The main technological challenge of a future extreme ultraviolet (EUV) light source is the required average power of 115W at the intermediate focus. High repetition rate laser produced plasma (LPP) sources are very promising to face this challenge. We report the current status of the laser produced light source system we started to develop in 2002. The system consists of the following main components: The plasma target is a liquid xenon jet with a maximum diameter of 50 μm and a velocity of more than 30 m/s. A Nd:YAG laser oscillating at 1064 nm produces the plasma. The laser is a master oscillator power amplifier (MOPA) configuration with a maximum repetition rate of 10 kHz and an average power of 1.3kW. The EUV system currently delivers an average EUV in-band power of 7.2 W (2% bandwidth, 2π sr). In order to decrease debris and to reduce the supply of target material we started the development of a xenon droplet target. Currently droplets are generated in vacuum at a frequency of 140 kHz, i.e. 140000 droplets/s, having a diameter of 100 μm and a velocity of 28m/s.

Recently, an electron-based ultrashort hard-x-ray source has been developed at the Laser Zentrum Hannover e.V. In this source x-ray pulses are produced by combining femtosecond laser technology with a specially designed x-ray diode. At first, ultrashort electron pulses are generated by photoemission from a photocathode. Then, these electron pulses are accelerated over a short distance towards a high-Z anode. Hard-x-rays are produced via Bremsstrahlung and characteristic line emission. Now detailed measurements of the hard-x-ray pulse duration have been performed using an advanced streak camera. The streak camera has a sub-picosecond time resolution in the keV range. With this camera hard-x-ray pulse durations of less than 10 ps were observed for electron pulse charges of the order of several pC. In this contribution we present our results on the x-ray pulse duration measurements and their dependence on different experimental parameters. A comparison with theoretical simulations is given.

For a number of years, ALFT Inc. has developed a laboratory soft X-ray source for the many analyses that are now being carried out at synchrotron locations. It is a Vacuum Spark source (VSX). The source is a pulsed point plasma emitting pulses of soft X-rays around 1 keV or 10 Angstroms wavelength. The average power is 728 mW in the VSX 700 machine. In terms of photon flux, it emits an average of 10¹⁵ photons/sec, with peak flux of 10¹⁸ photons/sec. Being a thermal source, the radiation is divergent. Because of its divergence, the source can be used along different directions, 4 beams being now part of the present commercial machine. This laboratory tool has been thoroughly developed to the point that it reliably runs continuously without deterioration of power or spectral purity. The plasma can be generated from among many elements, copper and tungsten being two of the presently used. A more powerful source, the VSX Z10, of 10 Watts average power, has been also developed by ALFT Inc. and has now reached the prototype stage. It is again a thermal divergent plasma source emitting in excess of 10¹⁶ photons/sec with peak flux of 10²⁴ photons/sec. Sources in the 50 Watts range are now being considered for further development.

A pulsed nanosecond x-ray generator based on an actively pumped field emission x-ray tube is described. The x-ray source is based on a high voltage Marx generator that drives a field emission tube without the need for an intermediate energy store. The Marx generator stores 12 Joules in ceramic capacitors and produces a voltage pulse > 380 kilovolts with a rise time of < 4 nanoseconds from an equivalent generator-impedance of 52 W. A numerical model is used in which the x-ray tube's cathode width and anode-cathode gap (AK) are permitted to change with time while electron current between the cathode and anode is treated as non relativistic and space-charge-limited (SCL). By coupling this model to an equivalent circuit representation of the Marx generator a calculation of the cathode current, anode-cathode potential and the output x-ray spectrum can be made. The radiation dose is 55 millirems at 30.4 cm from the anode of the x-ray tube and is Gaussian in shape with a 35 nanosecond (full width at half maximum) FWHM. The measured x-ray dose, pulse shape and width are consistent with model predictions. The source was successfully used to study high-velocity projectile induced cavatation in human tissue.

The development of an extremely soft x-ray generator with a tungsten-target tube and its applications to radiography and disinfection are described. This generator consists of a high-voltage power supply, a filament power supply, and an x-ray tube. Negative high voltages are applied to the cathode electrode in the x-ray tube, and the tube voltage and current are regulated by the input of a transformer and the filament voltage, respectively. The x-ray tube is a glass-enclosed double-focus diode with a tungsten target and a 0.2 mm-thick beryllium window. The maximum tube voltage and electric power were 60 kV and 400 W, respectively. The focal-spot sizes were 4×4 (large) and 1×1 mm (small), respectively. Extremely soft radiography was performed with a computed radiography system, and we observed fine blood vessels of about 100 μm with high contrasts. Using this generator, we performed the disinfection achieved with extremely soft x rays.

This paper presents simulated and measured spectra of a novel type of x-ray tube. The bremsstrahlung generating principle of this tube is based on the interaction of high energetic electrons with a turbulently flowing liquid metal separated from the vacuum by a thin window. We simulated the interaction of 50-150 keV electrons with liquid metal targets composed of the elements Ga, In, Sn, as well as the solid elements C, W and Re used for the electron windows. We obtained x-ray spectra and energy loss curves for various liquid metal/window combinations and thicknesses of the window material. In terms of optimum heat transport a thin diamond window in combination with the liquid metal GaInSn is the best suited system. If photon flux is the optimization criteria, thin tungsten/rhenium windows cooled by GaInSn should be preferred.

We have demonstrated a new electron-impact hard-x-ray source based on a liquid-metal-jet anode in a proof-of-principle experiment. Initial calculations show that this new anode concept potentially allows a >100x increase in source brightness compared to today's compact hard-x-ray sources. In this paper we report on the scale up of the system to medium electron-beam power resulting in a brightness comparable to current state-of-the-art sources. The upgraded system combines a ~20-μm diameter liquid-tin jet operating at ~60 m/s with a 50 kV, 600 W electron beam focused to ~150 μm FWHM. We describe the properties of the current system, experimental results, as well as a brief discussion of key issues for future high-power scaling.

A compact electron-based microfocus EUV/soft-x-ray source for applications in metrology and microscopy is developed. The source concept is based on the transfer of advanced microfocus x-ray tube technology into the EUV/soft-x-ray spectral range. This allows the realization of a flexible, debris-free, and long-term stable source. Detailed characteristics of the source performance are reported and different applications of the soft-x-ray tube in the field of at-wavelength metrology are presented.

The cerium-target x-ray tube is useful in order to perform cone beam K-edge angiography because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. The x-ray generator consists of a main controller and a unit with a high-voltage circuit and a fixed anode x-ray tube. The tube is a glass-enclosed diode with a cerium target and a 0.5 mm-thick beryllium window. The maximum tube voltage and current were 65 kV and 0.4 mA, respectively, and the focal-spot sizes were 1.3×0.9 mm. Cerium K-series characteristic x rays were left using a 3.0 mm-thick aluminum filter, and the x-ray intensity was 0.59 μC/kg at 1.0 m from the source with a tube voltage of 60 kV, a current of 0.40 mA, and an exposure time of 1.0 s. Angiography was performed with a computed radiography system using iodine-based microspheres 15 μm in diameter. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and scientific applications for our technology includes: a monochromatic X-ray collimater for medical diagnostics, a relay optic to transport an X-ray beam from the target in a scanning electron microscop0e to a lithium-drifted silicon and microcalorimeter detectors and a satellite mounted telescope to collect celestial X-rays. A wide variety of mono- and multilayer coatings allow X-rays up to ~100 keV to be reflected. Our paper presents data from a variety of diagnostic measurements on the properties of the PET foil and imaging results form single- and multi-shell lenses.

Three dimensional focusing of characteristic x-rays can be achieved by diffraction from doubly curved crystals (DCC). A focused beam total reflection x-ray fluorescence technique was developed based on these optics. This technique provides good detection sensitivity and spatial resolution for localized detection of surface deposits. Compact low power small spot x-ray sources were used to demonstrate the benefit of the x-ray optics for focusing Cr Kα, Cu Kα and Mo Kα radiation. The DCC optic was also applied to monochromatic micro x-ray fluorescence (MMXRF), providing good detection sensitivity and spatial resolution for deeper impurities. The detection capability of the focused beam TXRF and MMXRF systems was investigated with dried droplets of calibrated low concentration solutions. Additionally, the implementation of high contrast monochromatic imaging with a very low power source was demonstrated using the DCC optics at mammographic energies. Images of contrast phantoms were obtained with high clarity.

A compact monochromatic imaging system was designed with an optimal combination of a low power molybdenum source, collimating optic and monochromatizing crystal. The microfocus source was characterized for spot size, source depth, source intensity and source uniformity. Two different polycapillary collimating optics were characterized for collecting radiation from the low power divergent source and redirecting it into a parallel beam. The focal distance, transmission with respect to energy, output uniformity and exit angle divergence were measured. Monochromatization was then achieved by diffraction from a variety of single crystals. For each crystal, the rocking curve width was measured. To predict the actual resolution for the monochromatic imaging, a theoretical 3-dimension resolution calculation was developed. The measured angular resolutions for the horizontal and vertical directions were slightly different and were in good agreement with theoretical values. The measured and theoretical intensity after monochromator crystals showed the expected trade-off between high intensity and high resolution.

We present the theoretical design, the fabrication, and the performance of double gradient multilayers to be installed on a Kirkpatrick-Baez focusing system for the ESRF bending magnet beam line BM5. The lateral and the depth gradient of the two coatings were chosen in such a way as to obtain a flat reflectivity response of about 25% after two reflections over an energy range from 12keV to 14keV and at an angle of incidence of 0.5deg at the mirror center. Both mirrors were coated with a non-periodic Ru/B4C structure containing 71 individual layers. The overall depth gradient was identical for both multilayers and optimized at the mirror center while the lateral gradient was adapted to the different focal lengths of each of the two KB elements.

Zone plates with depth to zone-width ratios as large as 100 are needed for focusing of hard x-rays. Such high aspect ratios are challenging to produce by lithography. We are investigating the fabrication of high-aspect-ratio linear zone plates by multilayer deposition followed by sectioning. As an initial step in this work, we present a synchrotron x-ray study of constant-period multilayers diffracting in Laue (transmission) geometry. Data are presented from two samples: a 200 period W/Si multilayer with d-spacing of 29 nm, and a 2020 period Mo/Si multilayer with d-spacing of 7 nm. By cutting and polishing we have successfully produced thin cross sections with section depths ranging from 2 to 12 μm. Transverse scattering profiles (rocking curves) across the Bragg reflection exhibit well-defined interference fringes originating from the depth of the sample, in agreement with dynamical diffraction theory for a multilayer in Laue geometry.

We introduce a method for the determination of the thickness variation through the stack of multilayer structures deposited by magnetron sputter deposition. The deposited structure is determined by minimizing a merit function based on the difference between actual x-ray reflectivity data and the theoretical calculation of the reflectivity from a multilayer structure. This method uses only four parameters and is independent of the total number of layers deposited. Further, this simple method provides a good initial guess if one wishes to increase the number of independent parameters in order to investigate finer detail of the structure. We illustrate the usefulness of this method through comparison of a desired and deposited Ni/C multilayer. The thickness distribution through the stack was designed in such a way as to maximize integrated reflectivity over some angular range. Finally, we determine the dependence of layer thickness with annealing temperature for the depth graded Ni/C multilayer by use of our method.

Non periodic Ru/B₄C double gradient multilayers were deposited by Distributed Electron Cyclotron Resonance (DECR) sputtering. These coatings will allow focusing with a constant reflectivity of 50% over an energy range from 12 keV to 14 keV. In this case, a lateral gradient is needed to fulfill the Bragg condition along the multilayer length, and a depth gradient is required to obtain the expected energy bandwidth. Our design approach was based on numerical calculations to define each layer thickness independently. During calibration tests, we had to take into account intermixing between Ru and B₄C. We will present the importance of layer intermixing of each material (angular shift and bandwidth of first Bragg peak) and how these parameters can be integrated in the design without affecting the required reflectivity profile. We will also discuss compromises made to keep both lateral and depth gradient optimized in view of the technical limitations of our deposition process.

To develop narrow-bandpass multilayer monochromators, we have studied small d-spacing WSi₂/Si multilayers. We found that WSi₂/Si is an excellent multilayer system for achieving both the desired spectral resolution and peak reflectivity. Compared to other traditional multilayer systems such as W/Si, WSi₂/Si not only has a lower density and lower absorption, but also is a chemically more stable system, since WSi₂ is already a silicide. One thus expects better thermal stability and sharper interfaces for WSi₂/Si multilayers. There are two approaches to achieve high-resolution multilayers: either decrease the d spacing or use low absorption materials. By using WSi₂/Si, we can utilize both approaches in the same system to achieve good energy resolution and peak reflectivity. Another advantage of this system is that the sputtering rate for Si is much higher than other traditional low-Z materials. Several WSi₂/Si multilayers have been fabricated at the Advanced Photon Source (APS) deposition lab using dc magnetron sputtering with constant currents of 0.5 A in Ar at a pressure of 2.3 mTorr. A test sample of [9.65Å-WSi₂/10.05Å-Si] × 300 was studied at four institutions: using laboratory x-ray diffractometers with Cu Kα (8.048 keV) wavelength at the APS x-ray lab and at European Synchrotron Radiation Facility (ESRF), and using synchrotron undulator x-rays at 10 keV at MHATT-CAT and at 25 keV at ChemMatCARS-CAT of the APS. The measured first-order reflectivity was 54% with a bandpass of 0.46% at 10 keV and 66% reflectivity with a bandpass of 0.67% at 25 keV of undulator x-rays. Similar results were obtained from Cu Kα x-rays. This result is very attractive for the design of a multilayer monochromator for the ChemMatCARS-CAT to be used in the 20 to 25 keV range. Other small d-spacing multilayers are being studied. Comparison between WSi₂/Si and W/Si multilayers will be discussed.

A double multilayer monochromator with each multilayer composed of four stripes with different d-spacing providing spectral resolution of 0.3% to 0.8% in the energy range of 6keV to 19keV has been developed. Test multilayer structures with d-spacing from 2.3nm to 10.6nm have been deposited by magnetron sputtering. X-ray characterization has been performed at OSMIC by using a recently upgraded diffractometer setup and Cu-K_α radiation and at the APS. The following material combinations were studied before the final choice of materials for the high energy resolution monochromator has been made: Al₂O₃/B₄C, SiC/Si, SiC/B₄C and SiC/C. To minimize the effect of internal stress built in multilayer structure on X-ray characteristics flat and thick 1" diameter silicon substrates supplied by Wave Precision Inc. were used for all calibration coatings. Final coatings were deposited on two 145mm long, 60mm wide and 30mm thick silicon substrates. Resolution of SiC/Si structures with d₁=2.3nm, N₁=1000 and d₂=3nm, N₂=700 was measured at Cu-K_α with X-ray beam divergence of 14 arcsec to be 0.216% and 0.34% respectively. For plane waves the resolution is expected to be 0.13% and 0.19%, respectively.

Channel-cut monochromators can be easily incorporated in high-resolution image techniques. However, polishing on the inner diffracting surfaces is difficult because of blockage by the opposite face. To address this difficulty, an open-faced monolithic monochromator has been designed, produced and tested using x-rays at the Advanced Photon Source (APS). The open-faced channel cut has a “Z”-shape geometry with a hole in the mid section to allow passage of the diffracted beam. The open geometry allowed chemical mechanical polishing so that an optically smooth finish on both surfaces was achieved. The high-resolution x-ray imaging and topography measurements revealed that the new design introduces significantly less distortions in the phase-contrast images compared with conventional channel-cut monochromators produced using etching alone.

We present an optic for laboratory Mo-Kalpha single crystal diffraction systems. The optic is comprised of two elliptically bent focusing multilayers, which are arranged in the Montel scheme. The paper shows the design and performance of the optic. A comparison with a graphite monochromator shows a five-fold intensity enhancement. Especially small and weakly diffracting crystals benefit from the large intensity produced by the optic, as illustrated by diffraction analyses.

The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -50 to -70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean silver Kα lines are produced using a 30 μm-thick palladium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of -70 kV, the instantaneous tube voltage and current were 90 kV and 0.8 kA, respectively. The x-ray pulse widths were approximately 80 ns, and the instantaneous number of generator-produced Kα photons was approximately 40 M photons/cm² per pulse at 0.3 m from the source of 3.0 mm in diameter.

This paper describes the design and analysis of a contact-cooled channel-cut germanium monochromator for use on a high-heat-load x-ray beamline. This channel-cut monochromator is designed in the shape of a "Z" so that polishing the diffraction surfaces is easier. The incident x-ray beam, which is reflected from a mirror at a 0.15° angle, diffracts from one surface of the Z-monochromator, passes through an opening, and diffracts from the second surface. The monochromator is located 60 meters from the undulator x-ray source. The normal heat flux of the incident beam can be up to 7 W/mm². Thermal and structural analyses are presented, and the deformation caused by gravity is considered.