Source Of Extreme Ultraviolet Radiation Research Articles

Temporally resolved Schwarzschild microscope for the characterization of extreme ultraviolet emission in laser-produced plasmas

A temporally resolved monochromatic extreme ultraviolet (EUV) imager has been developed for use in EUV radiation source research. The imager consists of a Schwarzschild microscope, with near-normal-incident Mo/Si multilayer mirrors adjusted for 13.5 nm and 4% bandwidth, and an x-ray streak camera (XSC). The spatial resolution of the microscope was limited by the image detector’s resolution to 3.5 μm for the CCD camera and 15 μm for the XSC, respectively, for a field of view of 1.2 mm. With the high photon collection efficiency, clear streak images could be obtained on a single-shot basis with laser pulse energy as low as 50 mJ at an intensity of 1×1010 W/cm2. Expansion behavior of the EUV emission region was successfully observed for laser-produced Sn plasmas.

Increase of the Breakdown Voltage of a Pseudospark Discharge by Applying a Blocking Potential

Investigations of the static breakdown voltage in dependence of the gas pressure for a pseudospark (PS) discharge with an additional blocking electrode are presented. Experiments by variation of the position and geometry of the blocking electrode in the hollow cathode of PS and the applied blocking potential were performed. With respect to the potential use of a hollow-cathode-based gas discharge as source of extreme-ultraviolet radiation for future lithography, xenon as working gas has been used.

Direct versus sequential double ionization of Mg with extreme-ultraviolet radiation.

We present an ab initio calculation of multiphoton double ionization in atomic magnesium, the first of its type in an atom with a complex core, showing that direct correlated double electron ejection can be studied through analysis of the photoelectron energy spectrum, using currently or upcoming extreme-ultraviolet radiation sources.

Pinch-plasma radiation source for extreme-ultraviolet lithography with a kilohertz repetition frequency

An extreme-ultraviolet radiation source based on a xenon pinch plasma is discussed with respect to the demands on a radiation source for extreme-ultraviolet lithography. Operation of the discharge in a self-igniting-plasma mode and omitting a switch permits a very effective and low-inductive coupling of the electrically stored energy to the electrode system. The xenon plasma exhibits broadband emission characteristics that offer radiation near 11 and 13 nm. Both wavelengths are useful in combination with beryllium- and silicon-based multilayer mirrors. The plasma emits approximately 74 mW/sr at 11.5 nm and 40 mW/sr at 13.5 nm in a bandwidth of 2% when operated at a repetition frequency of 120 Hz. The source size is less than 500 microm in diameter (FWHM) when viewed from the axial direction. The pulse-to-pulse stability is better than 3.6%. First results with a repetition rate of as much as 6 kHz promise the possibility of scaling to the required emission power for extreme-ultraviolet lithography.

Highly repetitive, extreme-ultraviolet radiation source based on a gas-discharge plasma

An extreme-ultraviolet (EUV) radiation source near the 13-nm wavelength generated in a small (1.1 J) pinch plasma is presented. The ignition of the plasma occurs in a pseudosparklike electrode geometry, which allows for omitting a switch between the storage capacity and the electrode system and for low inductive coupling of the electrically stored energy to the plasma. Thus energies of only a few joules are sufficient to create current pulses in the range of several kiloamperes, which lead to a compression and a heating of the plasmas to electron densities of more than 10(17) cm(-3) and temperatures of several tens of electron volts, which is necessary for emission in the EUV range. As an example, the emission spectrum of an oxygen plasma in the 11-18-nm range is presented. Transitions of beryllium- and lithium-like oxygen ions can be identified. Current waveform and time-resolved measurements of the EUV emission are discussed. In initial experiments a repetitive operation at nearly 0.2 kHz could be demonstrated. Additionally, the broadband emission of a xenon plasma generated in a 2.2-J discharge is presented.

The soft X-ray and extremely ultraviolet filters with negligible pinholes transmittance

It is proposed to fabricate two-layer thin film filters without pinholes transmittance of visible and UV light. We describe the design and performance of these filters. Filter consists of two layers of thin metal films fixed to each side of porous membrane with thorough pores or transmission diffraction grating as support. As examples it was made Al or Rh two-layer thin film filters on metallized porous track membrane supports with the 10 −9–10 −10 level of visible and UV light rejection at transmittance T∼0.1 ÷ 0.01 in the Extreme ultraviolet region. Proposed filter is appropriate in the optical experiments with strong continuous X-ray and Extreme ultraviolet radiation sources such as laser plasma, SR sources and the Sun.

Epsilon Canis Majoris and the ionization of the local cloud

The Lyman continuum radiation from the brightest extreme ultraviolet (EUV) source, the B2 II star epsilon Canis Majoris (Adara), is so intense that it dominates the local stellar EUV radiation field at wavelengths longer than 450 A and therefore sets a lower limit to the ionization of hydrogen in the Local Cloud. Using the EUV (70-730 A) spectrum of epsilon CMa taken with the Extreme Ultraviolet Explorer Satellite (EUVE) and simple models that extrapolate this spectrum to the Lyman edge at 912 A, we have determined the local interstellar hydrogen photionizatin parameter Gamma solely from epsilon CMa to be 1.1 x 10(exp -15)/s. This fiugre is a factor of 7 greater than previous estimates of Gamma calculated for all nearby stars combined (Bruhweiler & Cheng 1988). Using measured values of the density and temperature of neutral interstellar hydrogen gas in the Local Cloud, we derive a particle density of ionized hydrogen n(H(+)) and electrons n(sub e) of 0.015-0.019/cu cm assuming ionization equilibrium and a helium ionization fraction of less than 20%. These values correspond to a hydrogen ionizatin fraction, chi(sub H) from 19% to 15%, respectively. The range of these derived quantities is due to the uncertainties in the local values of the neutral hydrogen and helium interstellar densities derived from both (1) solar backscatter measurements of Ly alpha lines of hydrogen and helium (1216 and 584 A), and (2) the average neutral densities along the line of sight to nearby stars. The local proton density produced by epsilon CMa is enough to allow the ionization mechanism of Ripken & Fahr (1983) to work at the heliopause and explain the discrepancy between the neutral hydrogen density derived from solar backscatter measurements and line-of-sight averages to nearby stars. A large value of electron density in the Local Cloud of n(sub e) is approximately 0.3-0.7/cu cm (T = 7000 K) has recently been reported by Lallement et al. (1994) using observations of Mg II and Mg I toward Sirius A. We show that if such a high value exists, it cannot result from the EUV stellar radiation field and, therefore, must be due to a strong diffuse source of EUV radiation.

A volume-limited survey of High Galactic latitude planetary nebulae with the Extreme Ultraviolet Explorer

We present the results of a complete survey, at extreme-ultraviolet (EUV) wavelengths (58-234 A), of the high Galactic latitude (absolute value of b greater than or = to 20 deg) planetary nebulae (PNs) with at least one determination of the distance within 1 kpc of the Sun. The sample comprises 27 objects observed during the Extreme Ultraviolet Explorer (EUVE) all-sky survey and represents the majority of PN likely to be accessible at EUV wavelengths. Six PNs (NGC 246, NGC 1360, K1-16, LoTr 5, NGC 4361, and NGC 3587) were detected in the shortest EUV band (58-174 A). A seventh PN (NGC 6853), not included in the sample, was also detected during the survey. The emission is consistent in all cases with that of a point source and therefore most probably originates from the PN central star. Accurate EUV count rates or upper limits in the two shorter EUVE bands (centered at approximately 100 and 200 A) are given for all the sources in the sample. NGC 4361 and NGC 3587 are reported here for the first time as sources of EUV radiation. As might be expected, attenuation by the interstellar medium dominates the PN distribution in the EUV sky.

Extreme-ultraviolet studies with laser-produced plasmas

A new multilaser multichannel spectrometer system has been developed that allows a wide range of investigations of the interaction of extreme-ultraviolet (EUV) photons with matter in the form of free atoms or ions, e.g., in gases or plasmas or bound as in solids. The EUV photons are generated by a laser-produced plasma. Applications to the study of photoabsorption by thin foils, gases, and ground- and excited-state atoms and ions are described. The design and performance of a collimated, quasi-monochromatic, intense source of EUV radiation based on the combination of a laser-produced plasma with a EUV multilayer mirror is also reported.

The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources – I. The Bright Source Catalogue

The first all-sky survey for cosmic sources of extreme-ultraviolet radiation has been carried out with the UK Wide Field Camera on ROSAT. A first reduction of the survey data has yielded a catalogue of 383 relatively bright EUV sources, forming the WFC Bright Source Catalogue. This represents a 30-fold increase in the number of astrophysical objects detected in the ~ 60–200 eV energy band and covers a flux range, in each of the two survey bands, of more than 2000. A search of the (typically ~ 1-arcmin) error circles of the WFC sources, using a variety of catalogues and the SIMBAD data base, has identified probable optical counterparts of ~ 73 per cent, including many active stars, white dwarf stars and a variety of other galactic and extragalactic objects. A follow-up programme of optical spectroscopy has since added further identifications, but some 13 per cent of the EUV sources remain unidentified. Details of the EUV source positions and count rates are given, together with optical identifications where known. Considerations of survey completeness allow source counts (log N–log S) to be derived for each survey band. It is found that the log N-log S distributions are unusually flat for the white dwarf stars, but almost Euclidean for the nearby main-sequence late-type stars. This is probably an effect of local ( ≲ 100 pc) interstellar absorption, since the more (EUV) luminous white dwarfs are potentially detected at correspondingly greater distances than the late-type stars. In addition, the sky distribution of identified white dwarfs is highly non-uniform, also suggesting gross variations in the opacity of the interstellar medium within ~ 100 pc.

An extreme ultraviolet radiation source for the simulation of the ionosphere

An extreme ultraviolet (EUV) radiation source for space simulation of plasma and other related phenomena in the laboratory has been developed. A total of forty-eight small EUV lamps are put together to give a radiation diameter of more than 30 cm. The intensity of this lamp at the hydrogen Lyman-alpha line is more than twenty five times stronger than sunlight at the same wavelength and at a distance of about 30 cm from the source. The source is capable of emitting EUV radiations from 110 nm to the longer wavelengths, either continuously or in pulses, and has been used to produce a plasma of 105 els/cm3 when the pressure of NO gas in the chamber was 10−4 Torr. Since this plasma is extremely calm and fairly Maxwellian, it can be used to study the electron collection mechanism of a probe in a collision dominant medium. The source was also utilized to study the interaction between vibrationally excited nitrogen molecules and thermal electrons.

Charge state populations in an extreme ultraviolet radiation pumped lithium vapor

Charge state populations are calculated evolving from an initially neutral lithium vapor. The vapor is pumped by the passage of an extreme ultraviolet radiation pulse of approximately one microsecond through the lithium. Photoionization and electron induced ionization processes result in a buildup of Li+ and Li++ in the vapor. When recombination is small, a 10% fraction of the atoms will be singly charged, and about 2.4×10−5 of the atoms will be doubly charged for the extreme ultraviolet radiation source considered. The temperature of the vapor can be related to the energy absorbed from the incident extreme ultraviolet radiation pulse. This results in a temperature of about 0.6 eV. Such a plasma is useful for ion diode particle beam fusion experiments.

High-resolution extreme-ultraviolet spectroscopy of potassium using anti-Stokes radiation

We report the use of a new extreme-ultraviolet radiation source based on spontaneous anti-Stokes scattering for high-resolution absorption spectroscopy of transitions originating from the 3p(6) shell of potassium. The region from 546.6 to 536.8 A is scanned at a resolution of about 1.2 cm(-1). Within this region, four previously unreported lines are observed.