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The propagation of energetic electrons from the focal spots of intense picosecond laser pulses was studied using targets consisting of planar foils and fine metal wires. High-resolution K-shell spectra of elements with atomic numbers in the range 46–74 (Pd to W) and with energies from 21 keV to 69 keV were recorded by a Cauchois-type spectrometer using a curved transmission crystal. The K-shell spectra resulted from the collisional ionization of 1 s electrons by energetic electrons that were generated in the laser focal spot and propagated into the planar foil region beyond the focal spot or into the metal wires adjacent to an irradiated wire. The lateral spread of the energetic electrons from the focal spot was determined from the source broadening of the K spectral lines and from the relative intensities of the K spectra from an irradiated wire and neighboring wires of different metals. The propagation distances up to 1 mm in a variety of materials indicated electron energies up to 1 MeV were generated in the laser focal spot. Inhibited propagation in an electrically insulating material was observed that results from a weak return current and incomplete space charge neutralization.

Conversion efficiencies of laser light into K x-ray radiation are used to characterize laser-solid interactions e.g. in measurements with back-lighter targets in Inertial Confinement Fusion research or in ultra short x-ray science where ultra short laser pulses are used to create x-rays for investigation of dynamic processes. In our measurements we observed high energy (few tens of keV) K x-ray radiation of element pairs created upon impact of a 1 ps, 100 J laser pulse on the target surface. The high-energy electrons created in this interaction ionise and excite the target material. We have used high purity alloy foils of Pd and Ag, as well as In and Sn and crystals of CsI and rare earth molybdates as target materials. Both constituents of these targets were simultaneously excited in one shot. The K x-ray radiation was dispersed and detected with the LCS (LULI Crystal Spectrometer), a Cauchois-type cylindrically bent transmission-crystal spectrometer. Measuring ratios in the x-ray spectra permits determination of relative conversion efficiencies for pairs of elements under identical laser-target interaction conditions.

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

The Nike KrF laser, with its very uniform focal distributions, has been used at intensities near 10 14 W/cm 2 to launch shock waves in polystyrene targets. The rear surface visible light emission differed between clear polystyrene (CH) targets and targets with a thin (125 nm) Al coating on the rear side. The uncoated CH targets showed a relatively slowly rising emission followed by a sudden fall when the shock emerges, while the Al-coated targets showed a rapid rise in emission when the shock emerges followed by a slower fall, allowing an unambiguous determination of the time the shock arrived at the rear surface. A half-aluminized target allowed us to observe this difference in a single shot. The brightness temperature of both the aluminized targets and the non-aluminized targets was slightly below but close to rear surface temperature predictions of a hydrodynamic code. A discussion of preheat effects is given.

Nike is a multi-kilojoule KrF laser with very high beam uniformity (ΔI/I< 0.2% with all 36 overlapped beams), and the capability to accelerate relatively thick targets on a low adiabat under conditions scalable to direct drive ICF. In a first set of experiments we determined the effect of the imprinting by varying the uniformity of the foot of the laser pulse and measuring the growth of the subsequent Rayleigh-Taylor instability. We found that the lower the imprint, the longer the mass modulations take to reach a given level. This is in quantitative agreement with our 2-D hydrodynamics simulations. The results are promising for direct drive with a very uniform laser.

The main goal of this paper is to present experimental results on comparison of lasing efficiency for Li III 13.5 nm (2-1 transition) line in LiF microcapillary plasmas using 0.25 and 1 /spl mu/m subpicosecond pumping lasers. A formula for soft X-ray laser efficiency calculation is presented and used for such comparisons. The results for discharge created preplasma in L=4 mm and L=14 mm microcapillaries are also presented and compared with the results for laser created preplasma.

A portable hard x-ray source has been developed for nondestructive testing, medical imaging, and flash x-ray radiography. The source is powered by a Marx generator that produces a 200 kV, 1.2 kA pulse of 60 ns full width at half maximum. The x-ray tube is composed of a tungsten anode and a mesh cathode. The time dependence of the voltage, current, and x-ray emission were measured and were in good agreement with computer simulations. The simulation model accounted for the 15 capacitors and 15 spark gap switches of the Marx generator and the perveance of the electron flow across the anode–cathode gap. The simulations indicated that the 5 J energy that was stored in the Marx generator was efficiently delivered to the x-ray tube. The measured x-ray exposure, 34 mR at a distance of 30 cm, was in good agreement with the calculated exposure. X-ray images are presented that demonstrate the capabilities of the x-ray source for medical imaging, nondestructive testing, and flash x-ray radiography.

The Nike laser group at the Naval Research Laboratory has an ongoing effort to improve and benchmark the radiation hydrodynamic simulations used to develop pellet designs for inertial confinement fusion. A new postprocessor, Virtual Spectro, has been added to the FAST code suite for detailed simulation of non-LTE spectra, including radiation transport effects and Stark line profile. This new combination enhances our ability to predict the absolute emission of soft x-rays. An absolutely calibrated transmission grating spectrometer and a high resolution grazing incidence spectrometer have been used to collect time integrated and time resolved spectra emitted by CH targets irradiated at laser intensities of ∼ 10 TW/cm 2 . Comparison between these observations and simulations using Virtual Spectro demonstrates excellent agreement (within factor of ∼ 1.5) for the absolute emission.

Plastic foils were irradiated by the NRL Nike KrF laser and were imaged in the x-ray and extreme ultraviolet regions with 2D spatial resolution in the 3–10 μm range. The CH foils were backlit by a silicon plasma. The silicon backlighter emission was recorded by an x-ray spectrometer, and the Si+12 1,865 eV resonance line emission was recorded by a fast x-ray diode. A spherically curved quartz crystal produced monochromatic images of the 1,865 eV radiation 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.

A spherical holographic ion-etched diffraction grating with low-blaze angle has been purchased for the purpose of vendor evaluation. We present the results of surface measurements made on the bare grating substrate using an atomic force microscope. The efficiency of the grating at grazing incidence and at EUV wavelengths was measured using a synchrotron light source. After coating the grating with a multilayer, the normal incidence efficiency was measured. The results of these measurements are compared to those obtained from samples from other vendors.

A Cauchois type hard x-ray spectrometer was developed that utilizes the (301) diffraction planes at an asymmetric angle of 23.51° to the normal to the surface of a cylindrically curved quartz transmission crystal. The energy coverage is tunable by rotating the crystal and the detector arm, and spectra were recorded in the 8 keV to 20 keV range with greater than 2000 resolving power. The high resolution results from low aberrations enabled by the nearly perpendicular angle of the diffracted rays with the back surface of the crystal. By using other asymmetric planes of the same crystal and rotating to selected angles, the spectrometer can operate with high resolution up to 50 keV.

High-resolution absorption spectra of radiatively-heated low-Z foils (CH and BN) have been recorded at the Nova II laser facility by a grazing-incidence spectrograph. Using a calibration curve for Kodak 101 photographic plates, the plate density was converted to relative intensity transmitted by the foil. Absorption spectra are presented for the elements B, C, and N. The absorption features near the nickel L edge in the wavelength region 11–15 A are also presented.

A zone plate composed of Mo zones having 4 mm outermost zone diameter, 100 nm outermost zone width, and supported on a silicon nitride membrane was characterized using monochromatic synchrotron radiation in the 2 to 20 nm wavelength range. The zero and first order efficiencies were measured and compared to ab initio calculations that account for the optical properties of the materials, the width and shape of the zones, and multiple-layer thin-film effects. It is shown that the thicknesses of the Mo zones and the membrane and the ratio of the zone width to zone period can be independently determined from the measured diffraction efficiencies in the zero and first orders and that the computational code can be used to reliably design zone plates that are optimized for applications such as solar irradiance monitors in the extreme ultraviolet region.

In an ionized atom the Kα and Kβ fluorescence lines have different, and usually slightly higher, energies than the same lines in a cold, un-ionized atom. The increase in fluorescence line energy Δ(hv) that pulsed power discharges can produce in high atomic number atoms is usually much smaller than the line energies hv themselves: typical numbers are hv = 60 keV and Δ(hv) = 10–20 eV, while the resolution obtained so far with a transmission crystal spectrometer developed for the purpose is around 100 eV. Hence any change in the energy of the fluorescence x-rays, from tungsten weakly ionized in the tungsten of the Plasma-Filled Rod Pinch (PFRP), could not be observed.

The efficiency of an ion-etched blazed holographic grating was measured by the use of synchrotron radiation in the 125–133-A 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 A. 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%.

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 A. 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-A wavelength region. The peak efficiency of the multilayer grating was 1.3% in the 133–137-A 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 A, and the microroughness of the gold grating was 16 A.

Chemical-vapor-deposited silicon-carbide mirrors were exposed to bombardment by 95-keV electrons and 100-keV protons with accumulated fluxes comparable with those expected in low-altitude Earth orbit for simulated periods of as many as 5 years. The reflectances of four mirrors were measured at five wavelengths (58.4, 73.6, 104.8, 121.6, and 161 nm) and at 11 angles of incidence from 5° to 80°. The electron and proton exposure resulted in no significant change in the reflectances of the mirrors.

The structure factors and normal-incidence reflectances of the alkali-metal-doped fulleride crystals M(6)C(60) (where M = K, Rb, or Cs) were calculated, and the peak reflectances are in the 2-20% range for incident wavelengths of 9-17 Å, which indicates that C(60) may be a promising transmissive (spacer) material for normal-incidence mirrors that have relatively high normal-incidence reflectance in the x-ray region.

Laser-produced plasmas were imaged by a microscope consisting of spherical, primary, and secondary mirrors in a Cassegrain-type optical configuration. The mirrors were coated with 40 periods of Mo and Si and had a peak reflectance of ∼60% at a wavelength of 130 A. Nb, Au, and Al targets were irradiated by as many as 24 beams of the Omega laser at the Laboratory for Laser Energetics at the University of Rochester. The images were recorded on Kodak 101 film, and the resolution was limited by the 10-µm emulsion grain size. Two different secondary mirrors produced images with a magnification of 0.8 or 2.2, and a variety of plasma emission features were recorded with 5-µm (0.6-arcsec) resolution in the target plane. The possibility of operating a similar microscope in the wavelength region of 34-50 A is discussed.

Using synchrotron radiation, we determined the optical constants of thin silicon films in the wavelength region near the silicon L(2,3) absorption edge. The extinction coefficient was determined from the transmittance of a thin, unbacked silicon film. The refractive index was determined from the reflectance of a sample consisting of an evaporated silicon film on gold. The thickness of the evaporated silicon film was chosen so that an interference feature appeared in the wavelength region above the edge where the silicon is transmissive. The shape of the interference feature is sensitive to the optical constants of silicon near the edge.

Saran foils of 4000-A thickness have been fabricated and used as transmission filters in the extreme ultraviolet spectral region. The transmittances of the Saran foils were determined for the 20–620-A wavelength region. The foils transmitted radiation with wavelengths between the L absorption edge of chlorine at 61.4 and ~120 A.

An experimental method is described in which a grazing incidence spectrograph is used to obtain spatially resolved spectra of laser heated plasmas in the 6-370-A region. In the experiment, small target spheres were irradiated by tightly focused laser beams. A tilted grazing incidence elliptical mirror placed 1.3 m from the target focuses the plasma radiation on the spectrograph slit at a distance of 0.7 m producing a useful degree of spatial resolution in the recorded spectral lines. The spectrum from a copper target is presented together with an X-ray pinhole camera image of the plasma.

Warm, dense plasmas can be produced at the tip of a plasmafilled rod-pinch diode1 (PFRP) on the Gamble II generator at the Naval Research Laboratory. The PFRP concentrates a high current (500 kA), 2 MeV, 60 ns electron beam at the pointed end of a 1 mm diameter tapered tungsten rod. At the time of maximum thermal energy density, the tungsten plasma parameters are estimated to be: 12 times ionized, near solid density (20 g/cm3), 25 eV, and 2.4 MJ/cm3.

We have performed measurements of the absorption spectra of x-ray heated thin (1 μm) CH foils in the spectral region of the carbon K-edge (200-500 eV). One arm of the Nova laser is incident on a 0.25 μm thick Au foil, producing a soft x-ray source that radiatively heats the CH sample, placed in close proximity to the foil. Absorption spectra are obtained by viewing the soft x-rays from the Au foil, passing through the sample, with a 3 m grazing-incidence spectrometer. We observe strong absorption from bound-bound transitions, in qualitative agreement with calculations (OPAL). These measurements resolve questions raised in earlier work (Edwards J. et al., Europhys. Lett., 11 (1990) 631) where thicker samples (5 μm) led to absorption saturation and the formation of an "edgelike" structure near the position of the cold-carbon edge.

Transitions to the 3s23p2 ground configuration from 3s3p3 and 3s23p3d were identified in Ge XIX, Se XXI, Sr XXV, Y XXVI and Zr XXVII in the extreme-ultraviolet spectra emitted from linear plasmas that were produced using line-focused laser beams. A grazing-incidence spectrograph viewed the plasma in the axial direction. Energy values, determined from the observed combinations were compared with values obtained from multi-configuration Dirac-Fock calculations. Fitted energy levels of 3s23p2, 3s3p3 and 3s23p3d are also presented for elements between arsenic and molybdenum.

We compare the performance, stability and microstructure of Si/Gd multilayers containing thin barrier layers of W, B(4)C, or SiN(x), and determine that multilayers containing 0.6 nm thick W barrier layers at each interface provide the best compromise between high peak reflectance in the extreme ultraviolet near lambda=60 nm and good stability upon heating. The Si/W/Gd films have sharper interfaces and also show vastly superior thermal stability relative to Si/Gd multilayers without barrier layers. We find that these structures have relatively small compressive film stresses, and show good temporal stability thus far. We measured a peak reflectance of 29.7% at lambda=62.5 nm, and a spectral bandpass of Deltalambda=9 nm (FWHM), for an optimized Si/W/Gd multilayer having a period d=32.0 nm.

A 4 mm diameter zone plate was calibrated in the 7 nm to 18.5 nm wavelength range using synchrotron radiation. The efficiency in the focused 1 st order was measured using the scanning monochromator at the Naval Research Laboratory beamline X24C at the National Synchrotron Light Source. The measured efficiencies were compared to efficiencies calculated by accounting for the partial transmittance through the molybdenum zone plate rings and the resulting phase enhancement of the efficiencies. Accurate absolute efficiency calibrations enable the use of zone plates in EUV solar irradiance monitors having excellent stability against contamination and oxidation.

Transitions in the magnesium like ions of the elements Mo, Rh, Ag, Cd, In, Sn, Sb, I and Cs have been identified in the extreme ultraviolet spectra from laser-produced plasmas. The configurations considered are 3s2, 3s3p, 3p2, 3s3d, 3p3d, and 3d2. Based on the observations, fitted energy values of 34 levels are presented for all of the elements from Nb to Nd (Z = 41-60). The interaction of the J = 2 levels of the 3p2 and 3s3d configurations in the range Z = 45-55 is considered in detail.

Si/Gd multilayers designed as narrowband reflective coatings near 63 nm were developed. The highest peak reflectance of 26.2% at a 5 degrees incident angle was obtained at 62 nm, and the spectral bandwidth was 7.3 nm FWHM. The fits for x-ray and extreme ultraviolet reflectance data of Si/Gd multilayers indicate the possibility of silicide formation at the Si-Gd interfaces. B(4)C, W, and SiN were deposited as interface barrier layers to improve the reflectance of Si/Gd multilayers. More than an 8% increase in reflectance was observed from the interface-engineered Si/W/Gd and Si/B(4)C/Gd multilayers.

MoRu–Be multilayer coatings were applied to two diffraction gratings for the purpose of enhancing their normal-incidence efficiency in the 11.1–12.0-nm wavelength range. The grating substrates were replicas of a holographic master grating that had a blazed groove profile with 2400 grooves/mm and a 2-m radius of curvature. The relatively low average microroughness (0.8 nm) of the grating surfaces contributed to the relatively high groove efficiency of the grating substrates and the reflectance of the MoRu–Be multilayer coatings. The peak efficiency, measured with synchrotron radiation, was 10.4% in the second diffraction order at a wavelength of 11.37 nm.

The normal-incidence efficiencies of two 4800-grooves/mm ruled replica gratings, one with a dual-bandpass molybdenum/silicon multilayer coating and the other with a gold coating, were measured by use of synchrotron radiation in the 125–325-A wavelength region. The peak reflectance of the multilayer coating was 22% in the first Bragg order near 235 A and 28% in the second Bragg order near 126 A. The peak efficiency of the multilayer grating was 2.6% in the first diffraction order near 225 A and 0.3% in the second diffraction order near 125 A. The efficiencies of the multilayer grating were much higher than the corresponding efficiencies of the gold grating. The characterization of the surfaces of the gratings by atomic force microscopy indicated rms microroughness values in the 5–18-µm-1 frequency range of 12–20 A for the multilayer grating and 22–32 A for the gold grating. Both gratings had bumpy surface features larger than the nominal groove height. The rather large surface roughness and groove irregularities had a detrimental effect on the grating efficiencies.

We characterized a laminar grating with a Mo/Si multilayer coating by using synchrotron radiation and atomic force microscopy. The grating substrate had 2400 grooves/mm, 40-Angstrom groove depth, and 2080-Angstrom groove width. The microroughness of the grating substrate was 5 Angstrom rms. The multilayer coating was optimized to have peak normal-incidence reflectance at a wavelength near 150 Angstrom. For an angle of incidence of 10 degrees the peak grating efficiency was 16.3% in the +1 order and 15.0% in the -1 order. The efficiency in the zero order was lower by a factor of 40 owing to the excellent matching of the groove depth and groove width to the wavelength of the incident radiation. By dividing the grating efficiencies by the measured reflectance of the multilayer coating, we obtained inferred groove efficiencies of 34% and 32% in the +1 and -1 orders, respectively. (C) 1991 Optical Society of America.

A MoRu–Be multilayer coating was applied to a diffraction grating to enhance the grating’s normal-incidence efficiency near 11.4 nm wavelength. The holographic grating substrate had a blazed groove profile with 2400 grooves/mm and a microroughness of 0.8 nm. The efficiency in the second diffraction order, measured with synchrotron radiation, was 10.4% at a wavelength of 11.37 nm.

The diffraction efficiencies of a Fresnel zone plate (ZP), fabricated by Xradia Inc. using the electron-beam writing technique, were measured using polarized, monochromatic synchrotron radiation in the extreme ultraviolet wavelength range 3.4-22 nm. The ZP had 2 mm diameter, 3330 zones, 150 nm outer zone width, and a 1 mm central occulter. The ZP was supported by a 100 nm thick Si 3 N 4 membrane. The diffraction patterns were recorded by CMOS imagers with phosphor coatings and with 5.2 μm or 48 μm pixels. The focused +n orders (n=1-4), the diverging -1 order, and the undiffracted 0 order were observed as functions of wavelength and off-axis tilt angle. Sub-pixel focusing of the +n orders was achieved. The measured efficiency in the +1 order was in the 5% to 30% range with the phase-shift enhanced efficiency occurring at 8.3 nm where the gold bars are partially transmitting. The +2 and higher order efficiencies were much lower than the +1 order efficiency. The efficiencies were constant when the zone plate was tilted by angles up to ±1° from the incident radiation beam. This work indicates the feasibility and benefits of using zone plates to measure the absolute EUV spectral emissions from solar and laboratory sources: relatively high EUV efficiency in the focused +1 order, good out-of-band rejection resulting from the low higher-order efficiencies and the ZP focusing properties, insensitivity to (unfocused) visible light scattered by the ZP, flat response with off-axis angle, and insensitivity to the polarization of the radiation based on the ZP circular symmetry. EUV sensors with Fresnel zone plates potentially have many advantages over existing sensors intended to accurately measure absolute EUV emission levels, such as those implemented on the GOES N-P satellites that use transmission gratings which have off-axis sensitivity variations and poor out-of-band EUV and visible light rejection, and other solar and laboratory sensors using reflection gratings which are subject to response variations caused by surface contamination and oxidation.

A novel technique, utilizing thin films with protective capping layers deposited onto silicon photodiode substrates, has been developed to accurately determine the optical constants of reactive elements such as the rare earths and transition metals. Depositing protected layers on photodiode substrates has three primary advantages over the study of the transmittance of free-standing films and the angle-dependent reflectance of coatings on mirror substrates. First, it is easy to deposit a thin protective capping layer that prevents oxidation or contamination of the underlying reactive layer. Second, very thin layers of materials that have intrinsically low transmittance can be studied. Third, the optical constants are determined from the bulk properties of the protected layer and are not influenced by reflectance from the top surface that can be affected by oxidation or contamination. These and other benefits of this technique will be discussed, and results for La and Tb will be presented. The determined optical constants are significantly different from the CXRO and other tabulated values. The rare earth (lanthanide) elements with atomic numbers 57-71 have 5d or 4f open shells, and this open shell structure results in transmission windows in the extreme ultraviolet wavelength range >45 nm where materials typically have low transmittance. These transmission windows make possible the fabrication of a new class of multilayer interference coatings, based on rare earth elements, with relatively high peak reflectances and narrow reflectance profiles, both important factors for the imaging of solar and laboratory radiation sources with multilayer telescopes.

The optical constants (n, k) of the wavelength-dependent index of refraction N = n+ik = 1-δ+ik of Nd (Neodymium) and Gd (Gadolinium) are determined in the wavelength range of 3 nm to 100 nm by the transmittance method using synchrotron radiation. Nd and Gd films with thicknesses ranging from 5 nm to 180 nm were fabricated on Si photodiodes (which served as the coating substrates as well as the detectors) and capped with Si layers to protect these reactive rare earth elements from oxidation. The imaginary part (k) obtained directly from the transmittance measurement is used in the derivation of the real part (δ) of the complex index of refraction N through the Kramers- Kronig integral. The measured optical constants are used in the design of currently developed Nd- and Gd-based multilayers for solar imaging applications. Our results on Nd and Gd optical constants and the reflectance of some Nd- and Gd-based multilayers are presented.

The extreme ultraviolet (EUV) optical constants ( ) and ( ) of amorphous carbon were determined on the basis of transmission measurements at =18-450 eV, the first-principles calculation of the dielectric tensor at < 25 eV, and the Kramers-Kronig calculation of ( ). Our optical constants generally agree with the CXRO data, excluding the vicinity of the K-edge. First-principles analysis shows that two thresholds of absorption (at 284 eV and 291 eV) f ound in the present study are caused, respectively, by the - and - bonds. Their weights are controlled by an orientation of graphene sheets in a-carbon. Keywords: optical constants, anisotropic EUV absorption, electronic structure, graphene sheets. 1. INTRODUCTION. Analysis of carbon-based materials is important for many ecological, biological, and industrial applications. Electron energy loss spectroscopy (EELS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) provide valuable information about the arrangement and bonding of atoms, as well as about the electronic structure of carbon materials. Numerous examples of such investigations can be found in Refs. [1-3]. In these investigations the attention of researchers is focused on the shape of the carbon K-edge, while the absorption spectrum in a wide energy region, as well as the optical constants, remain unstudied. A different situation takes place for the applications of carbon-based materials in soft X-ray multilayer optics. In this case both optical constants ( ) and ( ), which characterize the complex refractive index n( )=1- ( )+i ( ), are important for multilayer design. In the present study we concentrated on the measurements of the optical constants of amorphous carbon (a-carbon). This material is widely used in soft X-ray multilayer optics at short wavelengths ( =4.4-6.0 nm) because of its transparency and low roughness. In particular, the highest normal incidence reflectivity 15 % has been obtained at these wavelengths for a Co-C multilayer mirror [4]. To further improve multilayer optics based on a-C, precise information about its ( ) and ( ) is required. Currently available optical constants of a-carbon are only those from the atomic scattering factors of elements [5]. Despite many advantages of the CXRO data [5], they are not precise near the absorption edges, where the effect of interatomic bonding is of importance. This fact is disappointing, as the working interval of reflective multilayers is normally placed just below the absorption edge. The present study provides the optical constants of amorphous carbon in a wide EUV region from 40 eV to 450 eV. The determination of ( ) and ( ) is based on our transmission measurement, which is supplemented by the first-principles calculation of the dielectric tensor at 25 eV. Particular attention is given to the spectral region near the K-edge of carbon. To interpret our transmission spectra in this region, we invoke the results of our first-principles calculation that allows connection of the shape of the absorption K-edge with the atomic bonding in a-carbon.

Narrowband SiC/Tb and Si/Tb multilayers are fabricated with as much as a 23% normal-incidence reflectance near a 60 nm wavelength and spectral bandpass (FWHM) values of 9.4 and 6.5 nm, respectively. The structural properties of the films are investigated using extreme ultraviolet and x-ray reflectometry and transmission electron microscopy. Thermal stability is investigated in films annealed to as high as 300 degrees C. Because of their superior thermal stability, relatively high reflectance, and narrower spectral bandpass, Si/Tb multilayers are identified as optimal candidates for solar physics imaging applications, where the peak response can be tuned to important emission lines such as O v near 63.0 nm and Mg x near 61.0 nm. We describe our experimental procedures and results, discuss the implications of our findings, and outline prospects for improved performance.

The responsivity of a type 6H-SiC photodiode in the 1.5-400 nm wavelength range was measured using synchrotron radiation. The responsivity was 0.20 A/W at 270 nm and was less than 0.10 A/W in the extreme ultraviolet (EUV) region. The responsivity was calculated using a proven optical model that accounted for the reflection and absorption of the incident radiation and the variation of the charge collection efficiency (CCE) with depth into the device. The CCE was determined from the responsivity measured in the 200-400 nm wavelength range. By use of this CCE and the effective pair creation energy (7.2 eV) determined from x-ray absorption measurements, the EUV responsivity was accurately modeled with no free parameters. The measured visible-light sensitivity, although low compared with that of a silicon photodiode, was surprisingly high for this wide bandgap semiconductor.

The validity of approximating the efficiency of a multilayer grating operating at close to normal incidence in the soft-X-ray–EUV range with a product of the relative grating efficiency by the reflectance of its multilayer coating has been studied by the rigorous integral method. The widely used approximated approach has until recently been considered accurate enough for analysis of short- wavelength normal-incidence multilayer-coate d gratings. Real gr atings employed in the soft-X-ray–EUV range are used to demonstrate the inap plicability of this approximation to an analysis of precise positions of efficiency maxima for the external ( n > 0) and internal ( n < 0) diffraction orders, despite the small ratios of wavelength and groove depth to period. The present authors have performed an analysis of the accuracy inherent in a derived simple expression for spectral separation of the same plus and minus orders with respect to the wavelength, order’s number, incident angle, period, and groove depth. The reason for the observed substantial (a few Angstrom or even nm) wavelength separation between the maxima of positive and negative orders is related to oblique, close-to-normal incidence of radiation on a grating operating in the short-wavelength spectral region and different angles of deviation of respective orders. The modeling carried out with the commercial code PCGrat e-S(X) v.6.1 permitted not only prediction of the separation between positive and negativ e orders for a multilayer Mo/Si 4200-gr/mm grating with AFM-measured trapezoidal groove profile, which is designed for operation in the EIS spectrometer on the Solar-B spacecraft, but obtaining a good agreement with synchrotron radiati on measurements, including high orders as well. A conclusion is drawn that high-precision calculations of the efficiency of multilayer normal-incidence soft-X-ray–EUV range gratings have in some cases to be performed, although this may require increasing the computation time by several times compared to the co mmonly used approximate approach. Keywords: diffraction grating, soft -X-ray–EUV spectroscopy, integral method, efficiency modeling, multilayer-coated X-ray optics

Efficiency measurements of a grazing-incidence diffraction grating, planned for the Constellation-X Reflection Grating Spectrometer (RGS), were performed using polarized synchrotron radiation at the NRL Brookhaven beamline X24C. The off-plane TM and TE efficiencies of the 5000 groove/mm MIT test grating, patterned on a silicon wafer, were measured and compared to the efficiencies calculated using the PCGRATE-SX code. The calculated and measured efficiencies are in agreement when using groove profiles derived from AFM measurements. The TM and TE efficiencies differ, offering the possibility of performing unique astrophysical science studies by exploiting the polarization sensitivity of the off-plane gratings. The grating calibrations demonstrate the importance of using polarized synchrotron radiation and code calculations for the understanding of the Constellation-X grating performance, in particular the effects of the groove profile and microroughness on the efficiency. The optimization of grazing incidence gratings, for both the off-plane and in-plane mounts, planned for the RGS and x-ray spectrometers on other missions will require detailed synchrotron measurements and code calculations.

Absolutely calibrated, time-resolved spectral intensity measurements of soft-x-ray emission (hnu approximately 0.1-1.0 keV) from laser-irradiated polystyrene targets are compared to radiation-hydrodynamic simulations that include our new postprocessor, Virtual Spectro. This new capability allows a unified, detailed treatment of atomic physics and radiative transfer in nonlocal thermodynamic equilibrium conditions for simple spectra from low-Z materials as well as complex spectra from high-Z materials. The excellent agreement (within a factor of approximately 1.5) demonstrates the powerful predictive capability of the codes for the complex conditions in the ablating plasma. A comparison to data with high spectral resolution (E/deltaE approximately 1000) emphasizes the importance of including radiation coupling in the quantitative simulation of emission spectra.

The computational design of multilayer-coated diffraction gratings for the extreme ultraviolet (EUV) wavelength region and the experimental performance of the coated gratings depend on the optical constants of the layer materials. While accurate optical constants are available for many commonly used materials, the EUV optical constants can in practice differ significantly from the tabulated values. This is generally true near absorption edges, for reactive materials that may be subject to oxidation or contamination, and for the longer EUV wavelengths (>30 nm) where molecular effects can be important. Normal-incidence gratings with Mo/Si coatings operating in the 17-21 nm and 25-29 nm wavelength ranges were successfully designed and fabricated for the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Solar-B mission, the first satellite instrument to carry a multilayer grating. Examples of multilayer gratings designed and fabricated for wavelengths 40 nm, using materials other than Mo/Si, will be given that have in many cases required the experimental determination of the optical constants owing to inaccuracies in the tabulated values.

We compare the reflectance and stability of multilayers comprising either Si/Mo, Si/Mo2C, Si/B4C, Si/C, or Si/SiC bilayers, designed for use as extreme-ultraviolet (EUV) reflective coatings. The films were deposited by using magnetron sputtering and characterized by both x-ray and EUV reflectometry. We find that the new Si/SiC multilayer offers the greatest spectral selectivity at the longer wavelengths, as well as the greatest thermal stability. We also describe the optimization of multilayers designed for the Solar-B EIS instrument. Finally, we compare experimental reflectance data with calculations and conclude that currently available optical constants cannot be used to adequately model the performance of many of these multilayers.

The chemical reaction of a sample with atmospheric gases causes a significant error in the determinantion of the complex refractive index n = 1 - delta + ibeta in the extreme-ultraviolet region. The protection of samples removes this effect but hampers the interpretation of measurements. To overcome this difficulty, we derive the exact dependences on film thickness of the reflectivity and transmissivity of a protected film. These dependences greatly simplify the determination of delta and beta when the spectra of several films with different thickness and identical protection are measured. They also allow the verification of the delta(omega) obtained from the Kramers-Kronig relation and even make the Kramers-Kronig method unnecessary in many cases. As a practical application, the optical constants of Sc and Ti are determined at h omega = 18-70 eV and 18-99 eV, respectively. The essential feature of our experimental technique is deposition of a film sample directly on a silicon photodiode that allows easy operation with both thin (approximately 10-nm) and thick (approximately 100-nm) films. The comparison of calculated reflectivities of Si-Sc multilayers with the measured values shows the high accuracy of the determined delta(omega) and beta(omega).

The design of Mo/Si and Mo/Y multilayers as EUV polarizers is presented. The polarization performance of these multilayers was calculated based on their optical properties at around Brewster angles. The polarization results of a silicon photodiode that was coated with an interface-engineered Mo/Si multilayer are described. The sensitivity of this specially-coated photodiode and its polarization responses were determined from both reflectance and transmittance of the multilayer coating, using synchrotron radiation. The multilayer reflected 69.8% of s-polarized light and only 2.4% of p-polarized light, therefore transmitted about 0.2% s-polarized light and 8.4% p-polarized light at 13.5 nm to the underlying photodiode substrate. A polarization ratio based on transmittance values, (Tp-Ts)/(Tp+Ts), of 95% was achieved with sufficiently high sensitivity. This result demonstrates the usefulness of Mo/Si multilayer-coated photodiodes as future EUV polarimeters.

The performance characteristics of a silicon photodiode (type AXUV100) were determined using the beamline X24C at the National Synchrotron Light Source. The diode sensitivity was measured in the temperature range of −92° C to +41° C and in the wavelength region of 3.0 nm to 88.2 nm. This work is important for understanding variations of the diode sensitivity in environments that are colder or hotter than ambient room temperature, such as on a spacecraft or under intense synchrotron or laser irradiation. In addition, the sensitivity of a AVUV100 diode with a multilayer interference coating was measured as a function of the polarization of the incident radiation and the angle of incidence. The Mo/Si multilayer coating, when operating at an angle of incidence of 45°, was designed to selectively transmit the P polarized radiation for detection by the underlying diode and to efficiently reflect the S polarization. The results demonstrate the ability to accurately measure the polarization of radiation within the reflectance profile of the multilayer centered at 13.5 nm. By optimizing the transmittance and reflectance profiles of the multilayer coating for the desired wavelength range and angle of incidence, this new multilayer‐coated photodiode technique can be used to measure the polarization of incident radiation from solar, astrophysical, synchrotron, or other laboratory sources over a wide range of extreme ultraviolet and soft x‐ray wavelengths.

It is now possible to reliably implement multilayer-coated diffraction gratings in spaceflight and laboratory spectrometers that operate at normal incidence and with high efficiency in the 9 nm to 40 nm wavelength range. The design and fabrication of the grating groove profile and the matching multilayer coating are based on computational modeling using the computer program PCGRATE. The multilayer gratings are characterized using atomic force microscopy and by measuring the diffraction efficiency using synchrotron radiation. Recent research has focused on multilayer coatings other than Mo/Si such as Sc/Si for 40 nm, MoRu/Be for 11 nm, and Mo/Y for 9 nm.

To improve the thermal stability of Si/Sc multilayer mirrors, thin layers of W were deposited at interlayer boundaries. Using X‐ray scattering and transmission electron microscopy, we studied the interaction of Si and Sc layers at elevated temperatures. It was shown that the W layers of 0.5–0.8 nm thickness form dense WSi2 barriers, which prevent a direct contact between Si and Sc and greatly slow down the formation of scandium silicides. Presented measurements show that Si/W/Sc/W multilayers fabricated by dc‐magnetron sputtering possess long thermal stability up to 250° C and the normal incidence reflectivity of 24 %.

Processes going on at elevated temperatures between Sc and Si layers in Sc/Si coatings are studied by X-ray scattering and cross-sectional transmission electron microscopy. It is shown that the W layers of 0.5-0.8 nm placed at Sc-Si interfaces form effective barriers preventing the penetration of Si into Sc. The effects of Si-Sc diffusion and W-barriers on the reflectivity of coatings are calculated in good agreement with experimental results. Presented measurements show that the Sc/W/Si/W multilayers with the period of 20.5 nm fabricated by dc-magnetron sputtering possess thermal stability up to 250 C and the normal incidence reflectivity of 24% at wavelengths about 40 nm.