Electric Quadrupole Effects Research Articles

Relativistic coupled-cluster analysis of the second-order effects on the hyperfine structure in Cs133

Using the single and double approximated relativistic coupled-cluster method, we calculate the first-order hyperfine structure constants for the $6{p}_{3/2}, 8{p}_{3/2}, 6{d}_{3/2}, 7{d}_{3/2}$, and $7{d}_{5/2}$ states in $^{133}\mathrm{Cs}$, and also evaluate the second-order magnetic dipole--magnetic dipole, magnetic dipole--electric quadrupole effects caused by the off-diagonal hyperfine interaction. With these calculations, we reanalyze some recent high-precision experimental measurements of the hyperfine splitting intervals of $^{133}\mathrm{Cs}$. We find that the second-order magnetic dipole--magnetic dipole effects are especially sizable at the order of kHz in the $B$ constant for the ${d}_{3/2,5/2}$ states. Our calculations can provide a reference for future higher precision experimental measurements.

Subcycle-resolved strong-field tunneling ionization: Identification of magnetic dipole and electric quadrupole effects

Interaction of a strong laser pulse with matter transfers not only energy but also linear momentum of the photons. Recent experimental advances have made it possible to detect the small amount of linear momentum delivered to the photoelectrons in strong-field ionization of atoms. Linear momentum transfer is a unique signature of the laser-atom interaction beyond its dipolar limit. Here, we present a decomposition of the subcycle time-resolved linear momentum transfer in term of its multipolar components. We show that the magnetic dipole contribution dominates the linear momentum transfer during the dynamical tunneling process while the post-ionization longitudinal momentum transfer in the field-driven motion of the electron in the continuum is primarily governed by the electric quadrupole interaction. Alternatively, exploiting the radiation gauge, we identify nondipole momentum transfer effects that scale either linearly or quadratically with the coupling to the laser field. The present results provide detailed insights into the physical mechanisms underlying the subcycle linear momentum transfer induced by nondipole effects.

Effects of electric quadrupole interactions with tunable atomic mirrors

Recent studies have involved electric quadrupole effects in atoms interacting with the evanescent mode. This type of surface mode is usually produced by the total internal reflection in a dielectric-vacuum atz=0, and its intensity distribution is very close to the outer surface z>0 half-space. Coating the planar surface of a dielectric substrate with multilayer dielectric thin film of different thicknesses provides an enhanced in such evanescent modes. This type of mode can be used purely as an atomic mirror. We show that the use of such elements for atomic optics gives significant enhancement of the evanescent mode magnitude without degrading the quality of the atomic reflection process. In addition, the decay depth of the evanescent mode can be conveniently controlled by design parameters. This property keeps the atom-light interaction timeτ, and thus the probability of decay emission, very low, which means a high degree of coherence property.

A far-red emission Ca3La2W2O12:xMn4+ phosphor for potential application in plant growth LEDs

Many Mn4+ ion-doped Ca3La2W2O12 phosphors were produced using the conventional high-temperature solid-phase method. The microstructure, luminescence properties, quantum yield, and fluorescence lifetime of Ca3La2W2O12:xMn4+ phosphors were systematically researched by XRD, fluorescence spectrometer, and SEM. In 300–550 nm, Ca3La2W2O12:xMn4+ phosphor has an influential broad excitation band. In 650–800 nm, there is an emission peak at 715 nm, which corresponds to the 2Eg→4A2g energy level transition of Mn4+ ion. With the increase of the doping concentration of Mn4+ ions, the luminescence intensity first increases and then decreases. When the Mn4+ concentration is x = 0.07, the concentration quenching appears due to the electric dipole-electric quadrupole effect. The influences of various Mn sources on the luminescence performance of Ca3La2W2O12:0.07Mn4+ phosphor were investigated. The outcomes show that the emission spectrum of the Ca3La2W2O12:xMn4+ phosphor was well-matched with the absorption band of the plant photosensitive pigments PR and PFR. As a result, Ca3La2W2O12:xMn4+ phosphors are extremely promising applications in promoting plant growth, flowering, and fruiting.

Linear optical responses beyond the electric dipole approximation on reflection and transmission: a perturbation treatment

There exist in a material a wide range of linear optical responses to external electromagnetic fields beyond the electric dipole process. These responses reveal more detailed information on properties of the material through their corrections to the zeroth-order dielectric tensor. These corrections introduce small yet distinguishable modifications to reflection and transmission. I here describe a perturbation method for computing these modifications. The method simplifies the computation of optical reflection and transmission that include first-order contributions from processes such as magneto-optic effects, electro-optic effects, surface and ultrathin films, electric quadrupole effects, photoelastic effects, and effects of meta-materials.

Spatial dispersion contribution to second harmonic generation in inversion-symmetric materials

It is well known that second harmonic generation (SHG) from dipoles within the bulk vanishes in inversion-symmetric semiconductor materials as a consequence of parity symmetry. Hence SHG is then ascribed in the form of either surface dipole effects or bulk-related electric quadrupole or magnetic dipole effects. By incorporating the redefined spatial dispersion into the simplified bond-hyperpolarizability model, we show that the SHG spatial dispersion contribution for Si(001) and Si(111) facet orientations can be reformulated by a third-rank tensor containing one independent parameter, namely, the complex SHG spatial dispersion hyperpolarizability. Our results show that certain unexplained rotational anisotropy SHG intensity features for different incoming light wavelengths or optical penetration depths can be well reproduced only if the contribution from spatial dispersion is incorporated.

Second order optical nonlinearity of graphene due to electric quadrupole and magnetic dipole effects

We present a practical scheme to separate the contributions of the electric quadrupole-like and the magnetic dipole-like effects to the forbidden second order optical nonlinear response of graphene, and give analytic expressions for the second order optical conductivities, calculated from the independent particle approximation, with relaxation described in a phenomenological way. We predict strong second order nonlinear effects, including second harmonic generation, photon drag, and difference frequency generation. We discuss in detail the controllability of these effects by tuning the chemical potential, taking advantage of the dominant role played by interband optical transitions in the response.

Quadrupole effects in photoabsorption in ZnO quantum dots

Electronic transitions in the quantum confined states in the conduction band of spherical ZnO semiconductor quantum dot are studied. Photoabsorption spectra and oscillator strengths have been obtained for various sizes of quantum dot using effective mass approximation. Electric quadrupole effect has been included in addition to the electric dipole effect. The nonlinear contribution to photoabsorption spectra has also been studied. Results for transition energies of the quantum confined states are found to be in good agreement with the available experimental data.

Electric Quadrupole Effect in Clathrate Compound Pr3Pd20Si6

Electric quadrupole effects in a Pr-based clathrate compound Pr 3 Pd 20 Si 6 have been investigated by ultrasonic measurements. Elastic constants of ( C 11 - C 12 ) /2 and C 44 in Pr 3 Pd 20 Si 6 show curie-type softenings with decreasing temperature below 20 K, which are described in terms of quadrupole effects of 4f-electron for the ground state either Γ 3 doublet or Γ 5 triplet. H – T phase diagram of Pr 3 Pd 20 Si 6 under the magnetic fields along [110] is obtained from elastic anomalies in ( C 11 - C 12 ) /2 mode.

Static electric field effect in the second harmonic generation from phthalocyanine film/metal electrode

The effect of static electric field on the second harmonic generation (SHG) from copper phthalocyanine (CuPc) was investigated using metal/CuPc/metal structure. An external DC voltage was applied to the sample to induce an electric dipole which allowed second order polarization in the centrosymmetric molecular system (CuPc film). The second harmonic generation (SHG) spectra and its intensity vs. the external bias at fixed fundamental frequency were investigated. Considering the induced electric quadrupole transition and the electric field induced dipole transition, the SHG generated from the CuPc film was attributed to the electric quadrupole effect and the electric field induced SHG (EFISHG). A quadratic relation between the SHG intensity and the external applied bias was observed. It was in accordance with theoretical analysis.

Study of Second Harmonic Generation from Copper-tetra-tert-butyl-phthalocyanine Langmüir-Blodgett Film/Metal Interface

The second harmonic generation (SHG) from the copper-tetra-tert-butyl-phthalocyanine (CuttbPc) Langmüir-Blodgett (LB) film deposited on a glass substrate coated with evaporated metal electrode is investigated. Besides the electric quadrupole transition, the space charge induced electric field at the LB film/metal electrode interface breaks the centrosymmetry of the CuttbPc molecule and contributes to the generation of SH radiation. Based on the experimental results and theoretical analysis, the nonlinear susceptibilities of these two effects are calculated. It is found that at the incident fundamental light wavelength of 1100 nm, the electric quadrupole effect makes a main contribution to the SHG, while at the wavelength of around 1200 nm, it is attributed to the electric field induced SHG (EFISHG).

Second harmonic generation from copper-tetratert-butyl-phthalocyanine Langmuir–Blodgett film/metal interface: Electric quadrupole or electric field induced second harmonic generation effect?

It has been found that a high electric field is created at the interface between copper-tetratert-butyl-phthalocyanine (CuttbPc) Langmuir–Blodgett (LB) film/metal due to the exchanged charges. The symmetry of the CuttbPc molecule is broken by this space charge induced electric field (SCIEF), and optical second harmonic (SH) signal is generated from the CuttbPc LB film/metal interface. A theoretical expression of the reflected SH signal intensity is derived using a four-layer model with the SCIEF being treated as a mean field. The origins of the SHG are considered as the quadrupole effect and the electric field induced SHG (EFISHG) due to the SCIEF. On the basis of experimental results and the theoretical analysis, the nonlinear susceptibilities of these two effects are calculated. It is found that at the wavelength of incident fundamental light around 1100 nm the electric quadrupole effect makes a main contribution to the SHG from the interface, while at the wavelength around 1200 nm it is attributed to the EFISHG. It is expected that the SCIEF could be determined by SHG.

Effective second-order susceptibility in photonic crystals mode of centrosymmetric materials

A technique for obtaining efficient bulk second-order susceptibility in noncentrosymmetric photonic crystals (PC) made of centrosymmetric materials is discussed. The effect is based on the electric quadrupole effect, strong electromagnetic mode deformation, and nonhomogeneous contribution to volume polarization from different parts of the PC. The required symmetry breaking is introduced on the macroscale of the PC unit cell. The obtained structural ${\ensuremath{\chi}}_{\mathrm{str}}^{(2)}$ is comparable with the second-order susceptibility of ordinary nonlinear materials. Phase matching can be achieved by introducing symmetry modulation (quasi-phase-matching) during fabrication of the PC.

Nuclear magnetic resonance study of polycrystalline Sr1-xCaxRuO3 (0 x1.0)

A zero-field spin-echo nuclear magnetic resonance (NMR) study of 99,101Ru nuclei in polycrystalline powder samples of magnetically ordered Sr1 - xCaxRuO3 (0 x1.0) is reported. The NMR spectrum for SrRuO3 at 1.3 K consists of two peaks at 64.4 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru isotopes, respectively, and a hyperfine field of 329 kG. With the replacement of Sr by Ca, the peaks broaden somewhat, although there is essentially no change in the peak frequencies. However, the two resonance peaks show a significant reduction in height with intensity being shifted into the wings. Although electric quadrupole effects are present, the results suggest that the reduction of peak intensity when Ca is added is due mainly to a progressive loss of Ru moments participating in the magnetic ordering. The loss is a consequence of the dilution of the ferromagnetic exchange coupling between the moments. A measure of the spontaneous magnetization temperature dependence for SrRuO3 (21 K) has been obtained from the shift of the peak frequencies. It was found that the spontaneous magnetization decreases with a Bloch law T 3/2 temperature dependence characteristic of spin-wave excitations. From the coefficient of the temperature dependence, a value of 2.4 meV was obtained for the exchange integral which is consistent with the observed ordering temperature.

Electric quadrupole effects and nuclear spin relaxation in aAl72.4Pd20.5Mn7.1icosahedral quasicrystal studied by NMR

The ${}^{27}\mathrm{Al}\mathrm{}\mathrm{NMR}$ spectrum and the spin-lattice relaxation rate of an icosahedral ${\mathrm{Al}}_{72.4}{\mathrm{Pd}}_{20.5}{\mathrm{Mn}}_{7.1}$ quasicrystal were studied in the temperature range from 300 to 4 K at two magnetic fields. The results are compatible with the hypothesis that a screening electron cloud is formed around the Mn ions in an aluminum-rich environment, which together with the core electrons produces a large electric-field gradient (EFG) at the sites of the Al nuclei. The EFG is temperature dependent due to the polarization of the screening cloud and the core electrons by the magnetic moments of the Mn unpaired d electrons. The shift of the ${}^{27}\mathrm{Al}$ central line shows an inverse magnetic-field dependence and appears to be of an electric quadrupolar origin. The ${}^{27}\mathrm{Al}$ spin-lattice relaxation rate shows an ${aT+bT}^{3}$ temperature dependence that can be explained by approximating the quasicrystalline electronic structure by a two-band model, consisting of a broad s and a narrow d conduction bands. The ${T}^{3}$ term originates from the narrowness of the d band. The ${}^{27}\mathrm{Al}$ spin-lattice relaxation in ${\mathrm{Al}}_{72.4}{\mathrm{Pd}}_{20.5}{\mathrm{Mn}}_{7.1}$ is governed by two relaxation mechanisms of similar strength, the electric quadrupole and the magnetic hyperfine. The quadrupole mechanism is stronger at high temperatures such as room temperature whereas the magnetic relaxation dominates at low temperatures.

Depletion-electric-field-induced second-harmonic generation near oxidized GaAs(001) surfaces

Second-order nonlinear mixing is evaluated as a probe of the depletion electric field in the near-surface region of GaAs(001). A phenomenological model is presented whereby the nonlinear susceptibility is expanded in the depletion electric field. For GaAs, three terms contribute to the observed nonlinear mixing: the dipole-allowed bulk contribution and first- and second-order contributions in the depletion electric field. All three contributions can be isolated by a combination of rotational anisotropy and photomodulation studies. The second-harmonic signal from oxidized GaAs(001) surfaces was measured as a function of azimuthal sample orientation, photomodulation, and dopant density for fundamental photon energies in the region 1.17--1.51 eV. The first-order depletion-electric-field contribution dominates the second-order contribution, and can be comparable to the intrinsic bulk contribution for high surface fields. The results rule out significant contributions arising from either bulk electric quadrupole or surface dipole effects.

Effective cross‐sections for molecular aggregation in external orienting fields

AbstractEffects of an external orienting field and orientational cross‐section for molecular association on the kinetics of crystal nucleation and critical temperature of crystallization is discussed. Dipole and quadrupole effects of an electric (magnetic) field and quadrupole effects of hydrodynamic potential of uniaxial flow are considered. Critical temperature of crystallization, free energy barrier of nucleation and nucleation rates are orientation‐dependent. Smaller orientational cross‐sections result in stronger anisotropy of the nucleation rates.

Molecular Beam Laser Spectroscopy of ReF: Rotational and Hyperfine Analyses of Two Bands near 557 nm

An extensive survey of the electronic spectrum of the ReF molecule has been carried out in the region 15 150-29 600 cm −1 using laser-induced fluorescence spectroscopy. The ReF molecules were produced by chemical reaction in a laser-generated plasma and cooled by supersonic expansion. Both isotopomers 185Re 19F (37.1%) and 187Re 19F (62.9%) were studied. The observed bands are interpreted as transitions involving two different lower Ω = 0 states and a number of different excited electronic states. Using a ring dye laser, two of the bands were recorded at 100-MHz resolution, which was sufficient to resolve hyperfine structure. The analysis of these bands shows that both arise from Ω = 0 ← Ω = 0 transitions involving a common lower state a ( v″) and two strongly interacting upper states b( v′) and c( v′ = 2), located at, respectively, 17 931 and 17 966 cm −1 above a. The b( v′) state exhibits an avoided crossing with an unidentified state. Dispersed fluorescence studies reveal the presence of two low-lying states located at 2750 and 4240 cm −1 above the a state. The energy difference between the two low-lying Ω = 0 states is not known; neither is it known which one is the ground state. The observed hyperfine structure is attributed to electric quadrupole effects.

Second- and third-harmonic generation from cubic centrosymmetric crystals with vicinal faces: phenomenological theory and experiment

We present a general phenomenological theory for optical second- and third-harmonic generation obtained in reflection from all cubic centrosymmetric single crystals whose faces have macroscopic C1υ symmetry, including vicinal faces with such symmetry. This extends earlier research [ Phys. Rev. B35, 1129 ( 1987)] for crystals with low-index faces. As a test of the theory we offer experimental results for anisotropic harmonic generation from vicinal, single crystals of Si, with and without an oxide layer, for which we use 130-fs, λ = 765 nm pulses. Overall there is good agreement between the phenomenological theory and experimental results. It is demonstrated that third-harmonic generation, which is dominated by bulk electric dipole contributions, can be used as a diagnostic of crystal orientation and crystal miscut angle. The intensity and the anisotropy of second-harmonic generation (SHG), which arise from surface electric dipole and bulk electric quadrupole effects, are seen to be sensitive to surface steps, an effect that also varies with surface oxidation. Finally, the use of vicinal surfaces allows us to identify bulk and surface contributions to SHG separately.

Erratum: Charge dependence and electric quadrupole effects on single-nucleon removal in relativistic and intermediate energy nuclear collisions

Single-nucleon removal in relativistic and intermediate energy nucleus-nucleus collisions is studied using a generalization of Weizsacker-Williams theory that treats each electromagnetic multipole separately. Calculations are presented for electric dipole and quadrupole excitations and incorporate a realistic minimum impact parameter, Coulomb recoil corrections, and the uncertainties in the input photonuclear data. Discrepancies are discussed. The maximum quadrupole effect to be observed in future experiments is estimated and also an analysis of the charge dependence of the electromagnetic cross sections down to energies as low as 100 MeV/nucleon is made.