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Showing papers on "Absorption (logic) published in 1982"


Journal ArticleDOI
TL;DR: In this article, a variation from the statistical white-line intensity ratio of 2:1 has been observed across the $3d$ transition row, with values ranging between 0.8:1 for Ti to 5: 1 for FeO. It is suggested that the anomalous ratios may be explained by a breakdown of the exchange mechanism caused by an exchange mechanism.
Abstract: Excitations of the $2p$ subshell in the $3d$ transition metals and their oxides have been studied by inelastic scattering of 75-keV electrons. The ${L}_{23}$ "white lines" which arise from dipole transitions to unoccupied $d$ states have been investigated in terms of their threshold energies, widths, and intensity ratios. Shifts in the ${L}_{3}$ threshold energy between the metal and oxide are different from the chemical shifts measured by x-ray photoemission spectroscopy and this suggests the importance of relaxation effects. Single-particle calculations for the ${L}_{3}$ spectra are also discussed. Measured ${L}_{3}$ linewidths are generally larger than those predicted by suitably broadened theory. A variation from the statistical ${L}_{3}$-to-${L}_{2}$ white-line intensity ratio of 2:1 has been observed across the $3d$ transition row, with values ranging between 0.8:1 for Ti to 5:1 for FeO. This behavior appears to be associated with the white lines since Cu with a filled $3d$ band exhibits the statistical results. It is suggested that the anomalous ratios may be explained by a breakdown of $j\ensuremath{-}j$ coupling caused by an exchange mechanism. Finally, the extended x-ray absorption fine-structure-type structure extending several hundred eV above the white lines is analyzed for Cr to provide the radial distribution function.

610 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used rare gas matrix isolation techniques in combination with extended x-ray absorption fine structure (EXAFS) to study the variation in interatomic distances for small Fe molecules in solid neon.
Abstract: We have used rare gas matrix isolation techniques in combination with extended x-ray absorption fine structure (EXAFS) to study the variation in interatomic distances for small Fe molecules in solid neon. A considerable contraction in the interatomic distances was observed for the metal molecules. An Fe-Fe distance of 2.02 \ifmmode\pm\else\textpm\fi{} 0.02 \AA{} for the lowest concentration of metal was observed. This is in good agreement with early EXAFS measurements in ${\mathrm{Fe}}_{2}$-Ar. We also carried out a careful study of the x-ray-absorption near-edge structure (XANES), and observed the appearance of considerable structure for a 1.5-at.% Fe sample. The XANES spectra were analyzed in terms of $1s$-to-($3d,4s$) and $1s$-to-$4p$ transitions.

196 citations


Journal ArticleDOI
TL;DR: The x-ray-absorption near-edge structure (XANES) at the Fe$K$ edge has been measured and interpreted by means of multiple-scattering calculations as mentioned in this paper.
Abstract: The x-ray-absorption near-edge structure (XANES) at the Fe$K$ edge of ${\mathrm{K}}_{3}$Fe${(\mathrm{CN})}_{6}$ and ${\mathrm{K}}_{4}$Fe${(\mathrm{CN})}_{6}$ has been measured and interpreted by means of multiple-scattering calculations. The theory is able to account for the XANES over a 40-eV energy range. We demonstrate that the quasidiatomic "shape resonances" arising from multiple scattering within the CN groups play an important role in the XANES and suggest that this may be a common feature of XANES of metal atoms bound to molecular groups (e.g., CO, CN,...) containing multiple bonds. The effects on the XANES of bond-length changes and distortions of the coordination geometry of the Fe${(\mathrm{CN})}_{6}$ cluster have been estimated. The different XANES spectra of ${[\mathrm{F}\mathrm{e}{(\mathrm{CN})}_{6}]}^{2+}$ and of ${[\mathrm{F}\mathrm{e}{(\mathrm{CN})}_{6}]}^{3+}$ have been interpreted in terms of charge-induced structural modifications. Comparison of XANES with extended x-ray-absorption fine-structure (EXAFS) and diffraction data shows that XANES can be used as a quantitative probe of local structure distortions which are not detected by EXAFS.

168 citations


Journal ArticleDOI
J. Orenstein1, G. L. Baker1
TL;DR: In this paper, the first observation of photogenerated gap states in polyacetylene was reported, where a transient optical absorption, at photon energies less than the band gap, is produced by photogenation of electron-hole pairs.
Abstract: This paper reports the first observation of photogenerated gap states in polyacetylene, ${(\mathrm{CH})}_{x}$. A transient optical absorption, at photon energies less than the band gap, is produced by photogeneration of electron-hole pairs. The spectrum of this absorption is measured in both cis and trans isomers of ${(\mathrm{CH})}_{x}$. From a comparison of these spectra with similar spectra seen in molecular analogs of ${(\mathrm{CH})}_{x}$, it is concluded that these gap states are intrinsic, self-localized excitations of the semiconductor chain.

163 citations


Journal ArticleDOI
TL;DR: In this article, the optical-absorption spectra of pure cis- and trans-polyacetylene at various hydrostatic pressures, in the region 0-13 kbar, are reported.
Abstract: The optical-absorption spectra of pure cis- and trans-polyacetylene at various hydrostatic pressures, in the region 0-13 kbar, are reported. We find a large red shift of the absorption edge indicating a reduction of the energy gap ${E}_{g}$ as a function of increasing pressure in both isomers. At 13 kbar, ${E}_{g}$ is reduced in trans-${(\mathrm{CH})}_{x}$ by about 0.17 eV (i.e., \ensuremath{\sim} 10%). In addition, a decrease in the peak height and a broadening of the leading edge of the interband absorption coefficient are observed at high pressures. These changes result from an increase in the interchain transfer integral ${t}_{\ensuremath{\perp}}$. Comparison of the data with the result of tight-binding calculations leads to estimates of the transverse bandwidth, ${W}_{\ensuremath{\perp}}\ensuremath{\simeq}0.3$ eV, and a ratio of about 30 between ${W}_{\ensuremath{\perp}}$ and the total bandwidth. The resolved structure in the absorption spectrum of cis-${(\mathrm{CH})}_{x}$ is observed to red-shift with the absorption edge, to decrease in magnitude, and to broaden at high pressures. These secondary peaks are interpreted as vibronic transitions associated with the interband absorption in the solid. Their behavior with pressure is accounted for by a model for vibronic transitions which takes into account the band structure.

122 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the absorption efficiency of laser-irradiated plane-target experiments with various laser wavelengths (1.06, 0.53, and 0.26 \ensuremath{mu}m), pulse durations (100 ps, 2 ns), and intensities (${10}^{10}$-2\ifmmode\times\else\texttimes\fi{}
Abstract: Absorption efficiency has been measured in laser-irradiated plane-target experiments with various laser wavelengths (1.06, 0.53, and 0.26 \ensuremath{\mu}m), pulse durations (100 ps, 2 ns), and intensities (${10}^{10}$-2\ifmmode\times\else\texttimes\fi{}${10}^{15}$ W/cm). Results show a strong increase of absorption for long pulses, low intensities, and short wavelengths which favor inverse bremsstrahlung absorption. A one-dimensional Lagrangian hydrocode (film) is used to interpret these results.

108 citations


Journal ArticleDOI
TL;DR: In this paper, spin-echo NMR studies of small particles of Pt supported on alumina were performed at fields of 80 to 85 kG, with a frequency of 74$ MHz, and at a temperature of 77 K.
Abstract: The authors report spin-echo NMR studies of $^{195}\mathrm{Pt}$ in small particles of Pt supported on alumina. For the samples studied, the fraction of Pt atoms on the surface (called the dispersion) ranged from 4% to 58%. The studies were at fields ${H}_{0}$ of 80 to 85 kG, frequency ${\ensuremath{ u}}_{0}=74$ MHz, and at a temperature of 77 K. The lines are broad (3-5 kG), requiring special methods which permit substantial signal averaging (\ensuremath{\sim} 50 000 echoes). In the low-dispersion (large-particle) samples, there is a strong absorption at the position of the $^{195}\mathrm{Pt}$ NMR in bulk Pt metal ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}=1.138$ kG/MHz) which becomes progressively weaker as the particle size decreases. A peak which is near the $^{195}\mathrm{Pt}$ resonance in typical diamagnetic compounds ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}\ensuremath{\sim}1.09$ kG/MHz) is found in samples which are coated with adsorbed molecules. It disappears when the surface is cleaned. The authors show that this peak arises from the surface layer of Pt atoms, and that its position ($\frac{{H}_{0}}{{\ensuremath{ u}}_{0}}$) shows that coating the Pt atoms on the surface largely ties up the electron spins of the surface Pt atoms in bonds. The exact position of this peak depends on the chemical species which is adsorbed. The authors show that when Pt is cleaned, then exposed to air for long times, the surface peak reveals that the surface has reconstructed to form Pt${(\mathrm{OH})}_{6}$.

103 citations


Journal ArticleDOI
TL;DR: In this article, a survey of the spectra of elements from cesium to hafnium in two regimes of optical thickness is presented, and a table of plausible ground configurations is proposed.
Abstract: Spectra of the elements barium ($Z=56$) through Nd ($Z=60$) observed in laser-produced plasmas from pure-metal targets in the wavelength region 70- 130 \AA{} are presented. This completes our survey of the spectra of elements from cesium to hafnium in two regimes of optical thickness. The two sets of spectra show significant differences. In order to interpret the whole range of results, we need to know the ground-state configurations of ions in stages up to XVI for $Z=55\ensuremath{-}71$. From the limited-term analyses available, a table of plausible ground configurations is proposed. In the preparation of the table, the effect of increasing ionization, for a fixed $Z$, on wave-function contraction is studied, and it is inferred that the $4f$ electron becomes more tightly bound than $5p$ between the sixth and seventh spectra of the elements from cerium to lutetium; similarly the $4f$ electron attains a higher binding energy than does the $5s$ between the fourteenth and fifteenth spectra. Consequently, for a considerable range of ion stages, particularly in the rare earths, the ground configurations have a partially filled $4f$ shell. Furthermore, in the same ion stages, the $4f$, $5p$, and $5s$ energies stay relatively close together so that configurations of the type $5{p}^{l}4{f}^{n\ensuremath{-}l}$ lie very near the nominal ground configuration. A corresponding manifold of overlapping excited configurations of the type $4{d}^{9}4{f}^{n+1}$, $4{d}^{9}5{p}^{l}4{f}^{n\ensuremath{-}l+1}$ is also expected and the observed resonances arise from all of the $4d\ensuremath{-}4f$ transitions permitted between the upper and lower manifolds of configurations. The numbers of transitions are calculated and in the majority of cases are very great. Because the principal quantum number does not change, the transitions will tend to overlap for different ion stages of any one element. The widths and varying complexity of the resonances can be explained in a satisfactory, if qualitative, way by means of available theory. The very considerable difference between the compound and metal spectra can be explained in terms of the effect of number density of the active species on both emission and absorption processes in the two types of plasma.

94 citations


Journal ArticleDOI
TL;DR: In this article, the photoelectronic properties of nominally pure SrTi${\mathrm{O}}_{3}$ single crystals were studied in detail, and a sharp narrow peak near the fundamental absorption edge was observed in both photoconductivity and photoluminescence excitation spectra, although it was not detected in the absorption spectrum.
Abstract: The photoelectronic properties of nominally pure SrTi${\mathrm{O}}_{3}$ single crystals were studied in detail. A sharp narrow peak near the fundamental absorption edge was observed in both photoconductivity and photoluminescence excitation spectra, although it was not detected in the absorption spectrum. The temperature dependence of the half-width of this anomalous peak was found to have a behavior similar to that of the absorption bands of $F$ centers in alkali halides. The photocurrent associated with this peak was found to depend strongly on temperature. The photoconductive gain at 10 K was estimated to be at least 8\ifmmode\times\else\texttimes\fi{}${10}^{5}$. Marked thermal and optical quenching of the photocurrent were measured. In addition, a supralinearity phenomenon, by which the photocurrent varies as the 5th power of the light intensity, was observed. On the basis of the results of the varied experiments designed to elucidate the nature of the transition responsible for the anomalous peak, we have reasonably established that it is due to the descrete transition by which an electron is raised from the ground state of a highly localized sensitizing center to an excited state located in the conduction band; subsequently a free electron is produced by the process of autoionization. It has been shown that there is a strong correlation between photoconductivity and photoluminescence. The infrared emission, attributed to the electronic transition within a ${\mathrm{Cr}}^{3+}$ ion, can be excited by either the anomalous-peak radiation or band-to-band radiation; however, the visible emission, ascribed to the recombination of a free hole with a level below the conduction band, can be excited only by band-to-band radiation. These and other photoluminescence results are discussed in terms of charge-transfer processes and an association model involving the ${\mathrm{Cr}}^{3+}$ ion and the highly localized center responsible for the anomalous peak.

89 citations


Journal ArticleDOI
S. Venugopalan1, A. Petrou1, R. R. Galazka1, A. K. Ramdas1, S. Rodriguez1 
TL;DR: In this paper, a quasicontinuous feature in the Raman spectrum can be traced to first-order processes which become allowed as a result of the absence of strict translational symmetry and reflect the one-phonon density of states.
Abstract: ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}$ Te alloys possess a homogeneous crystal phase having a zinc-blende structure for $0\ensuremath{\le}x\ensuremath{\le}0.7$. Their Raman spectra exhibit two pairs of sharp lines characteristic of the zone center "CdTe-like" and "MnTe-like" LO-TO modes. Some quasicontinuous features in the Raman spectrum can be traced to first-order processes which become allowed as a result of the absence of strict translational symmetry and reflect the one-phonon density of states. In the antiferromagnetic phase of the alloys ($xg0.6$) and in the spin-glass phase ($0.17\ensuremath{\le}x\ensuremath{\le}0.6$), a new low-energy Raman line appears. We attribute it to an inelastic scattering involving the emission or absorption of a magnon. The polarization features and the temperature dependence of the magnon line are consistent with this assignment.

87 citations


Journal ArticleDOI
TL;DR: In this article, a model for the conjugation-length dispersion was presented and found to be in good agreement with absorption profiles, frequency shifts, and resonance Raman scattering intensities.
Abstract: Resonance Raman scattering (RRS) in conjugated polydiacetylene solutions is employed in order to determine the vibrational spectra of resonance-selected chromophores within a single conformationally disordered polymer chain. Although the polymer-chain length contains up to 1000 repeat units, the conjugation length (i.e., the length over which backbone planarity is maintained without interruption and which defines the chromophore) may be as small as three units. Variation of the solvent system can increase the conjugation length to essentially infinity. The absorption spectrum of the polymer in chloroform consists of an inhomogeneously broadened line shape with contributions from a distribution of individual chromophores. RRS can photoselect chromophores with specific transition energies and, therefore, with specific conjugation lengths. The delocalization of electron density along the conjugated unit, which decreases the absorption energy of the chromophore, also causes a decrease in frequency for those Raman modes which primarily correspond to multiple bond stretching, such as ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$. The change of ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$ and ${\ensuremath{ u}}^{\mathrm{C}\ensuremath{\equiv}\mathrm{C}}$ as the incident laser energy is tuned through the absorption band is reported here. Far from the absorption band an average value for ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$ is obtained. As the incident energy approaches the absorption band, long-conjugation-length chromophores are photoselected and ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$ decreases markedly. At higher energies within the absorption band, shorter-conjugation-length chromophores are photoselected and ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$ increases, becoming larger than the average value of ${\ensuremath{ u}}^{\mathrm{C}=\mathrm{C}}$. Similar results are obtained for ${\ensuremath{ u}}^{\mathrm{C}\ensuremath{\equiv}\mathrm{C}}$. A model for the conjugation-length dispersion is presented and found to be in good agreement with absorption profiles, frequency shifts, and RRS intensities.

Journal ArticleDOI
TL;DR: In this article, a self-consistent interpretation of the optical energy gap and gap-state densities with mixtures of different ratios of Si${\mathrm{H}}_{4}$ to Ge${H}$ is presented.
Abstract: Results on the optical absorption, photoluminescence, and photoconductivity spectra and on electrical-transport data of amorphous ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$:H alloys prepared from the plasma decomposition of silane and germane are presented An attempt is made to find a self-consistent interpretation of the data in terms of changes in the optical energy gap and in the gap-state densities with mixtures of different ratios of Si${\mathrm{H}}_{4}$ to Ge${\mathrm{H}}_{4}$ It is found that the photoconductivity and the photoluminescence intensity are much higher than would be expected from the previously deduced values of the ratio of Si\char22{}H to Ge\char22{}H bonds from infrared absorption spectra The principal conclusion of our results is that the changes in the intrinsic properties of a random tetrahedrally coordinated alloy as a function of alloy composition $x$ are often masked by the extrinsic effects of changes with $x$ in H content, defect density, and microstructure; the latter changes depend sensitively on the preparation method

Journal ArticleDOI
TL;DR: In this article, the infrared absorption of O${\mathrm{D}}^{\ensuremath{-}}$ and O${H}}^{-}6} ions is used to study diffusion rates of doped and undoped MgO crystals.
Abstract: Infrared absorption of O${\mathrm{D}}^{\ensuremath{-}}$ and O${\mathrm{H}}^{\ensuremath{-}}$ ions is used to study diffusion rates of ${\mathrm{D}}^{+}$ and ${\mathrm{H}}^{+}$ in doped and undoped MgO crystals heated at high temperatures in ${\mathrm{D}}_{2}$O and ${\mathrm{H}}_{2}$O vapors. Crystals doped with H, Li, Na, Al, V, Cr, Fe, Co, Ni, Cu, Ga, Ag, and Yb are studied. With the exception of the H- and Li-doped crystals, the diffusion characteristics of the doped and undoped MgO crystals are essentially the same. The minimum temperature observed for ${\mathrm{D}}^{+}$ diffusion is 1750 K, and the diffusion coefficient is \ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{2}$/sec at 1873 K. The ratio of the diffusion coefficients of ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ at 1873 K is $\frac{D({\mathrm{H}}^{+})}{D({\mathrm{D}}^{+})}=1.1\ifmmode\pm\else\textpm\fi{}0.1$. Complete removal of soluble ${\mathrm{H}}^{+}$ can be accomplished by application of an electric field at 1300 K. In H-doped crystals an exchange of ${\mathrm{H}}^{+}$ for ${\mathrm{D}}^{+}$ results in large concentrations of O${\mathrm{D}}^{\ensuremath{-}}$ ions. In Li-doped crystals, deuterons diffuse much more readily; the threshold temperature for ${\mathrm{D}}^{+}$ diffusion is only 800 K. The higher diffusivity is attributed to a catalytic behavior of ${\mathrm{Li}}_{2}$O precipitates.

Journal ArticleDOI
TL;DR: Anomalous microwave absorption has been observed in the organic superconductor below its metal-nonmetal transition near 12 K as mentioned in this paper, unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin-wave calculation and the pronounced dependence on temperature and magnetic field orientation.
Abstract: Anomalous microwave absorption has been observed in the organic superconductor ${\mathrm{TMTSF}}_{2}$${\mathrm{AsF}}_{6}$ (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin-wave calculation and the pronounced dependence on temperature and magnetic field orientation. This result dramatically confirms earlier indications of magnetic ordering or spin-density waves and, furthermore, indicates that the spin-density-wave amplitude is considerably larger than previous estimates of 1%.

Journal ArticleDOI
TL;DR: In this article, the 2.0-eV photoluminescence band in semiconductor alloys was investigated over the range of $0.4 to $ 0.7.
Abstract: The 2.0-eV photoluminescence band in ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ semiconductor alloys is investigated over the range $0.4\ensuremath{\le}x\ensuremath{\le}0.7$. The emission is ascribed to the $^{4}T_{1}(^{4}G)\ensuremath{\rightarrow}^{6}A_{1}(^{6}S)$ internal transition of ${\mathrm{Mn}}^{2+}$ within the $3{d}^{5}$ state. Excitation spectra reveal a drop in intensity near the fundamental edge; the decrease is a result of competitive intrinsic absorption that does not lead to ${\mathrm{Mn}}^{2+}$ emission. Onset of the $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{1}$ transition can be seen for $xg0.4$; excitation in samples with $xg0.6$ reveals the $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{2}$ transition as well. The strongly localized character of the emission is established from full width at half maximum data. A phonon energy of $\ensuremath{\hbar}\ensuremath{\omega}=53\ifmmode\pm\else\textpm\fi{}16$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and a Huang-Rhys factor of $S=26\ifmmode\pm\else\textpm\fi{}2$ is obtained with the use of a linear configurational coordinate model. In addition, a value of inhomogeneous broadening ${H}_{\mathrm{in}}=80$ meV (645 ${\mathrm{cm}}^{\ensuremath{-}1}$) is found from the analysis. Various sources of inhomogeneous broadening and line shift are discussed.

Journal ArticleDOI
TL;DR: In this article, the lifetime-broadened two-phonon difference processes, in contrast to energy-conserving two-and threephonons processes as previously thought, are explained by the intrinsic microwave absorption coefficient of alkali halides.
Abstract: The intrinsic microwave absorption coefficient $\ensuremath{\beta}$ of alkali halides is well explained by lifetime-broadened two-phonon difference processes, in contrast to energy-conserving two- and three-phonon processes as previously thought. A simple closed-form expression for $\ensuremath{\beta}$ with no adjustable parameters gives excellent agreement with the magnitude, frequency dependence, and temperature dependence of $\ensuremath{\beta}$ in LiF, NaCl, KBr, and KI. As $\ensuremath{\omega}$ increases from $\ensuremath{\omega}l\frac{{\ensuremath{\omega}}_{c}}{3}$ to $\ensuremath{\omega}={\ensuremath{\omega}}_{c}+{\ensuremath{\gamma}}_{293}$, the frequency and temperature dependence of $\ensuremath{\beta}$ at 293 K (or 1000 K) change from the low-frequency limit $\ensuremath{\beta}\ensuremath{\sim}{T}^{l}{\ensuremath{\omega}}^{2}$ to $\ensuremath{\beta}\ensuremath{\sim}{T}^{h}{\ensuremath{\omega}}^{2+}$, where $2.0\ensuremath{\le}l\ensuremath{\le}2.6$ (or $2.2\ensuremath{\le}l\ensuremath{\le}4.0$) and $0.9\ensuremath{\le}h\ensuremath{\le}1.2$ (or $0.6\ensuremath{\le}h\ensuremath{\le}1.6$) for the four materials. Here ${\ensuremath{\omega}}_{c}=20$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for NaCl is the frequency difference between the transverse-acoustical and transverse-optical phonon modes at the Brillouin-zone edge along the [111] direction, and $\ensuremath{\gamma}$ is the combined-phonon inverse lifetime at 293 K. The temperature dependence of the phonon frequencies and other parameters must be included in order to explain the temperature dependence of the experimental results. The present lifetime-broadened results reduce to previous energy-conservation results (apart from smoothing, which explains the lack of sharp structure in $\ensuremath{\beta}$, but otherwise has little effect in general) and agree with experimental results in the region $\ensuremath{\omega}g{\ensuremath{\omega}}_{c}+\ensuremath{\gamma}$. Previous energy-conserving results disagree with the $T$ and $\ensuremath{\omega}$ dependence and magnitude of the experimental results in the region $\ensuremath{\omega}l{\ensuremath{\omega}}_{c}$.

Journal ArticleDOI
TL;DR: In this article, the energy, wave function, and radial parameters of the low-lying triply excited resonances of the lithium atom were calculated using a saddle-point technique, and the results were used to identify the observed Auger spectra of R\o{}dbro, Bruch, and Bisgaard.
Abstract: The energy, wave function, and radial parameters of the low-lying triply excited resonances of the lithium atom are calculated using a saddle-point technique. A total of eleven resonances with $^{2}P^{o},^{4}P^{e},^{2}D^{e},^{2}S^{e},^{2}P^{e}$, and $^{2}D^{o}$ symmetries are investigated. These results are used to identify the observed Auger spectra of R\o{}dbro, Bruch, and Bisgaard. If the identifications suggested here are correct, then the agreement between the results of the present work with those of the experiment is excellent. The oscillator strengths and transition energies of these resonances in an optical absorption or emission process are calculated. In order to compute these oscillator strengths, the energies and wave functions of the Li $1s2s2p^{4}P,1s2p2p^{2}P$, and $1s2s2s^{2}S$ states are also tabulated. The energies of the two bound states agree to within 0.013 eV with the highly accurate results in the literature. The result for the $^{2}S$ resonance agrees with the more recent experiments and lies well within the quoted experimental error.

Journal ArticleDOI
TL;DR: In this article, the lateral distribution of EAS is well expressed by the NKG function of single age parameter in the range distance from 1 m to 50 m from the core.
Abstract: Extensive air showers with sizes from 8×10 4 to 5×10 6 particles were observed by the scintillator array in Kobe University near sea level. Results obtained in the experiment are as follows: (1) The lateral distribution of EAS is well expressed by the NKG function of single age parameter in the range distance from 1 m to 50 m from the core. (2) The average age parameter of EAS decreases with increasing shower size and approaches a constant value, and the fluctuation of age parameters decreases with increasing shower size monotonously. (3) The absorption length \(\varLambda_{\text{abs}}\) of EAS is almost constant in the observed size range, and it is 117±8 g/cm 2 . (4) The integral size spectrum of EAS in the size range 8×10 4 –5×10 6 can be expressed by a power law of single exponent, i.e. \begin{aligned} I({\geqq}N_{\text{e}}){=}(3.01{\pm}0.34){\times}10^{-6}(N_{\text{e}}/10^{5})^{-1.87{\pm}0.05}/\text{m$^{2}$.s.sr.} \end{aligned}

Journal ArticleDOI
TL;DR: In this article, the authors derived the cyclotron resonance linewidth in the quantum limit for a nondegenerate semiconductor using a previously derived formula, and compared their numerical results with the various approximations which are commonly employed.
Abstract: The cyclotron resonance line shape is dependent upon the current relaxation rate $\ensuremath{\Gamma}(k)$. We have numerically determined $\ensuremath{\Gamma}(k)$ and hence the cyclotron resonance linewidth $\ensuremath{\gamma}$ in the quantum limit for a nondegenerate semiconductor using a previously derived formula [J. Phys. Chem. Solids 41, 735 (1980)]. The electrons are assumed to interact with acoustic phonons via a deformation potential. For high temperatures we have found that the dependence of the linewidth $\ensuremath{\gamma}$ and peak absorption ${P}^{max}$ on the temperature and the resonance frequency ${\ensuremath{\omega}}_{0}$ is given approximately by $\ensuremath{\gamma}\ensuremath{\propto}{T}^{\frac{1}{2}}{\ensuremath{\omega}}_{0}$, ${P}^{max}\ensuremath{\propto}{T}^{\frac{\ensuremath{-}1}{2}}{\ensuremath{\omega}}_{0}^{\ensuremath{-}1}$, whereas for low temperatures $\ensuremath{\gamma}\ensuremath{\propto}{T}^{6.5}{\ensuremath{\omega}}_{0}^{\ensuremath{-}2}$, ${P}^{max}\ensuremath{\propto}{T}^{\ensuremath{-}6.5}{\ensuremath{\omega}}_{0}^{2}$. The line shape is found to be almost Lorentzian. We have compared our numerical results for $\ensuremath{\Gamma}(k)$ with the various approximations which are commonly employed.

Journal ArticleDOI
TL;DR: In this paper, high-resolution spectra for free $A$ excitons in CdS were obtained by two-photon absorption using photoconductivity techniques. The magnetic field dependences are analyzed in terms of linear Zeeman splitting and diamagnetic interactions.
Abstract: High-resolution spectra are obtained for the free $A$ excitons in CdS by two-photon absorption using photoconductivity techniques. At zero applied magnetic field the anisotropy splitting of the $2P$ and $3P$ exciton states is observed and interpreted with an anisotropic effective-mass Hamiltonian. The energies of these states are measured as a function of magnetic field up to $B\ensuremath{\simeq}$10 T. The magnetic field dependences are analyzed in terms of linear Zeeman splitting and diamagnetic interactions. At low fields the diamagnetic contribution gives the usual quadratic field dependence but deviates significantly at higher fields. At a given field, the deviation is found to increase dramatically with increasing quantum number $n$. This deviation is fitted by variational calculations developed by Larsen, which take into account the interaction of states through the diamagnetic term in the Hamiltonian. The magnetic field dependence of these states allow us to determine the masses as ${m}_{e}^{\ensuremath{\perp}}=(0.210\ifmmode\pm\else\textpm\fi{}0.003){m}_{0}$ and ${m}_{h}^{\ensuremath{\perp}}=(0.64\ifmmode\pm\else\textpm\fi{}0.2){m}_{0}$. At $B=0$ the narrow laser linewidths (0.05 meV) allow an accurate determination of the $A$-exciton binding energy of 27.4\ifmmode\pm\else\textpm\fi{}0.8 meV and the anisotropy parameter of 0.797\ifmmode\pm\else\textpm\fi{}0.013 from which the energy gap ${E}_{g}^{A}=2582.5\ifmmode\pm\else\textpm\fi{}0.2$ meV at $T=1.8$ K is calculated. Finally, the temperature dependence of the $A$ gap is determined.

Journal ArticleDOI
TL;DR: In this paper, extended x-ray absorption fine-structure measurements were made at the Kr $K$ edge for 0.10, 0.20, and 0.35 monolayer coverages of krypton adsorbed on Grafoil, an exfoliated form of graphite.
Abstract: Extended x-ray absorption fine-structure measurements were made at the Kr $K$ edge for 0.10, 0.20, and 0.35 monolayer coverages of krypton adsorbed on Grafoil, an exfoliated form of graphite. The Grafoil is measured to have 0.67\ifmmode\pm\else\textpm\fi{}0.05 of its surface area oriented with rms angular variation of 15\ifmmode^\circ\else\textdegree\fi{}. The adsorption site was explicitly determined to be the center of the carbon hexagons, and significant changes in this site were observed for the 0.10 monolayer coverage which were attributed to surface defects. The average Kr-C distance is determined to be 3.6\ifmmode\pm\else\textpm\fi{}0.1 \AA{} (corresponding to a mean distance of 3.35\ifmmode\pm\else\textpm\fi{}0.1 \AA{} between Kr and the graphite plane), and its mean-square deviation is found to increase by 0.051\ifmmode\pm\else\textpm\fi{}0.009 ${\mathrm{\AA{}}}^{2}$ as the temperature changes from 10 to 100 K for the 0.35 monolayer. Krypton coordination is observed only for the 0.35 monolayer coverage; in this case the number of Kr nearest neighbors was found to be 1.8\ifmmode\pm\else\textpm\fi{}0.5 and the distance to have the ($\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$) 30\ifmmode^\circ\else\textdegree\fi{} value of 4.26\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The Kr-Kr mean-square deviation and the third moment of the radial distribution of 10 K were determined to be 0.0166\ifmmode\pm\else\textpm\fi{}0.004 ${\mathrm{\AA{}}}^{2}$ and 0.0010\ifmmode\pm\else\textpm\fi{}0.0003 ${\mathrm{\AA{}}}^{3}$, respectively. The small Kr-Kr coordination is inconsistent with the generally accepted phase diagram.

Journal ArticleDOI
TL;DR: In this paper, the quantum theory of the three-energy-level two-mode laser in which all the levels are being pumped is investigated and the master equation of the laser operation is obtained.
Abstract: The quantum theory of the three-energy-level two-mode laser in which all the levels are being pumped is investigated and the master equation of the laser operation is obtained. It contains two variables, ${n}_{1}$, the photon number of the first mode, and ${n}_{2}$, the photon number of the second mode. There appear four terms in the master equation which represent two-photon processes between the two modes, the absorption of a photon from one mode, and emission of a photon to the other. They are absent in the single-mode case and in the two-mode case with pumping only to the upper level. The master equation can be represented by a diagram of probability in two dimensions which can be extended to infinity, and each arrow of it represents a term on the right-hand side of the master equation. By summing each variable (${n}_{1}$ or ${n}_{2}$) of the master equation, two equations can be obtained. Each equation contains only one variable, and can be expressed by a diagram of probability flow in one dimension. By considering the correspondence between macroscopic equilibrium and microscopic detailed balance the equations of motion in the steady state are obtained. By introducing a parameter $H$, the equation of motion is simplified and a formal solution can be deduced which is dependent on $H$. It appears that the parameter $H$ cannot be fully determined, but some properties of it can be deduced which prove that the introduction of $H$ is reasonable. The operation characteristics of the laser under different conditions are discussed on the basis of the formal solution: among them are the threshold condition, the condition for one-mode operation, and the change of the photon-statistical distribution. We especially discuss the laser output power curves under two-mode operation above threshold. The curve of one mode, which oscillates first, shows a bending-down phenomenon as the excitation increases when the other mode goes beyond its threshold as demonstrated experimentally by Otsuka. This phenomenon is explained qualitatively and is attributed to the two-photon processes between the two modes.

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TL;DR: In this article, the x-ray absorption spectra of vanadium in vanadium dichalcogenides and in their first-row transition-metal intercalates were measured using a two-crystal spectrometer.
Abstract: The x-ray $K$ absorption spectra of vanadium in vanadium dichalcogenides and in their first-row transition-metal intercalates ${M}_{\frac{1}{3}}\mathrm{V}{X}_{2}$ ($M=\mathrm{V},\mathrm{ }\mathrm{C}\mathrm{r},\mathrm{ }\mathrm{M}\mathrm{n},\mathrm{ }\mathrm{F}\mathrm{e},\mathrm{ }\mathrm{C}\mathrm{o},\mathrm{ }\mathrm{Ni}$; $X=\mathrm{S},\mathrm{ }\mathrm{Se}$) have been measured together with those in V, ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$, and VSe, using a two-crystal spectrometer. The spectra of vanadium dichalcogenides and their first-row transition-metal intercalates have strong resemblance to each other and exhibit a weak flat structure followed by strong absorption. They reflect the transitions to the unoccupied vanadium $d$ band with some $p$ character and to the unoccupied vanadium $4s\ensuremath{-}4p$ bands, respectively. The midpoint of the initial rise of absorption is shifted to higher energies by intercalating the first-row transition metals. This shift is explained in terms of the charge-transfer model. It is, consequently, concluded that the rigid-band-model approach is valid as a first approximation at least for the unoccupied levels of these intercalation compounds.

Journal ArticleDOI
TL;DR: In this paper, a model for laser-induced breakdown of argon and other gases at a wavelength of 0.35 µm has been described, and the results of short-pulse (${\ensuremath{\tau}}_{p}=0.4$ ns) and long-pulses (${\ensemblemath{tau}{p} =500$ ns] measurements in argon indicate that at $p=1$ atm the breakdown threshold scales as{I}_{\mathrm{th}}$
Abstract: Laser-induced breakdown of argon and other gases at a wavelength of 0.35 \ensuremath{\mu}m has been measured in the pressure range 200 to 2000 Torr. The results of short-pulse (${\ensuremath{\tau}}_{p}=0.4$ ns) and long-pulse (${\ensuremath{\tau}}_{p}=500$ ns) measurements in argon indicate that at $p=1$ atm the breakdown threshold ${I}_{\mathrm{th}}$ scales as ${\ensuremath{\tau}}_{p}^{\ensuremath{-}0.7}$. Practically complete absorption of the laser beam by the broken-down plasma has been observed at the highest pressures studied. A model for breakdown in Ar is described which gives satisfactory agreement with the data.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the emission from plane multilayered disk targets irradiated by nanosecond C${\mathrm{O}}_{2}-laser pulses at peak irradiances of 7.5.
Abstract: $K\ensuremath{\alpha}$ emission has been measured from plane multilayered disk targets irradiated by nanosecond C${\mathrm{O}}_{2}$-laser pulses at peak irradiances of 7.5 \ifmmode\times\else\texttimes\fi{} ${10}^{14}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$. Absolute levels of hot-electron preheat have been determined.

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TL;DR: In this article, it was shown that the room-temperature x irradiation of an europium-doped NaCl crystal produces the conversion of doubly valent Europium ions to the tripositive state.
Abstract: In the present paper evidence has been gathered to show for the first time that the room-temperature x irradiation of an europium-doped NaCl crystal produces the conversion of doubly valent europium ions to the tripositive state. This conversion occurs in both well-aged and fast-quenched samples. However, it is considerably enhanced in the former crystals in which precipitates with the Eu${\mathrm{Cl}}_{2}$ structure are present before irradiation. If one takes advantage of this fact, the optical absorption, emission, and excitation spectra of the ${\mathrm{Eu}}^{3+}$ ions can be obtained. In particular, transitions between the different Stark levels of the various $^{7}F$ manifolds and the excited levels $^{5}D_{2}$, $^{5}D_{1}$, and $^{5}D_{0}$ of ${\mathrm{Eu}}^{3+}$ have been identified in the visible region of the absorption, emission, and excitation spectra of the x-irradiated samples.

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TL;DR: In this paper, the authors measured the energy spectra and yields of neutrons above 1.2 MeV from nuclear capture of negative pions slowing down and stopping in C, N, O, Al, Cu, Ta, and Pb targets.
Abstract: We measured the energy spectra and yields of neutrons above 1.2 MeV from nuclear capture of negative pions slowing down and stopping in C, N, O, Al, Cu, Ta, and Pb targets. Each neutron spectrum was decomposed into an evaporation portion and a direct portion. The number of direct neutrons per stopped pion is substantially constant for all the targets with a mean value of 1.74\ifmmode\pm\else\textpm\fi{}0.28, whereas the yield of evaporation neutrons increases by an order of magnitude from about 0.7 for carbon to about 7 for lead. The total kinetic energy carried away by the neutrons is substantially constant also for all the targets with a mean value of 76.7\ifmmode\pm\else\textpm\fi{}2.0 MeV. The kinetic energy carried away by evaporation neutrons increases with mass number with an associated decrease in the kinetic energy carried away by direct neutrons. We obtained the nuclear temperature (in MeV) of the first residual nucleus formed in the evaporation process for each target: Pb (1.4), Ta (1.4), Cu (1.9), A1 (2.3), O (2.2), N (2.2), and C (2.1). The spectrum from a light target displays a shoulder in the region around 60 MeV which is consistent with a two-nucleon absorption mechanism. The direct neutron spectra are characterized by a rising yield as the neutron energy decreases in the region from 30 MeV down to about 10 MeV. The data are compared with previous measurements and with the predictions of intranuclear cascade and preequilibrium calculations.NUCLEAR REACTIONS C, N, O, Al, Cu, Ta, Pb (${\ensuremath{\pi}}^{\ensuremath{-}}$,$\mathrm{xn}$), ${E}_{{\ensuremath{\pi}}^{\ensuremath{-}}}\ensuremath{\approx}0$ MeV. Measured differential energy spectra and yields. Deduced nuclear temperature. Compared results to intranuclear cascade and preequilibrium model calculations.

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TL;DR: In this paper, an absorption cell containing low-pressure gas is placed inside a C${\mathrm{O}}$-${N}}_{2}$O infrared laser cavity and microwave resonances in the gas are detected through the off-resonant response of the infrared laser.
Abstract: An absorption cell containing low-pressure gas is placed inside a C${\mathrm{O}}_{2}$-${\mathrm{N}}_{2}$O infrared laser cavity and microwave resonances in the gas are detected through the off-resonant response of the infrared laser. The small variation in molecular population in certain rotational levels produced by a microwave pumping changes the bulk susceptibility of the gas through dispersion and thus changes the effective cavity length and the output power of the laser. This new mode of "double resonance" does not require exact coincidence between the laser lines and molecular transitions and is more widely applicable than the normal double-resonance method although its sensitivity is not as great. Characteristics of this method are theoretically studied and compared with experimental results obtained by using the simple molecules C${\mathrm{H}}_{3}$F, ${\mathrm{D}}_{2}$CO, ${\mathrm{D}}_{2}$O, and N${\mathrm{H}}_{3}$. Microwave resonances are observed through laser lines which are off from molecular infrared transitions by several ${\mathrm{cm}}^{\ensuremath{-}1}$. Some unexpected asymmetry of the signals with respect to laser settings has been observed and discussed.

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TL;DR: In this article, the local environment around an ion ion as a magnetic impurity in ErSb solid solutions was investigated by extended x-ray absorption fine structure measurements on the ion ion, and the nearest-neighbor distances around the ion were found to be nearly the same as in pure PrSb, almost independent of the pr concentration in the alloys.
Abstract: The local environment around Pr as a magnetic impurity in ErSb solid solutions was investigated by extended x-ray absorption fine structure measurements on ${\mathrm{Er}}_{x}{\mathrm{Pr}}_{1\ensuremath{-}x}\mathrm{Sb}(x=1,0.95,0.90)$. The nearest-neighbor distances around the Pr ion were found to be nearly the same as in pure PrSb, almost independent of the Pr concentration in the alloys. Thus, the usual assumption used in electron-spin-resonance measurements\char22{}that the impurity nearest-neighbor distance is the same as that of the host\char22{}is incorrect.

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TL;DR: In this paper, the authors measured the absorption of monochromatic phonons by electron-hole liquid over the frequency range 150-500 GHz using tunnel junction phonon spectroscopy.
Abstract: The absorption of phonons by the electron-hole liquid (EHL) in semiconductors has proven to be the principal process causing macroscopic transport of droplets of this Fermi fluid. A characterization of the phonon absorption for frequencies of several hundred gigahertz promises to elucidate this "phonon wind" transport mechanism as well as test the basic theory of deformation potential scattering within a degenerate Fermi liquid. Central predictions of this theory are an absorption rate which increases linearly with frequency at low frequencies and a transparency for phonon wave vectors greater than $2{k}_{F}$, where ${k}_{F}$ is the Fermi wave vector of the liquid. We have adapted the standard deformation potential theory to the case in which the phonon energies are comparable to the Fermi energy and have calculated the frequency and angle dependences of the phonon absorption by electron-hole liquid in Ge. The sharpness and position of the $2{k}_{F}$ cutoffs depend upon propagation direction and phonon polarization. Using the method of tunnel-junction phonon spectroscopy, we have measured the absorption of monochromatic phonons by electron-hole liquid over the frequency range 150-500 GHz. We concentrated on longitudinal phonons with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}\ensuremath{\parallel}〈111〉$, the long axis of an electron energy ellipsoid. By applying an appropriate uniaxial stress to the crystal we were able to vary the population of this valley, thereby continuously "tuning" the predicted $2{k}_{F}$ cutoff over a factor of about 4. The resulting absorption spectra agreed with theoretical predictions, displaying for the first time the $2{k}_{F}$ cutoff for this Fermi liquid. To determine the absolute phonon absorption length in EHL, we used a luminescence-imaging method to calibrate the volume of liquid in the phonon path. Our measured deformation potential is smaller than that obtained for free electrons in Ge via cyclotron resonance. We interpret this reduction in electron-phonon interaction strength as due to screening within the electron-hole liquid. This interpretation is consistent with a recent theoretical calculation.