X-ray spectra of He-like ions of Ga and Ge,excited in the low-inductance spark plasma

The spectra of Ga XXX and Ge XXXI ions in the interval 1.2–1.4 Å excited in the low-inductance vacuum spark plasma have been obtained for the first time. The resonance line 1s²?1s2p of Ga XXX and Ge XXXI and a group of satellites, corresponding to transitions in Ga XXIX and Ge XXX can be seen distinctly in the spectra. The spectra were obtained by an electronic-optical image-intensifier tube for one discharge.     

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.     

Structure of the XUV emitting regions in a laser produced plasma

The XUV spectra emitted by plasma produced by focusing a ruby laser on plane targets of carbon and beryllium have been observed with a novel stigmatic spectrograph fitted with a toroidal mirror. The observations have been made both side-on on the expanding plasma and end-on looking inside the crater. In the latter case the intensity emitted is very large and the lines broadened indication electron densities approacing the critical density at 2.2×10²¹ cm^-3. The relative intensity of resonance lines, free-bound and free-free continua and He-like and Li-like satellites has been determined. In particular the latter satellites appear to arise only from the region inside the crater.     

Ab-initio relativistic density functional calculations for spectral line shifts of Rb atoms in liquid helium

Accurate laser spectroscopic studies of the principal resonance transitions in Rb and Cs atoms embedded in liquid helium have shown appreciable line shifts and change in line profiles. A pilot attempt has been made here to compute ab-initio the spectral line shift of the resonance excitation lines in Rb under such a confinement. Relativistic density functional theory (RDFT) within local density approximation (LDA) has been adopted. A model cluster of fourteen helium atoms surrounding the central Rb is assumed. With an optimized radius of the cluster of 5.15 Å the RLDA estimate of the blue shift of the lowest ²S → ²P excitation line of Rb comes out to be 15.4 nm which compares very well with the experimental value of 16.4 nm.     

Characterization of compact bright soft X-ray source based on picosecond laser plasma

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 10¹⁴ W/cm² was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density N_e=(1-1.9)×10²¹ cm^-3 and the electron temperature T_e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. PACS 41.50.+h; 52.25.Os; 52.50.Jm     

高n双电子复合伴线对类氦镁离子Ka共振线贡献的理论计算

利用多组态Dixac-Foek方法计算了类氯镁离子的双电子复合截面．分析了类氨镁离子的高n双电子伴线结构及其对类氯镁离子Ka共振线的影响．结果表明类氨镁离子的高n双电子伴线几乎都分布于Ka共振线的长波一侧．随着n的增加，DS强度呈现明显减小的趋势．虽然来自KLM（n=3）的发射线最强．但n〉3的部分依然给出了非常重要的贡献．即便是来自n〉10的共振的贡献也是不可忽略的．并且高n双电子伴线随着n的增加不断接近Ka共振线，导致和Ka共振线的强烈混合．在实验测量中会使Ka共振线峰位的测量值向长波方向移动，使谱形加宽，并且增强了Ka共振线测量值强度．     

A 90° laser scattering experiment for measuring temperature and density of ions and electrons in a cold dense theta pinch plasma

In a 90° scattering experiment performed on a plasma with a density of some 10¹⁷cm^?3 and a temperature of some eV a scattering spectrum is expected which consists essentially of an intense central part and two very weak satellite peaks. In this investigation the spectrum of the central part (ion line) was resolved. From the ion line alone which was in good agreement with calculated spectra, the ion temperature, electron temperature and electron density were determined. At some plasma parameters only a few particles were included in the Debye volume. Also in these cases no deviations from calculated spectra have been observed. In addition the position and half-width of the satellites were measured. The position of the satellites yields an independent value of the electron density which agrees very well with that determined from the ion line. The half-width of the satellites was much broader than expected theoretically due to fluctuations of the electron density within the scattering volume. The measurement was performed on a theta pinch plasma. The energy of the condensor bank was 7.5 kJ, the voltage 18 kV. As a light source aQ-switch laser was used with a power of about 100 MW. Because of beam stops to prevent stray light only a fourth of the whole power reached the plasma.     

Generation and characterization of a bright X-ray source using picosecond laser

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N _e=(1?1.9)×10²¹ cm^?3 and the electron temperature T _e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.     

The influence from high-n dielectronic satellites to Kɑ resonance line in helium-like aluminium

Based on the multi-configuration Dirac-Fock method, this paper has made theoretical calculations for the dielectronic recombination cross-sections and the high-n dielectronic satellites to Kα resonance line in helium-like aluminium ions. It is found that high-n dielectronic satellites are seriously mixed with resonance line, which leads to a significant increase in both the apparent width and the intensity of Kα resonance line. They also induce a positional shift of Kα resonance line.     

Opacity broadening as a density diagnostic for spot spectroscopy

A significant advantage of the recently developed spot spectroscopy techniques for plasma diagnostics is that the blowoff resulting from the tracer dots originally imbedded in the target has a well-characterized size. The helium-like resonance line 1s²?1s 2p¹P may have appreciable optical depth in these blowoff regions, especially near the original target surface. The observed width of this line is largely determined by opacity broadening, which depends directly on the density. Calculations are presented for aluminum, which allow density determination as a function of measured line width. Scaling of the calculations to tracer elements other than aluminum is also discussed.     

Wavelength‐dependent amplitude of Teflon Raman lines

Raman and other spectroscopy systems operating in the deep ultraviolet (DUV) spectral region below 250 nm lack scattering standards. Such standards are particularly important for experiments that use multiwavelength excitation and/or when results are compared across different experiment platforms. Teflon has been used as an external standard in the visible and near‐IR spectral regions and has been suggested for use in the ultraviolet (UV). Comparison of the relative amplitudes of prominent Teflon Raman lines indicates a significant effect on line ratios when the excitation wavelength is below 250 nm. This dependence on excitation wavelength has been commented on previously and attributed to pre‐resonance effects, but no detailed examination had been undertaken to date. We present the results of a study of Teflon Raman line ratios obtained from closely spaced excitation wavelengths in the DUV from 210 to 320 nm. The 731 cm⁻¹ line is identified as well suited for a standard. Electronic transition energies associated with resonance of principal Teflon Raman lines are obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

Influencing the satellite transitions of half-integer quadrupolar nuclei for the enhancement of magic angle spinning spectra

Double frequency sweeps can induce spin transitions in a set of satellites of a half-integer quadrupolar nucleus by simultaneously passing through resonance for a satellite pair. It is shown that by transferring population from the outer spin levels to the inner |1/2 and |−1/2 levels an increased intensity for central transition spectra is obtained. Although Magic Angle Spinning in principle interferes with this process, and the adiabaticity of the passages is different for every crystallite in a powder, enhanced spectra with undistorted line shapes are obtained for I=3/2 (²³Na) and 5/2 (²⁷Al) spins experiencing quadrupolar interactions with ω_Q in the range 0.1–3 MHz. Even at spinning speeds up to 30 kHz significant enhancements are obtained. An analysis of the combined effects of double frequency sweeps (DFS) and MAS indeed shows strongly different effects for different crystallites in powder ranging from no gain at all to the theoretical maximum gain of 2I. As the effects are randomly distributed over all orientations on a sphere this is averaged over the whole line shape. Therefore, undistorted powder patterns are obtained enhanced by the average gain over the individual crystallites. Saturation of the satellite transitions, which can only be achieved if spin–spin relaxation is sufficiently strong, leads to identical results. Optimization of the sweeps should be toward an optimal effect on the population transfer to the central levels and chosen short with respect to spin–lattice relaxation times.     

N.M.R. spectra of molecules containing quadrupolar nuclei

The general expression giving the N.M.R. band-shape of a spin-1/2 nucleus coupled to a spin-1 nucleus is considered in detail for the ‘fast-exchange’ limit, where the quadrupolar-induced relaxation rates of the spin-1 spin states are much greater than the coupling constant between the nuclei. The problem of obtaining the coupling constant from measurements on the band-shape of the spin-1/2 resonance is discussed, and it is concluded that this is only possible without further information when departures from lorentzian shape are observed. Possible sources of extra data are mentioned. The case of 3,4,5-trichloro-2,6-difluoropyridine is examined. The (N, F) coupling constant is obtained from the ¹⁵N satellites in ¹⁹F resonance. Hence values of the spin-lattice relaxation time for ¹⁴N are derived as a function of temperature.     

Effects of the electron-electron interaction on the surface of three-dimensional topological insulators

In the GW approximation, it has been shown that, owing to the electron-electron interaction, plasma satellites appear in the spectral function of a two-dimensional electron system on the surface of a topological insulator. They are due to the resonance plasmon-hole scattering. The contribution of satellites to the single-electron density of states is responsible for the downward energy shift of the minimum of the density, which is compared to the Dirac point in the experiment. To analyze the effect of vertex corrections on the resulting spectrum, a method has been proposed that goes beyond the GW approximation by summing ladder diagrams in the expansion of both the polarization function and self-energy. It has been shown with this method that the multiple electron-hole scattering hardly changes the resulting spectrum.     

Heating of thin foils with a relativistic-intensity short-pulse laser

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda (2)=2 x 10(18) W microm(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At /=500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (approximately 100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.     

Linienform von Doppelresonanzsignalen bei zeitlich aufgelöster Beobachtung der zerfallenden Atomzustände

The influence on the line width and the line profile of optical double resonance signals due to a selective detection of quanta of resonance light emitted in a defined time interval after the moment of excitation has been studied. A narrowing of radio frequency signals in the5s 5p ³P₁ state of Cd by a factor of 1.4 has been observed. The resonance curves deviate considerably from the lorentzian line shape. Comparison has been made between the measured line profile and a theory developed for this experiment.     

Magneto-optical resonances in the field of counterpropagating waves

The resonance of the intersection of sublevels in a probe laser field resonant to the cyclic transition corresponding to the D ₂ ⁸⁷Rb line has been investigated in a zero magnetic field. The strong effect of an additional laser field acting on the adjacent transition has been revealed. In a cell without the buffer gas and antirelaxation coating, the amplitude of the probe-field absorption resonance can increase by more than an order of magnitude in the presence of a counterpropagating wave. The effect is observed at the laser frequency tuned to the cross resonance, when the counterpropagating waves simultaneously act on moving atoms at the cyclic and open transitions with the common lower level. The theoretical analysis of the effect of the additional field on the electromagnetically induced absorption resonance is in agreement with the experimental data.     

Pulsed far-infrared spectroscopy of GaAs:Cr at high magnetic fields in the field-modulation mode

A magnetic field-modulation technique has been developed for sensitive far infrared electron paramagnetic resonance (EPR) spectroscopy on Cr²⁺ centers in GaAs. A hundred-fold improvement in signal-to-noise ratio relative to non-modulation techniques was obtained. The results of this experiment have been analyzed and agree well with a spin Hamiltonian and parameters obtained from microwave EPR studies of Cr²⁺ in GaAs. No evidence could be found to support the view that this ground state is the terminal level of the finely structured 0.839 eV luminescence line reported in earlier high resolution absorption and luminescence studies.     

Features of FMR spectra observed in granular films formed by Fe+ implantation into PMMA

Magnetic phase consisting of α-Fe particles arranged in a thin near-surface layer has been synthesized in modified phosphorus-containing polymethylmethacrylate by Fe⁺ implantation at an energy of 40 keV with a dose of 1.2⊙10¹⁷ ion/cm². The spectrum of magnetic resonance of the obtained samples is a superposition of a wide anisotropic absorption line and a set of reproducible lowintensity noiselike signals registered in a wide range of magnetic field. It has been established that a wide absorption line is due to particle conglomerates (larger than 200 nm), each behaving as a thin ferromagnetic film. Noiselike lines can be explained as resonance signals from separate oblate/prolate nanoparticles (50–200 nm in size) randomly oriented with respect to the irradiated surface. Such complicated nanostructures can be formed at an appropriate combination of properties of a polymer matrix, types of bombarded ions and implantation regimes.     

Electronic structure of substitutional nitrogen impurity in TiO 2 studied by the β-NMR method

In order to study the local electronic structure of nitrogen impurity in rutile TiO₂, we have measured double-quantum NMR spectra of short lived β-emitter ¹²N(I = 1, T _1/2 = 11 ms) implanted into a rutile single crystal by means of the β-NMR technique. The resonance line obtained at room temperature is well accounted for by the second order shift due to the quadrupole interaction at the oxygen substitutional site. The spectrum at 25 K has shown the other lines than the central diamagnetic line shifted by 10?15 kHz to both sides, which has been already shown in the previous data obtained with a different crystal orientation and an external field. The present results supports the existence of a paramagnetic state formed by the substitutional nitrogen impurities.