Determination of electron-heated temperatures of petawatt laser-irradiated foil targets with 256 and 68 eV extreme ultraviolet imaging.

Measurements of plasma temperature at the rear surface of foil targets due to heating by hot electrons, which were produced in short pulse high intensity laser matter interactions using the 150 J, 0.5 ps Titan laser, are reported. Extreme ultraviolet (XUV) imaging at 256 and 68 eV energies is used to determine spatially resolved target rear surface temperature patterns by comparing absolute intensities to radiation hydrodynamic modeling. XUV mirrors at these two energies were absolutely calibrated at the Advanced Light Source at the Lawrence Berkeley Laboratory. Temperatures deduced from both imagers are validated against each other within the range of 75-225 eV.

Record high extreme-ultraviolet efficiency at near-normal incidence from a multilayer-coated polymer-overcoated blazed ion-etched holographic grating.

We have measured the extreme-ultraviolet (EUV) efficiency of a polymer-overcoated blazed ion-etched holographic test grating. The grating had a magnetron-sputtered Mo2C/Si multilayer coating matched to the grating blaze angle of 2.78 degrees. At an angle of incidence of 5.6 degrees and a wavelength of 15.79 nm, the measured efficiency peaks in the second outside order at 29.9%. The derived groove efficiency is 53.0%. To the best of our knowledge these are the highest values obtained yet at EUV wavelengths from a holographic ion-etched blazed grating.

Picosecond x-ray laser interferometry of dense plasmas.

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 microm of the target surface. A series of high-quality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.

First principles molecular dynamics of dense plasmas.

Ab initio molecular dynamics calculations are performed for the equation of state of aluminum, spanning condensed matter and dense plasma regimes. Electronic exchange and correlation are included with either a zero- or finite-temperature local density approximation potential. Standard methods are extended to above the Fermi temperature by using final state pseudopotentials to describe thermally excited ion cores. The predicted Hugoniot equation of state agrees well with earlier plasma theories and with experiment for temperatures from 0 to 3 x 10(6) K.

Efficiency calibration of the first multilayer-coated holographic ion-etched flight grating for a sounding rocket high-resolution spectrometer.

We have fabricated the four flight gratings for a sounding rocket high-resolution spectrometer using a holographic ion-etching technique. The gratings are spherical (4000-mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo/Si. Using an atomic force microscope, we examined the surface characteristics of the first grating before and after multilayer coating. The average roughness is approximately 3 A rms after coating. Using synchrotron radiation, we completed an efficiency calibration map over the wavelength range 225-245 A. At an angle of incidence of 5 degrees and a wavelength of 234 A, the average efficiency in the first inside order is 10.4 +/- 0.5%, and the derived groove efficiency is 34.8 +/- 1.6%. These values exceed all previously published results for a high-density grating.

High-Energy X-ray Microscopy Techniques for Laser-Fusion Plasma Research at the National Ignition Facility.

Multi-kilo-electron-volt x-ray microscopy will be an important laser-produced plasma diagnostic at future megajoule facilities such as the National Ignition Facility (NIF). However, laser energies and plasma characteristics imply that x-ray microscopy will be more challenging at NIF than at existing facilities. We use analytical estimates and numerical ray tracing to investigate several instrumentation options in detail, and we conclude that near-normal-incidence single spherical or toroidal crystals may offer the best general solution for high-energy x-ray microscopy at NIF and similar large facilities. Apertured Kirkpatrick-Baez microscopes using multilayer mirrors may also be good options, particularly for applications requiring one-dimensional imaging over narrow fields of view.

Preparation of multilayered materials in cross-section for in situ TEM tensile deformation studies.

The success of in situ transmission electron microscopy experimentation is often dictated by proper specimen preparation and sample design procedures. We have developed a novel technique permitting the production of tensile specimens of multilayered films in cross-section for in situ deformation studies. Of primary, importance in the development of this technique is the production of an electron transparent micro-gauge section. This micro-gauge section predetermines the position at which plastic deformation, crack nucleation and growth, and failure are observed. In short, we report in detail, a unique combination of specimen preparation procedural steps and the design of a multilayer foil sample. The ability of these procedures to facilitate the success of in situ TEM tensile studies of layered materials in cross-section is demonstrated using a Cu-Zr multilayer foil.

Measurement of spatial gain distribution for a neonlike germanium 19.6-nm laser.

We measure the transverse spatial distribution of the gain region for the 19.6-nm neonlike germanium laser line by use of a short amplifier, which is backlit by a longer laser, both of which are created by illumination of a germanium slab target with a series of short 100-ps pulses from the Nova laser. The backlighting technique enables us to reduce greatly the refraction effects that dominated previous imaging experiments and made direct gain measurements impossible. Measurements are made with a two-dimensional high-resolution spatial-imaging diagnostic, and simulations of the gain are compared with experiments.

Grazing-incidence efficiencies in the 28-42-A wavelength region of replicas of the Skylab 3600-line/mm concave grating with multilayer and gold coatings.

The efficiencies of replicas of the Skylab 3600-line/mm concave grating with multilayer and gold coatings were measured by using synchrotron radiation at an angle of incidence of 79 degrees and in the 28-42-A wavelength range. The blaze angle of the grating facets that faced the incident radiation was 3.1 degrees , and the average angle of the opposite facets was 6 degrees . For the gold grating, the -1 outside order had the highest efficiency of any diffracted order (excluding the zero order) over the entire wavelength range. Calculations of the grating efficiency indicated that the high efficiency in the -1 order resulted from the rather small angle (6 degrees ) of the facets opposite the incident radiation. For the multilayer grating, the efficiency in the on-blaze +2 inside order was enhanced in the 30-34-A wavelength region as a result of the high reflectance of the multilayer coating. The maximum efficiency in the +2 order occurred at the wavelength (32 A) corresponding to the peak of the reflectance of the multilayer coating on the facets facing the incident radiation. These results further demonstrate that a multilayer coating can be used to enhance the efficiency, in a selected wavelength range and in the on-blaze order, of a grating operating at a small grazing angle (11 degrees ).

Fringe formation and coherence of a soft-x-ray laser beam illuminating a Mach-Zehnder interferometer.

We investigated the fringe visibility produced by a Mach-Zehnder interferometer illuminated by a collisionally pumped yttrium x-ray laser operating at 15.5 nm. Fringe visibility varied as a function both of relative path delay and of relative spatial overlap of the beams. This visibility information was extracted quantitatively from several interferograms and analyzed to produce a characterization of the temporal coherence, yielding a gain-narrowed linewidth of 1.3 pm for the 15.5-nm laser transition and spatial coherence consistent with an effective source size of approximately 220 microm +/- 50% at the x-ray laser output.

Extreme-ultraviolet interferometry at 15.5 nm using multilayer optics.

The development of multilayer mirror technology capable of operating in the range of 3-30 nm and the construction of thin membranes with excellent uniformity and strength have made it possible to design and implement a Mach-Zehnder interferometer operating at 15.5 nm. We have tested this interferometer by using a soft x-ray laser as a source, and we show its use in probing high-density plasmas.

Normal-incidence efficiencies in the 115-340-Å wavelength region of replicas of the Skylab 3600-line/mm grating with multilayer and gold coatings.

Multilayer and gold coatings were applied to replicas of the 3600-line/mm ruled grating that was developed for the Naval Research Laboratory S082A spectroheliograph that was flown on the Skylab spacecraft. The Mo-Si multilayer coating had a peak normal-incidence reflectance of 50% at a wavelength of 136 Å. The normal-incidence efficiency of the multilayer-coated grating was measured by the use of synchrotron radiation and was compared with the efficiency of the gold-coated replica grating in the 115-340-Å wavelength region. The peak efficiency of the multilayer grating was 1.3% in the 133-137-Å region and was a factor of 65 higher than the efficiency of the gold grating. The multilayer and gold coated gratings, as well as an uncoated replica grating substrate, were characterized by the use of a scanning probe microscope. The rms microroughness of the uncoated and multilayer-coated gratings was 10 Å, and the microroughness of the gold grating was 16 Å.

Efficiency and long-term stability of a multilayer-coated, ion-etched blazed holographic grating in the 125-133-Å wavelength region.

The efficiency of an ion-etched blazed holographic grating was measured by the use of synchrotron radiation in the 125-133-Å wavelength range and at near-normal incidence. The grating had a Mo-Si multilayer interference coating that resulted in a peak normal-incidence efficiency of 13% in the second grating order and at a wavelength of 128 Å. This is the highest efficiency obtained to date from a multilayer-coated grating in this wavelength region and at normal incidence. These measurements are compared with similar measurements performed on the same grating 4.5 years later. Over this time the peak grating efficiency decreased from 13% to 8%, and this result is attributed to the decrease in the reflectance of the multilayer coating from 55% to 42%. Oxidation and contamination of the multilayer with carbon appear to be the causes of these losses. The groove efficiency of the grating substrate in the second order is 23%.

Polarization and efficiency of a concave multilayer grating in the 135-250-Å region and in normal-incidence and SeyaNamioka mounts.

A molybdenum/silicon multilayer coating was applied to a holographic ion-etched blazed grating substrate that had 2400 grooves/mm and a radius of curvature of 2.2 m. Scanning probe microscopy yielded the same surface microroughness (5 Å rms) before and after deposition of the multilayer. The efficiency and polarization performance of the grating was measured by synchrotron radiation in the 135-250-Å wavelength region. In the second grating order and the second Bragg order of the multilayer coating, the peak normal-incidence efficiency was 7.5% at a wavelength of 147 Å, representing a groove efficiency of 27%. At an angle of incidence of 35°, the polarization performance of the grating was 95%-100% in the 210-250-Å wavelength region. In a Seya-Namioka spectrometer mount at an angle of incidence of 30°-40°, the grating is a nearly perfect polarizing optical element in the wavelength bands between 125 and 300 Å, which are covered by the multilayer coating.

Measurement of Laser-Plasma Electron Density with a Soft X-ray Laser Deflectometer.

A soft x-ray laser (wavelength lambda = 15.5 nanometers) was used to create a moiré deflectogram of a high-density, laser-produced plasma. The use of deflectometry at this short wavelength permits measurement of the density spatial profile in a long-scalelength (3 millimeters), high-density plasma. A peak density of 3.2 x 10(21) per cubic centimeter was recorded.

Dual-waveband operation of a multilayer-coated diffraction grating in the soft x-ray range at near-normal incidence.

A concave diffraction grating (2400 grooves/mm) coated with a Si/Mo multilayer has an efficiency of 2.5% at 290 A and a resolving power of 14,000 in third order of 156 A.

Long-term stability of a Mo/Si multilayer structure.

The normal-incidence reflectance of a Mo/Si multilayer mirror, with peak reflectance near 130 A, was measured over a period of 20 months by using synchrotron radiation. The measured reflectances were unchanged over this period of time, and this indicates that the material layers and interfaces were stable.

On-blaze operation of a Mo/Si multilayer-coated, concave diffraction grating in the 136-142-A wavelength region and near normal incidence.

The efficiency and resolving power of a concave, 2400-groove/mm, blazed diffraction grating that had a Mo/Si multilayer coating were determined. The multilayer coating had a peak reflectance of 55% at 140-A near normal incidence. The efficiency of the multilayer grating for wavelengths in the 136-139-A range was 2% near normal incidence. This efficiency was a factor of 150 greater than the efficiency of a sister replica Au-coated grating in the same wavelength region. The resolving power of the multilayercoated grating in the third order of a V viii transition with a first-order wavelength of 140.451 A was 9100. Comparisons with the Au-coated grating indicated that the application of the multilayer coating did not affect the resolving power or the blaze angle.

X-ray laser microscopy of rat sperm nuclei.

The development of high brightness and short pulse width (< 200 picoseconds) x-ray lasers now offers biologists the possibility of high-resolution imaging of specimens in an aqueous environment without the blurring effects associated with natural motions and chemical erosion. As a step toward developing the capabilities of this type of x-ray microscopy, a tantalum x-ray laser at 44.83 angstrom wavelength was used together with an x-ray zone plate lens to image both unlabeled and selectively gold-labeled dried rat sperm nuclei. The observed images show approximately 500 angstrom features, illustrate the importance of x-ray microscopy in determining chemical composition, and provide information about the uniformity of sperm chromatin organization and the extent of sperm chromatin hydration.

Demonstration of x-ray microscopy with an x-ray laser operating near the carbon K edge.

High-brightness and short-pulse-width ( approximately 200 ps) x-ray lasers offer biologists the possibility of high-resolution three-dimensional imaging of specimens in an aqueous environment without the blurring effects associated with natural motions. As a first step toward developing the capabilities of this type of x-ray microscopy we have used a tantalum x-ray laser (lambda = 4.483 nm) together with an x-ray zone plate lens to image a test pattern. The observed image shows a detector-limited resolution of approximately 75 nm and paves the way to three dimensional biological imaging with high spatial resolution (20-30 nm).