Spectroscopic estimation of plasma parameters,in the 100–400 ns stage,of a laser-induced plasma in vacuum

This work is focused on the interpretation of the emission spectra in laser-induced plasma observed in the phase at 100–400?ns from after the laser pulse, when the discrete emission lines prevail on the continuum emission, can be important to retrieve the initial stage of expansion. A Q-switched neodymium-doped yttrium aluminum garnet laser has been used for the ablation of a lead sample in vacuum. The observed line profiles, corresponding to different species of lead, were analyzed in terms of delay time. Measurements of parameters of the produced plasmas are performed. The results obtained corroborate the importance of considering nonequilibrium effects in the initial stage of plasma expansion. Also, Stark width for two spectral lines of triply ionized lead is given.     

Spectral response of radiochromic gel detector in the near-ultraviolet region (200–400 nm)

Tissue-equivalent radiochromic gel detector is sensitive in the regions of ultraviolet radiation (UVR) and gamma and X-rays. This study aims to investigate the spectral response and other optical properties of the ferrous sulphate, xylenol orange and gelatin (FXG) radiochromic gel dosimeter at particular UVR wavelengths. A total of nine monochromatic wavelengths were selected in the range of 240–400 nm with an increment of 20 nm. The FXG spectral response was estimated from the variation of spectral absorbance at 560 nm resulting from 1 h exposure to UVR beam at each chosen wavelength. Experimental results show that the FXG responsivity depends on the wavelength of the radiation and the optical path in the gel material. UVC and UVB photons have relatively higher photochemical effect than UVA; however, UVA penetration is deeper. Investigations showed that the FXG gel response is relatively constant between 240 and 320 nm, but it varies rapidly with wavelength in the UVA range and takes a minimal value at 360 nm. UVR spectral absorbance curves for different gel sample thicknesses were examined. The experiment showed that 6 mm of neutral gelatin or FXG gel samples was capable of absorbing >99.7% of the beam in the UV range of 240–290 nm.     

Coverage dependence of glycine adsorption on the Ge(100) − 2 × 1 surface

A combination of infrared spectroscopy, X-ray photoelectron spectroscopy and density functional theory has been used to investigate the adsorption behavior of glycine at the Ge(100) ? 2 × 1 surface under ultrahigh vacuum conditions. Comparison of experimental and simulated IR spectra indicates that at 310 K, glycine adsorbs on Ge(100) ? 2 × 1 via O–H dissociation, with some fraction of the products also forming an N dative bond to a neighboring germanium atom. O–Ge dative bonding is not observed. As coverage increases, the surface concentration of the monodentate O–H dissociated adduct increases, while that of the N dative-bonded species appears constant. XPS data support and clarify the IR findings and reveal new insights, including the presence at higher coverage of a minor product that has undergone dual O–H and N–H dissociation. These findings are supported by the calculated energy diagrams, which indicate that the reaction of a glycine molecule on the Ge(100) ? 2 × 1 surface via O–H dissociation and interdimer N dative bonding is both kinetically and thermodynamically favorable and that N–H dissociation of this adduct is feasible at room temperature given incomplete thermal accommodation along the reaction pathway.     

Effect of the Oxygen Content on the Local Environment of Fe Atoms in Anion-Deficient SrFeO3 – δ

Physics of the Solid State - The specific features of the structure in a polycrystalline anion-deficient strontium ferrite SrFeO3 – δ have been studied at different...     

Fourier transform measurements of SO2 absorption cross sections:: I. Temperature dependence in the 24 000–29 000 cm−1 (345–420 nm) region

Absorption cross sections of SO₂ have been obtained in the 24 000–29 000 cm^?1 spectral range (345–420 nm) with a Fourier transform spectrometer at a resolution of 2 cm^?1. Pure SO₂ samples were used and measurements were performed at room temperature (298 K) as well as at 318, 338 and 358 K. This is the first time that temperature effects in this spectral region are reported and investigated. This paper is the first of a series that will report on measurements of the absorption cross section of SO₂ in the UV/visible region at a higher than previously reported resolution and that will investigate temperature effects in support of tropospheric, stratospheric and astrophysical or planetary applications.     

Investigation of the threshold intensity versus gas pressure in the breakdown of helium by 248 nm laser radiation

An investigation of the unexpectedly strong dependence of the threshold intensity on the gas pressure in the experimental study on the breakdown of He by short laser wavelength (Turcu et al., in Opt Commun, 134:66–68, 1997) is presented. A modified electron cascade model is applied (Evans and Gamal, in J Phys D Appl Phys, 13:1447–1458, 1980). Computations revealed reasonable agreement between the calculated thresholds and the measured ones. Moreover, the calculated electron energy distribution function and its parameters proved that multiphoton ionization of ground and excited atoms is the main source for the seed electrons, which contributes to the breakdown of helium. The effect of diffusion losses over pressures <1,000 Torr elucidated the origin of the strong dependence of the threshold intensity on the gas pressure. Collisional ionization dominates only at high pressures. No evidence for recombination losses is observed for pressures up to 3,000 Torr.     

Indirect optical orientation of atoms in He–Cs gas discharge plasma: an explanation of anomalous ratio of the magnetic resonance signals

This paper discusses the indirect orientation of Cs atoms, which was observed for the first time in our early works in a helium–cesium plasma discharge with use of an indirect registration method. We propose an explanation for the unusually small ratio of the magnetic resonance signals from Cs and metastable He atoms under condition of optical orientation of He atoms.     

H/D Isotope Effect in the Conductivity of CaZr1 – xScxO3 – α in Reducing Atmospheres

Physics of the Solid State - The ionic (proton and deuteron) conductivity of the system CaZr1&nbsp;–&nbsp;xScxO3&nbsp;–&nbsp;α (x = 0.03–0.20) is studied...     

Solutions of time-fractional Kudryashov–Sinelshchikov equation arising in the pressure waves in the liquid with gas bubbles

In this paper, analytical approximate solutions for time-fractional Kudryashov–Sinelshchikov equation have been obtained. Two different techniques have been implemented to calculate the solutions, namely, homotopy analysis method and residual power series method. The approximate solutions are represented numerically and graphically for different values of fractional order of derivative. The numerical results are expressed in Tables 1, 2, 3 and 4 which show that the approximate solutions are in good agreement with the exact solution. The comparative study of the numerical results reveal that both methods are reliable and effective tools for the solution of time-fractional Kudryashov–Sinelshchikov equation.     

Cavity size and temperature dependence of stimulated emission in single Zn1 − xCdxSe/ZnSe quantum-well lasers

We observed stimulated emission originating from light-hole transitions in single Zn_1 − xCd_xSe quantum-well structures, using high excitation photoluminescence spectroscopy as a function of temperature and cavity length. We found that the lasing wavelength depends on the cavity length, and can be switched by varying the sample temperature. The occurrence of lasing from light-hole recombinations in short cavities is also accompanied by an increase in the threshold of stimulated emission, with respect to larger cavities.     

Water-vapor continuum absorption in the 800–1250 cm−1 spectral region at temperatures from 311 to 363 K

About 200 pure water-vapor spectra covering the region from 800 to 3500 cm^?1 were recorded with resolution of 0.1 cm^?1 at temperatures 311, 318, 325, 339, 352, and 363 K using a 2 m base White cell coupled to the BOMEM DA3.002 FTIR spectrometer. The water-vapor pressure varied from 28 to 151 mbar (21–113 Torr). Under these conditions, the continuum absorbance is quite measurable with the available path lengths up to 116 m. A program was developed for spectral processing that calculates, fits, and removes ro-vibrational structure from the spectrum. The spectra obtained were used to retrieve averaged and smoothed binary absorption coefficients over the region from 800 to 1250 cm^?1. Our continuum data extrapolated to room temperature are in reasonable agreement with the MT_CKD continuum model. But at higher temperatures the MT_CKD model provides very low values, which are up to 50% less than those experimentally measured.     

Positive influence of Tm3+ on effective Er3+: 3 μm emission in fluoride glass under 980 nm excitation

Er³⁺ and Tm³⁺ singly doped and codoped new fluoride glasses were prepared by traditional melt-quenching method. Efficient 3 μm emission was obtained under 980 nm laser excitation. It is worthy to notice that one of the two ions can be the sensitizer to the other one by depressing the Er³⁺: 1.5 μm emission through the energy transfer process from Er³⁺:⁴I_13/2 level to Tm³⁺:³F₄ level. On the basis of measured absorption spectra, the Judd-Ofelt intensity parameters and radiation emission probability were calculated to evaluate the spectroscopic properties. Additionally, the micro-parameters together with the phonon assistance of Er³⁺:⁴I_13/2 → Tm³⁺:³F₄ and Er³⁺:⁴I_11/2 → Tm³⁺:³H₅ processes were quantitatively analyzed by using Dexter model. The theoretical micro-parameters results meet well with the experiments which indicates that Er³⁺/Tm³⁺ codoped fluoride glass is a potential kind laser glass for 3 μm laser.     

Terahertz laser-induced 1D–0D crossover in the density of states for electrons in a cylindrical semiconductor quantum wire

The effects of a linearly polarized, terahertz laser field on the density of states (DOS) for carriers confined in a cylindrical semiconductor quantum wire are investigated here within a nonperturbative scheme, based upon a Green’s function approach. In our model, the functional dependence of the DOS on energy is significantly modified in two ways: (i) an uniform blueshift with respect to the laser-free DOS; and (ii) a strong suppression, with the appearance of Franz–Keldysh-like oscillations. Interestingly, with the increase (decrease) of the laser intensity (frequency) the DOS profile evolves from the usual shape for one-dimensional (1D) systems to a discrete set of sharp peaks that resembles the DOS for quasi-zero-dimensional (quasi-0D) electrons confined in quantum dots.     

Spectral characteristics of the emission from a barrier discharge plasma based on an Ar–H2O mixture in the UV spectral region

We present the results of a study of a barrier-discharge plasma in an Ar–H₂O mixture in the UV region of the spectrum (200–500 nm). The saturated water vapor pressure was varied over the range 2.0–2.5 kPa. A comparative study of the spectral characteristics of the plasma based on water vapor and the Ar–H₂O mixture showed that the intensity of the emission of the A → X band of the OH^● radical increases three-fold in the mixture of water with argon.     

Cathodoluminescence of monoclinic Li3AlF6 crystals in the spectral region of 150–600 nm

Cathodoluminescence (CL) of monoclinic LiAF crystals was studied in the spectral (150–600 nm) and temperature (78–302 K) ranges using both the steady-state CL and pulse CL (PCL) techniques. Three CL emission bands were found in the spectral range of 150–600 nm. The dominant complex CL band at 350 nm obeys the Mott law (E = 0.072 eV and ω = 750). On heating, the 172 and 208–212 nm CL bands vary in intensity non-monotonically. At T = 78 K, the CL decay kinetics comprises three components: a dominant fast exponential component with a lifetime of 750 ns, and two low-intensity components with the lifetimes of 20 and 240 μs. The last two components were fitted by a second order hyperbolic law. Time-resolved PCL spectra were recorded using time-windows corresponding to the PCL decay components. Paper discusses the reasonable interpretation of the CL emission bands.     

Phenomenology of collinear photon emission from quark–gluon plasma in <Emphasis Type="Italic">AA</Emphasis> collisions

Multiple backscattering from layers with various thicknesses, including the case of half-space, is numerically simulated and a comparative analysis is performed for systems with the anisotropy of scattering described by the Henyey–Greenstein and Rayleigh–Gans phase functions. It is shown that the intensity of backscattering depends on the form of the phase function; the difference between the intensities obtained within the two models increases with anisotropy.     

Pressure and compositional dependence of electric conductivity in the (Mg1 − xFex)1 − δO (x = 0.01–0.40) solid-solution

(Mg_1 ? xFe_x)_1 ? δO (x = 0.01–0.43) single crystals (~ 8 mm in diameter) were made by a melt-growth method. Electrical conductivity measurements were carried out as functions of temperature and frequency by a complex impedance method under pressure (~ 43 GPa and ~ 673 K and at 0.1 MPa and ~ 1400 K). Our experimental results show a change in charge transport mechanism in the (Mg_1 ? xFe_x)_1 ? δO solid solution at high temperature. The temperature of inflection point of the slope in Arrhenius plots depend greatly on both composition and extrinsic factors of crystals. The low-temperature conduction mechanism in (Mg_1 ? xFe_x)_1 ? δO solid solution is small polaron. Pressure effect of the electric conductivity was observed and the conductivity increased to 0.5 at log scale of S/m with increasing pressure up to 43.4 GPa. The activation energy was decreased linearly with increasing pressure. Chemical composition and homogeneity of specimen rather than pressure greatly influence the electric conductivity. The activation energy of 2.37(4) eV for the (Mg_0.99Fe_0.01)_1 ? δO solid solution might correspond to a migration enthalpy of O ions through thermally formed defects. It is proposed that a possible dominant electrical conduction mechanism in ferropericlase under the lower mantle conditions, at least in the higher temperature region, is super ionic conduction.     

Peculiarities of the Composition and Morphology of CdxPb1 – xS Films Formed on Various Substrates

Physics of the Solid State - Chemical deposition from aqueous solutions of films of substitutional CdxPb1&nbsp;–&nbsp;xS solid solutions with a cubic B1 structure on substrates made...