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Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet (EUV) irradiation of 0.75-μm thick Al foil is investigated. The EUV radiation with the peak power density in the range of 0.19–0.54 TW/cm2 is provided by Z-pinch formed by W multiwire array implosion in the Angara-5-1 facility. Geometry of the experiment ensures that there are no plasma fluxes from the pinch toward the Al foil and plasma. The same EUV source is used as a back illuminator for obtaining the absorption spectrum of Al plasma in the wavelength range of 5–24 nm. It comprises absorption lines of ions Al4+, Al5+, Al6+, Al7+. Analysis of relative intensities of the lines shows that those ions are formed in dense Al plasma with a temperature of ∼20 eV. Dynamics of Al plasma has been investigated with transverse laser probing. We have also performed radiation-gas-dynamics simulations of plasma dynamics affected by external radiation, which includes self-consistent radiation transport in a plasma shell. The simulations show good agreement with an experimental absorption spectrum and with experimental data concerning plasma dynamics, as well as with the analysis of line absorption spectrum. This confirms the correctness of the physical model underlying these simulations.

Results from experimental studies on the implosion of arrays made of kapron fibers coated with different metals (Al, In, Sn, and Bi) are presented. It is shown that the power, total energy, and spectrum of radiation emitted by the imploding array depend on the number of metallized fibers and the mass of the metal layer deposited on them but are independent of the metal characteristics (density, atomic number, etc.). Analysis of frame X-ray images shows that the Z-pinches formed in the implosion of metallized kapron fiber arrays are more stable than those formed in wire arrays and that MHD perturbations in them develop at a slower growth rate. Due to the lower rate of plasma production from kapron fibers, the plasma formed at the periphery of the array forms a layer that plays the role of a hohlraum wall partially trapping soft X-ray emission of the Z-pinch formed in the implosion of the material of the deposited metal layer. The closure of the anode aperture doubles the energy of radiation emitted in the radial direction.

The effect of induced transparency of thin Al foils radiatively heated by intense extreme ultraviolet (EVU) radiation has been observed. The radiation of the plasma of Z-pinches appearing under the compression of tungsten liners at the Angara-5-1 facility has been used as the radiation that heats the Al foil (peak illumination on the foil ~0.55 TW/cm2) and is transmitted through it. The photoabsorption has been studied in the formed aluminum plasma at temperatures of ~10–30 eV in the density range of ~1–20 mg/cm3 in the wavelength range of ~5–24 nm. Absorption lines of Al4+...7+ ions have been identified in the experimental spectrum. In addition, radiative gas-dynamic simulations of the foil heating and expansion have been performed taking into account radiation transfer processes.

Conditions and applicability limits of a new method for formation of quasi-monochromatic, with a large solid angle of divergence, linear X-ray fluxes from laser-produced plasmas are considered. The method is based on a special combination of laser target elements and -absorption filters, when the spectra of [H]- and [He]-like ions are excited in laser-produced plasma and -absorption filters select only the resonance lines of these ions from the linear spectrum. Experimental and theoretical studies have shown that, in the fluxes formed, the degree of monochromatisation may reach at the radiation contrast ratio of 5 – 10 and angular divergence of .

Results are presented from experimental studies of the characteristics of the soft X-ray (SXR) source formed in the implosion of quasi-spherical arrays made of tungsten wires and metalized kapron fibers. The experiments were carried out at the Angara-5-1 facility at currents of up to 3 MA. Analysis of the spatial distribution of hard X-ray emission with photon energies above 20 keV in the pinch images taken during the implosion of quasi-spherical tungsten wire arrays (QTWAs) showed that a compact quasi-spherical plasma object symmetric with respect to the array axis formed in the central region of the array. Using a diffraction grazing incidence spectrograph, spectra of SXR emission with wavelengths of 20–400 A from the central, axial, and peripheral regions of the emission source were measured with spatial resolutions along the array radius and height in the implosion of QTWAs. It is shown that the emission spectra of the SXR sources formed under the implosion of quasi-spherical and cylindrical tungsten wire arrays at currents of up to 3 MA have a maximum in the wavelength range of 50–150 A. It is found that, during the implosion of a QTWA with a profiled linear mass, a redistribution of energy in the emission spectrum takes place, which indicates that, during 3D implosion, the energy of longitudinal motion of the array material additionally contributes to the radiation energy. It is also found that, at close masses of the arrays and close values of the current in the range of 2.4−3 MA, the average energy density in the emission source formed during the implosion of a quasi-spherical wire array is larger by a factor of 7 than in the source formed during the implosion of a cylindrical wire array. The experimental data were compared with results of 3D simulations of plasma dynamics and radiation generation during the implosion of quasi-spherical wire arrays with a profiled mass by using the MARPLE-3D radiative magnetohydrodynamic code, developed at the Keldysh Institute of Applied Mathematics, Russian Academy of Sciences.

Results are presented from experimental studies of the structure of the compressed plasma of a Z-pinch produced during the implosion of a foam-wire load at the current of up to 3 MA. The foam-wire load consisted of two nested cylindrical cascades, one of which was a solid or hollow cylinder made of low-density agar-agar foam, while the other was a wire array. The wall thickness of a hollow foam cylinder was 100–200 μm. The images of the pinch and its spectrum obtained with the help of multiframe X-ray cameras and a grazing incidence spectrograph with a spatial resolution were analyzed. Data on the spatial structure of the emitting regions and the soft X-ray (SXR) spectrum of the Z-pinch in the final stage of compression of a foam-wire load were obtained. The implosion modes characterized by the formation of hot regions during implosion of such loads were revealed. The characteristic scale lengths of the hot regions were determined. It is shown that the energy distribution of SXR photons in the energy range from 80 eV to 1 keV forms the spatial structure of Z-pinch images recorded during the implosion of foam-wire loads. It is revealed that the spectral density of SXR emission in the photon energy range of 300–600 eV from hot Z-pinch regions exceeds the spectral density of radiation from the neighboring Z-pinch regions by more than one order of magnitude. Groups of lines related to the absorption and emission of radiation by atoms and multicharged ions of carbon and oxygen in the outer foam cascade of a foam-wire load were recorded for the first time by analyzing the spatial distribution of the SXR spectra of multicharged ions of the Z-pinch. The groups of absorption lines of ions (C III, O III, O IV, and O VI) corresponding to absorption of SXR photons in the Z-pinch of a tungsten wire array, which served as the inner cascade of a foam-wire load, were identified. The plasma electron temperature measured from the charge composition of carbon and oxygen ions in the outer agar-agar foam cascade was 10–40 eV. During the implosion of foam-wire loads at currents of up to 3 MA, SXR pulses (hν > 100 eV) with a duration of 10 ns and peak power of 3 TW were detected. It is shown that the temporal profile of single-peak and double-peak SXR pulses can be controlled by varying the parameters of the outer and inner cascades of the foam-wire load.

Absorption spectroscopy was applied to wire-array Z-pinches on the 1 MA pulsed-power Zebra generator at the Nevada Terawatt Facility (NTF). The 50 TW Leopard laser was coupled with the Zebra generator for X-ray backlighting of wire arrays at the ablation stage. Broadband X-ray emission from a laser-produced Sm plasma was used to backlight Al star wire arrays in the range of 7–9 A. Two time-integrated X-ray conical spectrometers recorded reference and absorption spectra. The spectrometers were shielded from the bright Z-pinch X-ray burst by collimators. The comparison of plasma-transmitted spectra with reference spectra indicates absorption lines in the range of 8.1–8.4 A. Analysis of Al K-shell absorption spectra with detailed atomic kinetics models shows a distribution of electron temperature in the range of 10–30 eV that was fitted with an effective two-temperature model. Temperature and density distributions in wire-array plasma were simulated with a three-dimension magneto-hydrodynamic code. Post-processing of this code’s output yields synthetic transmission spectrum which is in general agreement with the data.

A comparison method of high-temperature plasma diagnostics, developed by Shevelko [Quantum Electron. 41, 726 (2011)] and Shevelko et al. [Plasma Phys. Rep. 34, 944 (2008)], is modified and applied for Mo laser-produced plasma analyses. This method consists in determining the electron temperature Te of the studied plasmas by comparing the spectra of the investigated radiation source with the spectra of well-diagnosed laser-produced plasmas recorded at different Te. The modified comparison method includes the theoretical modeling of X-ray spectra of laser-produced plasmas of different elements. The most complete correspondence between the structure of the theoretical spectrum and the experimental one is achieved by changing the single parameter in theoretical calculations—the electron temperature Te. Such a method made it possible to describe in detail the structure of the X-ray spectra of multiply charged Mo ions, improve the accuracy of measurements, and justify the methods used. In particular, for Mo laser plasma (3-2 transitions in Mo31+-Mo34+ ions), the electron temperatures determined experimentally by the comparison method (Te = 685 ± 55 eV) and calculated theoretically (Te = 650 eV) are in a very good agreement.

We investigate the spectral characteristics of new focusing multilayer structures used as dispersive elements in a high-transmission X-ray spectrometer with cylindrical geometry (Hamos scheme): W/B4C structures in a wavelength range of λ = 8.0−9.5 A and Cr/Sc structures in a range of λ = 30−40 A (the range is not accessible for natural crystals). The results of demonstration experiments on laser-produced plasma spectra recording are considered. It is shown that the luminosity of a Hamos spectrometer with multilayer dispersive elements is an order of magnitude higher than the luminosity of grazing-incidence grating spectrographs with a comparable spectral resolution.

The present study describes the data on the current implosion of arrays made of kapron fibers coated with layers of metals: Al, In, Sn, Bi. Experimental data on the energy and pulse power of soft X-ray radiation (SXR) in the axial and radial directions in the energy range 0.02–2 keV were obtained by two sets of XRD detectors [1]. Spectral characteristics of the SXR source in a Z-pinch implosion of kapron fiber arrays were obtained using a grazing incidence diffraction spectrometer (GIS) in the radial direction with spatial resolution along the radius of the array. It is shown that the presence of kapron fiber matter defines the characteristics of SXR emitted by a Z-pinch in the radial and axial directions. A distinctive feature of the time profiles of XRD signals, which measure the power of SXR in the axial direction, is the presence of the second peak, which is strongly suppressed in the radial direction. It was found that power, total energy and emission spectra depend on the amount of metal-coated fibers and the mass of the layer of metal deposited on them, but do not depend on the characteristics of the material: its density, atomic number, etc. Frames of X-ray images show that the Z-pinches obtained with metal-coated kapron fiber implosion are characterized by increased stability and a lower growth rate of MHD perturbations compared to wire arrays. Slower intensity of plasma production from kapron fibers [2] leads to the fact that the plasma formed in the fiber periphery out of its material forms a layer which acts as a hohlraum wall, locking in the SXR of the Z-pinch formed during the implosion of the material of the deposited layer. It is shown that the overlap of the anode aperture doubles emission energy in the radial direction.

In SRC RF TRINITI investigated implosion of cylindrical and quasi-spherical wire arrays. Such arrays are made of metal wires and plastic fibers both coated by metal. For three-dimensional quasi-spherical arrays implosion the technique was developed to produce wires or fiber with a given distribution of linear mass along the wires. That mass distribution needs for good implosion to the center of array. The wires and fibers was formed by spraying a metal on wire or fiber. We have also developed the technique of manufacture of only tungsten wire with a given distribution of mass per unit length.

The results of investigation of a capillary discharge plasma, used as a source of intense VUV radiation and soft X-rays, are presented. The plasma was generated during the discharge of low-inductance condensers in a gas-filled ceramic capillary. Intense line radiation was observed in a broad spectral range (30-400 A) in various gases (CO2, Ne, Ar, Kr, Xe). The absolute radiation yield for the xenon discharge was ~5 mJ (2π sr)-1 pulse-1 within a spectral band of width 9 A at 135 A. Such a radiation source can be used for various practical applications, such as EUV projection lithography, microscopy of biological objects in a 'water window', reflectometry, etc.

A compact focusing crystal spectrometer based on the von Hamos scheme is described. Cylindrically curved mica and graphite crystals with a radius of curvature of R=20 mm are used in the spectrometer. A front illuminated charge-coupled device (CCD) linear array detector makes this spectrometer useful for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength range of λ=1.8–10 A. Calibration of crystals and the CCD linear array makes it possible to measure absolute photon fluxes. X-ray spectra in an absolute intensity scale were obtained from Mg, Ti, and Fe laser-produced plasmas, with a spectral resolution λ/δλ=800–2000 for the mica and λ/δλ=200–300 for graphite crystal spectrometers. The spectrometer has high efficiency in a wide spectral range, it is compact (40 mm diam, 150 mm length), easy to align, and flexible. The spectrometer is promising for absolute spectral measurements of x-ray radiation of low-intensity sources (femtosecond laser-produced plasmas, micropinches, electron-beam–ion-trap sources, etc.).

New focusing short-period multilayer structures are developed which opens up wide possibilities for X-ray and VUV spectroscopy. Multilayer structures are deposited on a flat surface of a mica crystal which is then bent to a small-radius cylinder. The use of this structure in a von Hamos spectrometer for X-ray laser plasma diagnostics is demonstrated.

The spectra of a laser plasma in the soft x-ray (0.8–0.95 nm) and vacuum ultraviolet (3–4 nm) ranges are recorded with the use of new focusing multilayer structures. It is demonstrated that the electron temperature of the light-element plasma produced by a laser pulse with an energy of ∼1 mJ can be measured by using the relative intensities of the satellites and the lines of ions with different charges.

Characteristic K α x rays arising when a metallic target is irradiated by femtosecond infrared pulses that are generated by a terawatt chromium-forsterite laser system (1240 nm, 90 mJ, 80 fs) are studied. The absolute yield (up to 3 × 108 photons/sr pulse) and the coefficient of the transformation of laser radiation to K α radiation (maximum value ≈0.03%) are measured for an iron target. The dependence of the radiation intensity on the angle of incidence of p polarized laser radiation is analyzed. The mechanisms of the production of fast electrons responsible for generating characteristic x rays are discussed.

Summary form only given. At TRINITI cylindrical and conical wire liners are being studied on the Angara-5-1. The design of quasi-spherical wire arrays has been tested. 3-D compression take place in the quasi-spherical arrays. At the implosion on Angara-5-1 of the quasi-spherical arrays with spatially profiled linear mass the increase of density of plasma energy up to 5 times in comparison with cylindrical wire arrays. The different soft x-ray spectra with the spatial resolution obtain for cylindrical and quasi-spherical wire arrays. To obtain this spectra reflecting grating spectrometer is developed. The dependence of radiating area diameter on wave length at implosion of cylindrical and quasi-spherical wire arrays from soft x-ray spectra with spatial resolution was received. The SRC RF TRINITI started building a thermonuclear installation "Baikal" of 50 MA current with the goal of undertaking experiments on thermonuclear target ignition. Pulse power systems for this installation is developed by Efremov institute.

Modified comparison method is developed. In this method detailed theoretical calculations of spectra of heavy elements is conducted varying one parameter ( Te ) in order to find the most complete matching of the structure of the theoretical and the experimental Mo spectra in laser-produced plasmas.

Intense extreme ultraviolet (XUV) radiation was observed during the interaction of low-temperature laser plasmas and wall materials. Laser plasmas with electron temperature T-e similar to 40 eV were created on massive solid targets (CF2 and Al) by an excimer KrF laser (248 nm/0.5 J/13 ns/1 Hz). The wall was installed in the path of the laser-produced plasma expansion at distances between 0.5 and 3.5 mm. The spectral and spatial structure of XUV radiation (spectral range of lambda similar to 6-20 nm) was studied using a grazing incidence spectrometer with a back-illuminated CCD camera as a detector. XUV spectra of F and Al ions were analyzed. At large plasma-wall distances three-body recombination was identified as the dominant process responsible for ionic level population and radiation. The experiments demonstrate an effective way of creating low-temperature (T-e similar to 1-10 eV) plasmas interacting with solid surfaces (walls).

Results of optimization of an excimer laser-induced plasma x-ray source for projection lithography in the range λ = 13–15 nm are reported. A conversion efficiency of >0.7% in 2% BW has been achieved with high-Z target materials. Two methods of reducing contamination of optical elements by target debris have been tested: usage of a thin target layer (for Ta 1 μm was found to be optimal) and of a heavy buffer gas. The effect of the use of Ta-tape target and Kr buffer gas has been measured by determining the reflectivity of a Mo-Si multilayer sample after 10 5 shots.

Implosions in starlike triple and quadruple wire arrays were investigated in a 1 MA Zebra generator. Implosion in these loads is directed along the rays of the star and cascades from wire to wire to the center. Shadowgraphy shows improved homogeneity of imploding plasma and mitigation of instabilities. Despite the low azimuthal symmetry, starlike wire arrays produce a stable x-ray pulse with the highest peak power of >0.4 TW and the shortest duration of 8-12 ns among different types of tested loads. This can be linked to stabilization of instabilities due to the multiple nesting.

An electron-beam deposition method is used to fabricate spherical and flat mirrors with a peak reflectivity of 20% for wavelengths between 120 and 450 Å. It is experimentally shown that the fabricated mirrors can be employed to form an image with a resolution of 1 μm for ultrasoft x rays. The possibility of producing intense directional high-temperature plasma radiation by spherical multilayer mirrors is demonstrated. A radiation intensity of 107 W/cm2 around 182 Å has been experimentally obtained in the laser plasma image plane.

A compact, tabletop terawatt forsterite laser (1.24 μm /100 mJ/ 80 fs) is used for generation of fast hard x-ray radiation from laser-produced plasmas. Plasmas are created on massive solid Fe and Cu targets. X-ray radiation is studied using a focusing crystal von Hamos spectrometer with a CCD linear array as x-ray detector. High efficiency of the spectrometer in a wide spectral range allows us to record x-ray spectra by one laser shot. Intense K α radiation is studied with high spectral resolution (λ/δλ~1000) at various focusing conditions: main laser radiation and second harmonic radiation. With a copper target the K α radiation yield was equal to 4×10 9 photon/pulse in 4π steradian, that corresponds to conversion efficiency of 0.02%. Processes responsible for ultrafast hard x-ray radiation are discussed.

Absolute x-ray calibration of laser-produced plasmas was performed using a focusing crystal von Hamos spectrometer. The plasmas were created by an Nd-YAG laser (0.53 μm/200 mJ/3 ns/10 Hz) on massive solid targets (Mg, Cu, Zn, Sn, Mo, Ta, Ti, Steel). Cylindrical mica crystal (radius of curvature R=20 mm) and a CCD linear array detector (Toshiba model TCD 1304AP) were used in the spectrometer. Both the mica crystal and CCD linear array were absolutely calibrated in the spectral range of λ=7-15 A. The spectrometer was used for absolute spectral measurements and the determination of the plasma parameters. The unique target design allowed for multiple instruments to observe the plasma simultaneously which improved analysis. High spectrometer efficiency allows for the monitoring of absolute x-ray spectra, x-ray yield and plasma parameters in each laser shot. This spectrometer is promising for absolute spectral measurements and for monitoring laser-plasma sources intended for proximity print lithography.

A description is given of a simple luminescent detector of radiation in the VUV range (10–100 nm) and of a method for absolute calibration of the sensitivity (quantum efficiency) of this detector. The detector and multilayer normal-incidence mirrors were used in determination of the absolute yield of the radiation from a laser plasma and in absolute calibration of the UF-4 photographic film at the wavelength of 18 nm.

A set of spectral analytic instruments has been developed for absolute intensity measurements in a spectral range of 1 - 600 a: (1) several modifications of grazing incidence spectrographs; (2) EUV monochromator- spectrometer with a constant angle of deviation; (3) focusing crystal von Hamos spectrometer using cylindrical mica and pyrolytic graphite crystals and a CCD linear array as a detector. These instruments are useful for plasma diagnostics, x-ray and EUV spectroscopy of laser-generated plasmas and capillary discharge plasmas, x-ray and EUV reflectometry, radiometry and x-ray fluorescence application.

Multilayer mirror optics was used in a pulse-periodic laser-plasma source of quasimonochromatic polarised x-rays. A calculation was made of the reflectivity and polarisability of multilayer mirrors at wavelengths λ = 17–18 nm. The experimental results were compared with calculations.

Experimental results are reported on the development of a low-contamination laser-plasma source for extreme ultra-violet lithography (EUVL). The results concern the intensity in the 12.5 to 15.5 nm wavelength range and the pollution of EUV optics by plasma debris.

This paper describes a simple method for formation of quasi-monochromatic soft x-ray radiation from laser-produced plasmas. The method uses a special combination of laser target materials and x-ray filters. Targets with middle atomic numbers Za~10-25 are chosen, so hydrogen- and helium-like ions ([H]- and [He]-like ions) are excited in the laser-produced plasmas. The x-ray K-absorption filters isolate only a few lines in the spectrum: resonance lines and corresponding satellites of [H]- and [He]-like ions. These lines occupy a narrow spectral band λ/δλ=10-100. The contribution of continuum radiation out of the separated spectral band is studied theoretically and experimentally. It is shown that the continuum radiation contribution does not exceed 20% of the line radiation intensity. The method of formation of quasi-monochromatic soft x-ray radiation is used for reflectometry (measurements of crystal reflectivity, calibration of crystal spectrometers and x-ray detectors) and for radiometry (absolute radiatin yield measurements) of laser-produced plasmas.

Intense soft x-ray radiation is observed when a high temperature laser produced plasma collides with a solid surface (wall). The laser plasma is produced by Nd:YAG laser radiation (0.53 micrometers ; 200 mJ; 3 ns; 5x1012 w/cm2 focused onto a Mg target. The wall is placed in the path of the plasma expansion. Two experimental techniques are used. 1) One-dimensional x-ray images of the plasma-wall gap formed by a slit are observed using an absolutely calibrated CCD linear array. 2) X-ray spectra of [H]- and [He]-like Mg ions are recorded using a crystal focusing x-ray von Hamos spectrometer. At a measured electron temperature of Te equals 195 eV, emission of [He]-like ions Mg XI gives the main contribution to the observed x-ray intensity. The spatial structure and the intensity of the radiation are studied at various laser plasma-wall distances (r0 equals 0.3 - 3.0 mm). Intense radiation near the wall is caused by an electron density jump in a shockwave formed in front of the wall. At small wall distances r0<

A compact device, based on fast capillary discharge plasmas, is an intense EUV and soft x-ray source of radiation. Th plasma is created by a discharge of low-inductance capacitors through a gas-filled ceramic capillary. Parameters of the discharge are: maximum current of 25 kA at applied voltage 40 kV, a pulse duration of 20-30 ns at FWHM, and a rise time of 1.5 ns. The soft x-ray and EUV emission of multiply charged ions is investigated using a compact 1 meter grazing incidence spectrometer-monochromator with a constant angle of deviation. The use of various gases allows the observation of XUV spectra in a wide spectral range (4- 45 nm). A Xe-filled capillary discharge shows intense radiation near 13.5 nm - the region of interest for EUV lithography applications. A reflectometer is used for testing grazing incidence gratings.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Absolute x-ray calibration of laser-produced plasmas was performed using a CCD linear array and a focusing crystalspectrometer. The plasmas were created by a Nd glass laser (0.53 im/1O J/2 ns) and a high repetition rate Nd-YAG laser(0.53 jtm/2OO mJ/3 ns/lO Hz). A commercial CCD (Toshiba model TCD 1304AP) was used for x-ray detection. TheCCD linear array has 3724 pixels (8 jtm width and 200 pm height) giving a total length of -3O mm. First the CCDdetector was absolutely calibrated using laser-produced plasmas and an Fe55 isotope source. The sensitivity of thedetector was about two orders of magnitude higher than x-ray photographic film (Kodak RAR 2492). The CCD detectorwas used for monitoring the absolute x-ray yield, for finding the optimal focal position, for estimating the flux density onthe target and for measuring the electron temperature of the plasma. In combination with a focusing von Hamosspectrometer (curved mica and graphite crystals, radius of curvature R = 20 mm) the detector was used for absolutespectral measurements and determination of the plasma parameters. This spectrometer is promising for absolute spectralmeasurements of x-ray radiation of low-intensity sources and for numerous practical applications (e.g., x-ray fluorescence

A compact device, based on fast capillary discharge plasmas, is used as an intense EUV and soft x-ray source of radiation. The plasma is created by a discharge of low-inductance capacitors (30 nF) through a capillary (2 mm diameter, 20 mm length). Two types of capillary are used: a polyacetal (empty) and a gas-filled (Ar, Xe). All components are assembled in a coaxial geometry. The total size of the device including capacitors, switch and capillary is 30 cm long and 25 cm in diameter. Discharge current is monitored using a shunt circuit.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The use of bent crystals with high integrated reflectivity in focusing crystal spectrometers (Johann and von Hamos schemes) is considered. It is shown that in a von Hamos scheme mosaic focusing takes place. Thus a mosaic crystal simultaneously provides high spectral resolution and high efficiency. Expressions for the mosaic focusing are obtained. Focusing mica and graphite crystal von Hamos spectrometers (radius of crystal curvature is 20 mm) are investigated: spectral and spatial resolution and absolute efficiency are measured in a spectral range of 2 - 2.6 angstroms using laser-produced plasma and iron isotope x-ray sources. The mica crystal spectrometer showed high spatial (up to 10 micrometers ) and spectral ((lambda) /(delta) (lambda) approximately 1000) resolution, whereas the graphite spectrometer showed very high efficiency (30 - 70 times higher than the mica crystal) and moderate spectral resolution ((lambda) /(delta) (lambda) approximately 500 - 750). In the latter case mosaic focusing is observed: spectral resolution is 10 - 15 times higher than spectral resolution determined by the mosaic spread of the crystal ((lambda) /(delta) (lambda) approximately 50). The results allow one to estimate a maximum efficiency for focusing crystal spectrometers. Prospects for using the von Hamos spectrometers for x-ray spectroscopy and x-ray fluorescence are considered.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The observation of EUV spectra of multiply charged ions excited by an ultrafast capillary discharge suggest the possibility of developing an intense compact source of soft x- ray and EUV radiation for practical applications (EUV lithography, microscopy, etc.). The discharge is driven by a compact water transmission line having a very fast current pulse (12 ns FHWM, rise time approximately 1 ns). Spectra of OV-OVI ions from a polyacetal capillary and ArVII-ArVIII ions from an Ar filled capillary were observed and investigated in a spectral range of 100 - 300 Angstrom using a 1-m grazing incidence spectrograph. The resulting capillary discharge plasmas have an electron temperature of approximately 25 - 35 eV, which could be increased to approximately 100 eV using a more powerful transmission line.

Johann and DuMond quartz ciystal focusing spectrometers are proposed for hard x-ray spectra investigations of sub-ps laser-produced plasmas when the source is located on the focal circle. Because the ciystal intercepts and focuses a large solid angle of radiation, the schemes have extremely high efficiency, which could be iO times higher than those of flat crystal spectrometers. Due to the small size ofthe source (usually 4O xm) the schemes have a high spectral resolution (?/dA>2OOO).By using reflection (Johann spectrometer) and transmission (DuMond spectrometer) modes, the schemes cover a very widespectral range: 0.2-2.3 A (energy range E=5-60 key). Curved quartz crystal (jlane 1340, 2d=2.34 A, radius ofcurvature 150mm) is tested in the reflection mode using Fe K, radiation ()=1.94 A).Keywords: x-ray spectroscopy, plasma diagnostics, laser-produced plasmas, advanced x-ray instrumentation. 1. INTRODUCTION The interaction ofa sub-ps laser with a high-Z target produces a hard x-ray continuum, which has several potential applicationsfor spectroscopy, biology and medicine. The other feature of this interaction is a possibility to excite the characteristic lineemission of high-Z elements from a sub-ps laser-produced plasma. The electron oscillation energy €(keV) in a light field E0,intensity q (W/cm2) with a wavelength tm) is given by

The design and characteristics of a von Hamos spectrograph are considered. Efficiency of the von Hamos mica crystal spectrograph is absolutely calibrated using laser-produced plasmas as an x-ray source and a p-i-n diode as a detector. The value of integrated reflectivity of the mica crystal is also determined in the same spectral bands and diffraction orders: 5.5 - 11 angstrom (first order), 2.6 - 5.0 angstrom (second order), 1.84 - 3.22 angstrom (third order), 1.84 - 2.65 angstrom (fourth order), 1.84 - 1.92 angstrom (fifth order). The von Hamos spectrograph is used for x-ray spectroscopy and radiometry of laser-produced plasmas. The spectrograph possesses several advantages of interest: high spectral resolution ((lambda) /(delta) (lambda) up to 3000), a direct registration of one or two dimensional source images (spatial resolution up to 10 micrometers) and a high detecting efficiency over a wide spectral range. Focused intensities could be 10 2 - 10 3 times higher than those of flat crystal spectrographs. This type of spectrograph is ideal for the recording of the wide-range x-ray spectra of low intensity sources such as the femtosecond laser-produced plasma, micropinch, electron beam ion trap (EBIT), and others.

Spectra from various target materials from a KrF-laser plasma source have been investigated in the Extreme UV spectral range between 12 and 17 nm using an off-Rowland grazing-incidence spectrograph. The electron temperature T-e and mean ionization stages Z have been measured to amount to T-e = 80eV and Z = 10-12, respectively. Additional calibration and measurement of the spatial and temporal characteristics of the plasma has been done using a combination of a multilayer mirror and XUV diode or fiber image carrier system. The maximum yield at 13.5nm (2.4-3 x 10(15) phot/sr nm) has been observed for targets with atomic number Z(a) = 32, 50, 73-75, of which the radiative transitions have been identified as 3p-3d, 4d-4f and 4f-5d transitions respectively. The corresponding maximum conversion efficiency at 13.5nm was 0.43% in a 1% bandwidth. An option for further optimization of the KrF laser plasma source for application in EUV lithography is discussed.

Spectra from various target materials from a KrF-laser plasma source have been investigated in the extreme UV spectral range between 12 and 17 nm using an off-Rowland grazing-incidence spectrograph. Additional calibration of the yield at 13 nm and measurement of the spatial and temporal characteristics of the plasma has been done using a combination of a multilayer mirror and XUV diode or fiber image carrier system.

Using soft x-ray multilayer mirrors (MMs) and a laser-plasma broadband radiation source, we have implemented a pulsed 0.5-Hz-repetition-rate source of polarized quasimonochromatic radiation in the XUV. The x-ray optical setup comprises a focusing MM at near-normal incidence, a plane polarizing MM at 41 degrees off axis, and a plane multilayer analyzer which can be rotated by 90 degrees with respect to the polarizer. A stigmatic broadband spectrometer comprising a grazing incidence toroidal mirror and a large-aperture (5 cm2) transmission grating (TG) has proved to be useful in spectroscopic characterization of plane multilayer mirrors and the laser-plasma source. The second (reference) x-ray optical channel comprises a focusing MM and serves to monitor the energy of individual pulses. The focusing MMs image the laser-plasma source onto the sodium-salicylate-covered surfaces of flexible 0.7-cm-long light guides 13 mm in diameter coupled through light-guide disks to photomultipliers outside the vacuum tank. The visible and VUV radiation outside the resonance reflection peak is rejected by free-standing Al filters placed before the detectors. The dimension of the x-ray source was measured at 100 microns (width at base) using a CCD array covered with sodium salicylate. The polarizance of the plane MM was measured at 98.2% while the peak theoretical value for this Mo-Si multilayer structure (2d equals 240 angstrom, N equals 25, lambdao equals 171.4 angstrom, 41 degrees off axis) is 98.75%. The polarized source yields of the order of 5 (DOT) 108 photons per pulse in the resonance reflection band of the MMs.

Results on laser plasma EUV characteristics for various target materials and irradiation conditions are presented. Spectra of high-Z elements in the 12.5-15.4 nm range from plasmas generated with a high-power KrF laser at 2 X 1012 W/cm2 were measured. The highest conversion efficiency (CE) of 0.85% in 2% BW was found for Re near 13.6 nm, corresponding to a maximal EUV power of 550 mW in 2% BW at 50 Hz. The use of two successive laser pulses, investigated with 2.5 ns pulses of 0.53 micrometers radiation at (0.5-1) X 1013, resulted in an increase of the CE by a factor of 1.8-2.3 for the second pulse at specific delay values (6 and 12 ns for W). The total CE gain amounted to 1.4-2. The first demonstration of an alternative concept of a laser plasma raget for EUVL was performed, based on the usage of a centrufugal force for elimination of particluates. The principle of the approach is generation of laser plasmas at the edge of a fastly-rotating disc. The effect of re- direction of particulates was observed in experiments with a (phi) 50 mm Ta disc at 36.000 rpm at laser power densitites between 109 and 1011 W/cm2.

We report results on high power excimer lasers and their application to generating laser plasma soft x-ray sources. A conversion efficiency of laser light to monochromatized soft x- ray radiation of 0.7% has been achieved at 13.5 nm (2% BW). Two methods to mitigate the production of plasma debris have been analyzed: tape targets and the use of Kr as a buffer gas. The optimal coating thickness of tape targets coated with Ta has been determined as 1 micrometers . Ta tape targets and the Kr buffer were used in a debris contamination test of 105 pulses and evaluated by the loss in reflectivity of a normal incidence Mo-Si multilayer mirror.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Results are reported concerning high-repetition-rate excimer lasers with average powers up to 415 W and their usage for generating laser-plasma soft X-ray sources. A conversion efficiency of laser light into monochromatized soft X-ray radiation of 0.7% at 13.5 nm (2% bandwidth) was achieved using an excimer laser of which the beam quality was adapted for this application. Two methods to mitigate the production of plasma debris have been analyzed: tape targets and the use of Kr as a buffer gas. The optimum coating thickness of tape targets coated with Ta has determined to be 1 mum. Ta tape targets and the Kr buffer were used in a debris contamination test of 10(5) pulses. After this exposure, the reflectivity of a normal incidence Mo-Si multilayer mirror that faced the plasma, was found to be 18% lower. The contamination could be removed by cleaning, which restored the reflectivity to 97% of the initial value.

Radiative characteristics of laser-plasma XUV sources are reviewed. The dependence of the main plasma parameters on the heating laser wavelength is discussed, as well as the use of application-specific excimer lasers to generate XUV radiation. A comparison is given with other XUV sources, such as electron storage rings. Examples of the application of normal- incidence multilayer XUV optics, e.g., to collimate the laser-plasma radiation or for projection lithography, are given.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spectra of multiply-charged ions with one and two electrons are investigated when a laser-produced plasma interacts with a solid obstacle. The level population densities of the Mg ions, recom-bining in the region of dense cool plasma near the obstacle, are studied both experimentally and theoretically. Values of the gain coefficient are calculated for the case of carbon ions.

A new method for the determination of the absolute brightness of pointlike soft-x-ray sources is proposed, and an example of its application is shown at a laser-plasma source for a wavelength band from 0.8 to similar to 1.7 nm.

Experimental data and theoretical calculations are presented for X-ray spectra from a laser-produced plasma interacting with a solid surface and are compared with those obtained from the hot-burst core of the plasma. Intensities of the spectral lines of the principal series of the H-like and He-like magnesium ions were investigated. A close study of the resonance and intercombination lines was carried out with high spectral resolution in both regions of the intense X-ray emission: near the target and near the obstacle. The plasma near the target has an electron temperature of Te=500-700 eV and an electron density of Ne=1020-1021 cm-3, whereas near the obstacle Te=70-100 eV and Ne=2*1019-3*1019 cm-3. It is shown that the X-ray emission of high-Z ions from the near-obstacle plasma results from the three-body recombination followed by cascade transitions due to collisional and radiative processes.

A comparison is made between measured and calculated distribution of ionization stages in high-temperature low- (Tokamak) and high-density (laser produced) plasmas. The relative abundances of ionization species were derived from the dielectronic satellite spectra of Fe XXV-XVIII in the region λ = 1.85-1.95 A. New calculations for ionization balance included effects of autoionization accompanied by excitation of doubly-excited states of recombining ion and density-dependence of the dielectronic recombination rate were carried out. The results differ considerably from those of previous calculations which took into account these effects (Jacobs et al. [25]) as well as earlier ones made by Jordan [19]. There is a satisfactory agreement between the experimental ion concentration measured in laser plasmas and that predicted for the electron temperature Te = 1.3 × 107 K, ionization temperature Tz = 7.6 × 106 K and density Ne ≈ 1021-22 cm-1; transient or "quasi-steady-state" conditions are observed (Te ≠ Tz). In the low-density Tokamak plasma obtained by Hill et al. [5] an ionization equilibrium was found to exist at the ionization temperature Tz = Te.