Glenn E. Holland

High-resolution monochromatic x-ray imaging system based on spherically bent crystals.

We have developed an improved x-ray imaging system based on spherically curved crystals. It is designed and used for diagnostics of targets ablatively accelerated by the Nike KrF laser. A spherically curved quartz crystal (d = .?, R = mm) has been used to produce monochromatic backlit images with the He-like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 mum in selected places and 2-3 mum over a larger area. Time-resolved backlit monochromatic images of polystyrene planar targets driven by the Nike facility have been obtained with a spatial resolution of 2.5 mum in selected places and 5 mum over the focal spot of the Nike laser.

Efficiency of a grazing-incidence off-plane grating in the soft-x-ray region.

Efficiency measurements of a grazing-incidence diffraction grating in the off-plane mount were performed using polarized synchrotron radiation. The grating had 5000 grooves/mm, an effective blaze angle of 14 degrees, and was gold coated. The efficiencies in the two polarization orientations (TM and TE) were measured in the 1.5-5.0 nm wavelength range and were compared with the efficiencies calculated using the PCGrate-SX code. The TM and TE efficiencies differ, offering the possibility of performing unique science studies of astrophysical, solar, and laboratory sources by exploiting the polarization sensitivity of the off-plane grating.

On-blaze operation of a Mo/Si multilayer-coated, concave diffraction grating in the 136–142-Å 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 emission from plasmas created by smoothed KrF laser irradiation

The x‐ray emission from plasmas created by the Naval Research Laboratory Nike KrF laser [Phys. Plasmas 3, 2098 (1996) ] was characterized using imaging and spectroscopic instruments. The laser wavelength was 1/4 μm, and the beams were smoothed by induced spatial incoherence (ISI). The targets were thin foils of CH, aluminum, titanium, and cobalt and were irradiated by laser energies in the range 100–1500 J. A multilayer mirror microscope operating at an energy of 95 eV recorded images of the plasma with a spatial resolution of 2 μm. The variation of the 95 eV emission across the 800 μm focal spot was 1.3% rms. Using a curved crystal imager operating in the 1–2 keV x‐ray region, the density, temperature, and opacity of aluminum plasmas were determined with a spatial resolution of 10 μm perpendicular to the target surface. The spectral line ratios indicated that the aluminum plasmas were relatively dense, cool, and optically thick near the target surface. The absolute radiation flux was determined at 95 eV ...

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.

High-resolution x-ray imaging of planar foils irradiated by the Nike KrF laser

Thin plastic (CH) foils were irradiated by the Naval Research Laboratory Nike [Obenschain et al., Phys. Plasmas 3, 2098 (1996)] KrF laser and were imaged in the x-ray and extreme ultraviolet regions with two-dimensional spatial resolution in the 3–10 μm range. The CH foils were backlit by a silicon plasma. A spherically curved quartz crystal produced monochromatic images of the Si+12 resonance line radiation with energy 1865 eV that was transmitted by the CH foils. Instabilities that were seeded by linear ripple patterns on the irradiated sides of CH foils were observed. The ripple patterns had periods in the 31–125 μm range and amplitudes in the 0.25–5.0 μm range. The silicon backlighter emission was recorded by an x-ray spectrometer, and the 1865 eV resonance line emission was recorded by a fast x-ray diode. The multilayer mirror telescope recorded images of the C+3 1550 A emission (energy 8.0 eV) from the backside of the CH foils.

Absolutely calibrated, time-resolved measurements of soft x rays using transmission grating spectrometers at the Nike Laser Facility

Accurate simulation of pellet implosions for direct drive inertial confinement fusion requires benchmarking the codes with experimental data. The Naval Research Laboratory (NRL) has begun to measure the absolute intensity of radiation from laser irradiated targets to provide critical information for the radiatively preheated pellet designs developed by the Nike laser group. Two main diagnostics for this effort are two spectrometers incorporating three detection systems. While both spectrometers use 2500 lines/mm transmission gratings, one instrument is coupled to a soft x-ray streak camera and the other is coupled to both an absolutely calibrated Si photodiode array and a charge coupled device (CCD) camera. Absolute calibration of spectrometer components has been undertaken at the National Synchrotron Light Source at Brookhaven National Laboratories. Currently, the system has been used to measure the spatially integrated soft x-ray flux as a function of target material, laser power, and laser spot size. A...

Characterization of silicon photodiode detectors with multilayer filter coatings for 17 to 150 A

Silicon photodiode detectors with multilayer coatings were characterized using synchrotron radiation. The coatings were composed of thin layers of metals and other materials and were designed to provide wavelength bandpasses in the 17 - 150 angstrom wavelength region. The measured transmittances of the multilayer coatings are in good agreement with the calculated transmittances. The modeling accounts for the transmittance of the multilayer coating and the deposition of the radiation energy in the underlying silicon photodiode. Detectors with the following layer materials (and wavelength bandpasses were characterized: Fe/Al (17 - 30 angstrom), Mn/Al (19 - 30 Angstrom), V/Al (24 - 35 angstrom), Ti/C (27 - 40 angstrom), Pd/Ti (27 - 50 angstrom), Ti/Zr/Al (27 - 50 angstrom), Ag/CaF2/Al (36 - 50 angstrom), and Ti/Mo/C (50 - 150 angstrom).

Use of spherically bent crystals for Nike laser plasma spectral diagnostics and monochromatic imaging

A new x-ray imaging system based on spherically curved crystals has been developed. It is designed and used for diagnostics of targets ablatively accelerated by the Nike KrF laser. Applications of this instrument include spectroscopy with one-dimension of spatial resolution and two-dimensional monochromatic self-imaging and backlighting. The imaging system with various crystals of mica and quartz is used for plasma diagnostics of the main target and for characterization of potential backlighters. A spherically curved quartz crystal (2d equals 6.687 angstroms, R equals 200 mm) is used to produce monochromatic backlit images with the He- like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 micrometers in selected places and 2 - 3 micrometers over large area. Time resolved backlit monochromatic images of CH planar targets driven by the Nike facility have been obtained with 6 - 7 micrometers spatial resolution.

Absolutely calibrated vacuum ultraviolet spectra in the 150-250-nm range from plasmas generated by the NIKE KrF laser

High-resolution vacuum ultraviolet (VUV) spectra were recorded from plasmas generated by the NIKE KrF laser for the purpose of observing emission from the two-plasmon decay instability (TPDI) at 2∕3 the NIKE wavelength (165nm). The targets were irradiated by up to 43 overlapping beams with intensity up to ≈1014W∕cm2 and with beam smoothing by induced spatial incoherence (ISI). The targets consisted of planar foils of CH, BN, Al, Si, S, Ti, Pd, and Au. Titanium-doped silica aerogels in Pyrex cylinders were also irradiated. The spectra of the target elements were observed from charge states ranging from the neutral atoms to five times ionized. The spectrometer was absolutely calibrated using synchrotron radiation, and absolute VUV plasma emission intensities were determined. Emission from the TPDI at 165-nm wavelength was not observed from any of the irradiated targets. An upper bound on the possible TPDI emission was less than 4×10−8 the incident NIKE laser energy. The NIKE laser radiation backscattered fr...