Absorption (logic)

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

Robust population transfer by stimulated raman adiabatic passage in a Pr3+:Y2SiO5 crystal.

Abstract: We report on the experimental implementation of stimulated Raman adiabatic passage (STIRAP) in a ${\mathrm{Pr}}^{3+}\mathrm{\text{:}}{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal. Our data provide clear and striking proof for nearly complete population inversion between hyperfine levels in the ${\mathrm{Pr}}^{3+}$ ions. The transfer efficiency was monitored by absorption spectroscopy. Time-resolved absorption measurements serve to monitor the adiabatic population dynamics during the STIRAP process. Efficient transfer is observed for negative pulse delays (STIRAP), as well as for positive delays. We identify the latter by an alternative adiabatic passage process.

Optical Absorption and Nonradiative Decay Mechanism of E ′ Center in Silica

Abstract: We report ab initio configuration interaction calculations on the optical transitions of the ${E}^{\ensuremath{'}}$ center, a hole trapped at an oxygen vacancy, $(---\mathrm{O}{)}_{3}{\mathrm{Si}}^{\ifmmode\bullet\else\textbullet\fi{}}$ ${}^{+}\mathrm{Si}(\mathrm{O}---{)}_{3}$, in silica. We found two competing excitation mechanisms: (1) promotion of one electron from an $\mathrm{O}(2p)$ valence band orbital to the singly occupied Si dangling bond; (2) charge transfer (CT) transition from $(---\mathrm{O}{)}_{3}{\mathrm{Si}}^{\ifmmode\bullet\else\textbullet\fi{}}$ to ${}^{+}\mathrm{Si}(\mathrm{O}---{)}_{3}$. The two excitations occur at similar energies, $\ensuremath{\approx}5.8--6\mathrm{eV}$ (5.85 eV in the experiment), but only the CT has a strong intensity. The excitation is followed by a complex nonradiative decay process which may explain the absence of luminescence for this center.

Fougerite, a new mineral of the pyroaurite-iowaite group: Description and crystal structure

Abstract: Fougerite (IMA 2003-057) is a mixed M(II)-M(III) hydroxysalt of the green rust group, where M(II) can be Fe or Mg, and M(III) is Fe. The general structural formula is: ${[{\rm{Fe}}_{1 - }^{2 + }x{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{ + x}}{[x{\rm{/}}n{A^{ - n}}.m{{\rm{H}}_2}{\rm{O}}]^{ - x}}$ where A is the interlayer anion and n its valency, with 1/4 ≼ x/(1+y) ≼ 1/3 and m ≼ (1−x+y). The structure of green rusts and parent minerals can accommodate a variety of anions, such as OH−, Cl−, ${\rm{CO}}_3^{2 - },\;{\rm{SO}}_4^{2 - }$ . The structure of the mineral was studied by Mossbauer, Raman and X-ray absorption spectroscopies (XAS) at the FeK edge. Mossbauer spectra of the mineral obtained at 78 K are best fitted with four doublets: D1 and D2 due to Fe2+ (isomer shift δ ≈ 1.27 and 1.25 mm s−1, quadrupole splitting ΔEQ ≈ 2.86 and 2.48 mm s−1, respectively) and D3 and D4 due to Fe3+ (δ ≈ 0.46 mm s−1, ΔEQ ≈ 0.48 and 0.97 mm s−1, respectively). Microprobe Raman spectra obtained with a laser at 514.53 nm show the characteristic bands of synthetic green rusts at 427 and 518 cm−1. X-ray absorption spectroscopy shows that Mg is present in the mineral in addition to Fe, that the space group is and the lattice parameter a ≈ 0.30–0.32 nm. The mineral forms by partial oxidation and hydrolysis of aqueous Fe2+, to give small crystals (400–500 nm) in the form of hexagonal plates. The mineral is unstable in air and transforms to lepidocrocite or goethite. The name is for the locality of the occurrence, a forested Gleysol near Fougeres, Brittany, France. Its characteristic blue-green color (5BG6/1 in the Munsell system) has long been used as a universal criterion in soil classification to identify Gleysols. From a thermodynamic model of soil-solution equilibria, it was proposed that for the eponymous mineral, Fougeres-fougerite, OH− may be the interlayer anion. In other environments, the interlayer anion may be different, and other varieties of fougerite may exist. Fougerite plays a key role in the pathways of formation of Fe oxides.

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

Abstract: The femtosecond optical pump-probe technique was used to study dynamics of photoexcited electrons and coherent optical phonons in transition metals Zn and Cd as a function of temperature and excitation level. The optical response in time domain is well fitted by linear combination of a damped harmonic oscillation because of excitation of coherent ${E}_{2g}$ phonon and a subpicosecond transient response due to electron-phonon thermalization. The electron-phonon thermalization time monotonically increases with temperature, consistent with the thermomodulation scenario, where at high temperatures the system can be well explained by the two-temperature model, while below $\ensuremath{\approx}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the nonthermal electron model needs to be applied. As the lattice temperature increases, the damping of the coherent ${E}_{2g}$ phonon increases, while the amplitudes of both fast electronic response and the coherent ${E}_{2g}$ phonon decrease. The temperature dependence of the damping of the ${E}_{2g}$ phonon indicates that population decay of the coherent optical phonon due to anharmonic phonon-phonon coupling dominates the decay process. We present a model that accounts for the observed temperature dependence of the amplitude assuming the photoinduced absorption mechanism, where the signal amplitude is proportional to the photoinduced change in the quasiparticle density. The result that the amplitude of the ${E}_{2g}$ phonon follows the temperature dependence of the amplitude of the fast electronic transient indicates that under the resonant condition both electronic and phononic responses are proportional to the change in the dielectric function.

Universal features of terahertz absorption in disordered materials.

Abstract: Using an analytical theory, experimental terahertz time-domain spectroscopy data, and numerical evidence, we demonstrate that the frequency dependence of the absorption coupling coefficient between far-infrared photons and atomic vibrations in disordered materials has the universal functional form, $C(\ensuremath{\omega})=A+B{\ensuremath{\omega}}^{2}$, where the material-specific constants $A$ and $B$ are related to the distributions of fluctuating charges obeying global and local charge neutrality, respectively.