Extreme Ultraviolet Intensity Research Articles

Dependence of Extreme Ultraviolet Emission on Xenon Flow Rate from a Z-Pinch Discharge Plasma

Extreme ultraviolet (EUV) radiation with wavelengths of 11 to 14 nm is seen as the most promising candidate for a new lithographic technology. Compared to synchrotron radiation sources and laser produced plasmas, gas discharge produced plasma (GDPP) sources for EUV radiation are expected to offer lower cost of ownership. This paper describes the dependence of EUV emission on gas flow rate. Using xenon a broadband emission in the investigated wavelength range from 10 to 18 nm is observed. Very short current pulses were applied across the xenon-filled Z-pinch capillary (3 mm diameter and 5 mm length) to produce EUV radiation. A EUV radiation from the Z-pinch plasma was characterized, which is based on the temporal behavior of EUV intensity and the pinhole images.

Direct Evaluation of Surface Roughness of Substrate and Interfacial Roughness in Molybdenum/Silicon Multilayers Using Extreme Ultraviolet Reflectometer

In this study, we developed a method of measuring the intensity of rays scattered from a molybdenum/silicon (Mo/Si) multilayer film using an extreme ultraviolet (EUV) reflectometer. We examined the correlations between the peak reflectance, the interfacial roughness of multilayer films, and the substrate roughness. We measured the intensity of scattered rays 13.5 nm from the substrate surface for normal smooth quartz (NSQz), supersmooth quartz (SSQz), and Si substrates using the EUV reflectometer. The intensity of rays scattered from the substrate surface was proportional to the atomic force microscopy (AFM) roughness of the surface. For NSQz, there was a particular strong correlation between the surface roughness determined by AFM and the intensity of scattering rays determined using the EUV reflectometer. However, a week correlation was observed for SSQz and Si. The precisions of the AFM and X-ray reflectivity (XRR) measurement were low for the quartz substrate. A direct measurement of the intensity of rays scattered from the substrate surface was used to estimate the relative surface roughness independent of the substrate material. The EUV reflectivity and intensity of rays scattered from the Mo/Si multilayer films with two deposition geometries were measured using the EUV reflectometer. The peak reflectivity was related to the substrate roughness for each deposition geometry. Moreover, the peak reflectivity was related to the intensity of rays scattered from the multilayer films and was not influenced by the deposition geometry. The results obtained using the EUV reflectometer showed an obvious relationship between the intensity of scattering rays and the interfacial roughness of multilayer films.

Miniature hybrid plasma focus extreme ultraviolet source driven by 10kA fast current pulse

A miniature hybrid plasma focus device, operated in xenon gas medium and driven by a 10kA fast current pulse, has been used to generate extreme ultraviolet radiation in the range of 6–15nm. At present the radiation characteristics from xenon plasma were mainly assessed qualitatively using standard tools such as visible light framing camera, extreme ultraviolet (EUV) pinhole camera, and EUV photodiode. Strong pinching of xenon plasma is indicative from both visible and EUV imagings. The maximum size of the EUV emitting zone is estimated to be of the order of 0.21×1.55mm and the estimated value is within the accepted value as benchmarked by industries. The EUV intensity measurement by photodiode showed fairly isotropic radiation at least in a half solid angle. This device can be developed further as a competent source for EUV metrology or lithography applications.

Temperature dependence of the EUV responsivity of silicon photodiode detectors

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

Enhancement of laser plasma extreme ultraviolet emission by shockwave-laser interaction

A double laser pulse heating scheme has been applied to generate plasmas with enhanced emission in the extreme ultraviolet (EUV). The plasmas were produced by focusing two laser beams (prepulse and main pulse) with a small spatial separation between the foci on a xenon gas jet target. Prepulses with ps-duration were applied to obtain high shockwave densities, following indications of earlier published results obtained using ns prepulses. EUV intensities around 13.5 nm and in the range 5–20 nm were recorded, and a maximum increase in intensity exceeding 2 was measured at an optimal delay of 140 ns between prepulse and main pulse. The gain in intensity is explained by the interaction of the shockwave produced by the prepulse with the xenon in the beam waist of the main pulse. Extensive simulation was done using the radiative magnetohydrodynamic code Z*.

Spatial characterization of extreme ultraviolet plasmas generated by laser excitation of xenon gas targets

At Laser-Laboratorium Göttingen laser-plasma sources were tested, which are going to be used for characterization of optical components and sensoric devices in the wavelength region from 11 to 13 nm. In all cases extreme ultraviolet (EUV) radiation is generated by focusing a Q-switched Nd:YAG laser into a pulsed gas puff target. By the use of xenon or oxygen as target gas, broadband as well as narrowband EUV radiation is obtained, respectively. Different types of valves and nozzles were tested in order to optimize the emitted radiation with respect to maximum EUV intensities, small source diameters, and positional stability. The investigation of these crucial source parameters was performed with specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows both spatially and angular resolved monitoring of the soft x-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found. The data were compared with fluorescence measurements for visualization of the target gas jet. The experimental observations can be explained by reabsorption of the generated EUV radiation in the surrounding target gas, as supported by semiempirical model calculations based on the attenuation in the three-dimensional gas density according to Lambert–Beer’s law. As a consequence of the presented investigations, an optimization of the EUV source with respect to intensity, plasma shape, and angular dependence is achieved, resulting in a spherical plasma of 200 μm diameter and a 50% increase of the EUV pulse energy.

Resonance Scattering of FexviiX‐Ray and Extreme‐Ultraviolet Lines

Over the years, a number of calculations have been carried out to derive intensities of various X-ray and extreme-ultraviolet (EUV) lines in Fe XVII for comparing with observed spectra. The predicted intensities have not agreed with solar observations, particularly for the line at 15.02 A; resonance scattering has been suggested as the source for much of the disagreement. The atomic data calculated earlier by Bhatia & Doschek used seven configurations having n = 3 orbitals, and the scattering calculations were carried out only for incident energies above the threshold of the highest fine-structure level. These calculations have now been extended to thirteen configurations having n = 4 orbitals, and the scattering calculations are carried out below as well as above the threshold of the highest fine-structure level. These improved calculations of Fe XVII change the intensity ratios compared to those obtained earlier, bringing the optically thin F(15.02)/F(16.78) ratio and several other ratios closer to the observed values. However, some disagreement with the solar observations still persists, even though the agreement of the currently calculated optically thin F(15.02)/F(15.26) ratio with the experimental results of Brown and coworkers, and Laming and coworkers has improved. Some of the remaining discrepancy is still thought to be the effect of opacity, which is consistent with expected physical conditions for solar sources. EUV intensity ratios are also calculated and compared with observations. Level populations and intensity ratios are calculated as a function of column density of Fe XVII in the slab and cylindrical geometries. As found previously, the predicted intensities for the resonance lines at 15.02 and 15.26 A exhibit initial increases in flux relative to the forbidden line at 17.10 A and the resonance line at 16.78 A as optical thickness increases. The same behavior is predicted for the lines at 12.262 and 12.122 A. Predicted intensities for some of the allowed EUV lines are also affected by opacity.

Solar source regions of coronal mass ejections and their geomagnetic effects

It is generally accepted that the fast interplanetary manifestations of coronal mass ejections (ICMEs) are the major solar drivers of many space weather phenomena, including large, non-recurrent geomagnetic storms and solar energetic particle events. High-quality synoptic observations of the solar corona, as carried out by the EIT and LASCO experiments on SOHO, provide near real-time imaging of CMEs from the base of the corona out to a projected distance of 30 R ⊙ ( R ⊙ is the solar radius). The average characteristics of CMEs observed by LASCO are similar to those from earlier coronagraphs. Most CMEs travel with approximately constant speed through the LASCO field of view. However, a significant number accelerate as they move outward, and some fast events have been observed to decelerate. LASCO has observed a great deal of internal structure in many CMEs. Concave-outward structures that are interpreted as magnetic flux ropes are observed in approximately one third of all events. Complex structures are often observed in the trailing portions of CMEs. Halo CMEs, many of which are very faint, can be routinely observed with LASCO. Extreme-ultraviolet (EUV) images of the low corona and solar disk, as recorded by EIT, reveal a complex web of CME signatures. These include large-scale waves in the inner corona associated with CMEs, extended regions of depleted EUV intensity, and bright arcades that form following the occurrence of a CME. The combination of LASCO and EIT imagery allows the source regions of halo CMEs to be identified, and can be used to help predict the occurrence of geomagnetic disturbances several days in advance. The most important parameters in determining the geoeffectiveness of an ICME are the magnetic field strength and direction, and the speed of the disturbance. The most intense geomagnetic storms are associated with strong and persistent southward fields, either within the ICME itself or in the compressed sheath of solar wind plasma ahead of it.

Attosecond cross correlation technique.

A technique for the measurement of attosecond, extreme-ultraviolet pulses is proposed and theoretically analyzed that is based on cross correlation of the attosecond pulse with a strong laser pulse in a gas target. Pulse durations on the time scale of a fraction of the optical period can be resolved. The method is linear in the extreme-ultraviolet intensity, which ensures high efficiency and applicability for wavelengths to below 10 nm.

ITAL]SOHO[/ITAL] EIT Observations of Extreme-Ultraviolet “Dimming” Associated with a Halo Coronal Mass Ejection

A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a halo coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness—dimmings—that developed prior to the CME observed in white light and persisted for several hours following the CME. The most prominent dimming regions were located near the ends of a preflare SXR S-shaped (sigmoid) feature that disappeared during the event, leaving behind a postflare SXR arcade and cusp structure. Based upon these and similar soft X-ray observations, it has been postulated that SXR dimming regions are the coronal signatures (i.e., remnants) of magnetic flux ropes ejected during CMEs. This Letter reports new observations of coronal dimming at extreme-ultraviolet (EUV) wavelengths obtained with the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). A series of EIT observations in the 195 A Fe XII wavelength band were obtained simultaneously with SXT during the 1997 April 7 flare/CME. The EIT observations show that regions of reduced EUV intensity developed at the same locations and at the same time as SXR dimming features. The decrease in EUV intensity (averaged over each dimming region) occurred simultaneously with an increase in EUV emission from flaring loops in the active region. We interpret these joint observations within the framework of flux-rope eruption as the cause of EUV and SXR coronal dimmings, and as the source of at least part of the CME.

Density and temperature diagnostics of solar emission lines from Navii and Alix

Line intensity ratios of NeVI lines with respect to a resonance line of MgVI have been considered for electron density and temperature determinations within the chromosphere-corona transition region. The electron pressure within the transition region has been assumed to be constant. In addition, these ratios would enable us to estimate the relative element abundances of neon to magnesium. An attempt has been made to explain the extreme ultraviolet intensities of NeVI and MgVI lines as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum. Theoretical intensities for NeVI and MgVI lines have been computed using a model solar atmosphere. Theoretical intensities obtained by using the values 3.98 × 10−5 and 3.16 × 10−5 for element abundance of Ne and Mg, respectively, seem to agree well with the expected intensities. The agreement between some of the expected and computed intensities suggests the need for future observations at higher spectral resolutions to resolve difficulties arising out of blending due to two or more lines.

Extreme ultraviolet emissions for monitoring auroras in dark and daylight hemispheres

Observations of auroral extreme ultraviolet (EUV) emissions from the noon‐midnight polar‐orbiting Space Test Program (STP) 78‐1 satellite are used to investigate the spectral features of the dayside auroral oval, nightside auroral oval, and the dayglow. The purpose of this study is to evaluate the possibility of using EUV atmospheric emissions for global auroral imaging and to study the temporal variations of the auroral EUV intensity with geomagnetic activity. It is found that during geomagnetically quiet times, O II 834Å, O I 989Å, and N2 1009 Å measurements can provide a clear distinction of the auroral oval above the dayglow background. During the very active period, five other EUV emissions can give good aurora‐to‐dayglow ratios. The auroral EUV emissions are more intense during magnetospheric substorms; however, we have not found a clear one‐to‐one relationship between them. It is also found that the auroral oval brightness, especially the noonside, increased during the initial phase of a geomagnetic storm. Thus, the sudden solar wind dynamic pressure enhancement is another important geophysical parameter that affects the EUV auroral emission.

Impulsive extreme-ultraviolet and hard X-ray emission during solar flares

view Abstract Citations (60) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Impulsive extreme-ultraviolet and hard X-ray emission during solar flares. Donnelly, R. F. ; Kane, S. R. Abstract Impulsive solar bursts of hard X-rays observed with moderate spectral resolution and high time resolution by the OGO S satellite were compared with concurrent enhancements of extreme- ultraviolet (EUV) radiation observed by means of sudden frequency deviations. The impulsive EUV flux rises and decays, with a time structure most like that of the lowest-energy hard X-rays observed-the 10-20 keV X-rays-but slower than hard X-rays with photon energy greater than 32 keV. These results are interpreted in terms of the dominance of 10-25 keV electrons in exciting the high-density impulsive EUV source. The impulsive EUV emission varies with the central meridian distance of the flare, with a peak in EUV intensity for flares near the central meridian and a marked decline in intensity near the solar limb. These observations are consistent with a model of the impulsive phase in which the EUV burst originates in sources embedded deep in a cool absorbing atmosphere, including fine spatial structure smaller than an arcsec, and in which both the electron precipitation efficiency and the EUV radiation efficiency are small. Subject headings: Sun: flares - Sun: X-rays - ultraviolet: general Publication: The Astrophysical Journal Pub Date: June 1978 DOI: 10.1086/156222 Bibcode: 1978ApJ...222.1043D Keywords: Far Ultraviolet Radiation; Satellite Observation; Solar Flares; Solar X-Rays; Electron Precipitation; Ogo-5; Radiant Flux Density; Solar Activity Effects; X Ray Spectra; Solar Physics; Extreme UV:Solar Flares; Solar Flares:X Rays; Solar X Rays: Hard X Rays full text sources ADS |

C III density diagnostics in nonequilibrium plasmas

view Abstract Citations (48) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS C III density diagnostics in nonequilibrium plasmas. Raymond, J. C. ; Dupree, A. K. Abstract Mass flow through a temperature gradient can produce substantial departures of the ionization states from their equilibrium values and can change the character of line emission. The effect of such flows on extreme ultraviolet intensities in the solar atmosphere is evaluated for the beryllium-sequence ion C III, which is an easily observed and powerful diagnostic of electron density in a collisionally dominated plasma. A downflow of material in a transition region can lead to an underestimate of the electron density; outflow of material, as in a stellar or solar wind passing from chromospheric to coronal temperatures, yields a reliable density diagnostic. Ambiguities in the analysis of ultraviolet emission lines can be circumvented by measurement of several transitions. Publication: The Astrophysical Journal Pub Date: May 1978 DOI: 10.1086/156151 Bibcode: 1978ApJ...222..379R Keywords: Carbon Stars; Nonequilibrium Plasmas; Plasma Diagnostics; Solar Spectra; Stellar Atmospheres; Ultraviolet Astronomy; Astronomical Models; Beryllium; Late Stars; Metastable State; Nonequilibrium Ionization; Plasma Density; Radiative Recombination; Solar Corona; Solar Flares; Temperature Gradients; Transition Flow; Ultraviolet Spectra; Astrophysics; Solar Atmosphere:Motions; Solar Spectrum:UV; Sun: Transition Regions full text sources ADS |