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The Saturn pulsed power accelerator [R. B. Spielman et al., in Proceedings of the 2nd International Conference on Dense Z-pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3] at Sandia National Laboratories (SNL) and the Nova laser [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)] at Lawrence Livermore National Laboratory (LLNL) have been used to explore techniques for studying the behavior of ablator material in x-ray radiation environments comparable in magnitude, spectrum, and duration to those that would be experienced in National Ignition Facility (NIF) hohlraums [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)]. The large x-ray outputs available from the Saturn pulsed-power-driven z pinch have enabled us to drive hohlraums of full NIF ignition scale size at radiation temperatures and time scales comparable to those required for the low-power foot pulse of an ignition capsule. The high-intensity drives available in t...

The conversion efficiency of spectral emission from laser‐irradiated solid targets was investigated for short wavelength source development. The plasma brightness was quantified using absolutely calibrated detectors for 20 materials and spectra were obtained between 50 and 200 A. Laser parameters such as wavelength, pulse length, intensity, and spot size were systematically varied to establish a comprehensive database for source optimization. Qualitative differences in the underlying dominant emission features as a function of atomic number and laser wavelength were observed that accounted for the relatively high spectral conversion efficiencies produced. In the specific case of Sn, a conversion efficiency greater than 0.8%/eV has been observed in the technologically important region of λ=134.0 A using a laser intensity of 1–2×1011 W/cm2.

The development of a plasma environment that is appropriate for the study of laser‐plasma processes in laser‐fusion plasma is reported. A material (titanium) with medium atomic number (Z) was used to provide x‐ray measurements of radial and axial plasma symmetry as well as electron temperature. The electron density evolution was measured using stimulated scattering processes and odd half‐harmonic generation from probe lasers of different wavelengths. The plasmas were created by two‐sided irradiation of thin foils with 24 kJ of 351 nm laser light. When the peak electron density had decayed to about 4×1020 cm−3, the density profile was estimated to have a full width at half‐maximum of 2 mm and the electron temperature was measured to be about 3 keV using K‐shell spectroscopy. Two‐dimensional computer simulations were found to reproduce some features of both electron density and temperature evolution.

Good radiation drive symmetry will be crucial for achieving ignition in laboratory inertial fusion experiments. The indirect‐drive inertial confinement fusion (ICF) method utilizes the soft x‐ray field in a radiation‐containing cavity, or hohlraum, to help achieve a high degree of symmetry. Achievement of the conditions necessary for ignition and gain will require experimental fine tuning of the drive symmetry. In order to make tuning possible, a significant effort has been devoted to developing symmetry measurement techniques. These techniques have been applied to a series of experiments that give a graphic picture of the symmetry conditions in the complex hohlraum environment. These experiments have been compared with detailed, fully integrated theoretical modeling. The ultimate goal of this work is the detailed understanding of symmetry conditions and the methods for their control. Comparison with experiments provides crucial benchmarking for the modeling—a key element in planning for ignition.

A tentative schedule of experiments for the ignition campaign on the National Ignition Facility (NIF) has been developed. These experiments will be used to validate beam pointing and balance, to tune time history and symmetry of drive of NIF hohlraums, and to implode subignition and igniting targets. The initial target diagnostics are designed to validate beam pointing and to demonstrate the properties of the hohlraums.

Indirect‐drive inertial confinement fusion with laser beams requires focusing the beams through laser entrance holes (LEHs) onto the inside surface of the hi‐Z case comprising the hohlraum. The problem is how to illuminate the hohlraum so that the x‐ray flux upon the capsule is as highly symmetric as possible at all times. This approach involves putting four LEHs at the corners of an imaginary regular tetrahedron whose vertices lie on the spherical hohlraum and putting a multiple of three beams through each LEH. Strict tetrahedral symmetry is maintained, so that under any proper tetrahedral symmetry operation, beam cones map into beam cones and LEHs into LEHs. The radiation field can have no l=1, 2, or 5 spherical harmonic components. By using two sets of twelve beams with different pulse shapes, the single surviving l=3 and single surviving l=4 components of the radiation flux upon the capsule can be made to vanish at all times.

This paper examines the use of gas targets to create low‐ and mid‐Z plasmas ≊3 mm in size at 5% to 10% critical density for green and blue light (ne≊2×1020 to 1021 cm−3) with an electron temperature of several keV. At sufficiently high intensities (≊1014 W/cm2) the gas is ionized and heated by a laser absorption wave propagating faster than the sound speed. For pulses under 2 ns, the bulk of the plasma remains stationary, resulting in efficient heating minimizing density and velocity gradients, which are particularly important for instability thresholds in nonuniform plasmas. The propagation of a laser absorption wave in a preionized plasma is derived analytically. Ionization resulting from multiphoton and electron avalanche processes is studied by numerical methods and dimensional analysis. This establishes the length and time scales over which an absorption wave can be observed. Computer simulations, using the lasnex code, are presented for several implementations of this concept, applicable to the rele...

One‐ and two‐dimensional, time‐resolved x‐ray radiographic imaging at high photon energy (5–7 keV) is used to study shock propagation, material motion and compression, and the effects of shear flow in solid density samples which are driven by x‐ray ablation with the Nova laser. By backlighting the samples with x rays and observing the increase in sample areal density due to shock compression, the trajectories of strong shocks (∼40 Mbars) in flight are directly measured in solid density plastic samples. Doping a section of the samples with high‐Z material (Br) provides radiographic contrast, allowing a measurement of the shock‐induced particle motion. Instability growth due to shear flow at an interface is investigated by imbedding a metal wire in a cylindrical plastic sample and launching a shock in the axial direction. Time‐resolved radiographic measurements are made with either a slit‐imager coupled to an x‐ray streak camera or a pinhole camera coupled to a gated microchannel plate detector, providing ∼...

We have measured the 8–11‐keV emission spectra from plasmas produced by impinging 0.53‐μm, 100‐ and 200‐ps FWHM Gaussian laser pulses on targets of different materials. The experimental spectra from W and Zn are identified by comparison with local thermodynamic equilibrium plasma emission calculations.

Imaging faint companions (exoplanets and brown dwarfs) around nearby stars is currently limited by speckle noise. To efficiently attenuate this noise, a technique called simultaneous spectral differential imaging (SSDI) can be used. This technique consists of acquiring simultaneously images of the field of view in several adjacent narrow bands and in combining these images to suppress speckles. Simulations predict that SSDI can achieve, with the acquisition of three wavelengths, speckle noise attenuation of several thousands. These simulations are usually performed using the Fraunhofer approximation, i.e. considering that all aberrations are located in the pupil plane. We have performed wavefront propagation simulations to evaluate how out-of-pupil-plane aberrations affect SSDI speckle noise attenuation performance. The Talbot formalism is used to give a physical insight of the problem; results are confirmed using a proper wavefront propagation algorithm. We will show that near-focal-plane aberrations can significantly reduce SSDI speckle noise attenuation performance at several lambda/D separation. It is also shown that the Talbot effect correctly predicts the PSF chromaticity. Both differential atmospheric refraction effects and the use of a coronagraph will be discussed., 11 pages, 7 figures. To be published in Proc. SPIE Vol. 6269, p. 1147-1157, Ground-based and Airborne Instrumentation for Astronomy; Ian S. McLean, Masanori Iye; Eds

The success of recent static printing experiments at Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS) using the EUV LLC Engineering Test Stand (ETS) Set-2 optic has demonstrated the utility of synchrotron-based EUV exposure stations. Although not viable light sources for commercial lithography, synchrotrons provide clean, convenient, and extremely flexible sources for developmental microfield lithography. The great flexibility of synchrotron-based illumination arises from the fact that such sources facilitate active coherence reduction, thus enabling the coherence function, or pupil fill, to be actively sculpted in real time. As the commercialization of EUV progresses, the focus of developmental EUV lithography is shifting from low numerical aperture (NA) tools such as the 0.1-NA ETS to higher-NA tools such as the 0.3-NA Micro Exposure Tool (MET). To support printing with MET optics at the ALS, a new printing station has been developed, relying on a scanning illuminator to provide programmable coherence (pupil-fill) control. The illuminator is designed to operate up to a coherence factor (s) of 1 and support the full 200′600 design printed field of view. In addition to a new illuminator design, new focus sensing and dose-control systems have also been implemented. Here we describe the MET printing capabilities in detail and present preliminary printing results with the Sematech Set-2 MET optic.

Future extreme ultraviolet lithography (EUVL) steppers will, in all likelihood, have six-mirror projection cameras. To operate at the diffraction limit over an acceptable depth of focus each aspheric mirror will have to be fabricated with an absolute figure accuracy approaching 100pm rms. We are currently developing visible light interferometry to meet this need based on modifications of our present phase shifting diffraction interferometry (PSDI) methodology where we achieved an absolute accuracy of 250pm. The basic PSDI approach has been further simplified, using lensless imaging based on computational diffractive back-propagation, to eliminate auxiliary optics that typically limit measurement accuracy. Small remaining error sources, related to geometric positioning, CCD camera pixel spacing and laser wavelength, have been modeled and measured. Using these results we have estimated the total system error for measuring off-axis aspheric EUVL mirrors with this new approach to interferometry.

This report discusses one method of characterizing the variations in the physical thickness and refractive index of NIF doubler, tripler and switch crystals that are relatively thin ({approx}10mm thick). These particular measurements are difficult to perform with standard laser interferometers when the front and back substrate surfaces are near-parallel. A complicated interference pattern is formed from the interference of more than two beams due to the temporal coherence of the laser source. There are a number of methods that can be used to minimize this problem. They are referenced in a paper by Peter de Groot. In this report we discuss a method that eliminates the problem completely and show the results of measurements of two crystals.

We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response < 25 ps FWHM. A thin piece of scintillator material acts as a neutron-to-light converter. A zoom lens images light from the scintillator surface to a high-speed (15 ps) optical streak camera for recording. The zoom lens allows the scintillator to be positioned between 1 and 50 cm from a target. The camera simultaneously records an optical fiducial pulse which allows the camera time base to be calibrated relative to the incident laser power. Bursts of x rays formed by focusing 20 ps, 2.5 TW laser pulses onto gold disk targets demonstrate the detector resolution to be < 25 ps. We have recorded burn histories for deuterium/tritium-filled targets producing as few as 3 X 107 neutrons.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Soft X-ray Project Lithography (SXPL) may be used to fabricate high resolution structures for future integrated circuits. This technique will use a reflection mask which is a substrate coated with an x-ray multilayer mirror and patterned with a thin ({approximately}50 nm) layer of x-ray absorber. Mask patterning processes must not degrade the reflectivity of the x-ray mirror and mask repair techniques must be developed. The technical challenges of conventional reflecting optical imaging system designs are severe and mask technology can have a significant impact on this issue. Specifically, innovative mask designs can reduce the complexity of the optical system by decreasing the number of mirrors and replacing aspheric optical surfaces with spherical surfaces. We have developed a technique, called Encoded Mask Lithography, with which we have designed an optical system which uses only two (spherical) imaging mirrors and has 30 mm diameter field of view.

Optical interference lithography offers a robust patterning technology capable of achieving high spatial resolution over extremely large field sizes ( {approx}1 m ). Here, we compare two different approaches for fabricating arrays of holes using interferometric techniques. We show that by applying an image reversal process to standard two-beam interference lithography, arrays of high aspect ratio holes can be generated. This process scales to submicron periods and allows holes as small as 0.1 micron to be patterned. Next, we present an analysis of the multiple-beam approach for patterning holes. We demonstrate that while the formation of higher contrast intensity patterns is possible by interfering four or more beams, the shape and modulation depth of such patterns are inherently sensitive to relative phase variations.

X-ray production in the region ˜ 13 nm from laser-produced plasmas has been investigated as a source for projection x-ray lithography. The dependence of x-ray conversion efficiency on target material, intensity, and pulse length has been studied by using a 0.53-µm laser with a maximum of 0.3 J. A conversion efficiency of 1% into a 0.3-nm bandwidth has been demonstrated for Sn targets at intensities of ˜ 10(11) W/cm(2) by using a 7.5-ns pulse. Intensity scaling suggests that laser spot size and two-dimensional expansion are important for optimizing x-ray production at these low-irradiation intensities.

Laser‐produced plasmas are investigated as a source for soft x‐ray projection lithography. The dependence of conversion efficiency on target material, intensity, wavelength, and pulse width is determined using absolutely calibrated detectors. Conversion efficiency greater than 1% into a 2.2 eV bandwidth is demonstrated for Sn targets, fulfilling the system source requirements.

We present measurements of the X-ray emission characteristics of laser-irradiated flashlamp foils which are candidates to produce by resonant photoexcitation a population inversion in either a neon or fluorine lasant gas. Using the Shiva 1.06 μm laser, we heated Fe, Cr, and Ni foils to study tile brightness and centroid energies of X-ray lines stemming from L-M transitions. Results indicate that appropriately bright and uniform sources can be produced.

Experiments on an underdense plasma irradiated with high-intensity 1.064-..mu..m laser light have demonstrated that instabilities operating near (1/4) the critical electron density can produce high-energy electrons. Experimental conditions were as follows: 7000-A CH foil targets, 2.5 x 10/sup 15/ W/cm/sup 2/, 900 psec, 400-..mu..m spot diameter. The 3..omega../sub 0//2 light and 40-keV x rays occurred simultaneously at t = -120 psec (laser peak at t = 0) and lasted only 300 psec full width at half maximum. Ten percent of the laser energy appeared as Raman light and 0.04% as 3..omega../sub 0//2 light.

In this article we describe the operation and applications of a framing camera capable of four separate two‐dimensional images with each frame having a 120‐ps gate width. Fast gating of a single frame is accomplished by using a wafer image intensifier tube in which the cathode is capacitively coupled to an external electrode placed outside of the photocathode of the tube. This electrode is then pulsed relative to the microchannel plate by a narrow (120‐ps), high‐voltage pulse. Multiple frames are obtained by using multiple gated tubes which share a single bias supply and pulser with relative gate times selected by the cable lengths between the tubes and the pulser. A beam‐splitter system has been constructed which produces a separate image for each tube from a single scene. Applications of the framing camera to inertial confinement fusion experiments are discussed.

Parylene (C/sub 8/H/sub 8/) disks have been irradiated with a 1.06-..mu..m laser at fluxes of 10/sup 15/--10/sup 17/ W/cm/sup 2/. The spatial and temporal scattered light distributions, x-ray spatial and spectral emission properties, and ion spatial and energy distributions were measured. The results, together with two-dimensional magnetohydrodynamic code simulations, imply absorption via collective processes, laser generation of suprathermal electrons, and transport inhibition consistent with the presence of megagauss-level thermoelectric magnetic fields. (AIP)

A focusing system which utilizes two f/0.47 doublets in conjunction with ellipsoidal mirrors produces two focusing cones with half angles of 81.5/sup 0/. This system has been used with the LLL Janus laser system to irradiate and implode DT filled glass microshells approximately 80 ..mu..m diameter. The purpose of the system was to provide more uniform heating of the pusher and compression of the fuel than had been obtained with Janus irradiated targets using f/1 lenses. Neutron yields of approximately 10/sup 7/ per event have been obtained and x-ray micrographs indicate tha the heating of the pusher was more uniform. Also the implosions are definitely more spherical than those obtained with the f/1 lenses. Data is also presented which add further confirmation to the importance of absorption by plasma wave resonance for non normal incidence of the laser light with the target.

Gold M‐band x rays with energies above the sulfur K edge of 2.472 keV create sulfur Kα fluorescence with a quantum efficiency of 8.1%. The sulfur fluorescer was a 600×1500‐μm rectangle about 1100 μm from the gold plate. It was 25 μm of C6H4S plastic shielded by 50 μm of beryllium. The absolute brightnesses of both the M‐band spectrum and of the fluorescence line were measured by separate spectrographs. The spectrograph measuring the fluorescence did not have a direct line of sight to the hot gold. These measurements were made with 3512‐A laser light irradiating the gold plate for 1 ns over a number of intensities between 2×1014 and 1015 W/cm2.

Argus wavelength scaling experiments have been performed on low (Be) and high (Au) Z disk targets with laser wavelengths of 1.06, 0.53, and 0.35 µm. The laser provided a 700-psec pulse with up to 100 J at 1.06 µm, 200 J at 0.53 µm, and 40 J at 0.35 µm. Laser intensities on target ranged from 3×1013 to over 3×1015 W/cm2, using an f/2.2 focusing system. One goal of the experiments was to measure the levels of the parametric instabilities which generate suprathermal electrons as a function of both laser wavelength and intensity.

The absorption of 1.06 μ light focused on small C8H8 discs has been measured in the intensity range of 1015 – 1017 W/cm The data confirms the importance of collective plasma effects in determining the absorption of intense light. The measured absorption efficiencies are in the range of 30–40%, and the scattered light has a polarization dependence. The measured absorptions are shown to be inconsistent with classical inverse bremsstrahlung. Both the magnitude of the absorption and the observed polarization dependence of the scattered light are shown to be consistent with recent calculations of light absorption via collective processes. Comparisons are made, and improved models of the light absorption are discussed with reference to the data. In addition, the heated electron energies deduced from the X-ray data are consistent with those expected via collective processes.

Short, bright pulses of x-ray line emission are needed for flash radiography of laser-fusion targets. The experiments described here were carried out with the nominal laser pulse lengths of 60 and 120 ps. The M\ensuremath{\rightarrow}L spectra were for Y (2.00--2.35 keV), Pd (2.95--3.46 keV), and Cs (4.43--5.15 keV), and the L\ensuremath{\rightarrow}K spectra were for Cl (2.790 keV), Ti (4.749 keV), Mn (6.180 keV), and Ni (7.804 keV). The L\ensuremath{\rightarrow}K energies are for the 1s2p thinsp${;}^{1}$${P}_{1}$\ensuremath{\rightarrow}1${s}^{2}$ ${}^{1}$${S}_{0}$ transition. Both the duration and the absolute brightness of the x-ray line emission were measured. Even at 60 ps, the x-ray flashes from Y, Pd, and Ti were all bright and of duration comparable to or shorter than the laser pulse length. In particular, the Pd M\ensuremath{\rightarrow}L lines were as bright as 2\ifmmode\times\else\texttimes\fi{}${10}^{12}$ photons/j? and the Ti L\ensuremath{\rightarrow}K lines as bright as 5\ifmmode\times\else\texttimes\fi{}${10}^{10}$ photons/j?.

Spatial and temporal multiplexing of a 10-TW Nd:glass amplifier chain is described. A method of sharing the laser aperture between an x-ray backlighter pulse and a target heating pulse is demonstrated.

Temporally and spectrally resolved measurements of stimulated Raman scattering from high‐intensity, 0.532 μm laser–plasma experiments on disk targets are reported. The observed scattering is principally from densities below quarter‐critical, and is observed to occur nearly simultaneously over a wide range of wavelengths (0.72 μm

In this paper a study of stimulated Raman scattering (SRS) from relatively planar plasmas irradiated with short‐wavelength (0.53 μm) laser light is reported. The Novette Laser Facility [Laser Part. Beams 3, 173 (1985)] produced several kilojoules of light in 1 nsec, which allowed it to irradiate a large spot with enough intensity to produce significant Raman scattering. These experiments measured the fluence, angular distribution, spectrum, and timing of the Raman light, as a function of the average laser intensity. Reductions in the Raman fluence at low laser intensity are attributed to collisional damping. The measured SRS fluence was larger than that predicted from convective amplification of bremsstrahlung noise, as calculated using the average properties of the laser beam and the plasma. Possible contributions to the observed scattering from enhanced noise, Raman scattering within filaments, and the absolute Raman instability at density extrema are discussed.