extreme-UV Spectral Region Research Articles

Wideband multilayer mirrors with minimal layer thicknesses variation

Wideband multilayers designed for various applications in hard X-ray to Extreme UV spectral regions are based on a layered system with layer thicknesses varying largely in depth. However, because the internal structure of a thin film depends on its thickness, this will result in multilayers in which material properties such as density, crystallinity, dielectric constant and effective thickness vary from layer to layer. This variation causes the fabricated multilayers to deviate from the model and negatively influences the reflectivity of the multilayers. In this work we solve this problem by developing designs of wideband multilayers with strongly reduced layer thickness variations in depth, without essential degradation of their optical characteristics.

Influence of the metallic contact in extreme-ultraviolet and soft x-ray diamond based Schottky photodiodes

X-ray and UV photovoltaic Schottky photodiodes based on single crystal diamond were recently developed at Rome “Tor Vergata” University laboratories. In this work, different rectifying metallic contact materials were thermally evaporated on the oxidized surface of intrinsic single crystal diamond grown by chemical vapor deposition. Their impact on the detection performance in the extreme UV and soft x-ray spectral regions was studied. The electrical characterization of the metal/diamond Schottky junctions was performed at room temperature by measuring the capacitance–voltage characteristics. The diamond photodiodes were then tested both over the extreme UV spectral region from 10 to 60 eV by using He-Ne DC gas discharge as a radiation source and toroidal vacuum monochromator, and in the soft x-ray range from 6 to 20 keV at the Diamond Light Source synchrotron x-ray beam-line in Harwell (UK). In both experimental setups, time response and spectral responsivity were analyzed for all the investigated Schottky contact materials. A good agreement between the experimental data and theoretical results from Monte Carlo simulations is found

Secondary electron emission in extreme-UV detectors: Application to diamond based devices

A study on the effect of secondary electron emission, which strongly affects the detection of extreme-UV radiation, was performed on diamond detectors. Two different structures were compared: interdigitated contacts and a transverse Schottky diode configuration. Both devices were electrically characterized by I-V measurements and their responsivity was measured in the extreme UV spectral region (20–120 nm) by using He-Ne gas discharge radiation sources and a toroidal grating vacuum monochromator. Through an ad-hoc measurement configuration, the contributions of the internal photocurrent and of the photoemission current have been analyzed and separately evaluated. The results showed that secondary electron emission, which clearly depends on the experimental conditions (e.g., external electric field, pressure, etc.), is one of the most relevant processes affecting the spectral responsivity in the extreme UV band. In particular, for interdigitated devices, extreme care must be taken in order to obtain an absolute value of their responsivity, while detectors in the transverse configuration can be shielded in such a way to avoid secondary electron current contribution and therefore provide a more correct and reliable response.

Extreme UV photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration

We report on extreme UV (EUV) photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration fabricated and tested at Roma “Tor Vergata” University laboratory, operating in a sandwich geometry. Particular care has been devoted to the design of the device geometry in order to take advantage of the internal junction electric field and to minimize the signal contribution arising from secondary electron emission, which is known to strongly affect the detection properties in the UV and EUV regions. The device has been characterized in the EUV spectral region by using both He and He–Ne DC gas discharge radiation sources and a toroidal grating vacuum monochromator, with 5 Å wavelength resolution. The reproducibility test has been performed on several photodetectors showing a high uniformity of the device performances. The devices showed negligible undesired effects such as persistent photocurrent and memory effects, resulting in extremely promising stability features of the p-type/intrinsic/metal structured device. The devices have been tested at different bias voltages between 0 and 15 V, showing the best performances at 0 bias voltage. Finally, the external quantum efficiency (EQE), as well as the responsivity have been measured in the range 20 to 100 nm.

Observation of the Annular Solar Eclipse of May 31 2003 in far ultraviolet spectral region

Changes of extreme ultraviolet (EUV) Solar flux were registered during the Annular Solar eclipse of May 31 2003, when CORONAS-F satellite (Oraevsky et al., 2002) intersected thrice a zone of the Solar eclipse. During these periods the solar emission was measured in visible and extreme UV spectral regions (near nm) and the optical (visible) channel of EOS instruments on UTC scale for May 31, 2003 are given on Fig. 1.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Optical properties of hot-pressed B_4C in the extreme ultraviolet

Hot-pressed B(4)C is found to have a high normal reflectance in the extreme-UV spectral region above 49 nm. This reflectance is comparable with or higher than chemical-vapor-deposited SiC in the spectral region from 49 to 92 nm. Reflectance measurements as a function of the angle of incidence yielded the optical constants of B(4)C in the spectral range 49-121.6 nm.

Effects of space exposure on ion-beam-deposited silicon-carbide and boron-carbide coatings

Two recently developed optical coatings, ion-beam-deposited silicon carbide and ion-beam-deposited boron carbide, are very attractive as coatings on optical components for instruments for space astronomy and earth sciences operating in the extreme-UV spectral region because of their high reflectivity, significantly higher than any conventional coating below 105 nm. To take full advantage of these coatings in space applications, it is important to establish their ability to withstand exposure to the residual atomic oxygen and other environmental effects at low-earth-orbit altitudes. The first two flights of the Surface Effects Sample Monitor experiments flown on the ORFEUS-SPAS and the CRISTA-SPAS Shuttle missions provided the opportunity to study the effects of space exposure on these materials. The results indicate a need to protect ion-beam-deposited silicon-carbide-coated optical components from environmental effects in a low-earth orbit. The boron-carbide thin-film coating is a more robust coating able to withstand short-term exposure to atomic oxygen in a low-earth-orbit environment.

Continuous emission source covering the 50–300-Å band

We have developed a continuous emission source for use in the soft-x-ray and extreme-UV spectral regions. The source and its characteristics are described.

Continuous discharge Penning source with emission lines between 50 Å and 300 Å

We have developed a modified Penning discharge lamp for use in the soft x-ray and extreme uv spectral regions. The source produces a number of intense lines in the 50-300-A range and can be operated for substantial periods of time at high output levels before refurbishment is required. Refurbishment of this source, when required, is very easily effected.

Design criteria for reflection polarizers and analyzers in the vacuum ultraviolet

Reflection polarizers and analyzers for the extreme uv spectral region are discussed. The conditions for optimum polarization are presented, and the polarization characteristics of a number of metal coatings, including gold and some of the platinum metals, are given. The performance of three- and four-mirror polarizers, using these metal coatings, is discussed. The properties required of a polarization analyzer are presented, and the performance of single and three- and four-reflection analyzers are discussed in terms of the optical properties of coating materials that might be useful for analyzers.

New Techniques for Differential Pumping Systems

Differential pumping may be made more efficient by application of modified collimators of the grid type, first used for optical collimation only in spectrometers for the extreme uv spectral region. Compared with conventional types of differential pumping, either larger windows can be used, or the gas flow can be reduced. For optical purposes we had to build up a system with a rather large window, with an effective area of 15 mm2. The differential pumping properties of this system are compared to those of a conventional pumping system with an effective area of 3 mm2 and the results clearly show the advantage of the new design.