Showing papers on "Absorption (logic) published in 2003"
TL;DR: It is observed that a quantum coherence effect, coherent population oscillations, produces a very narrow spectral "hole" in the homogeneously broadened absorption profile of ruby, which leads to a large value of the group index.
Abstract: We have observed slow light propagation with a group velocity as low as $57.5\ifmmode\pm\else\textpm\fi{}0.5\text{ }\mathrm{m}/\mathrm{s}$ at room temperature in a ruby crystal. A quantum coherence effect, coherent population oscillations, produces a very narrow spectral ``hole'' in the homogeneously broadened absorption profile of ruby. The resulting rapid spectral variation of the refractive index leads to a large value of the group index. We observe slow light propagation both for Gaussian-shaped light pulses and for amplitude modulated optical beams in a system that is much simpler than those previously used for generating slow light.
651 citations
TL;DR: Ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase TiO2 thin film is investigated, using the magnetic circular dichroism (MCD) at the Co L(2,3) absorption edges to show that the ferromagnets are induced by a small amount of clustered Co.
Abstract: We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase ${\mathrm{T}\mathrm{i}\mathrm{O}}_{2}$ thin film, using the magnetic circular dichroism (MCD) at the Co ${L}_{2,3}$ absorption edges. The magnetic moment was observed to be $\ensuremath{\sim}0.1{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$ in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at $\ensuremath{\sim}400\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the MCD signal increases, and the moment reaches up to $\ensuremath{\sim}1.55{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$, which is $\ensuremath{\sim}90%$ of the moment in Co metal. In the latter case, the cluster size was observed to be 20--60 nm.
354 citations
TL;DR: In this article, the column density of free electrons along the light path, the so-called Dispersion Measure (DM), is measured from the early gamma-ray afterglows.
Abstract: We show a possible way to measure the column density of free electrons along the light path, the so-called Dispersion Measure (DM), from the early $[\sim 415 (
u/1 {\rm GHz})^{-2} ({\rm DM}/10^{5} {\rm pc} {\rm cm}^{-3}) {\rm s}]$ radio afterglows of the gamma-ray bursts. We find that the proposed Square Kilometer Array can detect bright radio afterglows around the time $\sim 10^{3}(
u/160 {\rm MHz})^{-2}$ s to measure the intergalactic DM ($\simg 6000$ pc cm$^{-3}$ at redshift $z>6$) up to $z\sim 30$, from which we can determine the reionization history of the universe and identify the missing warm-hot baryons. At low $z$, DM in the host galaxy may reach $\sim 10^{5}$ pc cm$^{-3}$ depending on the burst environment, which may be probed by the current detectors. Free-free absorption and diffractive scattering may also affect the radio emission in a high density.
246 citations
TL;DR: In this paper, the interface between the silicon nanocrystals and the surrounding is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphus stoichiometric, and this region plays an active role in the light-emission process.
Abstract: Light-emitting silicon nanocrystals embedded in ${\mathrm{SiO}}_{2}$ have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding ${\mathrm{SiO}}_{2}$ is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric ${\mathrm{SiO}}_{2}.$ This region plays an active role in the light-emission process.
240 citations
TL;DR: In this paper, the authors demonstrate all-optical quantum interference injection and control of a ballistic pure spin current (without an accompanying charge current) in quantum wells, consisting of spin-up electrons traveling in one direction and spin-down electrons travelling in the opposite direction.
Abstract: We demonstrate all-optical quantum interference injection and control of a ballistic pure spin current (without an accompanying charge current) in $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum wells, consisting of spin-up electrons traveling in one direction and spin-down electrons traveling in the opposite direction This current is generated through quantum interference of one- and two-photon absorption of $\ensuremath{\sim}100\text{ }\text{ }\mathrm{f}\mathrm{s}$ phase-locked pulses that have orthogonal linear polarizations We use a spatially resolved pump-probe technique to measure carrier movement of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{n}\mathrm{m}$ Results agree with recent theoretical predictions
238 citations
TL;DR: In this article, the authors demonstrate a quantum interference switch where a laser pulse with an energy per area of 23$ photons per ${\ensuremath{\sim}23$ photon per ${ \ensuremath{\lambda}}^{2}/(2 \ensureMath{\pi})$ causes a $1/e$ absorption of a second pulse.
Abstract: Electromagnetically induced transparency in an optically thick, cold medium creates a unique system where pulse-propagation velocities may be orders of magnitude less than c and optical nonlinearities become exceedingly large. As a result, nonlinear processes may be efficient at low-light levels. Using an atomic system with three, independent channels, we demonstrate a quantum interference switch where a laser pulse with an energy per area of $\ensuremath{\sim}23$ photons per ${\ensuremath{\lambda}}^{2}/(2\ensuremath{\pi})$ causes a $1/e$ absorption of a second pulse.
221 citations
TL;DR: The magnetic circular dichroism (MCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy at the Co, Fe, and Cr edges.
Abstract: The magnetic circular dichroism (MCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy ${\mathrm{Co}}_{2}{\mathrm{Cr}}_{0.6}{\mathrm{Fe}}_{0.4}\mathrm{Al}$ at the Co, Fe, and Cr ${L}_{II,III}$ edges. The comparison of XAS spectra before and after in situ cleaning of polished surfaces revealed a pronounced selective oxidation of Cr in air. For clean surfaces we observed a MCD for all three elements with Fe showing the largest moment per atom. The MCD can be explained by the density of states of the $3d$ unoccupied states, predicted by linear muffin-tin orbital atomic sphere approximation. For Fe and Cr the orbital angular momentum component of the magnetic moment is considerably larger than the values reported for metallic alloys, whereas for Co a value close to its bulk value is observed. This observation is discussed in comparison with band structure calculations.
182 citations
TL;DR: In this paper, a detailed site-selective spectroscopy has been performed as a function of temperature on the transition of the ions at both crystallographic sites, and the authors measured the temperature dependence of the optical dephasing, transition energy, and linewidth of the ion.
Abstract: Detailed site-selective spectroscopy has been performed as a function of temperature on the ${}^{7}{F}_{0}{\ensuremath{\leftrightarrow}}^{5}{D}_{0}$ transition of ${\mathrm{Eu}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ for ${\mathrm{Eu}}^{3+}$ concentrations of 002%, 01%, 05%, and 1% Time-domain optical dephasing, spectral hole lifetimes, anisotropic absorption coefficients, inhomogeneous linewidths, and fluorescence lifetimes for ${\mathrm{Eu}}^{3+}$ ions at both crystallographic sites were measured The temperature dependence of the optical dephasing, transition energy, and linewidth of the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ absorption was measured and interpreted in terms of Raman scattering of phonons Photon echo measurements of optical dephasing gave ${T}_{2}$ values as long as 26 ms, approaching the limit set by the fluorescence decay time Spectral hole lifetimes were measured for temperatures from 2 K to 18 K, with observed lifetimes varying from 1 s at 18 K to an estimated value of greater than 20 days at 2 K Anisotropic absorption coefficients were measured, and an increase in ${\mathrm{Eu}}^{3+}$ concentration from 002% to 7% produced an increase in the inhomogeneous linewidth ${\ensuremath{\Gamma}}_{\mathrm{inh}}$ from 05 GHz to \ensuremath{\sim}150 GHz, indicating that ${\mathrm{Eu}}^{3+}$ doping induces significant strain in the crystal New determinations of many energy levels of ${}^{7}{F}_{J}$ multiplets have been made for $J=0$ to 6
145 citations
TL;DR: In this paper, a simple one-step hydrothermal reaction among nanoparticles and KOH solution was found to result in potassium titanate nanowires, which were analyzed by a range of methods including powder x-ray diffraction (XRD), high resolution electron microscopy (HREM), selected area electron diffraction, electron energy loss spectroscopy, XRD and HREM image simulations.
Abstract: A simple one step hydrothermal reaction among ${\mathrm{TiO}}_{2}$ nanoparticles and KOH solution was found to result in potassium titanate nanowires. The diameters of these nanowires are about 10 nm and the lengths range from 500 nm to $2\ensuremath{\mu}\mathrm{m}.$ The nanowires were analyzed by a range of methods including powder x-ray diffraction (XRD), high resolution electron microscopy (HREM), selected area electron diffraction, electron energy loss spectroscopy, XRD and HREM image simulations. The structure of the nanowires is determined to be of the type of ${\mathrm{K}}_{2}{\mathrm{Ti}}_{6}{\mathrm{O}}_{13}.$ Based on HREM observations of the growth process of the nanowires, we propose that the growth of the namowire was initiated by the formation of the ${\mathrm{K}}_{2}{\mathrm{Ti}}_{6}{\mathrm{O}}_{13}$ nuclei inside the anatase matrix following the crystallographic relation ${(200)}_{\mathrm{nanowire}}{//(101)}_{\mathrm{anatase}}.$ These nuclei subsequently grew to form one-dimensional nanowires via preferential growth along the [010] direction. Absorption experiments show that the potassium titanate nanowires are wide-band semiconductors with a band width ${E}_{g}\ensuremath{\sim}3.45\mathrm{eV}.$
145 citations
TL;DR: The theory can satisfactorily explain a long-standing experimental result on the nonlinear absorption in the THz regime and it is shown that electron-disorder scatterings are important at low to intermediate field and the high field absorption is dominated by II processes.
Abstract: We have theoretically investigated nonlinear free-carrier absorption of terahertz (THz) radiation in $\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{S}\mathrm{b}$ heterojunctions. By considering multiple photon process and conduction-valence interband impact ionization (II), we have determined the field and frequency dependent absorption rate. It is shown that (i) electron-disorder scatterings are important at low to intermediate field, and (ii) most importantly, the high field absorption is dominated by II processes. Our theory can satisfactorily explain a long-standing experimental result on the nonlinear absorption in the THz regime.
118 citations
TL;DR: Sun et al. as discussed by the authors showed that the volume anisotropy is supported by scaling analyses of the shape of the magnetic absorption, which reveal distribution functions for the barriers also being consistent with the volume distributions observed by TEM.
Abstract: Based on the high-temperature organometallic route [Sun et al Science 287, 1989 (2000)], we have synthesized powders containing ${\mathrm{CoPt}}_{3}$ single crystals with mean diameters of 33(2) and 60(2) nm and small log-normal widths $\ensuremath{\sigma}=015(1)$ In the entire temperature range from 5 to 400 K, the zero-field-cooled susceptibility $\ensuremath{\chi}(T)$ displays significant deviations from ideal superparamagnetism Approaching the Curie temperature of 450(10) K, the deviations arise from the mean-field-type reduction of the ferromagnetic moments, while below the blocking temperature ${T}_{b},\ensuremath{\chi}(T)$ is suppressed by the presence of energy barriers, the distributions of which scale with the particle volumes obtained from transmission electron microscopy This indication for volume anisotropy is supported by scaling analyses of the shape of the magnetic absorption ${\ensuremath{\chi}}^{\ensuremath{''}}(T,\ensuremath{\omega})$ which reveal distribution functions for the barriers also being consistent with the volume distributions observed by TEM Above 200 K, the magnetization isotherms $M(H,T)$ display Langevin behavior providing $25(1){\ensuremath{\mu}}_{B}$ per ${\mathrm{CoPt}}_{3},$ in agreement with reports on bulk and thin-film ${\mathrm{CoPt}}_{3}$ The non-Langevin shape of the magnetization curves at lower temperatures is interpreted as anisotropic superparamagnetism by taking into account an anisotropy energy of the nanoparticles ${E}_{A}(T)$ Using the magnitude and temperature variation of ${E}_{A}(T),$ the mean energy barriers and `unphysical' small switching times of the particles obtained from the analyses of ${\ensuremath{\chi}}^{\ensuremath{''}}(T,\ensuremath{\omega})$ are explained Below ${T}_{b}$ hysteresis loops appear and are quantitatively described by a blocking model, which also ignores particle interactions, but takes the size distributions from TEM and the conventional field dependence of ${E}_{A}$ into account
TL;DR: In this article, Chandra observations of two high-redshift clusters of galaxies, ClJ1113.1-2615 at z = 0.725 and ClJ0152.7-1357 at z=0.833, have been used to detect the formation of a supernova.
Abstract: We present an analysis of Chandra observations of two high-redshift clusters of galaxies, ClJ1113.1-2615 at z=0.725 and ClJ0152.7-1357 at z=0.833. We find ClJ1113 to be relaxed with kT=4.3^{+0.5}_{-0.4}keV and a mass (within the virial radius) of 4.3^{+0.8}_{-0.7}*10^{14}Msol. ClJ0152, by contrast, is resolved into a northern and southern subcluster, each massive and X-ray luminous, in the process of merging. The temperatures of the subclusters are found to be 5.5^{+0.9}_{-0.8}keV and 5.2^{+1.1}_{-0.9}keV respectively, and their respective masses are 6.1^{+1.7}_{-1.5}*10^{14}Msol and 5.2^{+1.8}_{-1.4}*10^{14}Msol within the virial radii. 2D modelling of the X-ray surface brightness reveals excess emission between the subclusters; suggestive, but not conclusive evidence of a shock front.
We make a first attempt at measuring the cluster M-T relation at z~0.8, and find no evolution in its normalisation, supporting the previous assumption of an unevolving M-T relation. We also find little or no evolution in the L-T relation, the gas fraction-T relation, the beta-T relation or the metallicity. These results suggest that, in at least some massive clusters, the hot gas was in place, and containing its metals, at z~0.8.
We also highlight the need to correct for the degradation of the Chandra ACIS low energy quantum efficiency in high-redshift cluster studies when the low energy absorption is often assumed to be the Galactic value, rather than measured.
TL;DR: Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of SDS with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), as well as in β-cyclodextrin solutions as discussed by the authors.
Abstract: Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of sodium n-dodecyl sulfate (SDS) with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), and five nonionic surfactants (Brij 35, nonyl phenol 12, Triton X-100, Triton X-305, Tween 80), as well as in β-cyclodextrin solutions. The apparent dissociation constants, \(K_a^a\), of rhodamine B (HR+ ⇄ R + H+) were obtained. The distribution of the dye species HR+ and R in the ultramicroheterogeneous systems was studied using absorption and emission spectra, fluorescence life-times, τ, and the plots of p\(K_a^a\) versus surfactant concentration. The p\(K_a^a\) values under conditions of complete binding, p\(K_a^a\), were found to be markedly higher than that in water \({\text{p}}K_a^w\). The medium effects, \(\Delta {\text{p}}K_a^{{\text{a}}c} = {\text{p}}K_a^{{\text{a}}c} {\text{ - p}}K_a^w\), in organized solutions studied are in accord with the charge type of the acid-base couple +/±, confirming the zwitterionic nature of rhodamine B neutral species. Both τ and \(\Delta {\text{p}}K_a^{{\text{a}}c}\) a values of the dye were shown to sense the changes in the micellar microenvironments, and the possibility of using rhodamine B as an interfacial acid-base indicator, for example, for monitoring of surface potentials and of bulk ionic strength, were demonstrated.
TL;DR: In this article, the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES's) stimulated by microwave radiation in a transverse magnetic field was discussed.
Abstract: We discuss the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES's) stimulated by microwave radiation in a transverse magnetic field. The mechanism of ANC under consideration is associated with electron scattering on acoustic phonons accompanied by absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative $({\ensuremath{\sigma}}_{\mathrm{xx}}={\ensuremath{\sigma}}_{\mathrm{yy}}l0)$ due to negative values of the dc photoconductivity caused by microwave radiation at certain ratios of the microwave frequency $\ensuremath{\Omega}$ and the electron cyclotron frequency ${\ensuremath{\Omega}}_{c}.$ The phase of the oscillations of the dissipative dc photoconductivity associated with photon-assisted electron scattering on acoustic phonons is quite different from that in the case of the photon-assisted impurity scattering mechanism. The concept of ANC associated with an interplay of the scattering mechanisms can be invoked to explain the nature of the occurrence of zero-resistance ``dissipationless'' states observed in recent experiments.
TL;DR: In this article, the first soft x-ray diffraction experiments from a bulk single crystal were conducted, where the bilayer manganite was studied and the Bragg reflection exhibited a strong resonant enhancement at the absorption edges.
Abstract: We have conducted the first soft x-ray diffraction experiments from a bulk single crystal, studying the bilayer manganite ${\mathrm{L}\mathrm{a}}_{2\ensuremath{-}2x}{\mathrm{S}\mathrm{r}}_{1+2x}{\mathrm{M}\mathrm{n}}_{2}{\mathrm{O}}_{7}$ with $x=0.475$ in which we were able to access the (002) Bragg reflection using soft x rays. The Bragg reflection displays a strong resonant enhancement at the ${L}_{\mathrm{I}\mathrm{I}\mathrm{I}}$ and ${L}_{\mathrm{I}\mathrm{I}}$ manganese absorption edges. We demonstrate that the resonant enhancement of the magnetic diffraction of the (001) is extremely large, indeed so large that it exceeds that of the nonresonant Bragg diffraction. Resonant soft x-ray scattering of $3d$ transition metal oxides is the only technique for the atomic selective measurement of spin, charge, and orbital correlations in materials, such as high temperature superconductors, colossal magnetoresistance manganites, and charge stripe nickelates.
TL;DR: In this article, first-principle calculations of excited-state relaxations in small Si nanocrystals were performed, showing that the Franck-Condon shift is surprisingly large for a 2.2-nm-diameter nanocrystal.
Abstract: Excited-state relaxations in molecules are responsible for a redshift of the absorption peak with respect to the emission peak (Franck-Condon shift). The magnitude of this shift in semiconductor quantum dots is still unknown. Here we report first-principle calculations of excited-state relaxations in small (diameter $l~2.2\mathrm{nm})$ Si nanocrystals, showing that the Franck-Condon shift is surprisingly large $(\ensuremath{\sim}60\mathrm{meV}$ for a 2.2-nm-diameter nanocrystal). The physical mechanism responsible for the Stokes shift changes abruptly around $\ensuremath{\sim}1$ nanometer in size, providing a clear demarcation between ``molecules'' and ``nanocrystals.''
TL;DR: In this article, the authors studied the absorption properties of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) oligomers embedded in helium nanodroplets.
Abstract: Laser-induced fluorescence of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) oligomers embedded in helium nanodroplets has been studied in the spectral region where the strongest absorptions of PTCDA crystals and single PTCDA molecules dissolved in organic solvents have been observed before. The cold helium droplet environment allows a separation of excitonic and molecular excitations. We find narrow $(l1{\mathrm{cm}}^{\ensuremath{-}1})$ as well as broad $(\ensuremath{\approx}500{\mathrm{cm}}^{\ensuremath{-}1})$ absorptions which can be attributed to electronic molecular transitions of the PTCDA dimer and, respectively, to excitonic transitions of sandwichlike PTCDA oligomers. The maximum of the excitonic absorption lies at $22190{\mathrm{cm}}^{\ensuremath{-}1},$ slightly shifting to lower energies upon addition of more PTCDA molecules. The results are discussed in comparison with existing theories of exciton states in thin organic films or crystals.
TL;DR: The relation between the average delay time and the "norm-leakage" decay function is found and the relation of the time-delay matrix to the reflection matrix S dagger S is established at arbitrary absorption that gives the distribution of reflection eigenvalues.
Abstract: Absorption yields an additional exponential decay in open quantum systems which can be described by shifting the (scattering) energy E along the imaginary axis, $E+i\ensuremath{\Elzxh}/2{\ensuremath{\tau}}_{a}.$ Using the random-matrix approach, we calculate analytically the distribution of proper delay times (eigenvalues of the time-delay matrix) in chaotic systems with broken time-reversal symmetry that is valid for an arbitrary number of generally nonequivalent channels and an arbitrary absorption rate ${\ensuremath{\tau}}_{a}^{\ensuremath{-}1}.$ The relation between the average delay time and the ``norm-leakage'' decay function is found. Fluctuations above the average at large values of delay times are strongly suppressed by absorption. The relation of the time-delay matrix to the reflection matrix ${S}^{\ifmmode\dagger\else\textdagger\fi{}}S$ is established at arbitrary absorption that gives us the distribution of reflection eigenvalues. The particular case of single-channel scattering is explicitly considered in detail.
TL;DR: In this paper, the authors report on XMM-Newton and Rossi-XTE observations of the bright gamma-ray burst GRB 030329 associated to SN2003dh.
Abstract: We report on XMM-Newton and Rossi-XTE observations of the bright (fluence ~10 -4 erg cm -2 ) and nearby ($z=0.1685$) Gamma-Ray Burst GRB 030329 associated to SN2003dh. The first Rossi-XTE observation, 5 hours after the burst, shows a flux decreasing with time as a power law with index $0.9\pm0.3$. Such a decay law is only marginally consistent with a further Rossi-XTE measurement (at $t-t_{\rm GRB}\sim 30$ hr). Late time observations of this bright afterglow at X-ray wavelengths have the advantage, compared to optical observations, of not being affected by contributions from the supernova and host galaxy. A first XMM-Newton observation, at $t-t_{\rm GRB}\sim 37$ days, shows a flux of $4\times10^{-14}$ erg cm -2 s -1 (0.2–10 keV). The spectrum is a power law with photon index $\Gamma=1.9$ and absorption -2 , consistent with the Galactic value. A further XMM-Newton pointing at $t-t_{\rm GRB}\sim61$ days shows a flux fainter by a factor ~2. The combined Rossi-XTE and XMM-Newton measurements require a break at $t\sim 0.5$ days in the afterglow decay, with a power law index increasing from 0.9 to 1.9, similar to what is observed in the early part of the optical afterglow. The extrapolation of the XMM-Newton spectra to optical frequencies lies a factor of ~10 below simultaneous measurements. This is likely due to the presence of SN2003dh.
TL;DR: In this article, a series of all-trans-carotenes that have excited states with different energies has been investigated using femtosecond absorption and Raman spectroscopy.
Abstract: Relaxation kinetics in a series of all-trans-carotenes that have excited states with different energies has been investigated using femtosecond absorption and Raman spectroscopy. The dependence on the energies shows that the ${1B}_{\mathrm{u}}^{\ensuremath{-}}$ state plays an intermediate state of the relaxation from the initially photoexcited ${1B}_{\mathrm{u}}^{+}$ state to the ${2A}_{\mathrm{g}}^{\ensuremath{-}}$ state. After the relaxation to the ${2A}_{\mathrm{g}}^{\ensuremath{-}}$ state, the excess energy is held in a $\mathrm{C}=\mathrm{C}$ stretching mode $({\ensuremath{
u}}_{1})$ of the ${2A}_{\mathrm{g}}^{\ensuremath{-}}$ state. The lifetime of the ${\ensuremath{
u}}_{1}$ mode is longer than several picoseconds in short (mini) carotenes, but it is shorter than 1 ps in long (macro) carotenes. Vibrational feature in carotenoids is of importance in energy transfer of photosynthesis, because the excess energy of the photoexcitation is stored in the ${\ensuremath{
u}}_{1}$ mode during the relaxation kinetics.
TL;DR: In this article, experimental results on electromagnetically induced absorption spectra observed in the system which does not satisfy completely the conditions given by Lezama [Phys. Rev. A 59, 4732 (1999)].
Abstract: We report experimental results on electromagnetically induced absorption spectra observed in the system which does not satisfy completely the conditions given by Lezama [Phys. Rev. A 59, 4732 (1999)]. We were able to observe electromagnetically induced absorption signals on all transitions in the Rb ${D}_{1}$ line, where ${F}_{g}\ensuremath{\leftrightarrow}{F}_{e}{=F}_{g}\ifmmode\pm\else\textpm\fi{}1$ or ${F}_{g}$ as well as open systems. These signals were only observed in certain Rabi frequency ranges for the coupling field. Present theoretical models, which are good for the case ${F}_{g}\ensuremath{\leftrightarrow}{F}_{e}{=F}_{g}+1,$ considering spontaneous transfer of atomic coherences or populations have not been able to explain our experimental results obtained in both cases ${F}_{g}\ensuremath{\leftrightarrow}{F}_{e}{=F}_{g}\ensuremath{-}1$ and ${F}_{e}{=F}_{g}.$
TL;DR: In this paper, an orbital-level scheme for ground state and two metastable states SI and SII was proposed based on polarization analysis of the electronic transitions and density of states calculations using density functional theory.
Abstract: The ground state and the light-induced metastable states of ${\mathrm{Na}}_{2}[\mathrm{Fe}(\mathrm{CN}{)}_{5}\mathrm{NO}]\ensuremath{\cdot}2{\mathrm{H}}_{2}\mathrm{O}$ were investigated by polarized optical absorption spectroscopy on single crystals. An orbital level scheme is proposed for the ground state and the two metastable states SI and SII. Based on polarization analysis of the electronic transitions and density of states calculations using density functional theory (DFT), three electronic transitions were tentatively assigned to the calculated transitions of the orbital level scheme of SI and four to that of SII. Isosbestic points at 562 and 375 nm in the absorption spectra during the population of SI indicate that anions are transferred from the ground state into SI. No optical depopulation process from SI into the ground state is observed between 375 and 562 nm. An effective transfer from SI into SII can be performed by irradiation with light of wavelength above 770 or 910 nm and polarization of the light parallel to the c or a axis of the orthorhombic crystal, respectively.
TL;DR: In this article, it was shown that the lifetime broadening of $1s$ core holes is suppressed and that of the $2p$ hole determines the resolution, and numerical procedures can provide lifetime-broadening-free (LBF) XANES, where the remaining $ 2p$ broadening is also eliminated.
Abstract: The resonant inelastic x-ray scattering (RIXS) spectrum is uniquely related to the x-ray absorption oscillator strength distribution by the Kramers-Heisenberg equation via lifetime widths of the states involved. In this work it is shown that x-ray absorption near-edge structure (XANES), where the lifetime broadening of $1s$ core holes is suppressed and that of the $2p$ hole determines the resolution, can be analytically deduced from RIXS spectra. Furthermore, it is demonstrated that numerical procedures can provide lifetime-broadening-free (LBF) XANES, where the remaining $2p$ broadening is also eliminated. As examples, lifetime-broadening-suppressed (LBS) XANES and LBF-XANES of CuO and ${\mathrm{CuCl}}_{2}\ensuremath{\cdot}2{\mathrm{H}}_{2}\mathrm{O}$ are derived from RIXS spectra measured by the use of a third-generation synchrotron source SPring-8 and are compared with XANES obtained by other methods to discuss the significance of LBS and LBF XANES spectroscopy.
TL;DR: In this paper, an effective exchange-correlation kernel was defined for the Kohn Sham electronic structure calculated in the local-density approximation and that obtained from a quasiparticle calculation, which allows to obtain correct absorption and energy loss spectra starting from an electronic structure obtained within some given approximation.
Abstract: We define an effective exchange-correlation kernel ${f}_{\mathrm{xc}}^{\mathrm{eff}}$ which allows us to obtain correct absorption and energy loss spectra starting from an electronic structure obtained within some given approximation. We consider, in particular, the Kohn Sham electronic structure calculated in the local-density approximation and that obtained from a quasiparticle calculation. We show that in both cases the main feature able to account for the experimental spectra is a sizable, complex, and frequency- and material-dependent long-range contribution to ${f}_{\mathrm{xc}}^{\mathrm{eff}}.$ We write, in terms of this contribution, an expression for the macroscopic dielectric function which is a generalization of the well-known contact-exciton approximation. Accurate absorption (for silicon and diamond) and electron energy loss (for silicon) spectra are obtained.
TL;DR: In this paper, the authors report on XMM-Newton and Rossi-XTE observations of the bright gamma-ray burst GRB030329 associated to SN2003dh.
Abstract: We report on XMM-Newton and Rossi-XTE observations of the bright (fluence $\sim$ 10$^{-4}$ erg cm$^{-2}$) and nearby (z=0.1685) Gamma-Ray Burst GRB030329 associated to SN2003dh. The first Rossi-XTE observation, 5 hours after the burst, shows a flux decreasing with time as a power law with index 0.9$\pm$0.3. Such a decay law is only marginally consistent with a further Rossi-XTE measurement (at t-t$_{GRB}\sim$30 hr). Late time observations of this bright afterglow at X-ray wavelengths have the advantage, compared to optical observations, of not being affected by contributions from the supernova and host galaxy. A first XMM-Newton observation, at t-t$_{GRB}\sim$37 days, shows a flux of 4$\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ (0.2-10 keV). The spectrum is a power law with photon index $\Gamma$=1.9 and absorption $<2.5\times10^{20}$ cm$^{-2}$, consistent with the Galactic value. A further XMM-Newton pointing at t-t$_{GRB}\sim$61 days shows a flux fainter by a factor $\sim$2. The combined Rossi-XTE and XMM-Newton measurements require a break at t$\sim$0.5 days in the afterglow decay, with a power law index increasing from 0.9 to 1.9, similar to what is observed in the early part of the optical afterglow. The extrapolation of the XMM-Newton spectra to optical frequencies lies a factor of $\sim10$ below simultaneous measurements. This is likely due to the presence of SN2003dh.
TL;DR: In this article, the energy levels and wave vectors of the (independent) $4f}^{2}$ and$4f5d$ configurations of the crystal field energy level scheme were calculated using a model which includes spin-orbit coupling and crystal field and Coulomb interactions, as well as the configuration interaction of ${4f''2''$ with 4f''6p.$ using the eigenvector of the predominantly high-spin, lowest excited crystal field level of $4''5d''.
Abstract: The $4f5\stackrel{\ensuremath{\rightarrow}}{d}{4f}^{2}$ emission spectra of ${\mathrm{Cs}}_{2}M{\mathrm{PrCl}}_{6}$ $(M=\mathrm{N}\mathrm{a},\mathrm{L}\mathrm{i})$ and ${\mathrm{Cs}}_{2}{\mathrm{NaYCl}}_{6}:{\mathrm{Pr}}^{3+}$ have been recorded at temperatures down to 10 K. The spectra of ${\mathrm{Pr}}^{3+}$ in the cubic host ${\mathrm{Cs}}_{2}{\mathrm{NaYCl}}_{6}$ are the most clearly resolved, and 15 transitions to terminal crystal field levels of symmetry representations ${\ensuremath{\Gamma}}_{5g}$ and ${\ensuremath{\Gamma}}_{4g}$ have been observed and assigned, thereby inferring that the symmetry representation of the lowest $4f5d$ crystal field level is ${\ensuremath{\Gamma}}_{3u}.$ Each transition is characterized by strong progressions in two totally symmetric vibrational modes. The relative displacement of the potential energy curves for the ${4f}^{2}$ and $4f5d$ crystal field levels, along the ${\ensuremath{\alpha}}_{1g}$ internal mode coordinate, is small, being only about 5 pm. The 10-K ultraviolet absorption spectra of ${\mathrm{Cs}}_{2}{\mathrm{NaYCl}}_{6}:{\mathrm{Pr}}^{3+}$ are assigned to transitions from the ${[}^{3}{H}_{4}]$ ${\ensuremath{\Gamma}}_{1g}$ electronic ground state to terminal ${\ensuremath{\Gamma}}_{4u}$ crystal field levels of $4f5d.$ Nontotally symmetric gerade vibrational modes only provide minor intensity contributions. The large energy gap between the d-f emission and f-d absorption spectra of ${\mathrm{Pr}}^{3+}$ in the cubic elpasolite host is rationalized. The 8-K excitation spectra of ${\mathrm{Cs}}_{2}{\mathrm{NaPrCl}}_{6}$ and ${\mathrm{Cs}}_{2}{\mathrm{NaYCl}}_{6}:{\mathrm{Pr}}^{3+},$ excited by synchrotron radiation, show that the transitions to $4f5d$ fall into two groups. The energy levels and wave vectors of the (independent) ${4f}^{2}$ and $4f5d$ configurations of ${\mathrm{Pr}}^{3+}$ have been calculated using a model which includes spin-orbit coupling and crystal field and Coulomb interactions, as well as the configuration interaction of ${4f}^{2}$ with $4f6p.$ Using the eigenvector of the predominantly high-spin, lowest excited crystal field level of $4f5d,$ the emission intensities are reasonably well simulated. However, the refinement of the ${4f}^{2}\ensuremath{\rightarrow}4f5d$ absorption intensities requires a more detailed knowledge of the crystal field energy level scheme of $4f5d.$ The configuration interaction of $4f5d$ with $4f6s$ and $4f5g$ is discussed.
TL;DR: In this article, total energy density-functional theory electronic structure calculations for the neutral and charge states of H intrinsic (Frenkel pair) and extrinsic (H vacancy or interstitial) point defects in point defects have been calculated.
Abstract: We report first-principles total-energy density-functional theory electronic structure calculations for the neutral and charge states of H intrinsic (Frenkel pair) and extrinsic (H vacancy or interstitial) point defects in ${\mathrm{KH}}_{2}{\mathrm{PO}}_{4}.$ The relaxed atomic structures, the formation energy, the ionization energy, and electron and hole affinities for the various defects have been calculated. For the Frenkel pair, the additional hole leads to a decrease of the $\mathrm{O}\char22{}\mathrm{O}$ bond length between the two O atoms next to the H vacancy, while the effect of the additional electron is small. For the H vacancy, the added hole is trapped and shared by the two O atoms adjacent to the vacancy, reducing dramatically the $\mathrm{O}\char22{}\mathrm{O}$ bond length, thus forming a molecular-type polaron. We find that the positively charged H vacancy introduces states in the gap, in contrast with its neutral state, confirming the experimental suggestion that it is a relevant absorbing center. The negatively charged H vacancy leads to an increase of the two O atoms close to the H vacancy, and does not induce states in the gap. The H interstitial does not interact with the host atoms in the neutral state. However, the addition of an electron leads to the ejection of a H host atom and the subsequent formation of a ${\mathrm{H}}_{2}$ interstitial molecule and a H vacancy, in agreement with experimental suggestions. In the positively charged state the H interstitial binds to its nearest-neighbor O atom forming a hydroxyl bond. The H interstitial in both positive and negative charge states induces no defect states in the band gap, in contrast with its neutral state. The calculations provide insights into the role of the charged and neutral defects on the transient optical absorption under irradiation by high-intensity laser beam.
02 Oct 2003
TL;DR: This study suggests that C(60), C(59)N(+), and C(48)N (12), which differ in their optical gaps, have potential applications in polymer science, biology, and medicine as single-molecule fluorescent probes, in photovoltaics as the n-type emitter and/or p-type base of a p-n junction solar cell, and in nanoelectronics as fluorescence-based sensors and switches.
Abstract: Low-energy excitations and optical absorption spectrum of C{sub 60} are computed by using time-dependent (TD) Hartree-Fock (HF), TD-density functional theory (TD-DFT), TD-DFT-based tight-binding (TD-DFT-TB) and a semiempirical ZINDO method. A detailed comparison of experiment and theory for the excitation energies, optical gap and absorption spectrum of C{sub 60} is presented. It is found that electron correlations and collective effects of exciton pairs play important roles in assigning accurately the spectral features of C{sub 60} and the TD-DFT method with non-hybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C{sub 60} justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C{sub 59}N{sup +} exhibits distinguishing spectral features different from C{sub 60}: (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet-triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C{sub 59}N{sup +} characterize and explain well our measured ultraviolet-visible (UV-vis) and transient absorptionmore » spectra of the carborane anion salt [C{sub 59}N][Ag(CB{sub 11}H{sub 6}Cl{sub 6}){sub 2}]. For the most stable isomer of C{sub 48}N{sub 12}, we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C{sub 60}, and optical absorption maxima occur at 585, 528, 443, 363, 340, 314 and 303 nm. We point out that the characterization of the UV-vis and transient absorption spectra of C{sub 48}N{sub 12} isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C{sub 59}N{sup +} and C{sub 48}N{sub 12} as well as C{sub 60}, the TD-DFT-TB yields reasonable agreement with TD-DFT calculations at a highly reduced cost. Our study suggests that C{sub 60}, C{sub 59}N{sup +} and C{sub 48}N{sub 12}, which differ in their optical gaps, may have potential applications in polymer science, biology and medicine as single-molecule fluorescent probes.« less
TL;DR: In this paper, the authors investigate realistic atomic systems whose dispersion at line center switches from positive to negative and vice versa, as a particular experimental parameter is changed, and find that the preferred system for observing switchover in the sign of the dispersion from positive-to-negative, as the pump Rabi frequency increases, is the open near-degenerate 1/1/e = 1/2 system.
Abstract: We investigate realistic atomic systems whose dispersion at line center switches from positive to negative and vice versa, as a particular experimental parameter is changed. We concentrate on those systems which have low probe absorption or gain at line center leading to a high figure of merit, and simultaneously have low pump absorption. For this purpose, we study both open and artificially closed ${F}_{g}=\stackrel{\ensuremath{\rightarrow}}{1}{F}_{e}=1$ and ${F}_{g}=\stackrel{\ensuremath{\rightarrow}}{1}{F}_{e}=2$ transitions in ${}^{87}\mathrm{Rb},$ in the absence and presence of an applied magnetic field. We find that the preferred system for observing switchover in the sign of the dispersion from positive to negative, as the pump Rabi frequency increases, is the open near-degenerate ${F}_{g}=\stackrel{\ensuremath{\rightarrow}}{1}{F}_{e}=1$ system. In the presence of Doppler broadening, the dispersion is positive for all realistic experimental parameters. Thus the switchover in the sign of the dispersion is only observable in the absence of Doppler broadening.
TL;DR: Louca et al. as mentioned in this paper investigated the local structure of the octahedron of the Mn K-edge x-ray absorption fine structure at room temperature and room temperature as a function of x (0l~xl~0.475).
Abstract: The local structure of the ${\mathrm{MnO}}_{6}$ octahedron in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ was investigated by Mn K-edge x-ray absorption fine structure at $T\ensuremath{\approx}10\mathrm{K}$ and room temperature as a function of x $(0l~xl~0.475).$ For both temperatures, we observed that some distortion exists in a metallic phase observed using neutron scattering measurements [D. Louca et al., Phys. Rev. B 56, R8475 (1997)], but the bond-length splitting is significantly reduced. The observed reduction of distortion may be attributed to the partial charge transfer between the Mn ions by the double exchange mechanism. The details of the Mn-O bond length and the Debye Waller factor are presented.