migration, dissociation and reorientation energies of the defect are also reported.

The National Ignition Facility (NIF) laser has been designed to support high energy density science (HEDS), including the demonstration of fusion ignition through Inertial Confinement. NIF operated a single ''quad'' of 4 beams from December 2002 through October 2004 in order to gain laser operations experience, support target experiments, and demonstrate laser performance consistent with NIF's design requirement. During this two-year period, over 400 Main Laser shots were delivered at 1{omega} to calorimeters for diagnostic calibration purposes, at 3{omega} to the Target Chamber, and at 1{omega}, 2{omega}, and 3{omega} to the Precision Diagnostics System (PDS). The PDS includes its own independent single beam transport system, NIF design frequency conversion hardware and optics, and laser sampling optics that deliver light to a broad range of laser diagnostics. Highlights of NIF laser performance will be discussed including the results of high energy 2{omega} and 3{omega} experiments, the use of multiple focal spot beam conditioning techniques, the reproducibility of laser performance on multiple shots, the generation on a single beam of a 3{omega} temporally shaped ignition pulse at full energy and power, and recent results on full bundle (8 beamline) performance. NIF's first quad laser performance meets or exceeds NIF's design requirements.

Simulations of eight different regional climate models (RCMs) have been performed for the period September 1997-September 1998, which coincides with the Surface Heat Budget of the Arctic Ocean (SHEBA) project period. Each of the models employed approximately the same domain covering the western Arctic, the same horizontal resolution of 50 km, and the same boundary forcing. The models differ in their vertical resolution as well as in the treatments of dynamics and physical parameterizations. Both the common features and differences of the simulated spatiotemporal patterns of geopotential, temperature, cloud cover, and long-/shortwave downward radiation between the individual model simulations are investigated. With this work, we quantify the scatter among the models and therefore the magnitude of disagreement and unreliability of current Arctic RCM simulations. Even with the relatively constrained experimental design we notice a considerable scatter among the different RCMs. We found the largest across-model scatter in the 2 m temperature over land, in the surface radiation fluxes, and in the cloud cover which implies a reduced confidence level for these variables.

The Advanced Radiographic Capability (ARC) laser system at the National Ignition Facility (NIF) is designed to ultimately provide eight beamlets with a pulse duration adjustable from 1 to 30 ps, and energies up to 1.5 kJ per beamlet. Currently, four beamlets have been commissioned. In the first set of 6 commissioning target experiments, the individual beamlets were fired onto gold foil targets with energy up to 1 kJ per beamlet at 20–30 ps pulse length. The x-ray energy distribution and pulse duration were measured, yielding energy conversion efficiencies of 4–9 × 10−4 for x-rays with energies greater than 70 keV. With greater than 3 J of such x-rays, ARC provides a high-precision x-ray backlighting capability for upcoming inertial confinement fusion and high-energy-density physics experiments on NIF.

We present quantitative calculations of scattering lifetimes associated with isovalent anion and cation defects in GaSb/InAs detector heterostructures, and identify the dependence upon the proximity of the defects to the heterointerfaces. The carrier lifetimes arising through scattering from interface islands of anion defects are shown to depend non-linearly upon the presence of additional cation defects. These weakly scattering cation defects are shown to control the larger scattering from the anion islands, enabling lifetimes to be enhanced by more than an order of magnitude through the inclusion of additional lattice imperfections.

The erosive potentials of a number of commercially available artificial saliva substitutes have been investigated using an in vitro hydroxyapatite powder dissolution assay. Most of the saliva substitutes examined did not show any appreciable erosive potential, although one product resulted in greater mineral dissolution levels. There appeared to be little correlation between pH and mineral dissolution levels for the different saliva substitutes examined. Whilst saliva substitutes may be of assistance in maintaining some physiological function in patients with impaired salivary flow, it is important to choose a product with low erosive potential where the natural dentition is present.

We perform a systematic study of the factors governing the optical properties of type II Ga1-xInxSb/InAs superlattice structures. We map the parameter space corresponding to the layer widths, alloy concentrations and interface bonding types, and identify those structures for which the fundamental gap lies in the desired range for device application. In addition, we examine the higher lying miniband energies to assess the structures for favourable Auger recombination limits. The microscopic interface bonding configuration is shown to have a significant impact upon the magnitude of the fundamental gap, and confirms the requirement for full-bandstructure calculations in the evaluation of possible structures. We study the features of the optical spectra for those structures whose bandstructures are recognized as most suitable for detector applications.

Decreased physician visits for dyspepsia were predicted with the histamine-2 receptor antagonists (H2RA) release to over-the-counter (OTC) status. The aim of this study was to examine the presentation frequency for dyspeptic complaints before and after the OTC release of the H2RA and the self-reported effectiveness of OTC H2RA.Two cross-sectional surveys were used in a community sample. The patients comprised a random age- and sex-stratified sample of 1600 ambulatory adults in 1993 and 1800 in 1997. Self-report, valid mail surveys gathered information on healthcare seeking and gastrointestinal symptoms in 1993 and 1997 and antisecretory use in 1997.Presentation frequency for dyspepsia was 22% in 1993 versus 23.5% in 1997. Only 16% of chronic users of the OTC H2RA obtained complete relief of symptomatic episodes. Use of an OTC H2RA was highly associated with presentation to a physician in the past year.OTC H2RA infrequently provided the complete relief desired by patients. Presentation frequency to physicians for dyspeptic complaints did not change with availability of H2RA OTC.

This report is concerned with the manifestations associated with focal dermal hypoplasia (Goltz syndrome) in two patients. Goltz syndrome is a rare polydysplastic syndrome. Systemic findings were similar to those previously reported in the literature and are illustrated. More detailed descriptions of the dental abnormalities are presented. The possibility of root resorption being a previously unreported part of the syndrome is hypothesised.

The main requirements for a fast igniter laser beam are reviewed and shown to favour short wavelength and ultrahigh brightness. These requirements are met by the new KrF laser system at Rutherford Appleton Laboratory called TITANIA. TITANIA uses two schemes to enhance the laser beam brightness. The first is chirped pulse amplification which is used to enhance brightness by compressing the pulse into the femtosecond region. In this mode TITANIA produces in the region of 250 mJ on target in 700 fs. The second mode of operation uses a Raman technique for beam combining and beam clean-up which is designed to give a single beam of 80 joules on target in a pulselength of 60 ps. In this scheme the KrF wavelength is Raman shifted to 268 nm. The Raman amplifiers will use gaseous rather than solid windows and experiments which demonstrate their feasibility will be described. A concept for a reactor scale fast igniter beam using the Raman technique will be discussed.

Time resolved hard x-ray images (hv > 9 keV) and time integrated hard x-ray spectra (hv = 18-150 keV from vacuum hohlraums irradiated with four 351 nm wavelength NIF laser beams are presented as a function of hohlraum size and laser power and duration. The hard x-ray images and spectra provide insight into the time evolution of the hohlraum plasma filling and the production of hot electrons. The fraction of laser energy detected as hot electrons (f hot ) shows correlation with both laser intensity and with an analytic plasma filling model.

We present second-harmonic generation experiments in p-doped asymmetrically stepped quantum wells using the emission of a free-electron laser in the wavelength interval between 13 and 18 mu m. The wells are designed such that the three fewest valence-subbands are about equally spaced. We measured the angular and frequency dependence of the second-harmonic signal excited by intense laser irradiation chosen to be nearly resonant with the transitions between the three lowest valence subbands. We see evidence of the optical second-order susceptibility components chi(xxz)((2)), chi(zxx)((2)) and chi(zxy)((2)), chi(xyz)((2)) in the quantum wells and determine their enhancement with respect to chi(xyz)((2)) of bulk GaAs.

We report local-density ab-initio pseudopotential calculations designed to link structural properties of real interfaces to carrier dynamics and recombination observed in spectroscopic studies of Si–Ge and similar heterostructures. We find novel interface-related effects of deep localisation which may provide a fresh basis for explaining the optical and scattering phenomena reported in these systems. In particular, the electronic structure of Si–Ge interfaces is significantly modified by the presence of new well-localised levels due to dopants such as Sb which are commonly used to improve molecular beam epitaxy growth.

An experimental campaign to tune the initial shock compression sequence of capsule implosions on the National Ignition Facility (NIF) was initiated in late 2010. The experiments use a NIF ignition-scale hohlraum and capsule that employs a re-entrant cone to provide optical access to the shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of the shock sequence is diagnosed with velocity interferometry that provides target performance data used to set the pulse shape for ignition capsule implosions that follow. From the start, these measurements yielded significant new information on target performance, leading to improvements in the target design. We describe the results and interpretation of the initial tuning experiments.

Ignition implosions on the National Ignition Facility (NIF) [Lindl et al., Phys. Plasmas 11 , 339 (2004)] are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision in order to keep the fuel on a low adiabat. The first series of precision tuning experiments on NIF have been performed. These experiments use optical diagnostics to directly measure the strength and timing of all four shocks inside the hohlraum-driven, cryogenic deuterium-filled capsule interior. The results of these experiments are presented demonstrating a significant decrease in the fuel adiabat over previously un-tuned implosions. The impact of the improved adiabat on fuel compression is confirmed in related deuterium-tritium (DT) layered capsule implosions by measurement of fuel areal density (ρR), which show the highest fuel compression (ρR ∼ 1.0 g/cm2 ) measured to date.

An investigation has been carried out into the effects of variable inlet guide vanes (VIGVs) on the performance and stability margin of a transonic fan in the presence of inlet flow distortion. The study was carried out using computational fluid dynamics (CFD) and validated with experimental data. The capability of CFD to predict the changes in performance with or without VIGVs in the presence of an inlet flow distortion is assessed. Results show that the VIGVs improve the performance and stability margin and do so by reducing the amount of swirl at inlet to the rotor component of the fan.

NIF's ability to deliver precise, high-contrast pulses is limited by the fidelity of our numerical model. Model fidelity is enhanced by fitting small-signal gain and saturation parameters to measurements and by including temporal overlap effects.

We have achieved the NIF design goals for power and energy by delivering 1.86 MJ of ultra-violet energy in a wide dynamic range (>300:1), 22.5-ns shaped ignition pulse with a peak power of 520 TW.

High‐resolution spectra of KrF (B–X) amplified spontaneous emission from various discharge‐pumped and electron‐beam‐pumped KrF lasers have been analyzed. An underlying structured absorption spectrum has been discovered with a well‐resolved peak at 248.91 nm. The absorption coefficient of this peak was found to vary in exact proportion to the peak laser gain coefficient but was independent of laser gas purity. We suggest that the absorption arises internally within the KrF molecule and is due to transitions from the B state to a higher‐lying Rydberg state. This hypothesis was tested by simulating the absorption spectrum from KrF*(B) to a weakly repulsive state dissociating to Kr*(3P1)+F(2P3/2). A good agreement was obtained between simulated and experimental absorption spectra.

The Titania laser system, based around a 42 cm e-beam pumped KrF amplifier, is currently being installed at the Rutherford Appleton Laboratory and will come on line as a user facility in 1996. Like Sprite, its predecessor, it will operate in both CPA (249 nm) and Raman (268 nm) short-pulse modes, delivering up to 10 TW to target in high-quality beams. With brightness expected to reach 10 21 W cm -2 sterad -1 , it will be the world's brightest ultraviolet laser. The design of the Titania system includes a number of novel features. The multi-pass Ti :sapphire front-end amplifier uses an unusual beam-folding scheme. The Raman system will involve the first application of Raman multiplexing, combining high KrF efficiency with low transport cost. Reflective coatings with very high damage thresholds are being developed for the CPA compressor gratings and the UV transport optics. A windowless configuration for the final Raman amplifier is presently under analysis, to allow the performance of this maximally stressed component to be extended substantially. Finally the design of the Titania e-beam machine, featuring novel split-cathode diodes, has resulted in unusually high efficiency of electron transport into the laser gas. The laser's infrastructure has involved sophisticated mechanical and electrical design, and a computerized diagnostic, control and safety package is being developed to allow one-man operation of the whole 1000 m 2 installation.

Regular beta 2-adrenoceptor agonist therapy may lead to a rebound increase in bronchial responsiveness on discontinuation of therapy and a reduction in bronchoprotective effects. Formoterol, a long-acting beta 2-agonist, is effective in single doses in the prevention of methacholine-induced bronchoconstriction. In a double-blind, placebo-controlled cross-over study, we examined the effect of an inhaled long-acting beta 2-adrenoceptor agonist, formoterol (24 micrograms twice a day) for 2 wk on airway function and responsiveness in 17 subjects with mild asthma (mean age, 26.3 +/- 1.4 yr) who were not taking inhaled glucocorticosteroids. FEV1 and the provocative concentration of methacholine causing a 20% fall in FEV1 (PC20) were measured at 36, 60, and 108 h and at 2 wk after the last dose of regular treatment. In addition, PC20 was measured 12 h after the first and the last dose of formoterol and placebo. PC20 values at 36, 60, and 108 h and at 2 wk after formoterol treatment cessation were not significantly different from those after placebo. Mean FEV1 was 3.44 +/- 0.18 L after placebo compared with 3.79 +/- 0.20 L after formoterol (p0.001) 12 h after the first dose, and mean PC20 was 0.53 (GSEM 1.4) mg/ml after placebo compared with 2.0 (GSEM 1.4) mg/ml after formoterol (p0.001). After 2 wk of regular treatment, mean FEV1 at 12 h after the final dose of formoterol fell to 3.51 +/- 0.23 L compared with 3.41 +/- 0.18 L after the final dose of placebo (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

We are studying the implementation of polar direct drive (PDD) ignition experiments on the National Ignition Facility (NIF) laser system. Part of this preparation involves testing the performance of the NIF laser system over a broader span of center wavelengths, 3.6 nm, where the laser currently operates and that gain models describe. The temporal shape for the PDD pulses consists of a drive pulse preceded by three lower power "picket pulses". These picket pulses require a multi-FM sinusoidal phase modulation format with a bandwidth of ~ 200 GHz and a more dispersive grating in the preamplifier module (PAM) for smoothing-by-spectral-dispersion (SSD). In this paper we discuss recent measurements of gain on the NIF laser system over this broader wavelength range. We measured FM-to-AM conversion over the 3.6 nm wavelength range. The possibility of pinhole closure due to the larger bandwidth and dispersion associated with multi-FM SSD was studied at LLE on the OMEGA EP laser.

Ignition implosions on the National Ignition Facility [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision to keep the fuel entropy and adiabat low and ρR high. The first series of precision tuning experiments on the National Ignition Facility, which use optical diagnostics to directly measure the strength and timing of all four shocks inside a hohlraum-driven, cryogenic liquid-deuterium-filled capsule interior have now been performed. The results of these experiments are presented demonstrating a significant decrease in adiabat over previously untuned implosions. The impact of the improved shock timing is confirmed in related deuterium-tritium layered capsule implosions, which show the highest fuel compression (ρR~1.0 g/cm(2)) measured to date, exceeding the previous record [V. Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] by more than a factor of 3. The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

We present full pseudopotential band-structure calculations of the frequency dependence of the second-order susceptibility due to transitions between valence minibands in p-type asymmetric stepped-well superlattices. These theoretical predictions are supported by experimental observations of second-harmonic generation. From an analysis of the theoretical results the microscopic processes that contribute to the response are identified and the features of the response are related to the superlattice band structure over a range of temperatures. We demonstrate that simple particle-in-a-box models are unable to correctly describe the positions of the peaks, or the mechanisms involved, in the second-order susceptibility. Experimental results confirming the detection of second-harmonic generation in these structures are presented and compared with the theoretical predictions. An enhancement over the response in bulk of approximately 8 times is observed. The angular dependence observed is consistent with the directional properties of the second-order susceptibility predicted by the theoretical calculations.

Chirped pulse amplification (CPA) and recompression have been used in a large aperture KrF laser system. The power focused onto target in a 300 fs pulse reached 1 TW with an irradiance of ≈ 10 19 W/cm 2 .

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

The self-phase modulation of 10 ps laser pulses at 248 nm passing through a focus in a gas cell has been used to determine the nonlinear refractive indices of air, nitrogen, oxygen, methane, argon and neon and to put an upper limit on the value for helium.

This article describes the current status of the KrF development programme based on the Sprite laser system at the Rutherford Appleton Laboratory. High reliability and high shot rate have been demonstrated. Using a unique KrF-pumped Raman laser architecture, beam brightness exceeding 2×1019 Wcm-2 sterad-1 giving a focussed intensity >5 ×1017 Wcm-2 has been achieved. The development of transform-limited short-pulse oscillators is shown to be of importance in avoiding spectral broadening in air propagation of high-intensity beams. Beam smoothing of KrF beams in a multiplexed configuration has been demonstrated for the first time. The technique of echelon-free induced spatial incoherence has been shown to produce smooth intensity distributions in the far field, which remain essentially unchanged on amplification. The development of pulsed-power systems capable of exciting multikilojoule laser amplifiers for the next phase of development, the Supersprite system, is briefly discussed.

Calculations of the effects of amplified spontaneous emission (ASE) in laser amplifiers designed to amplify sub-picosecond pulses are presented. A one-dimensional code is used with some simple approximations to account for aspect ratio variation in cases of cylindrical symmetry. Gain depletion due to ASE is compared for various multi-pass geometries. Optimisation for short pulse amplification of a telescopic, beam-expanding, 4-pass amplifier is considered.

A unique high-power laser system is described that is based on stimulated Raman scattering in methane. KrF-laser pump beams of 10-ps duration are confined in a square-section light guide and amplify a 268-nm Stokes-shifted beam to 0.5 TW with extremely low prepulse. The near-diffraction-limited beam quality gives a peak brightness of >1020 W cm−2 sr−1.

The input/output characteristic of a large aperture (270‐mm diam) electron‐beam‐pumped KrF laser amplifier is obtained for pulses of 6‐ and 40‐ps duration. The off‐resonance absorption coefficient is estimated by measurement of loss at 268 nm. The gain‐to‐loss ratio is found to decrease from 8 to 6 as the specific pump rate is increased from 0.3 to 0.65 MW cm−3. Gain depumping due to amplified spontaneous emission (ASE) is treated by a simple 1D code and found to give good agreement with experiment. A 3D code incorporating wall reflections gives even better agreement. The spatial distribution of gain and ASE is recorded using visible and ultraviolet imaging.

A kinetic model for KrF is presented that, by neglecting all but the most important kinetic processes, adequately describes the performance of electron-beam-pumped KrF lasers by a few, simple analytical expressions. The expression for the saturation intensity as a function of pump rate and gas composition is checked by measurements of gain saturation in both argon-rich and krypton-rich laser mixtures. The effects of fluorine burn-up are considered and are shown to impose a fundamental relationship between output fluence and efficiency of KrF laser amplifiers.

A technique for producing uniform target irradiation by applying induced spatial incoherence to a high power multiplexed KrF laser system has been demonstrated. The image of a smooth spatial profile is relayed on four beams through a large aperture, electron beam pumped KrF laser and to the focal plane of a concave mirror. Single pulses of 20 ns duration have been amplified to energies of 30 J while observing the effect of amplification on the output profile uniformity.