We review the development of compact laser-plasma soft x-ray sources based on microscopic liquid drops or liquid jets as target. It is shown that such sources provide practically debris-free, high-flux operation at wavelengths suitable for EUV and x-ray lithography. This regenerative and liquid- density target system holds promise for high-average power x- ray and EUV generation using high-repetition-rate lasers. Application of the method to compact x-ray microscopy is also briefly discussed.

Soft x-ray emission from plasmas produced using a laser- irradiated gas puff target have been investigated. The use of the gas puff targets, created by pulsed injection of high- density gas from a solenoid valve through a nozzle, eliminates the production of debris associated with solid targets. To improve the gas puff target two approaches have been used: (1) cooling of the valve with liquid nitrogen to increase condensation of gas and (2) formation of the target by injection of gas in gas surrounding the nozzle output using the double nozzle setup. The gas puff targets created with these two approaches were characterized with x-ray backlighting method using laser-produced x-ray source. Laser pulses of 1 ns time duration with energy up to 10 J from a Nd:glass laser and of either 0.9 ns or 10 ns time duration with energies up to 0.7 J from a Nd:YAG laser were used to produce plasmas. Emissions in the soft x-ray range from laser- produced gas puff plasmas were studied for various gases. Significant improvement of x-ray production from the double stream gas puff target has been observed.

An x-ray power of 2.8 Watts at the 1 nm x-ray lithography wavelength was generated by a copper plasma formed by a single laser beam focused to an intensity of greater than 10¹⁴ W/cm² on a copper tape target. The all solid state Britelight^TM YAG laser has 700 ps pulse duration, 300 Hz pulse repetition rate, average power of 75 Watts, and less than 2 times diffraction limited beam quality at the fundamental 1.064 micrometer wavelength. The single beam laser system has a master oscillator, a preamplifier and one power amplifier, all diode pumped. Measurements confirmed negligible copper vapor debris at 8 cm from the laser-plasma source with atmospheric pressure He gas and modest gas flow. The point source x-ray radiation was collimated with either a polycapillary or grazing mirror collimator. The near-parallel beam of x-rays has good divergence both globally (0.5 mrad) and locally (less than 3 mrad), good uniformity (2% achievable goal) and large uniform field size (20 mm X 20 mm full field and 25 mm X 36 mm scanning system). High-resolution lithography was performed for the first time with collimated 1 nm point source x-rays. A power scaling system is being built with eight amplified beams in parallel on the x-ray target, and is expected to achieve 24 - 30 Watts of x-rays. A 16 beam laser plasma x-ray lithography system could achieve a throughput of 24 wafer levels per hour using 300 mm diameter wafers.

We present the exciting results obtained by using a natural (i.e. as long as the active medium gain) 120 ns-duration excimer laser pulse focused on relatively thick targets (100 micrometer): a conversion efficiency exceeding 20% has been obtained in the 40 - 70 eV (170 - 300 Angstrom) spectral interval from Cu and Ta targets, with more than 100-ns-FWHM X- ray pulses and low speed (less than 100 m/s) emitted debris. A fast CCD camera is used to reveal the debris and to measure their speed for different laser parameters. These values of debris speed are compatible with the use of a mechanical device to separate them from the X-ray beam and hence to protect the optics of a projection-microlithography system.

Collimating of the x-ray beam is essential to point source proximity x-ray lithography for controlling radial magnification and increasing the beam intensity. Polycapillary optic collimators were developed to meet the challenges of point source proximity x-ray lithography. Sophisticated modeling software was developed for design and optimization of polycapillary collimators to meet specific requirements. Using this software, a highly efficient collimator was designed to deliver a well-collimated beam centered at 1.1 keV for a 20 mm X 20 mm field. The collimator was constructed and was tested with both an electron bombardment source and a laser generated plasma source. The design goals of intensity gain and divergence controls have been achieved. The intensity variation within the printing field can be less than 2%.

An x-ray optic suitable for use in x-ray proximity lithography is described. It employs multiple flat mirror facets arranged at grazing incidence, each of which creates an optically independent channel that covers the entire target. The facets are arranged so that many channels can simultaneously illuminate the target, thereby achieving high flux at the target with high uniformity. Lithographic constraints on local and global divergence at the mask are met by making the optic small and placing it sufficiently distant from the target.

The combination of a table-top laser produced plasma X-ray source and spherically bent crystals for the soft X-ray region is used in traditional X-ray microscopy schemes. The X-ray source is well localized both spatially (approximately 20 micrometer) and temporally (1 ps - 10 ns, it depends on the used laser) and it is spectrally tunable in a relatively wide range (6 - 19 angstrom). High quality monochromatic ((delta) (lambda) /(lambda) approximately 10^-5 - 10^-3) images with high spatial resolution (up to approximately 4 micrometer) and in a large field of view (few mm) are presented. For many applications, these low-cost compact systems can offer a simple alternative to the larger installations which are usually used. It was demonstrated that the spherically bent crystals can be efficiently used in a wide ((Theta) equals 40 - 90 degrees) range of reflection angles, thus allowing wide wavelength selection. A very efficient concentration of monochromatic X-Ray radiation into different spot shapes (line, circle spot, etc) is demonstrated.

We present a novel design of a refractive x-ray lens. It is shown that a lens with a simple saw-tooth profile will have the same focusing properties as one with parabolic surfaces. The lens can be made in two symmetric pieces, and be fabricated with a standard record-cutting machine at a very low cost. Furthermore, the focal length for a given energy can be adjusted by a simple mechanical procedure. A prototype in vinyl with a focal length of 20 cm for 25 keV x-rays has been manufactured. Measurements in a table-top setup with a conventional x-ray tube are in good agreement with calculations based on geometrical optics and ray-tracing simulations.

Polycapillary collimating optics collect x rays produced by a point source over a wide solid angle (as large as 10 - 15 degrees cone angle) and a large energy bandwidth, and provide a quasi-parallel beam with a small divergence (a few milliradians). These optics are emerging as important tools in materials analysis, medical imaging, x-ray lithography and protein crystallography. Results of measurements carried out on three multi-fiber polycapillary x-ray collimating optics are described. Parameters influencing efficient employment of these optics, such as transmission versus photon energy, output beam uniformity, and divergence are characterized. Monte Carlo simulations based on ray-tracing geometrical optics are compared with experimental performances to extract additional information.

Polycapillary optics are shaped arrays of tiny hollow tubes through which x rays are guided by total external reflection at grazing incidence. In previous work, it has been demonstrated that a small prototype optic can provide nearly total scatter rejection at mammographic energies with simultaneous resolution enhancement due to geometrical-blur- free magnification. Recent measurements on straight capillaries and lenses show that capillary optics could possibly be applied to higher energy imaging applications, such as angiography and chest radiography. Transmission efficiency for straight bundles was measured to be fairly flat out to 60 keV and in excess of 30% at 80 keV. Extensive simulations and measurements have been performed for prototype capillary optics at photon energies from 20 to 100 keV. Transmission of the central part (0.5 mm diameter) of a 166 mm long prototype tapered lens was as high as 60% near 30 keV and in excess of 40% up to 70 keV. The reduction of transmission at high energies was found to be caused by optic profile defects: surface waviness and centerline bending. Absorption and scatter rejection measurements indicate that almost total scatter rejection is achievable at high energies. Scatter transmission of the tapered borosilicate glass lens is around 5% at 60 keV. Even better scatter rejection could be achieved by using lead glass capillaries. By estimating the contrast improvement factor and Signal to Noise Ratio (SNR) with the scaled up lenses, this paper demonstrates the potential for polycapillary optics in various medical x-ray imaging applications.

This paper reports on the development of a deterministic method of specifying the finish glancing-incidence mirrors in terms of their imaging performance. As a first step we have calculated the two-dimensional intensity distribution in the focal region of an elliptical mirror including the effects of small, arbitrary finish errors. This calculation is based on the physical-optics diffraction model, using the sampling theorem to interpolate between measured profile points, thereby avoiding numerical integration and leading to simple analytic results. In addition to giving deterministic image intensity distributions for particular profile data, it provides a means for validating and extending earlier test methods based on profile statistics -- the root-mean-square (RMS) finish error and its power-spectral density (PSD).

Three-dimensional focusing of x-rays can be achieved by doubly-curved crystals through diffraction from a small laboratory x-ray source. Recently it has been demonstrated that an intense monochromatic x-ray microprobe can be obtained with the use of a doubly-curved mica crystal. Due to monochromatic excitation using doubly-curved crystal optics, exceptionally low background has been demonstrated in the application to micro x-ray fluorescence (MXRF). Low background and high intensity gain significantly improve the detection limit for MXRF. In this paper, the focusing and diffraction properties of a doubly-curved Johann point-focusing crystal optic for Cu K(alpha) x-rays from a microfocus x-ray source is presented. Experimental data on spot size, beam intensity, effect of source position for the optics, and MXRF spectra are discussed.

A clean, high-power Extreme Ultraviolet (EUV) light source is being developed for Extreme Ultraviolet Lithography (EUVL). The source is based on a continuous jet of condensable gas irradiated with a diode-pumped solid state laser producing a time-averaged output power of 1700 W at 5000 - 6000 Hz. An illumination system is being assembled to collect and deliver the EUV output from the source and deliver it to a reticle and projection optics box to achieve an EUV exposure rate equivalent to ten 300-mm wafers per hour.

Superpolished optical flats with high spatial frequency roughness below 0.1 nm have been commercially available for years. However, it is much more difficult to obtain figured optics of similar quality. We have obtained and tested the finish of figured optics from different vendors by atomic force microscopy and optical profilometry and have investigated how the substrate quality can be improved by the deposition of thin films. We have determined the growth parameters of several thin-film structures. From these parameters we can determine how the surface topography of a coated mirror differs from that of the substrate, select the best thin-film structure, and predict the possible improvement.

The extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PS/PDI) was developed and implemented at Lawrence Berkeley National Laboratory to meet the significant measurement challenge of characterizing EUV projection lithography optics. The PS/PDI has been in continuous use and under ongoing development since 1996. Here we describe recent improvements made to the interferometer, and we summarize metrology results from state-of-the-art 10x-reduction EUV projection optics.

A three-aspherical mirror system for extreme ultraviolet lithography (EUVL) has been developed. The mirrors were fabricated using a computer-controlled optical surfacing (CCOS) process and a phase-shift interferometer. The figure error of the mirrors is 0.58 nm. To achieve a high reflectivity in the clear aperture, Mo/Si multilayer films with an optimized d-spacing were successfully deposited on the mirrors. These results show that we have nearly achieved the target specifications for EUVL mirrors.

Simple arguments are given that elucidate the need for x-ray collimator optics in point source proximity lithography. Seven recent collimator optics deigns are briefly described. Three of these designs are described in greater detail: a flat mirror array developed by Xmetrics, Inc.; a polycapillary array developed by X-Ray Optical Systems, Inc.; and a scanning paraboloidal collimator developed by Lawrence Livermore National Laboratory. For the latter two collimators test results using the JMAR Technologies, Inc. laser plasma x-ray point source are given.

Periodic multilayers are well known as Bragg reflectors for X- rays. A high reflectivity and a wide reflection width are their outstanding features. However, if multilayers shall be used as reflective coating for X-ray optics, especially for wide acceptance angles, uniform layer thicknesses cause chromatic aberrations. These aberrations can be overcome by laterally graded multilayer optics. Their Bragg angle is matched laterally to the incidence angle so that for all points on the reflector, Bragg reflection is obtained for the same wavelength. Three major types of laterally graded multilayer mirrors ('Gobel Mirrors') are applied in X-ray diffractometry: (1) parabolic, (2) elliptic and (3) planar. In this paper, we give design criteria and formulae for these mirrors. Furthermore, we discuss the requirements on the dimensions and the fabrication process. Two different processes suitable for the fabrication, sputter coating and pulsed laser deposition (PLD), are described. The X-ray optical parameters and their characterization are presented for various mirrors designed for Cu K(alpha) , Mo K(alpha) and Cr K(alpha) radiation. From Ni/C and Ni/B₄C multilayers, high-photon-flux monochromators with a Cu K(beta) /K(alpha) intensity ratio of about 1:1000 have been realized. The divergence of the 'parallel' beam reflected from parabolic mirrors is about 0.02 degrees, which is one order of magnitude lower than the divergence of polycapillary optics, monocapillary optics and waveguides. Comparing the photon flux density in a high resolution diffraction setup with and without mirror optics a gain factor of 16 was achieved for parabolic Ni/B₄C multilayer mirrors.

Polycapillary optics, shaped arrays consisting of hundreds of thousands of hollow glass capillary tubes, can be used to redirect, collimate, or focus x-ray and low energy neutron beams. X rays emitted over a large angular range from conventional, laboratory-based sources can be transformed into a beam with a small angular divergence or focused onto a small sample or sample area. Focused spot sizes as small as 20 micrometer have been achieved, with flux densities more than two orders of magnitude larger than that produced by pinhole collimation. This results in a comparable decrease in data collection times due to the increase in direct beam intensity and reciprocal space coverage. In addition, the optics can be employed to reduce background and provide more convenient alignment geometries. The inverse dependence of the critical angle for total external reflection on photon energy results in suppression of high energy photons. This effect can be employed to allow the use of higher tube potentials to increase characteristic line emission. Using parallel beam geometries peak shapes are found to be symmetric and independent of angle and sample alignment. Measurements of x- ray diffraction data and crystallographic analysis have been assessed for powders, thin films, minerals, elemental crystals, polymers, and protein crystals.The benefits and limitations of polycapillary optics for such measurements will be reviewed.

We present the results of coating the first set of optical elements for an alpha-class extreme-ultraviolet (EUV) lithography system, the Engineering Test Stand (ETS). The optics were coated with Mo/Si multilayer mirrors using an upgraded DC-magnetron sputtering system. Characterization of the near-normal incidence EUV reflectance was performed using synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Stringent requirements were met for these multilayer coatings in terms of reflectance, wavelength matching among the different optics, and thickness control across the diameter of each individual optic. Reflectances above 65% were achieved at 13.35 nm at near-normal angles of incidence. The run-to-run reproducibility of the reflectance peak wavelength was maintained to within 0.4%, providing the required wavelength matching among the seven multilayer-coated optics. The thickness uniformity (or gradient) was controlled to within plus or minus 0.25% peak-to-valley (P-V) for the condenser optics and plus or minus 0.1% P-V for the four projection optics, exceeding the prescribed specification for the optics of the ETS.

Extreme Ultraviolet Lithography (EUVL) is a candidate for future application by the semiconductor industry in the production of sub-100 nm feature sizes in integrated circuits. Using multilayer reflective coatings optimized at wavelengths ranging from 11 to 14 nm, EUVL represents a potential successor to currently existing optical lithography techniques. In order to assess lifetimes of the multilayer coatings under realistic conditions, a series of radiation stability tests has been performed. In each run a dose of EUV radiation equivalent to several months of lithographic operation was applied to Mo/Si and Mo/Be multilayer coatings within a few days. Depending on the residual gas concentration in the vacuum environment, surface deposition of carbon during the exposure lead to losses in the multilayer reflectivity. However, in none of the experimental runs was structural damage within the bulk of the multilayers observed. Mo/Si multilayer coatings recovered their full original reflectivity after removal of the carbon layer by an ozone cleaning method. Auger depth profiling on Mo/Be multilayers indicate that carbon penetrated into the Be top layer during illumination with high doses of EUV radiation. Subsequent ozone cleaning fully removed the carbon, but revealed enhanced oxidation of the area illuminated, which led to an irreversible loss in reflectance on the order of 1%.

A condenser for a ring-field extreme ultra-violet (EUV) projection lithography camera is presented. The condenser consists of a gently undulating mirror, that we refer to as a ripple plate, and which is illuminated by a collimated beam at grazing incidence. The light is incident along the ripples rather than across them, so that the incident beam is reflected onto a cone and subsequently focused onto the arc of the ring field. A quasi-stationary illumination is achieved, since any one field point receives light from points on the ripples, which are distributed throughout the condenser pupil. The design concept can easily be applied to illuminate projection cameras with various ring-field and numerical aperture specifications. Ray-tracing results are presented of a condenser for a 0.25 NA EUV projection camera.

Fabrication process of soft X-ray multilayer mirrors composed of Sc/Cr having shown high reflectances above 10% including the highest 14.8% for a wavelength of 3 nm is described. The multilayers were prepared by ion beam sputtering of an electron cyclotron resonance type enabling sputter deposition at the highest vacuum of 0.03m Torr. The multilayers were prepared at a stable deposition rate within 4 hours to suppress period instability and also at various substrate temperatures to find the best condition to suppress the interface roughness.

Molybdenum/Silicon soft x-ray optical coatings for extreme ultraviolet lithography are being developed for both projection optics and masks, and have only recently been produced on a production scale via magnetron sputtering. A number of critical factors must be met for successful development of these coatings for implementation into commercial EUV Lithography. We report on our results for several factors with a state-of-the-art in-line sputtering system. All coatings in a lithography system must match to obtain maximum energy transmission. Hence, process repeatability and characterization of the reflectivity and central wavelength is essential. Run-to-run performance and substrate uniformity is shown to have achieved less than 1% deviation in soft x-ray central wavelength between any two points on any two substrates coated in separate batches; coating uniformity on a given wafer is on the order of 0.3% total deviation. Hard x-ray measurements of d-spacing and reflectivity were correlated to soft x-ray measurements; these correlations were used to improve process control. Furthermore, the coatings must be as defect-free as possible; elimination of aerosol-based particulate generation has allowed improvements by nearly four orders of magnitude. Finally, efforts to understand and control coating stress as a function of processing parameters and post-coating annealing schedules will be reviewed. Results of the effects of deposition method, ion bombardment and interactions between sputter power, sputter pressure and deposition rate are reviewed.

Beryllium (Be) has been recently receiving considerable attention as the key material for a range of potential applications in the extreme ultraviolet (EUV) and x-ray region. Most notably, it has been successfully implemented as the spacer material in beryllium-based multilayer mirrors for EUV lithography, achieving experimental reflectivities of about 70% at wavelengths around 11.4 nm. Knowledge of the absorptive and dispersive properties of this material thus becomes important for the modeling of these optics. Experimental photoabsorption results in the region 40 - 250 eV, derived from transmission measurements on free-standing beryllium foils, are presented in this work. The measured absorption in the region extending a few tens eV below the K edge (111.7 eV) appears to be significantly (up to 50%) lower than the tabulated values. Fine structure above the K edge is also demonstrated in the measurements. These data are incorporated in an updated set for the atomic scattering factors of beryllium, obtained in the range 0.1 - 30,000 eV. Finally, the Bragg reflectivity of Mo/Be multilayer optics is modeled using the new experimental results.

The performance of beryllium-based multilayer coatings designed to reflect light of wavelengths near 11 nm, at normal incidence, is presented. These multilayer coatings are of special interest for extreme ultraviolet lithography (EUVL). The beryllium-based multilayers investigated were Mo/Be, Ru/Be and a new material combination Mo₂C/Be. The highest reflectivity achieved so far is 70% at 11.3 nm with 70 bilayers of Mo/Be. However, even though high reflectivity is very important, there are other parameters to satisfy the requirements for an EUVL production tool. Multilayer stress, thermal stability, radiation stability and long term reflectance stability are of equal or greater importance. An experimental characterization of several coatings was carried out to determine the reflectivity, stress, microstructure, and long term stability of these coatings. Theoretically calculated reflectivities are compared with experimental results for different material pairs; differences between experimental and theoretical reflectivities and bandwidths are addressed.

A beamline combining the highest possible photon density on the sample with medium energy resolving power is under construction at the third generation storage ring ELETTRA in Trieste. It is designed to meet the requirements for the best instrumental performance of two imaging microscopes, which are going to be used for surface science research and micro- characterization of magnetic materials. The high photon density on the sample will be preserved within a rather wide photon energy range, between 20 to 1000 eV. In order to meet these requirements, building a simple while economical beamline we use a Variable Line Space (VLS) grating solution for the monochromator and adaptive plane elliptical mirrors for the re-focusing. In particular two low groove density VLS plane gratings (made by Jobin-Yvon) will cover the energy range between 20 and 1000 eV and a spherical grating will cover the lower energy (less than 20 eV) and focus the zero order light, still in grazing incidence mode. Before the monochromator, an internally cooled toroidal mirror (developed at ELETTRA) will pre-focus the radiation in different positions for the sagittal and tangential directions. After the exit slit, two different branches will host two couples of adaptive plane elliptical mirrors (developed in collaboration with S.E.S.O.) mounted in a Kirkpatrick-Baez configuration. The minimum final spot size will be of the order of 4 micrometer² with a maximum photon density of the order of 10¹⁴ ph/sec/micrometer². The advantage of the selected solutions and the overall expected performance will be described in detail.

The neutron spin echo spectrometer IN15 at the Institut Laue- Langevin, Grenoble, has been constructed with a focusing mirror option, designed to increase the intensity for measurements at longer neutron wavelengths, and thus to reduce the minimum Q value by an order of magnitude to approximately equals 10^-3 Angstrom^-1, and to increase the maximum spin echo Fourier time by at least a factor of 2. In this paper we describe the results of analytical calculations and ray-tracing simulations which compare the performance of IN15 in its standard and focusing mirror instrument configurations, taking into account the mirror size and geometry, the wavelength, the wavelength distribution, and the incident beam intensity and divergence. We analyze the intensity profiles for both configurations, presenting the results as plots of intensity at the sample against minimum achievable Q in horizontal and vertical directions at the detector. We show that the gains predicted by ray-tracing simulations, for realistic instrument set-ups, differ considerably from those anticipated by analytical calculations. The deviations are principally attributed to gravitational effects, which rapidly worsen with increasing wavelength.

Numerical simulation studies are carried out on a new type of ultracold neutron generator for a pulsed spallation facility which is operated in a synchronized integral velocity conversion from pulsed very cold neutrons into quasi- continuous ultracold neutrons.

The neutron optics of three-axis spectrometers with bent perfect crystals and position sensitive detection (PSD) has been developed. Theoretical analysis in the phase space and in the scattering space shows that simultaneous PSD scans can be performed along any given direction in the scattering (h(omega) ,Q) plane, including energy transfer scans or Q- scans. For instance, to perform a simultaneous energy transfer scan the curvature of the monochromator must be set for 'monochromatic focusing' while the curvature of the analyzer must be significantly away from the 'monochromator focusing' value. A new kind of focusing was found to be possible. Under the right conditions the resolution in scattering becomes insensitive to the thickness of the analyzer crystal. Packets of commercial thin silicon wafers can then give resolutions corresponding to a single wafer at considerable gains in intensity. Control experiments with a 14-wafer assembly have confirmed this conclusion. Resolutions below 3 minutes of arc on the angular scale were obtained (corresponding to energy transfer resolutions in the range of 10 to 150 (mu) eV, depending on the neutron energy). A practical difficulty is that very high spatial resolutions of the PSD, in the submillimeter range, are needed to take full advantage of the possibilities offered by commercial thin silicon wafers.

The neutron interferometry technique provides direct access to phase of the neutron wave. If properly applied, the use of phase information in imaging materials can provide an advantage over normal intensity techniques, which use absorption to provide image contrast. The National Institute of Standards and Technology Neutron Interferometry and Optics Facility has been working on new methods and devices to exploit the neutron phase information to image materials. We will present here the latest results of this effort and an overview of the instruments available at NIST for Neutron Phase Contrast Imaging.

We have performed two separate experiments using glass capillary fibers to transport (1) polarized neutrons, and (2) cold neutrons with the fiber at high temperature. The same type of capillary fibers has been used to construct neutron and x-ray focusing lenses. The purpose was to observe whether multiple glancing angle collisions during transport could change either the polarizations or the transmission and exit divergence. In the first case, polarized 0.235 nm neutrons were transmitted through a bent glass capillary fiber, and the spin states of the emergent neutrons were measured. In the second experiment, 0.5 nm neutrons were passed through a glass capillary fiber heated to 200 degrees Celsius, and transmission and divergence were compared to the values at room temperature. The negative result for the first experiment indicates that capillary fibers can be used to transmit polarized neutrons. The heating experiment demonstrated that thermal vibrations of the capillary walls or collisions with heated air molecules did not significantly affect fiber properties; however, some mechanical shifting took place at high temperature.

A new type of ultracold neutron generator is proposed for a pulsed spallation facility which can be operated in a synchronized integral velocity conversion from pulsed very cold neutrons into quasi-continuous ultracold neutrons.

VESTA (the Viennese nEutron STorage Apparatus) is an experiment for storing cold neutrons with a wavelength of 6.27 Angstrom, installed at the pulsed neutron source ISIS. A highly monochromatic neutron beam ((Delta) k/k approximately 4*10^-5) is trapped by Bragg reflections between two precisely parallel silicon crystal plates in backscattering geometry. Entry and exit of the neutrons into and from the storage system is achieved by using the Zeeman energy shift caused by a short pulsed magnetic field at the crystal plates when the neutron pulse, to be stored or released, is passing by. With a significantly improved signal to background ratio, it was possible to store up to 6 neutron pulses simultaneously for the first time. By varying the storage time separately for each pulse, the feasibility of neutron beam manipulations in time and space was demonstrated. The influence of the magnetic field strength on the transmission of a perfect crystal has been investigated. After optimizing the alignment of the storage cavity, neutrons were stored for up to 4.2 seconds, which corresponds to a flight path of 2.66 km inside VESTA, or to 2500 consecutive Bragg-reflections. Currently, a new storage device, 'VESTA Type 2,' is under construction. In this case the energy shift for neutron entry and exit will be achieved by using a pulsed hf-spin flipper and a static NMR magnet. It can be expected that by removing the pulsed magnets of the existing device and by reducing other sources of vibration, the storage time and efficiency can be further improved.

The experience in manufacturing and testing of neutron multilayer structures, interference filters, is described. Construction of a gravity UCN spectrometer based on the use of such devices is also reported. Some results of the test experiment of the UCN dispersion law performed with such a spectrometer are presented. Among them are the resonant mode mixing effect due to scattering by the roughness. Some possibilities of new experiments based on a similar method are investigated.

We describe an experimental test on transmission of neutrons with velocities near 70 m/s through a Si single crystal with ultra-high precision polished surfaces, when neutrons undergo total reflection at a grazing angle lower than the critical angle. The transmission probability estimated from our measurements is at the level 9 X 10^-5, which is consistent with theoretical expectations, and previous measurements.

Bent crystals are well suited to high-brilliance sources and add flexibility to the design of synchrotron radiation (SR) monochromators. A double crystal monochromator for high resolution in elastic scattering of SR is examined by methods developed for neutron optics. Computations with a neutron code adapted to the case of SR show that bending the first crystal can improve performance by strongly reducing the beam size at marginal gain in full beam intensity.

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.

We have developed a new family of EUV multilayer mirror coatings using uranium. Using this approach we have coated a set of six mirrors for the EUV Imager, a component of the IMAGE mission. This mission is a Medium Explorer (MIDEX) program, which is scheduled for launch early in 2000. The EUV Imager will study the distribution of He⁺ in the Earth's plasmasphere by detecting its resonantly scattered emission at 30.4 nm (41 eV) and will produce images of the structure and dynamics of the cold plasma on a global scale. There is, however, a bright emission at 58.4 nm (21 eV), which comes from neutral helium in the earth's ionosphere which also must be blocked. These photons are at too high an energy to filter with aluminum but at too low an energy to have negligible reflectance from most materials commonly used in EUV mirrors. Thus, a multilayer system which satisfied two optical functions, high reflectance (greater than 20%) at 41 eV and low reflectance (less than 2%) at 21 eV, were designed and successfully fabricated. Such mirrors with dual optical functions in the soft x-ray/EUV had not previously been designed or built. These specifications were particularly challenging because many materials have higher single layer reflectances at 58.4 nm than at 30.4 nm. Essentially, the mirror must have low reflectance at 21 eV without loss of reflection at 30.4 nm. This was accomplished. The top part of the multilayer, which reflects well at 30.4 nm, also acts as antireflection layers at 58.4 nm. In the past, multilayers usually have consisted of periodic bilayers. We have explored the use of a periodic mirrors in place of the standard periodic designs. Along the way we have created the computational tools, which include genetic algorithms, to optimize selection of materials and thicknesses. We are currently in the process of building up an EUV characterization system and developing a general way of measuring the optical constants of air-sensitive thin films. We discuss the other material and fabrication challenges faced, which include: (1) The high absorption of almost everything in the EUV. This means that only a few interfaces in a multilayer will contribute to its reflectance. (2) Surface contamination and corrosion. (3) The deposition on flight mirrors that are highly curved (f equals 0.8).

This paper is a report on our effort to use reflectance measurements of a set of amorphous silicon (a-Si) and uranium (U) multilayer mirrors with an uranium oxide overcoat to obtain the optical constants of a-Si and uranium. The optical constants of U, its oxides, and Si, whether crystalline or amorphous, at 30.4 and 58.4 nm in the extreme ultraviolet (EUV) are a source of uncertainty in the design of multilayer optics. Measured reflectances of multilayer mirror coatings do not agree with calculated reflectances using existing optical constants at all wavelengths. We have calculated the magnitude and the direction of the shift in the optical constants of U and a-Si from reflectivity measurements of DC magnetron sputtered a-Si/U multilayers at 30.4 and 58.4 nm. The reflectivity of the multilayers were measured using a UV hollow cathode plasma light source, a 1 meter VUV monochromator, a back-thinned CCD camera, and a channeltron detector. These reflectance measurements were verified by measurements made at LBNL. The reflectances of the multilayer coatings were measured at 14.5 degrees from normal to the mirror surface. The optical constants were calculated using IMD which uses CURVEFIT to fit the optical constants to reflectivity measurements of a range of multilayer mirrors that varied over a span of 150 - 25.0 nm bilayer thickness. The effects of surface oxide and roughness, interdiffusion, and interfacial roughness were numerically subtracted in fitting the optical constants. The (delta) , (beta) determined at 30.4 nm does not well match the values of c-Si published in the literature (HBOC¹), but do approach those of a-Si as reported in literature (HBOC). The difference in the optical constants of c-Si and a-Si are larger than can be attributed to differences in density. Why the optical constants of these two materials vary at 30.4 remains an open question.