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The technical challenges and motivations for high-energy, short-pulse generation with the National Ignition Facility (NIF) and possibly other large-scale Nd : glass lasers are reviewed. High-energy short-pulse generation (multi-kilojoule, picosecond pulses) will be possible via the adaptation of chirped pulse amplification laser techniques on NIF. Development of metre-scale, high-efficiency, high-damage-threshold final optics is a key technical challenge. In addition, deployment of high energy petawatt (HEPW) pulses on NIF is constrained by existing laser infrastructure and requires new, compact compressor designs and short-pulse, fibre-based, seed-laser systems. The key motivations for HEPW pulses on NIF is briefly outlined and includes high-energy, x-ray radiography, proton beam radiography, proton isochoric heating and tests of the fast ignitor concept for inertial confinement fusion.

Several low-Z refractory materials are evaluated for use as the NIF first wall in terms of their cost and ability to survive laser light, target emissions and debris, as well as be cleanable and not outgas excessively. Best performers contain B, C, or both, with B{sub 4}C being the best overall. It appears possible at this time that plasma-sprayed B{sub 4}C can be fabricated with low enough porosity and cost to be preferred to hot-pressed B{sub 4}C, the conservative choice.

Some of the best neutron supermirrors currently in production are made of alternating layers of nickel and titanium, with carbon added to the Ni to eliminate preferential growth. Reflectivities of 75–95% in the θc-2θc range are currently obtained from the Ni/C-Ti system. The Ti-Be multilayer system is presented here as a possible alternative to the Ni/C-Ti system. Titanium is one of the few elements which has a negative neutron scattering length, while beryllium has a relatively large positive scattering length. This makes for bilayer structures which have excellent neutron contrast, a necessary requirement of supermirror devices. Single-bilayer-spacing Ti-Be multilayers were prepared by magnetron sputtering onto 2mm thick silicon (001) substrates. Depositions were made with 10–80 bilayers at two different bilayer thicknesses of approximately 90 and 110 A. Bulk layers of Ti and Be were also prepared to determine the scattering length density of each deposition component. The samples were measured at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory on the POSYII reflectometer. First order Bragg peak reflectivities of up to 64% were observed. Data from the two bulk depositions and one multilayer deposition have been fitted using a genetic algorithm developed at IPNS. For the bulk depositions, the scattering length densities of Ti and Be depositions are −2.2 × 10−6 and 10.3 × 10−6 A−2, respectively. In addition, results clearly indicate the presence of a 50 A thick oxide layer on the bulk Ti deposition. The neutron scattering length density profile obtained from the neutron reflectivity measurements are in good agreement with XPS analysis of the oxide film which showed a mixture of TiO2 and Ti2O3.

We report on a series of normal-incidence reflectance measurements at wavelengths just longer than the beryllium K-edge (11.1 nm) from molybdenum/beryllium multilayer mirrors. The highest peak reflectance was 68.7 ± 0.2% at λ = 11.3 nm obtained from a mirror with 70 bilayers ending in beryllium. To our knowledge, this is the highest normal-incidence reflectance that has been demonstrated in the 1-80-nm spectral range.

We report here on the detailed analysis of a gold-coated tungsten wire of the type used in many multi-wire proportional chambers and drift chambers. The wire was attached under tension to a printed circuit board bond pad using standard tin/lead9 solder and was observed to pull out of the solder under uniform tensile loading. Examinations of the failed wire end were performed using electron beam microprobes to study the elemental composition of the residual material on the wire. It is found that the thin gold coating is removed from the surface of the tungsten and alloyed with tin from the solder, forming a nonuniform coating on the wire surface. A surroundung lead-rich region is inferred from this result, leading to the wire failure because of the low shear strength of lead. Discussions of previous work on wire failure and wire aging in high energy physics experiments and similar experiences in the electronics industry are presented.

The large Nd-doped glass laser preamplifier system for the National Ignition Facility (NIF) is comprised of 192 separate beam lines that each produce about 20 kJ of 1.05 micron light. The architecture consists of a central, all-fiber master oscillator system, where the light is generated, shaped, modulated, and distributed to 192 beam lines. Next, 192 preamplifier modules amplifier the tailored pulses from 1 nJ up to 10 J, whereupon they are transported to the large amplifier chains where the laser energy is increased to the 20 kJ level. The preamplifier modules contain a diode-pumped regenerative amplifier (regen), two optical subsystems for spatial beam shaping and smoothing by spectral dispersion (SSD), and a larger four-pass amplifier. In this paper we describe the current design and performance of this high gain preamplifier.

Summary form only given. The preamplifier module or PAM is a high gain, Nd:glass laser system that amplifies the temporally and frequency formatted pulse produced in the master oscillator room (MOR), up to a level that is sufficient for seeding the main amplifier chains of the NIF laser system. The PAM consists of two separate laser amplifiers, a diode-pumped, regenerative amplifier, and a 5 cm., flashlamp-pumped-rod, four-pass amplifier. The amplifiers boost the 1 nJ input pulse from the MOR up to 10-20 Joules in a pulse that ranges from 0.2 to 20 ns. In addition to amplification, the PAM spatially shapes the beam to precompensate for the spatial gain profiles of the main amplifiers, and angularly disperses the beam as part of the smoothing by spectral dispersion (SSD) feature of the laser system. In the past we have demonstrated the performance specifications of the preamplifier on a tabletop, development system. We assembled the first engineering prototype PAM and are conducting final measurements on a system that will become the first of 48 PAMs in the NIF laser system. We made improvements to various subsystems in the PAM that are now included in the engineering prototype. We now operate the regenerative amplifier in energy saturation to reduce the pulse-to-pulse variation in the PAM. We improved the efficiency of the spatial beam shaping masks by including the effects of diffraction from the chrome pixels in designing the masks. We eliminated temporal pulse overlap in the four-pass amplifier by lengthening the relay telescopes in the four-pass optical layout. In the presentation we discuss the latest results from performance measurements of PAM engineering prototype.

Al/Cu sputtered‐sliced phase zone plates, designed to operate with a focal length of 18 cm at 8.05 keV, were tested at the Stanford Synchrotron Radiation Laboratory. First‐, second‐, and third‐order peaks are measured, along with a defocused condition. The first‐order focusing efficiencies ranged from 13% to 19% for the two lenses presented here. Monte Carlo simulations are compared to the data.

Initial measurements are reported for the Mercury laser system, a scalable driver for rep-rated high energy density physics research. The performance goals include 10% electrical efficiency at 10 Hz and 100 J with a 2-10 ns pulse length. This laser is an angularly multiplexed 4-pass gas-cooled amplifier system based on image relaying to minimize wavefront distortion and optical damage risk at the 10 Hz operating point. The efficiency requirements are fulfilled using diode laser pumping of ytterbium doped strontium fluorapatite crystals.

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 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 authors 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.

Multilayer (ML) structures composed of Mo-Be, Ru-Be and Rh-Be with bilayer periods of - 6 nm have been grown using dc magnetron sputter deposition. The ML microstructure has been characterized using x-ray diffraction and high-resolution transmission electron microscopy, and the normal incidence reflectivity has been measured at soft x-ray wavelengths.

Al/Cu sputtered-sliced phase zone plates, designed to operate with a focal length of 0.18 m and 1.12 m at 8.05 keV, were tested at the Stanford Synchrotron Radiation Laboratory. The results of lens characterization and the implementation of a microscope are reported.

A series of experimental measurements was conducted for the characterization of a transmission circular zone plate. The zone plate (ZP), with a primary focal length of 40 cm for 8 keV photons, was illuminated by monochromatized synchrotron x rays. Focusing efficiency of the ZP was measured as a function of x-ray energy between 5 - 1 keV, from which the ZP thickness was determined. Focal spot sizes at the first, second, and third order focus were measured, and they agreed very well with the calculated values. Images of a 1000 mesh/inch gold grid were also obtained at the three focal planes. The grid scans indicated that the spatial resolution is about 2 (mu) in the image obtained at the third order focus.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe the implementation of an 8 keV microscope that operates with a conventional x-ray source in our lab. Samples are scanned pixel-by-pixel through a focused x-ray spot produced by a phase-modulating zone plate fabricated with the sputtered-sliced technique. The micro- focused x-ray source uses a Cu target and produces 8 keV photons that are detected with a Si(Li) spectroscopy system. The microscope currently achieves 10 µm resolution.