Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Optical Properties of the Rubidium and Cesium Halides in the Extreme Ultraviolet

Abstract: The absorption spectra of evaporated thin films of all rubidium and cesium halides in the 50- to 250-eV region are reported. In this range, transitions from the $3d$ shell of ${\mathrm{Rb}}^{+}$ and from the $4d$ and $4p$ shells of ${\mathrm{Cs}}^{+}$ can be seen, as well as some transitions from inner shells of the halogen ions. Besides the absorption fine structure near the threshold for inner-shell transitions, broad absorption structure is observed and explained as due to $d\ensuremath{\rightarrow}f$ continuum transitions. The number of effective electrons whose oscillator strength has been exhausted in our spectral region has been computed from the absorption data; it is particularly strong for materials containing either Cs or I. Differences in the spectra of materials with NaCl and with CsCl structure are discussed. The measurements were performed using the DESY electron synchrotron as a light source.

Optical and magneto-optical properties and electronic structures of single-crystalline RAl2 (R=Y, La, Ce, Pr, and Lu)

Abstract: The diagonal optical conductivity spectra of single crystals of $R{\mathrm{Al}}_{2}$ $(R=\mathrm{Y},$ La, Ce, Pr, and Lu) were measured at room temperature by spectroscopic ellipsometry in the $1.5--5.6\ensuremath{-}\mathrm{eV}$ range. All the compounds exhibit two strong interband absorption peaks at about 1.8 and 3.6 eV for ${\mathrm{YAl}}_{2}$ and ${\mathrm{LuAl}}_{2},$ and at about 2.0 and 3.0 eV for ${\mathrm{LaAl}}_{2},$ ${\mathrm{CeAl}}_{2},$ and ${\mathrm{PrAl}}_{2}.$ Such differences in the second peak position appear in the theoretical optical conductivity spectra calculated from their band structures obtained by the tight-binding linear-muffin-tin-orbitals method. Most of the contributions to the two peaks in ${\mathrm{LaAl}}_{2}$ are from the p and d states, i.e., $\stackrel{\ensuremath{\rightarrow}}{p}d$ and $\stackrel{\ensuremath{\rightarrow}}{d}p$ transitions, while those involving f states are negligible. These results suggest that f character near ${E}_{F}$ for ${\mathrm{LaAl}}_{2},$ ${\mathrm{CeAl}}_{2},$ and ${\mathrm{PrAl}}_{2}$ distorts their conduction bands significantly through hybridization, leading to different optical spectra compared to those of ${\mathrm{YAl}}_{2}$ and ${\mathrm{LuAl}}_{2}.$ The magneto-optical properties of ${\mathrm{CeAl}}_{2}$ and ${\mathrm{PrAl}}_{2}$ were measured at low temperatures. The Kerr rotation $({\ensuremath{\Theta}}_{K})$ and ellipticity $({\ensuremath{\epsilon}}_{K})$ for both compounds show similar spectral variations with maximum ${\ensuremath{\Theta}}_{K}$ of $0.35\ifmmode^\circ\else\textdegree\fi{}$ and $0.55\ifmmode^\circ\else\textdegree\fi{}$ at about 2.1 eV for ${\mathrm{CeAl}}_{2}$ and ${\mathrm{PrAl}}_{2},$ respectively. The evaluated off-diagonal conductivity spectra of the two compounds are also similar, with two structures at about 2.1 and 3.8 eV for ${\mathrm{CeAl}}_{2}$ and 2.1 and 3.4 eV for ${\mathrm{PrAl}}_{2}.$ The energy difference in the second structures is interpreted as due to the different conduction-band structures of the two compounds caused by different hybridization strengths of their f states with conduction bands, because of the difference in their degree of localization.

Ligand field parameters obtained from and chemical shifts observed at the Cr L 2,3 edges

Abstract: Using synchrotron radiation, we have measured the Cr ${L}_{2,3}$ absorption edges for the three most common Cr oxidation states. Significant chemical shifts (0.7 eV for a one electron change) are observed between the ${L}_{2,3}$ edges of hexavalent, trivalent, and divalent Cr. The absorption edges are also compared to ligand field atomic multiplet calculations. The different oxidation states clearly show the ``fingerprints'' of final states belonging to the different ${d}^{n}$ ground states. The ligand field parameters obtained for hexavalent ${\mathrm{K}}_{2}{\mathrm{CrO}}_{4}$ $(10Dq=\ensuremath{-}1.6\mathrm{eV})$ and trivalent ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ $(10Dq=2\mathrm{eV})$ are quite comparable to ligand field parameters determined from the forbidden $3d\ensuremath{-}3d$ optical transitions. A large tetragonal splitting of 3.1 eV is obtained for the ${e}_{g}$ electrons in the Jahn-Teller ${d}^{4}$ compound ${\mathrm{CrF}}_{2}.$ The $10Dq$ value obtained is 1.1 eV, which indicates that the ordering of the $3d$ orbitals has changed. The ${d}_{{z}^{2}}$ and ${d}_{\mathrm{xy}}$ orbitals have changed position, with the ${d}_{\mathrm{xy}}$ orbital being the highest occupied orbital. The ligand field splittings obtained for ${\mathrm{CrF}}_{2}$ are inconsistent with values obtained in two other studies based on the forbidden $3d\ensuremath{-}3d$ optical transitions. The positions of the first two optical transitions are consistent with $3d\ensuremath{-}3d$ excited states calculated with our parameters. The ${\mathrm{CrF}}_{2}$ system shows that a clear ligand field analysis is possible for distorted octahedral systems using ${L}_{2,3}$ edges absorption experiments.

Orbital Angular Momentum Transfer to Stably Trapped Elastic Particles in Acoustical Vortex Beams.

Abstract: The controlled rotation of solid particles trapped in a liquid by an ultrasonic vortex beam is observed. Single polystyrene beads, or clusters, can be trapped against gravity while simultaneously rotated. The induced rotation of a single particle is compared to a torque balance model accounting for the acoustic response of the particle. The measured torque ($\ensuremath{\sim}10\text{ }\text{ }\mathrm{pN}\text{ }\mathrm{m}$ for a driving acoustic power $\ensuremath{\sim}40\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) suggests two dominating dissipation mechanisms of the acoustic orbital angular momentum responsible for the observed rotation. The first takes place in the bulk of the absorbing particle, while the second arises as dissipation in the viscous boundary layer in the surrounding fluid. Importantly, the dissipation processes affect both the dipolar and quadrupolar particle vibration modes suggesting that the restriction to the well-known Rayleigh scattering regime is invalid to model the total torque even for spheres much smaller than the sound wavelength. The findings show that a precise knowledge of the probe elastic absorption properties is crucial to perform rheological measurements with maneuverable trapped spheres in viscous liquids. Further results suggest that the external rotational steady flow must be included in the balance and can play an important role in other liquids.

Observation of antiferromagnetic resonance in an organic superconductor

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%.