Showing papers on "Absorption (logic) published in 1996"
TL;DR: The size evolution of ten quantum dot absorption features is followed, and the size-dependent data exhibit two strong avoided crossings, demonstrating the importance of valence-band structure in the description of the excited states.
Abstract: We use photoluminescence excitation to study the electronic spectrum of CdSe quantum dots ranging from \ensuremath{\sim}12 to \ensuremath{\sim}53 \AA{} in radius. We follow the size evolution of ten quantum dot absorption features. Comparison of the spectra with theoretical predictions allows us to confidently assign six of these transitions. We discuss the most likely assignments for the remaining four. We find that the ${\mathit{n}}_{\mathit{hS}3/2}$1${\mathit{S}}_{\mathit{e}}$ and ${\mathit{n}}_{\mathit{hS}1/2}$1${\mathit{S}}_{\mathit{e}}$ transitions dominate the spectra, accounting for half of the observed features. Our size-dependent data exhibit two strong avoided crossings, demonstrating the importance of valence-band structure in the description of the excited states. \textcopyright{} 1996 The American Physical Society.
1,016 citations
TL;DR: In this paper, the authors used photoluminescence excitation and fluorescence line narrowing spectroscopies to examine structure observed in the band-edge absorption feature of CdSe quantum dots.
Abstract: We use photoluminescence excitation and fluorescence line narrowing spectroscopies to examine structure observed in the band-edge absorption feature of CdSe quantum dots. We study eight samples ranging from \ensuremath{\sim}15 to \ensuremath{\sim}50 \AA{} in radius to probe the size dependence of this structure. We compare our results with recent theories, which predict band-edge exciton splittings in CdSe dots due to their internal crystal structure, nonspherical shape, and the exchange interaction between the electron and hole. We find reasonable agreement between our data and theory, supporting the observation of exciton fine structure. \textcopyright{} 1996 The American Physical Society.
492 citations
TL;DR: The results suggest that strong small polaron effects, which contribute to a charge fluctuation energy of $\ensuremath{\sim}1.5$ eV, are responsible for the insulating behavior above ${T}_{C}$ which has been enigmatic in the double-exchange model.
Abstract: We have investigated the electronic structure associated with the ferromagnetic transition of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ and ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pb}}_{x}{\mathrm{MnO}}_{3}$ using high resolution photoemission, Mn 2p resonant photoemission, and O 1s x-ray absorption spectroscopies. The data clearly show that the band gap collapses below the Curie temperature $({T}_{C})$ and the density of states at the Fermi level increases with cooling, providing a conclusive microscopic evidence for an insulator-metal transition. Our results suggest that strong small polaron effects, which contribute to a charge fluctuation energy of $\ensuremath{\sim}1.5$ eV, are responsible for the insulating behavior above ${T}_{C}$ which has been enigmatic in the double-exchange model.
233 citations
TL;DR: Improvement associated with particle clustering is found for a number of optical processes, including four-wave mixing (FWM), third-harmonic generation (THG), Raman scattering, and nonlinear refraction and absorption in Kerr media.
Abstract: Strong fluctuations of local fields may result in very large optical nonlinearities in small-particle composites. Enhancement associated with particle clustering is found for a number of optical processes, including four-wave mixing (FWM), third-harmonic generation (THG), Raman scattering, and nonlinear refraction and absorption in Kerr media. Field fluctuations and optical nonlinear susceptibilities are especially large in fractal clusters. The enhancement of optical processes is expressed in terms of the resonant linear absorption by collective dipolar eigenmodes in a cluster, and quality factors, q, of the modes (q\ensuremath{\gg}1). It is shown that the susceptibility of a composite material consisting of random small-particle clusters is proportional to ${\mathit{q}}^{3}$ for Raman scattering and the Kerr optical nonlinearity, and to ${\mathit{q}}^{4}$ and ${\mathit{q}}^{6}$ for THG and FWM, respectively. For all of these processes, a spectral dependence of the effective susceptibility is found. Broad-scale numerical simulations of the optical response in small-particle composites are performed to complement the theory. The simulations are in reasonable agreement with available experimental data. \textcopyright{} 1996 The American Physical Society.
216 citations
TL;DR: In this paper, it was shown that the hydrogen-bond symmetrization occurs at 62.1 GPa in room temperature in ice and that the bending peak disappears before the transition to symmetric ice X.
Abstract: Infrared measurements at room temperature have shown that the hydrogen-bond symmetrization occurs at 62.1 GPa in ice. The OH stretching frequency initially located at 3500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at ambient pressure falls toward zero around 60 GPa. An absorption band appears in the low-frequency region below 800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at about 65 GPa, growing a definite peak with a shift to a high frequency by further compression. Such a turn in the pressure dependence of the stretching frequency is an evidence for the transition from ice VII to symmetric ice X. The OH bending peak disappears before the transition. Two absorption peaks, which are originated from the OH stretching and librational vibrations in ice VII, persist above the transition pressure, being assigned to a translational and distortional lattice vibrations in ice X. \textcopyright{} 1996 The American Physical Society.
163 citations
TL;DR: In this paper, the authors measured the index of refraction in the region of a coherent population trapping resonance in a cesium vapor cell with an interferometric technique and found very high normal dispersion (up to 9.7 ± 0.7 ) at low absorption.
Abstract: We have measured the index of refraction in the region of a coherent population trapping resonance in a cesium vapor cell with an interferometric technique. We find very high normal dispersion (up to $\frac{\mathrm{dn}}{\mathrm{df}}=9.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ ${\mathrm{Hz}}^{\ensuremath{-}1}$) at low absorption. From our spectra we obtain very small group velocities below $\frac{c}{3000}$. This corresponds to a delay time of more than 200 ns for a cesium cell 20 mm in length, equivalent to more than 60 m of propagation in vacuum.
145 citations
TL;DR: The multigroup and P{sub 1} and simplified P {sub N} equations were shown to be a family of asymptotic approximation to the multigroup transport equation with anisotropic scattering in this article.
Abstract: The multigroup and P{sub 1} and Simplified P{sub N} equations are shown to be a family of asymptotic approximation to the multigroup transport equation with anisotropic scattering. The physical assumptions are that the material system is optically thick, the probability of absorption is small, and the mean scattering angle {anti {mu}}{sub o} is not close to unity.
130 citations
TL;DR: It is shown for the first time how intense laser irradiation in this spectral region leads to the removal of thermal energy by the frequency up-conversion process, and thus lowers the temperature of the sample.
Abstract: Frequency up-conversion has been observed in fluid solutions of the laser dye, rhodamine 101, when excited at 1.96 eV into the low energy absorption tail 0.15 eV from the 0-0 band origin. The emission intensity is temperature dependent and is demonstrated to be an excellent measurement of the temperature of the sample. We show for the first time how intense laser irradiation in this spectral region leads to the removal of thermal energy by the frequency up-conversion process, and thus lowers the temperature of the sample. A decrease in temperature at a rate of $0.7\mathrm{K}{\mathrm{h}}^{\ensuremath{-}1}$ is demonstrated for a sample with a $3\mathrm{J}{\mathrm{K}}^{\ensuremath{-}1}$ heat capacity, when irradiated with 350 mW of laser light at 1.96 eV.
120 citations
TL;DR: Examination of post growth materials processing in rare-earth-doped lithium niobate crystals indicates that increasing the Li/Nb ratio and the O content of Er not only reduces the cluster site concentration by 30% but also increases the amount of light absorbed in the crystal by 15%.
Abstract: Rare-earth (e.g., ${\mathrm{Er}}^{3+}$, ${\mathrm{Nd}}^{3+}$) based, guided wave optical amplification in lithium niobate (${\mathrm{LiNbO}}_{3}$) integrated optic systems is a new and important addition to the field of integrated optics. The application of total site selective spectroscopy to rare-earth-doped ${\mathrm{LiNbO}}_{3}$ provides the most complete spectroscopic characterization of this class of materials to date. In a previous publication we identified six spectroscopic sites in Er:${\mathrm{LiNbO}}_{3}$ using total site selective spectroscopy, two of which are cluster sites which upconvert light using nonradiative energy transfer between Er ions within a given site. In this paper ${\mathrm{Er}}^{3+}$ site identifications are made based on a consideration of solid solution defect equations in conjunction with an experimental study of the site distribution as a function of dopant concentration (0.4--2.0 mol % Er:${\mathrm{LiNbO}}_{3}$) and the Li/Nb ratio in the crystal. The Li/Nb ratio was altered using a vapor phase equilibration technique. Our results indicate that increasing the ${\mathrm{Li}}_{2}$O content of Er:${\mathrm{LiNbO}}_{3}$ not only reduces the cluster site concentration by \ensuremath{\sim}30% but also increases the amount of light absorbed in the crystal by \ensuremath{\sim}15%. This observation is, to the best of our knowledge, the first report of post growth materials processing in rare-earth-doped ${\mathrm{LiNbO}}_{3}$ to effect a change in absorption or cluster site concentration. In addition, increasing the dopant concentration increases ${\mathrm{Li}}_{2}$O deficiency in Er:${\mathrm{LiNbO}}_{3}$ crystals. Simple solid solution defect model calculations agree with these experimental results. \textcopyright{} 1996 The American Physical Society.
120 citations
TL;DR: In this article, the authors present a systematic evaluation of the shape of the neutrino energy spectrum produced by beta decay of the Be(2.1) decay chain, and determine the range of uncertainties permitted by existing laboratory data and theoretical ingredients.
Abstract: We present a systematic evaluation of the shape of the neutrino energy spectrum produced by beta decay of $^{8}\mathrm{B}$. We place special emphasis on determining the range of uncertainties permitted by existing laboratory data and theoretical ingredients (such as forbidden and radiative corrections). We review and compare the available experimental data on the $^{8}\mathrm{B}$(${\mathrm{\ensuremath{\beta}}}^{+}$${)}^{8}$Be(2\ensuremath{\alpha}) decay chain. We analyze the theoretical and experimental uncertainties quantitatively. We give a numerical representation of the best-fit (standard-model) neutrino spectrum, as well as two extreme deviations from the standard spectrum that represent the total (experimental and theoretical) effective \ifmmode\pm\else\textpm\fi{}3\ensuremath{\sigma} deviations. Solar neutrino experiments that are currently being developed will be able to measure the shape of the $^{8}\mathrm{B}$ neutrino spectrum above about 5 MeV. An observed distortion of the $^{8}\mathrm{B}$ solar neutrino spectrum outside the range given in the present work could be considered as evidence, at an effective significance level greater than three standard deviations, for physics beyond the standard electroweak model. We use the most recent available experimental data on the Gamow-Teller strengths in the A=37 system to calculate the $^{8}\mathrm{B}$ neutrino absorption cross section on chlorine: ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{Cl}}$=(1.14\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}42}$ ${\mathrm{cm}}^{2}$ (\ifmmode\pm\else\textpm\fi{}3\ensuremath{\sigma} errors). The chlorine cross section is also given as a function of the neutrino energy. The $^{8}\mathrm{B}$ neutrino absorption cross section in gallium is ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{Ga}}$=(2.${46}_{\mathrm{\ensuremath{-}}1.1}^{+2.1}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}42}$ ${\mathrm{cm}}^{2}$ (\ifmmode\pm\else\textpm\fi{}3\ensuremath{\sigma} errors). \textcopyright{} 1996 The American Physical Society.
117 citations
TL;DR: In this paper, an abstract approach based on the Limiting Absorption Principle has been proposed for the Boltzmann equation (1.1) for low-density flow of neutrons.
Abstract: Consider the Boltzmann equation {partial_derivative}/{partial_derivative}{sub t}u(t,x,v)=-v. {del}{sub x}u(t,x,v)-{sigma}{sub a}(x,v)u(t,x,v)+{integral}{sub v}k(x,v{prime},v)u(t,x,v{prime})dv{prime} in R{sup n} x V {such_that} (x,v), V being an open subset of R{sup n}, n {ge} 2. Equation (1.1) describes the dynamics of a flow of particles in R{sup n} under the assumption that the interaction between them is neglectable (no non-linear terms). This is the case for example for a low-density flow of neutrons. The term involving {sigma}{sub a} describes the loss of particles from (x,v) {epsilon} R{sup n} x V due to absorption or scattering into another point (x,v{prime}), while the last term in (1.1) involving k represents the production at x {epsilon} R{sup n} of particles with velocity v form particles with velocity v{prime}. The total rate of this production at (x,v{prime}) is given by {sigma}{sub p}(x,v{prime}) = {integral}{sub V} k (x,v{prime},v)dv. Following [RS] we say that the pair ({sigma}{sub a}, k) is admissible, if (i) O {le} {sigma}{sub a} {epsilon} L{sup {infinity}}(R{sup n} x V), (ii) O {le} k(x,v{prime}, {center_dot}) {epsilon} L{sup 1}(V) for a.e. (x,v{prime}) {epsilon} R{sup n} x V and {sigma}{sub p} {epsilon} L{sup {infinity}}(R{sup n} x V), (iii) There is an open bounded set X {contained_in} R{sup n}, such that k(x,v{prime},v) andmore » {sigma}{sub a}(x,v) vanish if x {epsilon} X. One can define the wave operators associated with T, T{sub O} by W{sub -} = s-lim/t{r_arrow}{infinity} U(t)U{sub O}(-t), W{sub +} = s-lim/t{r_arrow}{infinity} U(O)(-t)U(t). if W{sub -}, W{sub +} exist, then one can define the scattering operator S = W{sub +}W{sub -} as a bounded operator in L{sup 1}(R{sup n} x V). Scattering theory for (1.1) has been developed by other authors and we refer to these papers for sufficient conditions guaranteeing the existence of S. An abstract approach based on the Limiting Absorption Principle has been proposed. 22 refs.« less
TL;DR: It is reported direct evidence that the prominent triplet photoexcitations in pristine MEH-PPV are effectively quenched in MEH -PPV/${\mathrm{C}}_{60}$.
Abstract: Photoexcitations in poly[2-methoxy-5-(${2}^{\ensuremath{'}}$-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and composites of MEH-PPV and ${\mathrm{C}}_{60}$ (MEH-PPV/${\mathrm{C}}_{60}$) were studied by photoinduced absorption and absorption-detected magnetic-resonance spectroscopies. We report direct evidence that the prominent triplet photoexcitations in pristine MEH-PPV are effectively quenched in MEH-PPV/${\mathrm{C}}_{60}$. In contrast, the dominant photoexcitations in MEH-PPV/${\mathrm{C}}_{60}$ are spin-1/2 excitations: polarons on the polymer chains; and polarons on the ${\mathrm{C}}_{60}$ (${\mathrm{C}}_{60}^{\mathrm{\ensuremath{-}}}$). \textcopyright{} 1996 The American Physical Society.
TL;DR: This paper presents a probabilistic procedure for estimating the intensity of the response of the laser of the proton-proton beam during the transition from solid to liquid phase.
Abstract: By monitoring changes in excitonic photoluminescence that are induced by far-infrared (FIR) radiation, we observed resonant FIR absorption by magnetoexcitons in GaAs/AlGaAs quantum wells. The dominant resonance is assigned to the $1s\ensuremath{\rightarrow}{2p}^{+}$ transition of the heavy-hole exciton, and agrees well with theory. At low FIR and interband excitation intensities, the $1s\ensuremath{\rightarrow}{2p}^{+}$ absorption feature is very narrow and broadens as either of these intensities is increased. The $1s\ensuremath{\rightarrow}{2p}^{+}$ absorption feature persists even when the FIR electric field is comparable to the electric field which binds the exciton.
TL;DR: Using electron paramagnetic resonance two types of Ti-related centers are identified in BaTi and an optical absorption precursor of the fundamental absorption is identified and attributed to the creation of an exciton bound to the ${V}_{\mathrm{O}}$-Na(K) complex.
Abstract: Using electron paramagnetic resonance two types of ${\mathrm{Ti}}^{3+}$-related centers are identified in BaTi${\mathrm{O}}_{3}$, which are attributed to ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$ and to ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$ associated with Na or K, respectively. This assignment is based on the chemical and illumination conditions leading to the detection of the defects. It is furthermore supported by the Ti hyperfine structure, resolved for ${\mathrm{Ti}}^{3+}$-${V}_{\mathrm{O}}$-Na(K). The symmetry of the centers is broken in the sense that an electron is localized near one of the two equivalent ${\mathrm{Ti}}^{4+}$ ions next to ${V}_{\mathrm{O}}$. Also the observed Ti hyperfine structure points to electron capture at one Ti site. The ${V}_{\mathrm{O}}$-type centers are contrasted to isolated ${\mathrm{Ti}}^{3+}$, representing a free small polaron in crystals containing ${\mathrm{Nb}}^{5+}$ and no oxygen vacancies. The participation of the ${V}_{\mathrm{O}}$ centers in photochromic processes in BaTi${\mathrm{O}}_{3}$ is studied. In crystals doped with Na or K an optical absorption precursor of the fundamental absorption is identified and attributed to the creation of an exciton bound to the ${V}_{\mathrm{O}}$-Na(K) complex.
TL;DR: From transient measurements it was concluded that for lightly doped samples the green upconverted emission is originated due to both processes ESA and ET, however, for heavily doping samples ET is the dominant process.
Abstract: Fluorindate glasses containing 1,2,3,4 ${\mathrm{ErF}}_{3}$ mol % were prepared in a dry box under argon atmosphere. Absorption, Stokes luminescence (under visible and infrared excitation), the dependence of $^{4}$${\mathit{S}}_{3/2}$, $^{4}$${\mathit{I}}_{11/2}$, and $^{4}$${\mathit{I}}_{13/2}$ lifetimes with Er concentration, and upconversion under Ti-saphire laser excitation at \ensuremath{\lambda}=790 nm were measured, mostly at T=77 and 300 K. The upconversion results in a strong green emission and weaker blue and red emissions whose intensity obeys a power-law behavior I\ensuremath{\sim}${\mathit{P}}^{\mathit{n}}$, where P is the infrared excitation power and n=1.6, 2.1, and 2.9 for the red, green, and blue emissions, respectively. The red emission exponent n=1.5 can be explained by a cross relaxation process. The green and blue emissions are due to excited state absorption (ESA) and energy transfer (ET) processes that predict a factor n=2 and n=3 for the green and blue emissions, respectively. From transient measurements we concluded that for lightly doped samples the green upconverted emission is originated due to both processes ESA and ET. However, for heavily doped samples ET is the dominant process. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the mid-infrared optical absorption spectrum of the one-dimensional Mott insulator S${r}$Cu${\mathrm{O}}_{3} was analyzed in terms of the phonon-assisted absorption in the onedimensional quantum spin chain model.
Abstract: The midinfrared optical absorption spectrum is reported of the one-dimensional Mott insulator S${\mathrm{r}}_{2}$Cu${\mathrm{O}}_{3}$. The spectrum has an asymmetric cusplike structure at 0.48 eV and is analyzed in terms of the phonon-assisted absorption in the one-dimensional quantum spin chain model. A good agreement is obtained between experiment and theory, and the exchange energy J is estimated to be $J\ensuremath{\approx}0.26$ eV, which is consistent with the magnetic susceptibility measurement.
TL;DR: An extended x-ray-absorption fine structure study has been carried out on a range of rare-earth metaphosphate glasses of growing interest in optical communications and laser technologies, showing no evidence for R-R correlations within the short-range order.
Abstract: An extended x-ray-absorption fine structure (EXAFS) study has been carried out on a range of rare-earth metaphosphate $R{(\mathrm{P}{\mathrm{O}}_{3})}_{3}$ glasses of growing interest in optical communications and laser technologies. Phosphate glasses modified using the rare-earth oxides ${\mathrm{Pr}}_{6}$${\mathrm{O}}_{11}$, ${\mathrm{Nd}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Eu}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Gd}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Tb}}_{2}$${\mathrm{O}}_{3}$, and ${\mathrm{Ho}}_{2}$${\mathrm{O}}_{3}$, have been investigated using their respective rare-earth ${L}_{\mathrm{III}}$ absorption edges. The data provide information on the local environment of the rare-earth ion within the phosphate glass matrix constructed from linked P${\mathrm{O}}_{4}$ tetrahedra. The rare-earth ions occupy sites with an average coordination number in the range, $6l~Nl~8$, the surrounding atoms being oxygen. The first shell interatomic distance over the range of rare-earth ions establishes the rare-earth contraction of ionic radii with increasing atomic number in a series of glasses. There is also evidence for a rare-earth-phosphorus correlation between 2.7 and 3.6 \AA{}, and a further rare-earth-oxygen correlation at approximately 4 \AA{}. The EXAFS spectrum shows no evidence for R-R correlations within the short-range order, a result especially pertinent to the optical and magnetic properties of the glasses. The fractal dimensionality 4${\mathrm{C}}_{11}$/B of these glasses, obtained from the elastic stiffnesses determined from ultrasonic wave velocities, ranges between 2.3 and 2.8, indicating that their connectivity tends towards having a three-dimensional character.
TL;DR: The macroscopic dielectric function in the random-phase-approximation without local field effect has been implemented using the local density approximation with an all electron, full-potential linear muffin-tin orbital basis-set to investigate the optical properties of the semiconductors Si, Ge, and GaAs under hydrostatic pressure.
Abstract: The macroscopic dielectric function in the random-phase approximation without local-field effect has been implemented using the local-density approximation with an all-electron, full-potential linear muffin-tin orbital basis set. This method is used to investigate the optical properties of the semiconductors Si, Ge, and GaAs under hydrostatic pressure. The pressure dependence of the effective dielectric function is compared with the experimental data of Go\~ni, Syassen, and Cardona [Phys. Rev. B 41, 10 104 (1990)], and excellent agreement is found when the so-called ``scissors-operator'' shift is used to account for the correct band gap at \ensuremath{\Gamma}. The effect of the 3d semicore states in the interband transitions hardly changes the static dielectric function ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{\ensuremath{\infty}}}$; however, their contribution to the intensity of absorption for higher photon energies is substantial. The spin-orbit coupling has a significant effect on ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{\ensuremath{\infty}}}$ of Ge and GaAs, but not of Si. The ${\mathit{E}}_{1}$ peak in the dynamical dielectric function is strongly underestimated for Si, but only slightly for Ge and GaAs, suggesting that excitonic effects might be important only for Si. \textcopyright{} 1996 The American Physical Society.
TL;DR: Absorption and excitation spectra, fluorescence line narrowing, and time-resolved spectroscopy show that the impurity ions are accommodated in two different site distributions, one related to a silicate environment, and the other onerelated to a borate environment.
Abstract: A borosilicate glass of molar composition 0.${01\mathrm{E}\mathrm{u}}_{2}$${\mathrm{O}}_{3}$\ensuremath{\cdot}0.99(${25\mathrm{N}\mathrm{a}}_{2}$O\ensuremath{\cdot}${50\mathrm{B}}_{2}$${\mathrm{O}}_{3}$\ensuremath{\cdot}${25\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$) has been studied through the optical spectroscopy of the ${\mathrm{Eu}}^{3+}$ ion. Absorption and excitation spectra, fluorescence line narrowing, and time-resolved spectroscopy show that the impurity ions are accommodated in two different site distributions, one related to a silicate environment, and the other one related to a borate environment. These results have been corroborated by crystal-field calculations and comparison with the crystal-field parameters for the ${\mathrm{Eu}}^{3+}$ ion in silicate and borate glasses. The presence of phonon sidebands indicates strong coupling with high-frequency Si-O and B-O stretching vibrational modes. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the photoabsorption cross sections for the photon energies ranging from 200 to 800 MeV have been measured for the first time for the heavy nucleus and the results show clearly the changes in the nucleon resonances in going from ${1}-H$ to ${3}-He$.
Abstract: The total photoabsorption cross sections for $^{1}\mathrm{H}$, $^{2}\mathrm{H}$, and $^{3}\mathrm{He}$ have been measured for incident photon energies ranging from 200 to 800 MeV. The $^{3}\mathrm{He}$ data are the first for this nucleus. By using the large acceptance detector DAPHNE in conjunction with the tagged photon beam facility of the MAMI accelerator in Mainz, cross sections of high precision have been obtained. The results show clearly the changes in the nucleon resonances in going from $^{1}\mathrm{H}$ to $^{3}\mathrm{He}$. In particular, for the ${\mathit{D}}_{13}$ region the behavior for $^{3}\mathrm{He}$ is intermediate between that for $^{1}\mathrm{H}$, $^{2}\mathrm{H}$, and heavier nuclei. This will provide a strong constraint to the theories that are presently being developed with a view to explaining the apparent ``damping'' of higher resonances in heavy nuclei. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, it was shown that the electrons transferred from intercalated lithium atoms are not only located on Ti $3d$ orbitals, as previously assumed, but also on the S $3p$ states.
Abstract: Sulfur K-edge x-ray-absorption spectra have been recorded for lithium intercalated titanium disulfides ${\mathrm{Li}}_{x}{\mathrm{TiS}}_{2}$. The near-edge features up to 30 eV above threshold are interpreted in the framework of full multiple-scattering theory. We show that the electrons transferred from intercalated lithium atoms are not only located on Ti $3d$ orbitals, as previously assumed, but also on the S $3p$ states. For comparison, we present the S $p$-projected density of states derived from linear muffin-tin-orbital band structure calculations. An overall agreement between measurement and theory is very well achieved.
TL;DR: In this article, the authors obtained the UV spectra of the nucleus of the elliptical galaxy Arp 102B using the Faint Object Spectrograph (FOS) in order to investigate the UV emission-line counterparts of its unusual double-peaked Balmer lines.
Abstract: UV spectra of the nucleus of the elliptical galaxy Arp 102B were obtained with the {ital HST}`s Faint Object Spectrograph in order to investigate the UV emission-line counterparts of its unusual double-peaked Balmer lines Broad MgII {lambda}2798 is present with nearly the same profile as the Balmer lines (peaks separated by {approx_equal}12,000 kms{sup -1}), and a typical MgII/H{beta} ratio of 1 But there is little, if any CIII {lambda}1909 or CIV {lambda}1550 emission corresponding to the displaced Balmer-line peaks Most important, there is no double-peaked component detected in Ly{alpha}; the Ly{alpha}/H{beta} ratio is less than 012 in the displaced peaks However, there is an ``ordinary``, nondisplaced broad-line component with FWHM{approx_equal}3500 kms{sup -1} in {ital all} of the permitted lines, demonstrating the need to invoke different locations and different physical conditions for double-peaked and single-peaked line components in the same object The striking absence of displaced peaks in Ly{alpha} probably cannot be explained solely by reddening Rather, it indicates that high density and large optical depth in Ly{alpha} are required to destroy the line photons by collisional de-excitation and possibly by bound-free absorption out of the {ital n}=2 level of hydrogen These results strongly support the application, at least to Arpmore » 102B, of the accretion-disk model of Dumont & Collin-Souffrin, in which the disk produces only low-ionization lines and a Ly{alpha}/H{beta} ratio that agrees with our observed upper limit Also present is an extraordinary system of absorption lines at the systemic redshift of Arp 102B, in which metastable levels of FeII up to 11 eV above the ground state participate in addition to the more common resonance transitions Absorption from metastable levels of FeII have been seen previously only in two unusual, low-ionization broad absorption-line QSOs, Q0059-2735 and Mrk 231« less
TL;DR: High resolution Cu L(2,3) x-ray absorption spectra of bulk fee Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers to compare with fully relativistic first-principles calculation.
Abstract: High resolution Cu ${\mathit{L}}_{2,3}$ x-ray absorption spectra of bulk fcc Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers. Comparison of the measured fine structure with that obtained from a fully relativistic first-principles calculation for fcc and bcc Cu reveals that Cu is bcc in Cu(3 \AA{})/Fe(10 \AA{}) and fcc in Cu(10 \AA{})/Fe(3 \AA{}) multilayers. This result indicates that the thicker layer simply acts as a template for the structure of the thinner layer. The excellent agreement between experimental and theoretical spectra also demonstrates the validity of the theoretical approach. The theoretical spectra are discussed in terms of their angular momentum composition and the energy dependence of the radial transition matrix elements. \textcopyright{} 1996 The American Physical Society.
TL;DR: A population inversion has been created between the two adjacent fluxoid wells (with energy difference {var_epsilon}) in an rf SQUID subject to weak radiation at 100 GHz.
Abstract: A population inversion has been created between the two adjacent fluxoid wells (with energy difference $\ensuremath{\varepsilon}$) in an rf SQUID subject to weak radiation at 100 GHz. The states in the two wells have opposite currents, of magnitude \ensuremath{\sim}2 \ensuremath{\mu}A, circulating through an inductance of 0.2 nH. The steady state population of the upper well ${n}_{u}(\ensuremath{\varepsilon})$ shows local maxima whose positions correspond to calculated photon absorption resonances between the ground state and an intermediate state. The maximum ${n}_{u}(\ensuremath{\varepsilon})$ is 0.94 compared to the expected thermal equilibrium value of ${n}_{u}(\ensuremath{\varepsilon})=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$.
TL;DR: Calculations for the intradonor transition strengths for x-polarized radiation and absorption coefficients are performed for finite-barrier potentials and as functions of applied magnetic and electric fields and quantum-well thicknesses.
Abstract: The effects of magnetic and electric fields on the infrared-absorption properties associated to transitions between the 1s-like and 2${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$-, 3${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$-, and 4${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$-like excited states of hydrogenic donors in GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum wells are studied. The magnetic and electric fields are applied along the growth direction of the heterostructure, and donor envelope wave functions and energies are obtained within a variational procedure in the effective-mass approximation. Calculations for the intradonor transition strengths for x-polarized radiation and absorption coefficients are performed for finite-barrier potentials and as functions of applied magnetic and electric fields and quantum-well thicknesses. A discussion of a sum rule associated to donor transitions in quantum wells is presented. Theoretical results for the absorption spectra are in good agreement with available infrared-magnetospectroscopy measurements on doped quantums wells. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, the 1-2 intersubband absorption in a single 40 nm wide modulation-doped channel was experimentally measured as a function of frequency, intensity, and charge density, and the low-intensity depolarization-shifted absorption occurs near $80.1$ (10 meV or 2.4 THz).
Abstract: We have experimentally measured the 1--2 intersubband absorption in a single 40 nm wide modulation-doped ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}/\mathrm{GaAs}$ square quantum well as a function of frequency, intensity, and charge density. The low-intensity depolarization-shifted absorption occurs near $80{\mathrm{cm}}^{\ensuremath{-}1}$ (10 meV or 2.4 THz), nearly 30% higher than the intersubband spacing. At higher intensities, the absorption peak shifts to lower frequencies. Our data are in good agreement with a theory proposed by Za\l{}u\ifmmode \dot{z}\else \.{z}\fi{}ny, which attributes the redshift to a reduction in the depolarization shift as the excited subband becomes populated.
TL;DR: Polaronic features similar to those previously observed in the photoinduced spectra of cuprates have been detected in the reflectivity spectRA of chemically doped parent compounds of high-critical-temperature superconductors, both {ital n} type and {ital p} type.
Abstract: Polaronic features similar to those previously observed in the photoinduced spectra of cuprates have been detected in the reflectivity spectra of chemically doped parent compounds of high-critical-temperature superconductors, both {ital n} type and {ital p} type. In Nd{sub 2}CuO{sub 4{minus}{ital y}} these features, whose intensities depend both on doping and temperature, include local vibrational modes in the far infrared and a broad band centered at {approximately} 1000 cm{sup {minus}1}. The latter band is produced by the overtones of two (or three) local modes and is well described in terms of a small-polaron model, with a binding energy of about 500 cm{sup {minus}1}. Most of the above infrared features are shown to survive in the metallic phase of Nd{sub 2{minus}{ital x}}Ce{sub {ital x}}CuO{sub 4{minus}{ital y}}, Bi{sub 2}Sr{sub 2}CuO{sub 6}, and YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}}, where they appear as extra-Drude peaks. The occurrence of polarons is attributed to local modes strongly coupled to carriers, as shown by a comparison with tunneling results. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this paper, the 8-band superlattice crystal was extended to include higher-lying antibonding $p$ states perturbatively, which introduced a finite heavy-hole mass.
Abstract: The eight-band superlattice crystal K\ifmmode\cdot\else\textperiodcentered\fi{}p formalism is extended to include the higher-lying antibonding $p$ states perturbatively. The initial 14\ifmmode\times\else\texttimes\fi{}14 Hamiltonian matrix is block diagonalized (or folded down) so that corrections due to these states appear in the modified 8\ifmmode\times\else\texttimes\fi{}8 matrix. Their principal effect is to introduce a finite heavy-hole mass. The use of the eight-band formalism for band-structure and interband optical calculations is validated because other corrections are very small. The approximate wave functions associated with the original 14\ifmmode\times\else\texttimes\fi{}14 Hamiltonian are used to calculate intersubband optical matrix elements. These include new terms, present in crystals lacking inversion symmetry, which increase the magnitude of conduction intersubband absorption by about three orders of magnitude for in-plane polarized (TE) photons, while leaving absorption due to growth-axis polarized (TM) photons relatively unaffected. The TE absorption in narrow $\mathrm{GaAs}/{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wells (QW's) is shown to be observable. However, use of the $f$-sum rule and the cyclotron-resonance-determined conduction-band effective-mass anisotropy indicate an upper limit of about 20% relative to TM absorption. Comparison with the measured TM absolute absorption coefficient for a system used for quantum-well infrared photoconductors (QWIP's) yields excellent agreement. The conductivity sum rule involving these intersubband transitions is used to confirm the observed broadening associated with very small QW width fluctuations for this system.
TL;DR: The propagation of short-pulse lasers through several Rayleigh lengths of underdense plasma is studied using multidimensional fully explicit particle-in-cell simulations and the figure of merit is the amount of Raman forward scattering exponentiation within a Rayleigh length.
Abstract: The propagation of short-pulse lasers through several Rayleigh lengths of underdense plasma $[(1\char21{}4)%{n}_{\mathrm{cr}}]$ is studied using multidimensional fully explicit particle-in-cell simulations. The simulations model 80 to 600 fs, 1 \ensuremath{\mu}m wavelength pulses in the intensity range of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{17}$ to $3.5\ifmmode\times\else\texttimes\fi{}{10}^{19}$ W/c${\mathrm{m}}^{2}$. A detailed account is given for the energy lost out of the focal cone due to a combination of collective absorption and scattering losses. The figure of merit for the nonlinear transmission losses of a given pulse length is the amount of Raman forward scattering exponentiation within a Rayleigh length.
TL;DR: The physical data presented are discussed in the context of a soft Mott insulator and the first transition attributed to an intermolecular charge-transfer process while the second transition most likely corresponds to an intramolecular excitation.
Abstract: Analysis of x-ray diffraction from a single crystal of bis-benzene-1,2-dithiolato-Au(IV) [Au${(\mathrm{bdt})}_{2}$] at 125 K reveals a superstructure along the stacks of Au${(\mathrm{bdt})}_{2}$ molecules corresponding to a dimerization of the molecules along the stack. Within a dimer, intermolecular sulfur-sulfur contacts are shortened from 3.7 to 3.6 \AA{} whereas a lengthening to about 3.8 \AA{} is found between dimers. Electrical resistivity measured by a four-probe method between 230 and 450 K uncovers an activated resistivity with a characteristic energy of 0.30 eV. The room-temperature conductivity at zero applied pressure is 0.11 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{m}}^{\ensuremath{-}1}$ rising smoothly to 0.67 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{m}}^{\ensuremath{-}1}$ at 0.55 GPa isotropic pressure. The magnetic susceptibility $\ensuremath{\chi}$ is low compared to the spin susceptibility of a system with one free spin per molecule. An activated behavior of $\ensuremath{\chi}$ is observed, which gives rise to a monotonic increase in $\ensuremath{\chi}$ at between 275 and 420 K. Reflectivity measurements along the $b$ axis (stacking direction) of a single crystal of Au${(\mathrm{bdt})}_{2}$ shows a transition around 5000 ${\mathrm{cm}}^{\ensuremath{-}1}$ (0.6 eV) possessing an oscillator strength \ensuremath{\approx}0.5 electron/molecule. Along the $c$ axis an absorption centered around 8000 ${\mathrm{cm}}^{\ensuremath{-}1}$ is observed. The first transition (5000 ${\mathrm{cm}}^{\ensuremath{-}1}$) is attributed to an intermolecular charge-transfer process while the latter transition (8000 ${\mathrm{cm}}^{\ensuremath{-}1}$) most likely corresponds to an intramolecular excitation. The physical data presented are discussed in the context of a soft Mott insulator.