Electron paramagnetic resonance of Fe3+ in orthorhombic KNbO3

EPR spectra of KNbO₃:Fe single crystals are obtained in the - 10–110°C temperature range. The angular dependence of resonant lines is well reproduced by spin Hamiltonian parameters relevant to a Fe³⁺ impurity ion substituted to Nb ion in KNbO₃ crystal. The temperature behaviour of resonant lines is explained by a quadratic dependence of axial parameter D vs polarization P_s of the form D = βP²_s in the orthorhombic phase.     

Experimental study of the resonance radiation group delay in degenerate systems

The dependence of the polarization-and intensity-modulation group delay on the polarization of electromagnetic wave was studied experimentally for different transitions between the hfs components of the ⁸⁷Rb D₁ absorption line. It was found that the polarization-modulation delay strongly depends on the degeneracy structure of resonant transition and, in the general case, on the ellipticity of light-wave polarization. It is demonstrated that the polarization-modulation delay does not occur for the transitions not involving dark states. The polarization delay was studied as a function of the polarization ellipticity angle. The intensity-modulation delay was measured for the resonance radiation to show that it is observed for all ⁸⁷Rb D₁-line transitions and is independent of polarization.     

Two-exciton transition in the antiferromagnetic KNiF3 and K2NiF4

For the sharp band located at 31,200 cm^?1 in the three dimensional antiferromagnetic KNiF₃, the dependence of the oscillator strength on the Ni ion concentration and the stress-induced linear dichroic spectrum are studied. The polarization dependence of the corresponding band in the two dimensional antiferromagnetic K₂NiF₄ is also measured. The weak structure located at 30,780 cm^?1 is assigned as two-exciton transition, and the band at 31,200 cm^t?1 as a two-exciton transition accompanied with a T_1u phonon.     

Selection rules for direct creation of biexcitons by giant two-photon absorption

The selection rules for direct creation of biexcitons by two-photon absorption processes are discussed on symmetry basis. A detailed analysis is performed for CuCl and CdS crystals, with the energy levels given by Bassani et al. It is found that only Г^biex₁ states can be created by giant two-photon absorption when the photons have the same frequency. The polarization dependence is given for the other cases.     

Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells

We present a detailed study of the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration ofp_s2.8×10¹² cm², bothp- ands-polarized absorptions have been observed and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger-Kohn type calculations. The photoconductivity is surprisingly insensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsitivity.     

Magneto-optical absorption spectrum of D- Ion in GaAs-Ga0.75Al0.25As quantum well

The magneto-optical absorption spectrum of a D^- ion in a GaAs-Ga_0.75Al_0.25As quantum well is calculated. We used the variational method based on a two orbital picture of a D^- ion, in which each single electron orbital is represented by a linear combination of anisotropic Gaussian orbitals. The calculated magnetic field dependence of the binding energy of a D^- ion agrees semi-quantitatively with the experimental result. In a magnetic field perpendicular to the well interface, the energies of the one-electron excited states of a D^- ion are completely quantized, and broadening is essential for the calculation of the line shape of the magneto-optical absorption spectrum. We considered two types of broadening effect, lifetime broadening and inhomogeneous broadening. Only the lifetime broadening effect reproduces fairly well the observed line shape of the magneto photo-conductivity spectrum. The assumed value of the lifetime is consistent with the measured Hall mobility. The effects of correlation on the one electron excited states of a D^- ion are also discussed.     

Contribution of hexadecapole alignment to the polarization of quadrupole emission under laser excitation conditions

The linear polarization of quadrupole emission by the J=2-J ₀=0 transition under conditions of laser excitation in a gas medium is studied. Cases of excitation through dipole and quadrupole absorption of monochromatic laser radiation are considered. Taking into account the anisotropy of collisional relaxation, the contributions of polarization moments of the second and fourth ranks, i.e., those with usual and hexadecapole alignments, to the signal of linear polarization of quadrupole emission are calculated. The dependence of this signal on the laser frequency, the density of the gas medium, and the angles determining the orientation of the system of axes of observation of light polarization relative to a laser ray is studied. The numerical calculations of contributions of usual and hexadecapole alignment to the signal of linear polarization are made for the magnetic quadrupole transition J=2-J ₀=0 between the states 2p ⁵(² P ₁ ^2/0 )3p′[3/2]₂ and 2p ⁵(² P ₁ ^2/0 )3s 3s′[1/2]⁰ of neon atoms in the xenon atmosphere.     

Electron-lattice interaction of Ag− and Cu− centers in alkali halides

Absorption, emission, and excitation spectra of Ag^? centers in KCl, RbCl, CsCl, and CsBr are measured at low temperatures. The positions of theA emission bands are slightly different afterC andA band excitation, respectively. This is believed to be due to the existence of two different types of minima in the adiabatic potential energy surface of the³ T _1u state. The symmetry of the energy minima in the¹ T _1u state is trigonal for KCl∶Ag^? and Cu^?, but tetragonal for CsBr∶Ag^?. This becomes evident from the polarization properties of the emission. The energy and temperature dependence of the polarization is discussed. Uniaxial stress causes polarized emission of Ag^? and Cu^? centers measured from LHeT to 100 K. This is due to a splitting and mixing of the relaxed excited states by the stress. The effects are used to calculate the coupling constants between thep electron and theE _g andT _2g lattice modes. They are compared with predictions from the point-charge model for different lattice structures. A new assignment of the absorption bands of KCl∶Cu^? to the excited states of Cu^? is established on measurements of emission spectra and lifetimes.     

Polarized photoluminescence from bound magnetic polarons in (Cd,Mn) Se

Luminescence from Cd_1-xMn_xSe, with x～10^-1, shows strong circular polarization in the presence of a weak magnetic field. The polarization saturates at fields much smaller than does the magnetization. The carrier-Mn²⁺ exchange interaction is responsible for the field and temperature dependence of the polarization. At high temperatures, the polarization is similar to that inferred from band splittings; at lower temperatures, it is modified by bound magnetic polaron effects and a spin diffusion bottleneck.     

Reciprocal and nonreciprocal magnetic linear birefringence in the γ-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript> sesquisulfide

A study has been made of the spectral dependence of the Cotton-Mouton effect (CME) quadratic in magnetic field, nonreciprocal birefringence (NB) linear in magnetic field, and the Faraday effect (FE) in the cubic magnetic semiconductor γ-Dy₂S₃. Unlike the FE, the CME and the NB in this crystal are anisotropic, with the pattern of the anisotropy being dependent on the photon energy. The dependence of the CME and NB dispersion on the direction of the magnetic field B indicates contribution from a variety of electronic transitions and mechanisms to these phenomena. It is shown that the resonant contributions to the CME and NB in the transparency region originate from electronic transitions near E?3.4 eV (beyond the band edge E _g=2.8 eV), which are likely transitions from the localized ground state of the Dy³⁺ ion to states derived from mixing of the band and 4f ^N?1 5d states of the dysprosium ion. The character of the CME anisotropy in the transparency region and near the local electronic transition ⁶ H _15/2 → ⁶ F _3/2 connecting states of the unfilled 4f shell of the Dy³⁺ ion suggests the presence of a strong axial component of the crystal field acting on the rare earth ion.     

Applications of photoelectron spectroscopy to molecular propertles: XVIII. The vertlcal ionization potentials of diphosphene as calculated by perturbation corrections to koopmans' theorem

The vertlcal ionization potentials (VIP's) of dimethyl diphosphene have been computed using perturbation corrections to Koopmans' theorem. These corrections allow an estimate of the effects of polarization and correlation, and show for this molecule an important contribution of the specific correlation of the ion for the ²A_g and ²B_u states. The results predict for the first three VIP's the ordering ²A_g, ²A_u, ²B_u, in agreement with our previous assignment.     

Neon 3p-excitation by proton impact (100 keV-1 MeV): Cross sections and line polarization

The excitation of all ten levels of the neon 2p ⁵3p configuration by proton impact (100 keV-1 MeV) has been investigated by the spectral analysis of photon emission. Absolute emission cross sections have been obtained by calibration with a standard light source. Cascade effects are shown to be very important especially in the case ofJ=1 levels. For the 3p(¹ S ₀) level, which we studied additionally for electron impact excitation (100 eV-1 keV), our experimental cross sections are compared with the first Born approximation. Furthermore the polarization of sixteen 3p—3s emission lines has been measured as a function of impact energy. The energy dependence of the line polarization is characterized by theJ quantum numbers of the atomic states involved in the respective transition. An anomalous polarization of all lines originating from the decay ofJ=1 levels has been found and is referred to dominant cascade effects.     

Polarization of single particle states in heavy ion induced nuclear reactions within the two center shell model

In “slow” nucleus-nucleus collisions the single particle states will adjust continuously to an instantaneous two center potential. Transfer reactions will occur between polarized rather than between asymptotic states. In order to employ two center states in reaction calculations, an expansion in terms of asymptotic states with good angular momentum is required. This expansion is formulated, and equations for the expansion coefficients are derived. Model calculations for the system ⁴⁰Ca+¹⁶O indicate that the polarization of unoccupied proton states in ⁴⁰Ca is strong, while it is very weak for the tightly bound 1p_{$\text{1}\text{2}$} proton in ¹⁶O. The dependence of the polarization effect on several relevant parameters is discussed.     

Molecular orbital analysis of the CO32− ion by studies of the anisotropic X-ray emission of its components

The K X-ray emission spectra of carbon and oxygen in calcite single crystals CaCO₃ were measured. Owing to the polarization of the radiation the shape of both spectra shows a pronounced angular dependence, which makes it possible to separate the contributions of the π- and σ-valence electrons of the CO₃^2? ion to the X-ray spectra, and to determine the sequence and the binding energies of the valence orbitals.     

Magnetoelectric and magnetoelastic properties of easy-plane ferroborates with a small ionic radius

The magnetic, magnetoelectric, and magnetoelastic properties of RFe₃(BO₃)₄ ferroborates are studied. The measurement of the field dependences of the magnetoelectric polarization along the a axis in holmium ferroborate and in the mixed composition Ho_0.5Sm_0.5Fe₃(BO₃)₄ revealed the following dependences for easy-plane ferroborates: (a) the longitudinal and transverse magnetoelectric effects have the opposite signs and (b) magnetically induced polarization changes its sign in a field close to the field of exchange between rare-earth and iron ions. These dependences agree well with theoretical predictions based on the symmetry of the compounds. The relatively low f-d exchange field in holmium ferroborate (about 20 kOe), which magnetizes the rare-earth subsystem, causes smaller polarization jumps (about 30 ??C/m²) in fields lower than 10 kOe as compared to the jumps in other easy-plane ferroborates (R = Sm, Nd). The increase in the electric polarization induced in HoFe₃(BO₃)₄ in magnetic fields higher than 100 kOe (200?C300 ??C/m²) is found to be significantly smaller than in neodymium ferroborate, which indicates a substantial dependence of the magnetoelectric effects on the electronic structure of a rare-earth ion.     

Secondary ion emission from Si under nitrogen ion bombardment

The yield and energy distribution of positive secondary ions emitted from Si under N₂⁺ ion bombardment were measured. The obtained mass peaks correspond to three types of secondary ion species, that is, physically sputtered ions (Si⁺, Si₂⁺), chemically sputtered ions (SiN⁺ Si₂N⁺) and doubly charged ions (Si²⁺). The dependence of secondary ion emission on the primary ion energy was studied in a range of 2.0–20.0 keV. The yields of physically and chemically sputtered ions were almost independent of the primary ion energy. The yield of the doubly charged ion strongly depended on the primary ion energy. The energy distribution of secondary ions of the three types showed the same dependence on the primary ion energy. The most probable energy of the distribution increased with the primary ion energy. On the other hand, for the energy distribution curves of sputtered ions, the tail factors N in E^?N were constant and showed a m/e dependence.     

Polarization effects in ionizing thermal energy collisions of laser-excited Ne(3p 3 D 3) atoms with Ar atoms

Using transverse and longitudinal excitation of a collimated metastable Ne(3s ³ P _2.0) beam with average velocities of 500, 800, and 1,200 m/s by means of a single mode dye laser on the²⁰Ne(3s ³ P ₂→3p ³ D ₃) transition, we have investigated ionizing collisions of polarized Ne(3s ³ P ₂) and Ne(3p ³ D ₃) atoms with Ar atoms. The product electrons were energy analyzed with high resolution (9–25 meV). The resulting Ne(3p ³ D ₃) electron spectra exhibit a strong dependence on the three types of laser polarization (π _∥,π_⊥, σ_?), chosen to prepare the excited atoms. In contrast, the Ne(3s ³ P ₂) spectra are only weakly dependent on polarization. Detailed model calculations have been carried out for the Ne(3p)+Ar cross sections, using computed excited-state potential curves, semi-empirical ionic potentials, and local autoionization width functions. A semiclassical closecoupling method is applied to describe the evolution of the polarized collision system in the coupled entrance channels. It is found that a single autoionization widthΓ(R) is not sufficient to describe the measured polarization effects properly. The dependence ofΓ on the initial and final state is expressed in terms of few reduced electronic transition matrix elements, which are determined by comparison of measured and calculated total cross sections and Ar⁺(² P _3/2)/Ar⁺(² P _1/2) branching ratios for ionizing collisions of the various Ne(3pJ=1,2,3) multiplet states with Ar. The matrix elements corresponding to Ar(3pσ)→Ne(2pσ) electron transfer during autoionization are found to dominate, but Ar(3pπ)→Ne(2pπ) transfer has also to be included. The resulting calculated electron spectra reproduce the measured polarization effects in a semi-quantitative way.     

Multi-photon absorption in mercury

Three-and four-photon resonant excitations of the mercury atom from its ground state have been observed and their dependence on the polarization of the incident light investigated. The energies of the nG states (n = 5 to 13) have been measured. In addition two photon excitation from the ground state to the 6³P states (J = 1 and 2) were observed. The pressure dependence of the relative signal sizes is briefly reported.     

Magnetooptical properties of a molecular D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>-ion in a quantum wire

In the framework of a model of zero-range potential, the problem of bound states of an electron in the field of two D0 centers (a two-center problem) in a semiconductor quantum wire is considered in the presence of a longitudinal magnetic field. It is shown that the magnetic field produces a significant shift of g and u terms and stabilizes the D ₂ ^? states in quantum wires. It is found that, in the case of transverse polarization of light, the spectral dependence of the photoionization cross section of a D ₂ ^? center exhibits the quantum-confined Zeeman effect with strongly pronounced oscillations of interference nature.