Spherical Multilayer Mirror Research Articles

Homogenized ion milling over the whole area of EUV spherical multilayer mirrors for reflection phase error correction

For accurate reflection phase manipulation of spherical multilayer mirrors used in extreme ultraviolet (EUV) imaging, a wide-area ion beam with a homogenized radial distribution was produced for period-by-period ion milling. Measured variations of the milling depth with incident angle showed that Si and Mo have the same angular dependence within the effective aperture used in our imaging optics. By using the designed homogenizer mask, the ion-milling depth was successfully homogenized to within an error of ±1.9% over a 50-mm-wide concave mirror. Furthermore, a versatile homogenizer mask with adjustable opening angle plates was developed. With this mask, an ion-milling depth-profile homogeneity of ±1.7% was realized. Although a slight decrease in the peak EUV reflectance was measured as the incident angle decreased, the effectiveness and practicality of our correction method has been demonstrated.

Photoelectric Effect at Ultrahigh Intensities

In the spectral range of the extreme ultraviolet at a wavelength of 13.3 nm, we have studied the photoionization of xenon at ultrahigh intensities. For our ion mass-to-charge spectroscopy experiments, irradiance levels from 10(12) to 10(16) W cm(-2) were achieved at the new free-electron laser in Hamburg FLASH by strong beam focusing with the aid of a spherical multilayer mirror. Ion charges up to Xe21+ were observed and investigated as a function of irradiance. Our surprising results are discussed in terms of a perturbative and nonperturbative description.

Ultrasoft x-ray telescopes for fluctuation imaging in fusion plasmas

We present the design for a novel spectroscopic instrument for two-dimensional imaging of low-amplitude, fast fluctuations from magnetically confined fusion devices. The instrument is similar in principle to an ultrasoft x-ray (USXR) telescope recently developed for astrophysics application and uses a large (10–20-cm-diam), spherical multilayer mirror to select and concentrate a bright USXR impurity line (e.g., C VI Lyα at 33.7 Å, or C VI Hα at 182 Å), onto a low-noise fast, two-dimensional detector. A first version of the telescope will use a fast phosphor to convert the USXR image into visible light, which is then guided using fiber optics to a fast/gated charge-coupled-device camera outside the vacuum. Detailed signal-to-noise analysis indicates that, due to the high energy and brightness of the USXR line emission and large reflectivity of the present mirrors, such an instrument would allow imaging of subpercent amplitude fluctuations with ⩽10 μs time resolution and sub-cm spatial resolution. At the same time, ray-tracing calculations show that a quite large plasma region (up to a few tens of cm extent) can be imaged. Another version of the telescope would use a two-dimensional array of extreme ultraviolet diodes at the focal plane, in which case fluctuations up to ≈0.1% could be imaged.

Photoemission microscopy with microspot-XPS by use of undulator radiation and a high-throughput multilayer monochromator at BESSY

We present a new experiment for photoelectron microspectroscopy by use of undulator radiation, which has been set up at the beamline U2 at the Berlin electron storage ring BESSY 1. This approach employs a non-imaging simulated hemispherical electron energy analyser attached to an imaging photoemission electron microscope (FOCUS IS-PEEM) with integrated microarea selector. The photoemission microscope exhibits a lateral resolution of 25 nm (with 4.9 eV UV-excitation), while the resolution with incident synchrotron radiation in the soft X-ray range is about 100–120 nm (mainly due to chromatic aberrations). Photoemission microscopy as well as photoelectron microspectroscopy of selected areas on the sample surface were performed by using the third harmonic of the direct undulator beam which was monochromatized and refocused by a two-element multilayer optic in the 70–95 eV energy range. The multilayer monochromator operating at near-normal incidence consists of a concave spherical multilayer mirror (r=650 mm) and a plane multilayer grating (blazed grating 1221 L/mm, blaze angle 0.8 deg). Both elements were coated with a Mo/Si multilayer of equal d-spacing (20 doublelayers, d=10.5 nm) to enhance the reflectivity for EUV radiation at near-normal incidence angles. The characterization of the individual optical components by EUV reflectometry shows a peak reflectance of about 47% at a photon energy of 95 eV in the case of the focusing multilayer mirror while the first order diffraction efficiency of the multilayer blaze grating was measured to be up to 32%. The evaluation of the photoelectron spectra measured with this set-up displays that the spectral resolution of the incident radiation is better than 0.7 eV, while it is about 2–4 eV in the case of a two-multilayer-mirror configuration. Analysis of the surface topography and the chemical composition of inhomogeneities of thin evaporated layers on a mesoscopic scale are the main applications of this experiment.

Normal-incidence multilayer mirrors for the 120–450 Å wavelength region

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 10 7 W/cm 2 around 182 Å has been experimentally obtained in the laser plasma image plane.

Normal-Incidence Multilayer Mirrors for the 120–450 Å Wavelength Region

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.

Imaging of laser-produced plasmas at 44 Å using a multilayer mirror

Images of imploding laser-fusion targets have been obtained using a spherical multilayer mirror. The mirror was coated to reflect Si XII 44.1 Å radiation and produced images of the coronal plasma regions of the glass microballoon and stalk. Clearly visible in the images are emission features as small as 40 μm.