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[en] A number of properties of EUV bursts are found to be consistent with the conclusion that they are at the low energy extreme of the family of events including flares. The incidence of EUV bursts exceeds that of flares by over two orders of magnitude, which suggests the possibility that, in total, they may be as important energetically as flares. The faster EUV bursts havelight curves resembling those observed in hard X-rays at the times of flares. (orig.)
[en] The Hinode EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) were designed in part to work together. They have the same spatial resolution and cover different but overlapping coronal temperature ranges. These properties make a combined data set ideal for multithermal analysis, where EIS provides the best information on the cooler corona (log T < 6.5) and XRT provides the best information on the hotter corona (log T > 6.5). Here, we analyze a warm non-flaring loop detected in images made in a strong EIS Fe XV emission line with a wavelength of 284.16 A and peak formation temperature of log T = 6.3. We perform differential emission measure (DEM) analysis in three pixels at different heights above the footpoint and find multithermal results with the bulk of the emission measure in the range 6.0 < log T < 6.6. Analysis with the EIS lines alone gave a DEM with huge amounts of emission measure at very high temperatures (log T >7.2); analysis with XRT data alone resulted in a DEM that was missing most of the cooler emission measure required to produce many of the EIS lines. Thus, both results were misleading and unphysical. It was only by combining the EIS and XRT data that we were able to produce a reasonable result, one without ad hoc assumptions on the shape and range of the DEM itself.
[en] In extreme ultraviolet lithography (EUVL), the technology specific requirements on the mask are a direct consequence of the utilization of radiation in the spectral region between 10 and 15 nm. At these wavelengths, all condensed materials are highly absorbing and efficient radiation transport mandates the use of all-reflective optical systems. Reflectivity is achieved with resonant, wavelength-matched multilayer (ML) coatings on all of the optical surfaces - including the mask. The EUV mask has a unique architecture - it consists of a substrate with a highly reflective ML coating (the mask blank) that is subsequently over-coated with a patterned absorber layer (the mask). Particulate contamination on the EUVL mask surface, errors in absorber definition and defects in the ML coating all have the potential to print in the lithographic process. While highly developed technologies exist for repair of the absorber layer, no viable strategy for the repair of ML coating defects has been identified. In this paper the state-of-the-art in ML deposition technology, optical inspection of EUVL mask blank defects and candidate absorber patterning approaches are reviewed
[en] Interferometric testing at the design wavelength is required for accurately characterizing the wave front of an imaging system operating in the extreme ultraviolet. The fabrication of point-diffraction interferometer apertures for extreme ultraviolet wave-front aberration analysis is described. The apertures are formed in a 200-nm-thick low-pressure chemical-vapor-deposited Si3N4 film and vary in size from approximately 0.10 to 0.50 μm to generate a reference wave front of varying numerical aperture. A graded absorber overcoat is used to control the intensity of the aberrated wave front. Optimal fringe contrast can be obtained when the aperture that provides the maximum uniformity and contrast in the interference plane is selected
[en] We report on the development of plasma-based sources of extreme ultraviolet radiation for the next-generation lithography and mask inspection and the development of equipment for spectral diagnostics of such sources. (conferences and symposia)
[en] Despite significant progress in understanding the dynamics of the corona, there remain several unanswered questions about the basic physical properties of coronal loops. Recent observations from different instruments have yielded contradictory results about some characteristics of coronal loops, specifically as to whether the observed loops are spatially resolved. In this paper, we examine the evolution of coronal loops through two extreme-ultraviolet filters and determine if they evolve as a single cooling strand. We measure the temporal evolution of eight active region loops previously studied and found to be isothermal and resolved by Aschwanden and Nightingale. All eight loops appear in 'hotter' TRACE filter images (Fe XII 195 A) before appearing in the 'cooler' (Fe IX/Fe X 171 A) TRACE filter images. We use the measured delay between the two filters to calculate a cooling time and then determine if that cooling time is consistent with the observed lifetime of the loop. We do this twice: once when the loop appears (rise phase) and once when it disappears (decay phase). We find that only one loop appears consistent with a single cooling strand and hence could be considered to be resolved by TRACE. For the remaining seven loops, their observed lifetimes are longer than expected for a single cooling strand. We suggest that these loops could be formed of multiple cooling strands, each at a different temperature. These findings indicate that the majority of loops observed by TRACE are unresolved.
[en] Complete test of publication follows. For low gas densities and negligible ionization, the so-called atomic dipole phase, connected with the electronic dynamics involved in the generation process, is the main source of phase modulation and incoherence of high-order harmonics. To accurately determine these laser-intensity-induced phase shifts is therefore of great importance, both for the possible spectroscopic applications of harmonics and for the controlled generation of attosecond pulses. In a semiclassical description, only two electronic trajectories contribute to generate plateau harmonics during each pump optical half-cycle. Electrons appearing in the continuum by tunnel ionization may follow two different quantum paths, namely a long (l) and a short (s) trajectory before recombination. According to the SFA approximation, the harmonic of qth order acquires a phase proportional to the electronic classical action, and simply given by: ψ0j (r,t) -αqj I(r,t) with j = l, s where αqj are non-linear phase coefficients, roughly proportional to the time that the originating electron spends in the continuum before recombination. The space and time variation of the laser intensity (I(r,t), causes just a little phase modulation for the s-trajectory harmonic component, while the l-trajectory component becomes strongly chirped and spatially defocused; this gives rise to two spatially-separated regions having different temporal coherence. Here we report the first direct measurement of such atomic dipole phase in the process of high-order harmonic generation. Differently from previous measurements based in the most natural way, i.e., by interferometry. Two phase-locked pump pulses generate two phase-locked harmonic pulses in two nearby positions in a gas jet; one of them is used as a fixed phase reference while the generating intensity of the other is varied. The shift of the XUV interference fringes observed in the far field then gives a direct estimate of the intensity-dependent dipole phase. Besides being a conceptually much simpler kind of measurement, our approach has the important advantage of being able to clearly discriminate between the contributions of the two different quantum paths leading to harmonic emission.