Experimental results on radiative properties of laser produced and pinch plasmas are discussed in comparison and with respect to the specific sets of requirements defined by proximity printing x-ray lithography and full field imaging x-ray microscopy.

X-ray emission spectra in the wavelength range of 2 - 13 nm from 21 kinds of material (carbon through tin) irradiated either by a 4 J/35 ns slab Nd:glass laser or by a 0.5 J/8 ns Nd:YAG laser were recorded with a grazing incidence spectrometer equipped with a microchannel plate detector. The absolute photon intensities of these spectra were determined by simultaneous measurement of the emission from a molybdenum plasma with the grazing incidence spectrometer and a transmission grating spectrometer. For the carbon plasma, the electron temperature and density are derived from the spectrum and the conditions for intense Lyman (alpha) line are discussed. Finally, we describe the application to an x-ray microscope with the laser-produced carbon plasma.

This paper reports the first experimental investigations of soft x-ray generation from Nd laser- irradiated gas puff targets. The gas puff targets were made by the pulsed injection of gas (SF₆ or Kr) into a vacuum chamber. To irradiate the gas puff targets a Nd-glass laser was used, which generated 1-ns pulses of up to 15 J in energy. The gas flow was initiated by a fast solenoid valve synchronized with a laser pulse. Spatial, spectral and temporal measurements show that intense soft x-ray emission from the laser-irradiated gas puff targets is produced. Using the presented technique one can obtain a new type of a laser plasma x-ray source (LPXS), which has some advantages over LPXS with a solid target, such as reproducibility of target conditions and no sputtering by target debris produced in the laser plasma.

X-ray spectroscopy with high spectral (up to (Delta) (lambda) /(lambda) equals 10^-4) and spatial resolution (up to microns) is discussed. Devices based on crystals, diffraction, and Bragg-Fresnel elements and their application in Z- and X-pinches and laser plasma experiments are observed.

X-ray microscopy of biological specimens is discussed with respect to the observation in a hydrated condition. Most of the possible problems could be circumvented if a single exposure of short-pulsed intense x rays is used. For this purpose laser plasma x rays are the most suitable x ray source. The results for the observation of hydrated human chromosome fibers by x-ray contact microscopy with laser plasma x rays indicated that x-ray microscopy has a big potential to reveal intact live structure of biological specimens at high resolution.

The use of laser-plasma generated soft x rays for contact microscopy offers several advantages over electron microscopy. After chemical development the exposed photoresist can be examined by interference light, scanning electron, or atomic force microscopy. The advantages and disadvantages of each are briefly described and biologically significant results using soft x-ray contact microscopy, followed by examination of the resist by atomic force microscopy, are presented.

This article describes the first experiment of our groups to combine monochromatic x-ray imaging with a time-resolving detector i.e., a streak camera and a 120 ps gated framing camera. The aim of setting such a time-resolved diagnostic is to image the x-ray emission from colliding plasmas with high spatial resolution in a very narrow spectral window. Both camera types were tested and the adjustment procedure for the crystal was tested with film as a detector. The obtained spectral and spatial resolution of the x-ray microscope was measured.

The construction of an extreme ultraviolet reflection imaging microscope at CREOL using an Ealing Schwarzschild objective and a laser-produced plasma source is summarized. Proposed operation of the present system in the 50 - 60 nm wavelength region is discussed.

Soft x-ray contact microscopy (SXCM) is a technique which can image the ultrastructure of living biological specimens at a resolution considerably better than light microscopy (LM). Two such laser systems have been developed for the generation of water window x rays. A small beam line of the large Nd:GLASS laser `Vulcan' at the Rutherford Appleton Laboratory (RAL), UK, has been set up, giving approximately 6 - 8 J on target at a wavelength of 1.06 micrometers . In addition, a smaller discharge pumped KrF excimer laser, based at the Clarendon Laboratory, University of Oxford, UK, has been built, giving approximately 2 J at a wavelength of 249 nm. A comparison of the x-ray emission from plasma generated by the two laser systems using various target materials has been made and evaluated with respect to their application to SXCM.

We report progress in two areas of technology relevant to the development of high-resolution x-ray microscopy techniques based on laser plasma x-ray sources for the analysis of wet and dry biological specimens. The approach we discuss involves the use of ultrashort x-ray emission from a laser plasma source. Precision x-ray optics are used to collimate and filter this light onto the specimen. Imaging and image magnification are accomplished with a combination of x-ray and electron-optical systems. We discuss our progress towards establishing a flexible laser-plasma x-ray source for the development of biological imaging and contact microscopy, and progress we have made towards the development of an electro-optical imaging system having high magnification and spatial resolution.

Laser plasma sources convert 1 - 2% of the incident laser energy into soft x rays that can be used in multilayer-based reflective systems. These sources are useful in the laboratory for development of soft-x-ray projection lithography (SXPL). In the commercialization of SXPL technology, the laser plasma source offers the advantages of modularity and lower cost, when compared to the alternative synchrotron source. The characteristics of the source define requirements for other system components. The condensing system, which collects radiation from the plasma source and directs it onto the mask, must be designed to match the source size and the aperture of the imaging objective. The first surface of the condenser is subject to damage by unwanted debris from the plasma source. This paper discusses several of the major issues involved in using laser plasma sources in SXPL experiments and provides examples of experimental solutions. Simulated and actual soft-x-ray images are shown.

Measurements of the velocity and particulate size distributions as well as calculations of ejected mass have been made on solid Sn and Au laser-produced plasma (LPP) targets. The experiments were conducted under conditions associated with soft x-ray projection lithography (SXPL). Results indicate that small particulates, less than 1 - 2 micrometers in diameter, with speeds in excess of 9000 cm/s, are the dominant constituents of the debris.

X-ray focusing using square channel capillary arrays is reviewed. We present some experimental results obtained using a variety of array configurations and we deduce that channel misalignment and surface roughness are the prime factors limiting the performance of these devices. We present results obtained using a stacked array of commercial precision bore square tubing and deduce that the reflectivity from these unetched surfaces is superior to that from etched micro-channel plate blanks. The improved surface quality implied by this reflectivity result is confirmed using atomic force microscopy. We also present results of a new drawing technique that we have developed.

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.

Mo-based multilayers show high reflectivities in the 8 - 20 nm region at normal incidence. We have evaluated the soft x-ray reflectivities and the effects of thermal annealing on both reflectivity and the layered structures of these Mo-based multilayers. The Cu-K (alpha) x-ray first-order Bragg-peak reflectivity of the Mo/Si multilayer markedly decreases at annealing temperatures above 400 degree(s)C. TEM observation reveals that the thermally induced deteriorations of Mo/B4C and Mo/SiC multilayers are smaller than those of the Mo/Si multilayer. The Mo/Si multilayer reflectivity at a wavelength of about 13 nm decreases greatly with 600 degree(s)C annealing. However, the Mo/B4C and Mo/SiC multilayers maintain higher reflectivities at the same wavelength. These results suggests that the Mo/B4C and Mo/SiC multilayers are superior to a Mo/Si multilayer in terms of thermal stability.

To date, image contrast in the soft-x-ray spectral region has been determined from the optical constant data for n and k. Uncertainties in these constants obtained from different sources suggest that direct measurement of image contrast would be useful. An experimental arrangement using a laser produced plasma is described for such a direct measurement of image contrast.

We propose the use of mass-limited, line emitting cryogenic targets for SXPL, which permit a continuous supply of targets without the problem of particulate debris and excessive heating of multilayer optics by an intense x-ray flux in wavelength regions outside the multilayer bandwidth. In preliminary experiments we measured the oxygen line emission in the vicinity of 13 nm. The x-ray emitting plasma was produced by using a laser intensity of 2 X 10¹² W/cm² on the surface of an ice target. From the observed crater on target we can deduce that clusters are also ejected from cryogenic targets.

X-ray spectroscopy of laser-generated plasmas has been performed by using two non- conventional variants of the double-crystal spectrometer and the Johann spectrometer. They provide a very high spectral resolution in a limited spectral range that covers, for example, the range of a resonance line and its satellites. The excellent luminosity of the vertical variant of the Johann spectrometer makes its application very attractive, in spite of the need for exact testing and alignment.

We present calculations on X-UV refraction through a laser-created plasma. We propose to study the overcritical zones of a laser-created plasma on plane target. The work consists in probing the laser created plasma by an X-UV radiation (100 - 200 angstrom) and in deducing the refraction through the plasma of a collimated probe beam. Experiment images can demonstrate how inhomogeneities in laser deposition propagate to the ablation front of the laser plasma. The use of computer simulations to reproduce the X-UV images can characterize completely the plasma i.e., its density and its temperature profiles inside the probed layer.

Intense thermal x rays with a brightness temperature up to 130 eV have been generated by focusing the iodine laser ASTERIX IV (200 J/400 ps at 0.44 micrometers wavelength) into 1 mm diameter spherical microcavities. The intense radiation has been used to study the radiative heating of low-Z material by replacing a gold wall element by a carbon foil. We performed measurements of the re-emission and the radiative burnthrough by time-resolved x-ray spectroscopy in the sub-keV spectral range at a resolution of 0.1 nm. The results are compared with MULTI simulations.

We present preliminary results of L-shell absorption spectroscopy in an expanding germanium laser-produced plasma. The experiments were performed on the Octal laser at the Centre d'Etudes de Limeil-Valenton. The ion state distribution was inferred from the absorption spectrum. The radiation used to probe the plasma is produced by interaction of an auxiliary laser beam with a 80-micrometers diameter praseodymium wire, allowing a spatial resolution of the absorption spectrum. Temporal resolution is obtained by adjusting the delay between the driving beams and the probe beam. Modeling with a radiative hydrocode and an atomic kinetics code gives qualitative agreement with the experiments.

To simulate the interaction of high laser intensity with solid targets, we have used the 1D code FILM in which the collisional plasma absorption is calculated by solving the linear electromagnetic field for p and s polarization. For p-polarized light the collision frequency is adjusted so that the field in the critical region of the plasma never exceeds the maximum field allowed by the wave breaking limit. Energy transport by thermal conduction is described with the help of the delocalized heat flux theory. The ponderomotive force resulting from the huge filed is taken into account. The calculated temperatures and ion densities are used as an input to a time-dependent atomic physics code. Non-stationary ionization dynamics is demonstrated.

A soft x-ray laser plasma source is described, its laser system can produce laser pulses of nano- to pico-second durations that were obtained by a multicascade compression due to stimulated scatterings. Results of the pulse energy stabilization are presented. Investigations of x-ray emissions from highly charged ions show that a subnanosecond asymmetric partially compressed pulse generates plasmas with a number of isoelectronic sequences.

In situ x-ray diffraction from laser-shocked crystals provides one means of diagnosing high strain-rate (10⁸ - 10⁹ s^-1) compression/tension waves in solids. Typically the radiation diffracted from the shocked crystals is relatively broadband, consisting of the resonance and intercombination lines of the helium-like ions of medium Z atoms, and their associated lithium-like dielectronic satellites. Deconvolution of this time-dependent x-ray spectrum will yield more detailed information on the strain profiles within the crystal. Preliminary results of a maximum entropy routine are presented.

This study deals with the mechanic impulse transmitted to a solid target by soft x rays. We have measured the impulse transmitted to thin aluminum layers by x-ray radiation around 1.2 keV produced by a laser-irradiated copper target. The results are compared to radiative hydrocode simulations with the code XRAD.

A self-healing target has been demonstrated for synchronous photo-pumping of extreme- ultraviolet lasers. The threaded, mercury-wetted copper rod, rotating in a pool of mercury, offers similar photoionization efficiency as gold targets, but without target-surface degradation. A gain coefficient of 1.4 cm^-1 was obtained with mercury for the 1089 angstrom Xe²⁺ laser at a pump-laser intensity of 140 GW(DOT)cm^-2, comparing favorably with results from gold targets.

Modeling of x-ray emission from targets heated by an ultrashort-pulse high-intensity optical laser is discussed. One application, using the emitted x rays, is pumping inner-shell photo- ionized x-ray lasers. Short wavelength lasing ((lambda) <EQ 15 angstrom) requires fast rise- time 1 - 3 keV x rays to ionize inner K-shell electrons. It has been shown that structured targets, consisting of grooves on a solid material or a composite of clusters, have high absorption. We model grooved targets as an ensemble of exploding foils finding that the rise time of x rays is rapid enough for pumping inner-shell x-ray lasers. We show that simple atomic models can overestimate the energy in x-ray emission bands: High-Z materials are found to have the highest conversion efficiency but mid-Z materials can be used to provide a band of emission at a particular energy. We show that the pondermotive inhibition of expansion has only a small effect on the x-ray emission.

At Rutherford Appleton Laboratory we developed a high repetition rate, picosecond, excimer laser system which generates a high temperature and density plasma source emitting approximately 200 mW (78 mW/sr) x ray average power at h(nu) approximately 1.2 KeV or 0.28 KeV < h(nu) < 0.53 KeV (the `water window'). At 3.37 nm wavelength the spectral brightness of the source is approximately 9 X 10¹¹ photons/s/mm²/mrad²/0.1% bandwidth. The x-ray source serves a large user community for applications such as: scanning and holographic microscopy, the study of the biochemistry of DNA damage and repair, microlithography and spectroscopy.

X-ray emission and laser absorption have been studied with pulses of 1.5 ps duration irradiating solid targets at intensities of 10¹⁸ W/cm². Absorption as a function of the incident laser flux and the irradiation angle in respect to the polarization reaches maximal values of 50% and is discussed in comparison to theoretical works published recently. This gives basic guidelines for efficient x-ray production which we have investigated in the hard (E_x > 50 keV, Bremsstrahlung) and soft (E_x < 1 keV, line emission of ions) spectral region. The feasibility of a short pulse and a plasma source with an extension of only some microns is proofed with an experiment using a spherically bent Mica crystal for collimation of the x-ray beam. The brightness and divergence of that x-ray beam being relevant for applications are given.

We report results of Thomson scattering measurements of optically ionized gases produced using 12 psec pulses from a KrF-pumped Raman laser at intensities of 3 X 10¹⁷ W cm^-2. Electron densities and temperatures are determined from the scattered Thomson spectra in both He and Ne (static and gas jet targets) at pressures of 10^-3 - 1 bar. The central, low frequency region of the spectra from low pressure shots clearly shows an enhanced intensity above that given by the Salpeter approximation, and is indicative of a high electron-to-ion temperature ratios of at least 10 - 20. These observations are consistent with the long electron-ion collision time relative to the pulse length.