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The feasibility of the realization of a HOPG-based von Hamos spectrometer with a high energy resolution is discussed on the basis of the acquired theoretical and experimental data. The spectrometer makes use of HOPG films, which can be deposited on a mould of any shape, including the cylindrical form. In this way focusing geometry of a von Hamos scheme can be easily realized. The mosaic structure of HOPG crystals leads to additional focusing known as mosaic focusing, which increases further the intensity. In spite of a relatively large value of the mosaic spread (typical value 0.4°), energy resolution over 1200 can be achieved. Possible applications include simultaneous registration of spectra in plasma diagnostic and spectroscopy.

Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlorophyll a and peridinin, were measured. The energies of the lowest unoccupied molecular levels of these pigments appearing in the carbon NEXAFS spectrum were resolved. Individual contributions of the pigments and the protein to the measured NEXAFS spectrum of PCP were determined using a "building block" approach combining NEXAFS spectra of the pigments and the amino acids constituting the PCP apoprotein. The results suggest that absorption changes of the pigments in the carbon near K-edge region can be resolved following excitation using a suitable visible pump laser pulse. Consequently, it may be possible to study excitation energy transfer processes involving "optically dark" states of carotenoids in pigment-protein complexes by soft X-ray probe optical pump double resonance spectroscopy (XODR).

We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, using a tabletop femtosecond laser-based plasma source. We demonstrate a 23 µm focus with a toroidally bent Ge single crystal. A maximum flux of 7 × 10 8 photons/(s mm 2 ) is generated in a 32 µm focus using a multi-layer mirror. An elliptical glass capillary yields the highest number of photons per Bragg angle (2 × 10 5 photons/(s mrad)). The largest number of photons (3 × 10 6 photons/s) per second is obtained in the 105 µm focus of a poly-capillary optical lens system. All numbers are given for characteristic Cu Kα photons.

In this article we present a setup of a spectrometer for near edge x-ray absorption spectroscopy at the carbon K-edge (284 eV). The spectrometer works with a laser produced plasma as x-ray source and a single x-ray optical element in grazing incidence configuration called off-axis reflection zone plate. Using different sample foils we were able to demonstrate a spectral resolution of E/ΔE≈600. The positions of specific absorption peaks are in agreement with data measured at synchrotron sources. Since the off-axis zone plate is a focusing system, the x-ray flux in the detector plane is high enough to record an absorption spectrum on a charge-coupled device detector with a single shot. In the single shot modus a spectrum can be recorded before a sample degradation takes place. This will enable time-resolved experiments using pump-probe techniques.

Permeability due to domain wall motion and spin rotation is studied on CoZr and CoZrRe thin films presenting different distributions of anisotropy. The influence of the amplitude and frequency of the exciting field on the two magnetization processes, domain wall motion and spin rotation, is studied, showing the existence of a critical field for domain wall depinning and a domain wall relaxation. We show that it is possible to separate and evaluate the contribution of the two magnetization processes to the permeability and analyse the influence of the anisotropy dispersion on the frequency spectra of the permeability.

We present experiments of magnetization reversal by spin injection performed on pillar-shaped Co/Cu/Co trilayers. The pillars (200×600 nm2) are fabricated by electron beam lithography and reactive ion etching. Our data for the magnetization reversal at a threshold current confirm previous results on similar pillars. In addition, we present another type of experiment that also clearly evidences the control of the magnetic configuration by the current intensity. Our interpretation is based on a version of the Slonczewski model in which the polarization of the current is calculated in the Valet&#8211 ; Fert model of the giant magnetoresistance with current applied perpendicular to plane.

Soft X-ray laser have recently shown a dramatic reduction in the pump energy needs. Grazing incidence pumping geometry constitutes the last achieved milestone on the way to real repetitive soft X-ray lasers. We present the results of the experimental investigation on such a laser scheme using Mo as a slab target. The preplasma conditions are discussed in detail and compared with those of other experiments. Estimates of some of the output parameters and the development prospects for the new scheme are given as well. Additionally, the results of the measurements on wavelength nonselective capillary XUV optics are presented.

Thin films of highly oriented pyrolytic graphite (HOPG) give the opportunity to realize crystal optics with arbitrary geometry by mounting it on a mould of any shape. A specific feature of a HOPG is its mosaicity accompanied by mosaic focusing and high integral reflectivity. These characteristics are of interest for compact x-ray diagnostic tools and spectrometers. Another interesting feature is, due to the mosaic spread of the HOPG crystals, that it is possible also with a beam of low divergence to record a spectrum in a broad energy range even within one laser shot. That means that the HOPG spectrometer can act as a polychromator. The latter feature is important if irreversible changes in samples should be investigated or, e.g., if in time-resolved pump-probe experiments a spectrum should be recorded before sample degradation takes place due to high pump intensities. Different design considerations for a compact HOPG-spectrometer based on experimental and theoretical studies will be presented. For applications in plasma diagnostics and XAFS (x-ray absorption fine structure) the attainable energy resolution plays a central role and has been intensively investigated. The results of our investigations demonstrate that HOPG can be used as powerful optics for x-ray diagnostics as well as for x-ray absorption and emission spectroscopy.

Technological reasons stimulated enormous interest in the spectral range between 10 nm and 15 nm. One of the most important, apart from the potential to be applied in the microlithography, was the existence of the high-efficiency, spectrally highly selective (narrow-band) reflective multi-layer (ML) optics in this spectral range. Applying these optics to plasma based XUV (extreme ultra violett) sources the debris from the plasma is a serious problem. For transmissive multi-layer optics we have additionally the low figures of merit. For example, the best beam splitters have an efficiency of about 30% (energy in both parts of the splitted beam). This type of element is crucial for efficient single-shot interferometry being the main application using table-top soft x-ray lasers. We applied capillary optical elements, to our knowledge for the first time, to XUV radiation at 13.9 nm. These optical elements help overcome the limits discussed above or at least remarkably reduce the existing difficulties. A capillary beam splitter and a focussing capillary were applied to an incoherent XUV radiation source. For the beam splitter we measured a throughput of about 80%. With the focussing capillary we obtained a spot size of 27 μm (FWHM) with a gain (intensity in the focal spot compared to the intensity behind a pinhole of the focal spot size) of 600. Advantages and disadvantages of these optics in the discussed spectral range are analyzed.

Summary form only given. In the present paper, artificially nanostructured uniaxial giant magnetostrictive (Tb/sub x/Fe/sub 1-x//Fe/sub 0.6/Co/sub 0.4/)*n multilayers have been investigated for future MEMS purposes. For this goal, such multilayer films have been RF sputtered onto glass and silicon under various conditions to obtain different Tb ratios in the TbFe layers, with and without a bias field applied along the substrate in order to induce a magnetic easy axis. The authors show that uni-axial magnetostrictive TbFe/FeCo films were obtained with a greatly enhanced magnetoelastic coupling coefficient (b/sup /spl gamma/,2//spl ap/18 MPa) compared to TbFe/Fe (b/sup /spl gamma/,2//spl ap/11 MPa) without an annealing post process.

Summary form only given. In recent years the development of semiconductor devices like SESAMs has led to a substantial progress in the generation of ultrashort pulses in solid-state lasers. The use of semiconductor materials makes it possible to combine strong nonlinear properties with short recombination times. In this work we describe a novel mode locking device based on low-temperature-grown GaAs (LT-GaAs) combined with a double-clad silica fiber laser being doped with Nd/sub 2/O/sub 3/ (1300 ppm) emitting at 1.06 /spl mu/m. The mode locking mechanism is based on the intensity dependent defocusing in the LT-GaAs.

Thin films of highly oriented pyrolytic graphite (HOPG) give the opportunity to realize crystal optics with arbitrary geometry by mounting it on a mould of any shape. A specific feature of HOPG is its mosaicity accompanied by a high integral reflectivity, which is by an order of magnitude higher than that of all other known crystals in an energy range between 2 keV up to several 10 keV. These characteristics make it possible to realize highly efficient collecting optics, which could be also relevant for compact x-ray diagnostic tools and spectrometers. For these applications the achievable spectral resolution of the crystal optics is of interest. In this article measurements with a spectral resolution of E/DeltaE=2900 in the second order reflection and E/DeltaE=1800 in the first order reflection obtained with HOPG crystals are presented. These are by far the highest spectral resolutions reported for HOPG crystals. The integral reflectivity of these very thin films is still comparable with that of ideal Ge crystals. The trade-off between energy resolution and high integral reflectivity for HOPG is demonstrated by determining these parameters for HOPG films of different thickness.

It is shown that, in amorphous thin anisotropic films presenting different distributions of the magnetic anisotropy, the contribution of each magnetization process to the permeability may be separated and evaluated.

Polar Kerr rotation and ellipticity of the synthetic single crystal magnetite are measured at room temperature in the 400 to 2400 nm spectral region. Using these magnetooptical measurements together with the earlier optical data the diagonal and the off-diagonal tensor elements of the dielectric function are deduced. In the infrared region the dependences are dominated by the presence of the charge carriers while the behaviour in the visible part of the spectra is mainly due to the 3d crystal field transitions of the tetrahedral and octahedral iron ions. La rotation et l'ellipticite Kerr polaire d'un monocristal de magnetite synthetique ont ete mesurees dans la bande spectrale de 400 a 2400 nm a la temperature ambiante. En utilisant ces mesures magnetooptiques combines avec les resultats optiques recents on a deduit les elements diagonaux et non-diagonaux du tenseur dielectrique. Dans la bande infrarouge les spectres sont domines par la presence des porteurs de charge electrique tandis que le comportement dans la partie visible du spectre est du principalement aux transitions des electrons entre des niveaux 3d des ions de fer occupant des sites tetraedriques et octaedriques.

International audience; Summary form only given. We reflect the results of the latest investigations on giant magnetostrictive multilayers in which a field induced spin reorientation transition (SRT) is used to develop new ways of control for magnetostrictive MEMS such as the possibility of "sub-harmonic" excitation. During the study of the SRT, experiments showed the existence of an extra singularity when decreasing the polarising field towards negative values. Calculations showed a critical sensitivity of the excitation levels on the alignment of the polarising field. We study in detail the influence of this alignment on near SRT magnetoelastic dynamics.