Phase Zone Plate Research Articles

Use of low-density foams as pressure amplifiers in equation-of-state experiments with laser-driven shock waves

The applicability of foams to equation of state experiments with laser-produced shocks has been studied. The pressure increase due to impedance mismatch at the payload-foam interface was measured experimentally using sub-ns laser pulses smoothed with phase zone plates. Foams of density in the range 5-900 mg/cm(3) and of thicknesses of 50-150 microm were used. A model has been developed to study pressure amplification and the conditions under which the shock is stationary. Two-step two-material targets, allowing simultaneous measurements of the shock velocities in the two materials, were then used to obtain relative equation of state data. Pressures higher than 100 Mbar were achieved in gold.

Foam-induced smoothing studied through laser-driven shock waves

The influence of foams on the uniformity of laser energy deposition has been studied by measuring laser-driven shock waves breakout from foam-aluminum layered targets. Well characterized laser nonuniformities have been produced first by using phase zone plates to get a smooth beam and then by inserting different opaque grids before the foam. Smoothing has been studied as a function of foam density and grid materials (producing different radiative effects).

Equation of state data for gold in the pressure range <10 TPa

We report experimental data on the equation of state of gold in the pressure range 2--10 TPa obtained using laser-driven shock waves. The experiments have been realized using an iodine high-power laser with subnanosecond pulses and techniques like phase zone plates and hohlraums to produce spatially uniform shocks. Our data are compared with existing equation of state models.

EOS Data Experiments for Plastic Foams Using Smoothed Laser Beams

The importance of foams on laser-produced plasmas has been recently pointed out. In this paper EOS measurements of plastic porous materials have been experimentally determined using ns laser pulses smoothed with phase zone plates. Foams of density in the range 50-200 mg cm-3 and thickness about 20 microns were used. An original scheme for the targets has been designed which allowed us to obtain, for the first time, EOS data for pressures between 0.2-0.8 Mbar. Results are discussed and compared with EOS models.

Feasibility of transmission x-ray microscopy at 4 keV with spatial resolutions below 150 nm

The feasibility of a transmission x-ray microscope operating in the 3-7 keV photon energy range using phase zone plates (ZPs) has been tested. It has been demonstrated that, at a photon energy of 4 keV, structures smaller than 150 nm can be resolved with good contrast using exposure times in the second to minute range. A large diameter gold ZP was used as condenser and a tungsten ZP with an outermost zone width of 128 nm was used as a high spatial resolution imaging objective lens. Images with a field size of 10×10 μm2 were acquired using a charge coupled device camera optically coupled to a phosphor screen. The corresponding pixel size in the object plane was 70 nm.

Equation of state data experiments for plastic foams using smoothed laser beams

The importance of foams in laser produced plasmas has been recently pointed out in both Inertial Confinement Fusion (ICF) and astrophysics laboratory dedicated experiments. In this paper, Equation of State (EOS) data measurements of plastic porous materials have been experimentally determined using ns laser pulses smoothed with Phase Zone Plates (PZP). Foams of density in the range 20–400 mg/cm3 and thickness about 20 μm were used. A new original scheme for the targets has been designed which allowed, for the first time with laser, EOS data to be obtained for pressures ranging from 0.1 to 2.5 Mbars. Results are discussed and compared with available models.

Shock impedance matching experiments in foam-solid targets and implications for “foam buffered ICF”

We studied the influence of foams on laser produced shocks. Experiments were performed at LULI using a Nd laser converted to second harmonic, and at MPQ (Max Planck Institut für Quantenoptik) using the iodine Asterix laser converted to third harmonic. In both cases, sub-ns lasers with pulse energies of several tens of joules were focused on large focal spots (hundreds of microns) to reduce 2D effects. The laser beams were optically smoothed with phase zone plates (PZP) and directly focused on layered targets made of a foam layer on the laser side and a stepped Al layer on the other side. A visible streak camera was used to detect shock breakthrough at the base and at the step of the Al target, allowing shock velocity to be determined. Using the well known SESAME Al equation of state, we determined shock pressure. A stronger pressure increase was measured when foam was present, compared to what was obtained by focusing the laser beam directly on the Al target. This was due to the impedance mismatch effect at the Al-foam interface.

Nanometer focusing of hard x rays by phase zone plates

Focusing of 8 keV x rays to a spot size of 150 and 90 nm full width at half maximum have been demonstrated at the first- and third-order foci, respectively, of a phase zone plate (PZP). The PZP has a numerical aperture of 1.5 mrad and focusing efficiency of 13% for 8 keV x rays. A flux density gain of 121 000 was obtained at the first-order focus. In this article, the fabrication of the PZP and its experimental characterization are presented and some special applications are discussed.

A Fresnel Phase Zone Plate of Polymer‐Network Stabilized Liquid Crystals

AbstractA simple structure for a Fresnel phase zone plate is proposed using the techniques of polymer‐network stabilized liquid crystals. This kind of structure can give a high value of diffraction efficiency and the diffraction light intensities can be controlled electrically. The detail fabrication process and experimental results will be given.

X-ray microdiffraction studies to measure strain fields in a metal matrix composite

An x-ray diffraction microscope (XDM) has been used to map the strain field in a fiber-reinforced composite material. The monochromatic x-ray (11 keV) beam was focused by a phase zone plate to produce a focal spot of 1×4 μm2 on the specimen. The microfocusing method using a zone plate enables the XDM to produce a high spatial resolution of ∼1 μm. The change in the peak position of diffraction patterns due to interatomic spacing change, caused by stress in the sample, was measured by using a two-dimensional charge coupled device detector. The radial residual strain field in the fiber-reinforced composite (SCS–6/Ti–14Al–21Nb) was measured from diffraction patterns with a sensitivity of ∼10−4 and an average standard deviation of 9.4×10−5.

Dynamics of laser produced shocks in foam–solid targets

The influence of foams on laser shocks was studied with ns laser pulses smoothed with phase zone plates and focused onto layered foam–aluminum targets. Foams of 5–200 mg/cm3 density and 60 μm thickness were used. A strong pressure increase was measured with the foam in comparison to focusing the beam directly onto aluminum due to impedance mismatch at the aluminum–foam interface. Below a particular density, the measured pressure decreased as a result of hydrodynamics effects. Results are compared with computer simulations.

Design and fabrication of Fresnel zone plates with large numbers of zones

The advent of high-brightness x-ray sources in the 10–40 keV region opens new possibilities of experiments with microbeams. Techniques to form these focused beams may be based on glancing mirrors, phase elements, or diffractive optics, in particular Fresnel zone plates (FZPs). Because of the long focal length and large acceptance, FZPs designed to work in the hard x-ray region tend to have quite large diameters and large numbers of zones. For instance, the zone plate described in this article has a 1860 μm diam, a focal length of f=3 m (for 8 keV), and 1860 zones. On a standard pattern generator, circular shapes are always approximated as simpler structures. The tolerance requirement for shape and positions of zones depends on the number of zones, and it is necessary to guarantee that the circular structures are approximated to the required degree of accuracy while keeping the size of the data structure to a reasonable size for processing by the exposure system. For instance, if polygons are used to approximate circular zones, a formula for the minimum acceptable number of polygon sides can be derived. An x-ray mask for a Fresnel phase zone plate (FPZP) with 1860 zones was designed directly in Cambridge source pattern data format and fabricated using the Leica Cambridge e-beam tool installed in the CXrL. The zone plates presented in this article were designed for hard x rays, and multilevel x-ray lithography was employed as a fabrication technique to form absorber thickness sufficient to provide the necessary phase shift. Minimum gold features of 0.25 μm with thicknesses of 1.6 and 3 μm, were formed to be used with 8 and 20 keV photons, respectively. Finally, in order to estimate the quality of the zone plates during fabrication, a scanning electron microscope based moiré method was used.

Color temperature measurement in laser-driven shock waves

A simultaneous measurement of color temperature and shock velocity in laser-driven shocks is presented. The color temperature was measured from the target rear side emissivity, and the shock velocity by using stepped targets. A very good planarity of the shock was ensured by the phase zone plate smoothing technique. A simple model of the shock luminosity has been developed in order to estimate the shock temperature from the experimental rear side emissivity. Results have been compared to temperatures obtained from the shock velocity for a material of a known equation of state.

X-ray Optics Developments at the APS for the Third Generation of High-Energy Synchrotron Radiation Sources

Third-generation hard-X-ray synchrotron radiation sources simultaneously provide both a need and an opportunity for the development of new short-wavelength optical components. The high power and power densities of the insertion-device-produced X-ray beams have forced researchers to consider what may seem like exotic approaches, such as cryogenically cooled silicon and highly perfect diamond crystals, to mitigate thermal distortions in the first optical components. Once the power has been successfully filtered while maintaining the high beam brilliance, additional specialized optical components can be inserted into the monochromatic beam that take advantage of that brilliance. This paper reviews the performance of such optical components that have been designed, fabricated and tested at the Advanced Photon Source, starting with high-heat-load components and followed by examples of several specialized devices, such as an meV resolution (in-line) monochromator, a high-energy X-ray phase retarder and a phase-zone plate with submicrometer focusing capability.

Fabrication of a hard x-ray sputtered-sliced Fresnel phase zone plate

A Fresnel phase zone plate for hard x ray was fabricated by physical vapor deposition alternating transparent and opaque layers onto a fine gold wire core 47 μm in diameter. The zone plate, which is comprised of 25 pairs of alternating Ag and C layers, is designed to operate with a focal length of 124 mm for a parallel beam at 8.1 keV. The thickness of the zone plate is less than 10 μm and is capable of operating as a phase zone plate. Using the brilliant monochromatized x-ray beam from the TRISTAN Main Ring, with an undulator, the minimum focal spot size attained for the first order focal beam was 0.5 μmφ. The light collecting efficiency was determined to be near 11%.

Indirect and direct laser driven shock waves and applications to copper equation of state measurements in the 10-40 Mbar pressure range.

High quality shock waves with direct- and indirect-laser drive were generated. We used the phase zone plate smoothing technique in the case of direct drive and thermal x rays from laser heated cavities in the case of indirect drive. The possibility of producing homogeneous, steady shock waves without significant preheating effects with both methods has been proved. By using such shocks, copper equation of state measurements have been performed up to 40 Mbar, which was previously obtained only with nuclear explosions. \textcopyright{} 1996 The American Physical Society.

ゾーンプレートを用いたモノクロメータ

Monochromators making use of a Fresnel zone plate and a phase zone plate as the dispersing element were fabricated on trial. The monochromators had a pair of pinholes or optical fibers of 0.01 mm diameter for entrance and exit of light. The properties of the monochromators were examined by investigating the shape of spectra of mercury and cadmium discharge lamps in the visible region taking notice of the effects of central stops on the zone plate. Central stops were effective to reduce wings of spectral lines.

Nanostructuring high resolution phase zone plates in nickel and germanium using cross-linked polymers

Nanostructuring high resolution phase zone plates in nickel and germanium using cross-linked polymers

Binary phase zone plate designs using calculations of far-field distributions

Binary phase Fresnel zone plate arrays have been used recently to generate circular top hat intensity profiles for high intensity laser irradiation of targets. A simple analysis of these binary phase zone plates using diffraction theory is presented and used both to optimise the uniformity of the focal spot by modifying the Fresnel zone structure and to produce noncircular foci.

Development of a hard x-ray imaging microscope

A hard x-ray imaging microscope based on a phase zone plate has been developed and tested. The zone plate, with a 5 cm focal length and a 0.2 μm smallest linewidth, was used to image 8 keV x rays from the samples. The imaging microscope can be used to obtain nearly diffraction-limited resolution over the entire imaging field, and its resolution is almost independent of source size and source motions. We have tested such an imaging microscope, and a resolution of about 0.4 μm was obtained. The images were obtained with an exposure time of less than 1 min, for a magnification factor of 30 in the x rays. The x rays were then converted into visible light, and another 7 times magnification were obtained by using a lens system coupled to a charge coupled device camera. The results from the imaging microscope, and possible applications, will be discussed.