Development of an experimental database of EUV spectra from highly charged ions of medium to high Z elements in the Large Helical Device plasmas

We are developing an experimental database of extreme ultraviolet spectra from highly charged ions using optically thin high-temperature plasmas produced in the Large Helical Device. Spectra from a variety of elements with atomic numbers ranging from 36 to 83 have been systematically recorded in the range of 1–20 nm by a grazing incidence spectrometer. For higher Z elements from tin onward, discrete or quasicontinuum spectral features from n=4 (N-shell) ions are mainly observed depending upon the plasma temperature, which leads to some new experimental identifications of spectral lines. On the other hand, major emitters are n=3 (M-shell) ions for medium Z elements from krypton to ruthenium. The calculated wavelengths for Δn≠0 transitions agree well with the measurements and the calculated wavelengths are systematically shifted to shorter wavelengths for Δn=0 transitions associated with inner-subshell excited configurations.     

Long-wave X-ray radiation mirrors

Problems of obtaining mirrors for long-wave length (200-20 Å) X-radiation are discussed. Results of the investigation of roentgenooptical characteristics of multilayer periodical C-Re, C-W and C-Ta structures with periods 60–80 Å have been analyzed. The layer thickness of the heavy elements varied from 3 to 25 Å. The following characteristics have been recorded in the wavelength range λ = 50–80 Å; reflection coefficient up to 20%, resolution λ/Δλ = 7–14, width of the angular dependence R(θ)Δθ ≈ 2°. The number of effectively reflecting pairs of layers, N_max = 17, has been determined from the position of secondary diffraction maxima.     

Analysis of transitions from autoionization states of the Bi III, Bi IV, and Bi V ions

The spectra of transitions from the autoionization states of bismuth ions are studied in the wavelength region from 170 to 500 Å. More than twenty transitions from the levels of configurations accompanied by excitation of the inner 5d subshell in the Bi V, Bi IV, and Bi III ions are identified and their autoionization widths are measured. In addition, transitions from the highly excited 5d ¹⁰ np levels (n=8–11) in the Bi V ion are identified and the ionization potential is refined.     

On the verification of atomic data for <Emphasis Type="Italic">K</Emphasis><Subscript>α</Subscript> radiation spectra from the TEXTOR tokamak

High-resolution spectra from the Ar¹⁶⁺ and Ar¹⁵⁺ ions measured at the TEXTOR tokamak are used to verify atomic data necessary for simulation and diagnostics of a hot coronal plasma with an accuracy of about 5%. A self-consistent approach based on solving the inverse problem by the Bayesian iteration method in the framework of the proposed semiempirical “spectroscopic” model is used. The perturbation calculations of the atomic characteristics for [He] and [Li] argon ions by means of the ATOM and MZ codes require 10% correction of the ratios of the effective excitation rates for the intercombination line of the [He] ion and the group of dielectronic satellites corresponding to the 1s2p3l — 1s ²3l′ transitions in the [Li] ion to the resonance line of the [He] ion. The spectra calculated with this correction are in agreement with the measured spectra within the measurement accuracy ?10% in the wide ranges ～0.8–2.5 keV and ～10¹³–10¹⁴ cm^?3 of the central electron temperature and density, respectively. It is found that the central temperature value can be determined in the framework of the spectroscopic model with an accuracy of ～5%, and the abundances of the [Li] and [II] argon ions with respect to the [He] ions can be determined with an accuracy of ～20 and 50%, respectively. It has been shown that the use of the isothermal approximation when measuring the temperature from the ratio of the intensities of the dielectronic satellites to the resonance line can lead to a large error of ～20% in the presence of gradients typical for tokamak plasmas.     

Quantitative investigation of critical slowing down in all-optical bistability

We have observed optical bistability in rubidium vapor enclosed in a Fabry-Perot cavity for λ ～ 7779 Å (two-photon transition) and λ ～ 7800 Å (one-photon transition). We have measured the switching time τ_S as a function of (l?l_c) where l_c is the last value of the length of the cavity for which switching occurs. In all the experimental situations, we have found a similar law τ_S ～ (l?l_c)^-α with α ～ 0.5. This result is in agreement with theoretical predictions.     

Determination of the depth of formation of magnetooptical effects in CoNi films

The optical constants of CoNi films with magnetic properties that are nonuniform across their thickness are determined in reflected light by two methods, viz., optical and magnetooptical measurements. The values of the parameters L=λ/4πk and Z ₀=λ/8n, one of which (specifically, the one which has the smaller value at a given value of λ) determines the depth of formation of reflective magnetooptical effects (l _mo) according to the current theories, are calculated on the basis of the values obtained for the optical constants n and k of the films (λ is the wavelength of the light used, and n and k are the refractive index and the absorption coefficient of the magnet). It is established for the CoNi films investigated that l _mo is determined by L and varies from about 200 to 300 ? in the range 0.33 μm⩽λ⩽0.83 μm. In CoNi films, which are inhomogeneous across their thickness and are characterized by significant variation of the magnetic properties over distances ∼l _mo, variation of the form of the magnetization curves determined by measuring the equatorial Kerr effect is observed as λ increases. Zh. Tekh. Fiz. 68, 69–72 (February 1998)     

Specific features of the reflection of infrared radiation by crystalline dielectrics in a magnetic field

Magnetic-field-induced variations in the reflection spectra R(λ) of the crystalline dielectrics Al₂O₃, LiF, and MgO in the infrared band (λ = 2.5–25 μm) are investigated. It is found that the reflection spectra exhibit specific features in the neighborhood of wavelengths corresponding to the excitation of optical phonon modes in the above-mentioned crystals and that a magnetic field causes an appreciable variation in the reflectivity at these wavelengths. To qualitatively describe the effect of a magnetic field on the reflection of light, the magnetoreflection spectra ΔR/R are investigated. The spectra ΔR/R exhibit sharp peaks in the neighborhood of wavelengths at which the materials under investigation are characterized by minimal reflectivity. The values of ΔR/R for p-polarized infrared radiation in a magnetic field of about 12 kOe amount to about 0.5% for Al₂O₃ at λ ≈ 9.6 μm, 7% for LiF at λ ≈ 11.1 μm, and 0.07% for MgO at λ ≈ 11.7 μm.     

Effect of magnetic field on the IR optical properties of dielectrics

Magnetic-field induced changes revealed in reflectance spectra R(λ) of nonmagnetic dielectrics Al₂O₃, LiF, and MgO in the IR range (λ = 2.5–25 μm) are reported. The reflectance spectra are shown to have specific features in the vicinity of the wavelengths corresponding to optical phonon mode excitation in these crystals, with the magnetic field giving rise to a noticeable change of reflectance ΔR/R(λ) at these wavelengths. The value of ΔR/R(λ) for p-(s-) polarized IR radiation in a magnetic field of ～13 kOe is ～0.6% (～0.4%) for Al₂O₃ at λ ≈ 9.6 μm, ～1.63% (～1.15) for LiF at λ ≈ 11.1 μm, and ～ 0.07 (～0.2%) for MgO at λ ≈ 11.7 μm, respectively. These changes can be increased substantially by irradiating the dielectric crystals by x-ray radiation. It is shown that the optical and magnetooptical properties of the above dielectrics in the IR spectral region can be described in terms of the polaron excitation theory.     

Soft X-ray bands of highly ionized tungsten,gold and lead emitted by the TEXT tokamak plasma

Spectra of highly ionized tungsten, gold and lead emitted from the TEXT tokamak have been recorded in the 20–70 Å range by means of a grazing incidence, time-resolving spectrograph. The narrow and bright emission bands centered around 40, 45 and 50 Å in Pb, Au and W respectively, and bands of lesser intensities at lower wavelenghts, are emitted by a very large number of superimposed lines originating from transitions of the type 4d¹⁰4fⁿ−4d⁹4fⁿ⁺¹, 4d¹⁰4fⁿ−4d⁹4fⁿ5p and 4fⁿ−4fⁿ⁻¹5l (l=d, g). The isoelectronic analysis shows that at the electron temperatures prevailing in the present experiment, T_e≈800 eV, there are no contributions to the bands from ions having a 4p⁶4dⁿ ground state. This, together with the experimental measurement of the electron temperature profile, indicates that the heavy ion impurity distribution in the tokamak plasma is very close to ionization equilibrium.     

Absolute photoabsorption cross sections for H2O and D2O from λ 180–790 Å

Absolute photoabsorption cross sections for H₂O and D₂O have been measured photoelectrically from λλ 180 to 790 Å using synchrotron radiation. The cross sections increase smoothly with wavelength to ～λ610 Å, with both H₂O and D₂O displaying a broad absorption band extending above a nearly linear background from λλ 400 to 490 Å. The continuum has a maximum of ～ 22.5 Mb at λ 640 Å. Above λ 615 Å, superimposed on the continuum, a diffuse structure appears which is similar to the vibrational structure of the ²B₂ states of H₂O⁺ and D₂O⁺ as observed in photoelectron spectra. The structure is believed to arise from excitation of a 1b₂ electron to the vibrational levels of a Rydberg orbital with n¹ ≈ 2.64.     

Features of the Emission Spectra of Ni-Like Ions. Application to Calculating the Wavelengths of Self-Photo-Pumped X-Ray Lasers

The energy levels and probabilities of radiative transitions to the ground state of Ni-like ions with Z = 36–51 are calculated. The energies of the upper working level 3d_3/24f_5/2 [J = 1] and the lower working level 3d_3/24d_3/2 [J = 1] of self-photo-pumped X-ray lasers along the sequence of Ni-like ions are studied. It is shown that, at the points of intersection of levels of the same parity, a strong interaction of these levels takes place, which leads to a redistribution of the oscillator strengths of the radiative transitions from these levels. Near the intersection points, the emission spectra change abruptly with variation in the nuclear charge Z.     

Beam-foil excitation studies of hydrogen-like ions

Ratios of initial populations of foil-excited hydrogen-like ions of He, B, C, N and O have been measured. Combined with earlier results for H obtained by Tielert they show aZ-dependence of the population process and indicate a velocity dependence as well. For the population of thenp-levels (n=2–5) of He⁺ ann-dependence ∞n ^?(3.6±0.4) has been observed.     

Trivalent zirconium and hafnium ions in yttrium oxide ceramics

An analysis of the electron spin resonance (ESR) spectrum of transparent ceramics composed of yttrium oxide with zirconium and hafnium additives has revealed the presence of signals (with similar parameters) from Zr³⁺ and Hf³⁺ ions, which have a similar electron configurations of the ground states: [Kr]4d ¹ and [Xe]5d ¹, respectively. It is shown that the pulsed cathodoluminescence spectra of these ions consist of two bands peaking at λ ≈ 818 and 900 nm.     

Collinear diffraction of a divergent light beam by ultrasound in a paratellurite crystal

The collinear acousto-optical interaction of a divergent light beam with ultrasound along the approximate [110] direction in a TeO₂ paratellurite crystal is investigated theoretically and experimentally. The collinear diffraction is studied at an ultrasonic frequency f ≈ 149 MHz under exposure of the crystal to an uncollimated laser light beam at a wavelength λ = 633 nm and at an angle of divergence as large as 4°. It is shown that the collinear diffraction along the direction forbidden for acousto-optical interactions of plane waves occurs only under conditions where the light beam is uncollimated and the diffraction efficiency increases with an increase in the divergence of the light beam. It is proved that the attenuation of an acoustic wave brings about a decrease in the diffraction efficiency and an increase in the transmission bandwidth of the device used. A model of the collinear acousto-optical filter based on a paratellurite crystal with an interaction length l = 2.7 cm is analyzed. The collinear acousto-optical filter is characterized by a high resolving power (～3000), a high diffraction efficiency (I₁/I₀ ≈ 0.8), and a large angular aperture (Δ? ≈ 4°). This makes collinear diffraction promising for use in acousto-optical filters based on paratellurite crystals.     

A general local-mode theory for high energy polyatomic overtone spectra and application to dichloromethane

A new model is developed to describe the overtone spectra of polyatomic molecules containing XH_n moieties. The infrared absorption is described as corresponding to excitation of localized modes of vibration rather than a set of symmetry allowed combinations of anharmonic normal modes. The possibility of assigning new bands in the more complex regions of the overtone spectra which involve combinations of both stretching and bending modes is examined and illustrated using the overtone spectrum of ammonia. The overtone spectrum of dichloromethane is recorded in the range λ = 9260 Å to λ = 5300 Å, and the CH overtone bands at 8850 Å, 7223 Å, and 6165 Å corresponding to the Δv_CH = 4, 5, and 6 overtones are identified. Specific features of these bands are discussed in detail in relation to the model. The common features and simplicity of the Δv_CH = 4 overtone bands of a series of halomethanes and ethanes are also interpreted in terms of the model.     

X-ray masks based on epoxygraphite

A simple fabrication technology of hard X-ray masks with thin (50–150μm thick) X-ray transparent bearing membranes made of a new material, i.e., polymerized epoxy resin with graphite filler (hereafter, epoxygraphite), is described. The first results of using such masks in pattern scanning synchrotron X-ray lithography in the exposing radiation wavelength range λ ≈ 0.5–3 Å are presented. The prospects of applications of such masks in the softer spectral range λ ≈ 3–7 Å are considered.     

Experimental microwave collision diameters in the rotational spectrum of H2CO

Collision diameters for some select transitions in the rotational spectrum of H₂CO have been determined using pressure broadening of the spectral lines. Transitions of the type ΔJ = 0, K_?1 = 1, and ΔK₊₁ = 1 with 1 ≤ J ≤ 5 were investigated for both self-broadening and foreign gas broadening (He and H₂) of the spectral lines. Pressure ranges from 0.001 Torr to 0.1 Torr were explored in obtaining the line width parameters Δν_p for each transition. Collision diameters were found to be very nearly constant (14 Å) over the J states studied for H₂COH₂CO interaction, 2.5–5.8 Å for H₂COH₂ interaction and 2.7–3.5 Å for H₂COHe interaction.     

Relativistic atomic level calculations with nuclei carrying additional fractional charges

One-electron energy levels and wavelengths have been calculated for Na-like ions whose nuclei carry quarks with additional charges ±e/3, ±2e/3. The calculations are based on relativistic self-consistent field procedures. The deviations from experimental values exhibit regularities which allow an extrapolation for the wavelengths of 3s-3p, 3s-4p, 3p-3d, and 3p-4s transitions for the nuclear chargeZ=11+1/3, ±2/3. A number of transitions are found in the region of visible light which could be used in an optical search for quark atoms.     

Observation of line radiation from highly charged Mo ions in a vacuum-spark plasma

Using a curved-crystal spectrograph of the transmission type the X-ray emission from a low-inductance vacuum-spark with Mo-electrodes has been investigated in the wavelength range 0.5Å<λ}<0.9Å. By means of a noise suppression technique, a number of weak lines have been resolved from the continuum. Comparing the measured wavelengths to results of relativistic energy level calculations these lines are identified as belonging to electronic transitions within singly excited heliumlike MoXLI ions and doubly excited lithiumlike MoXL ions. Continuum and line emission are used to estimate electron temperature and density.     

Spectroscopic constants of VUV laser transitions in ions of the palladium isoelectronic sequence

Spectroscopic characteristics of ions of the palladium isoelectronic sequence with nuclear charge Z=50–63 are theoretically studied. The Pd-like scheme of x-ray lasers is one of the most efficient schemes. Optical transitions promising for the development of lasers operating in the vacuum ultraviolet region are determined. The wavelengths and probabilities of these radiative transitions are presented, along with their cross sections and the rates of electron-impact excitation of the active levels. The results obtained are compared with experimental data and calculations available in the literature.