Reactions induced in (CF3I) n clusters by femtosecond UV laser pulses

The excitation and ionization of CF₃I molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CF₃I molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CF₃I) _n clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I ₂ ⁺ ion is produced in reactions induced in (CF₃I) _n clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I ₂ ⁺ ions with characteristic times ??₁ ?? 1 ps and ??₂ ?? 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results.     

Modulation of the shape of the photon echo pulse by a pulsed magnetic field: Zeeman splitting in LuLiF4:Er3+ and YLiF4:Er3+

A spectroscopy method has been proposed involving a change in the time shape of the echo signal in the presence of a perturbation, which splits the frequencies of the transitions of two or more ion subgroups of the echo-active ions. This method has been applied to optical systems in which the Zeeman effect is manifested. The ion transition frequencies of ions are switched by a weak pulsed magnetic field acting during the time of the radiation of the photon echo pulse. The modulation of the photon echo signal shape was observed in LuLiF₄:Er³⁺ and YLiF₄:Er³⁺. The time interval between the two nearest minima corresponds to the accumulated phase of the electric dipole moment ?? and makes it possible to determine the difference of the g factors of the ground and excited ⁴ F _9/2(I) states of the Er³⁺ ion in the LuLiF₄ the YLiF₄ matrices for the known amplitude of the pulsed magnetic field. It has been shown that the echo response of the system can be programmed by the weak magnetic field pulses.     

Experimental preparation of entangled Bell’s vacuum-single exciton and vacuum-biexciton states for pair centers of neodymium ions in a crystal

The process of low temperature laser excitation of neodymium ion M pair centers in CaF₂ crystals at the ⁴I_9/2-⁴G_5/2 optical transition is analyzed. It is shown that maximally entangled Bell’s vacuum-single exciton and vacuum-biexciton states are experimentally prepared when irradiating these crystals by nanosecond laser pulses.     

Plasma satellites of X-ray lines of ions in a picosecond laser plasma

We present the results of our measurements of the spectra for multicharged ions in a plasma produced by moderately intense (about 10¹⁷Wcm^?2) picosecond laser pulses. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed spectrum for the plasma satellites of the Lyman Ly_α doublet of the hydrogenic F IX ion in a dense plasma was modeled theoretically. The resulting doublet profile was shown to have a complex structure that depends non-trivially both on the plasma density and on the frequency and amplitude of the plasma oscillations. The positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude of (4–6)×10⁸Vcm^?1 and a frequency near (0.7–1)×10¹⁵s^?1. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements and estimates of this quantity. Our theoretical analysis allowed explanation of the emission spectra observed when flat fluoroplastic targets were heated by intense picosecond laser pulses.     

Control of cluster multielectron ionization in ultraintense laser fields

We performed classical molecular dynamics simulations to explore the controllability of the inner ionization process in Xe_n clusters (n = 2?2171), driven by ultraintense infrared Gaussian laser fields (peak intensity I _M = 10¹⁵?10¹⁸ W cm^?2, temporal pulse length τ = 10?100 fs, and frequency ν = 0.35 fs^?1). Controllability of ion charge abundances and of their spatial distributions inside the cluster emerges from the different pulse length dependences of classical barrier suppression ionization (BSI) and of electron impact ionizations (EII), as well as from the time scale of the Coulomb explosion (CE). For large clusters (Xe₂₁₇₁), low intensities (10¹⁵ W cm^?2), and long pulses (τ = 100 fs), EII is the dominating ionization channel, which favors the formation of maximum charged ions (Xe¹⁰⁺, Xe¹¹⁺) in the cluster center. In contrast, BSI forms an inverse radial charge ordering with the highest charges in the exterior cluster shells. This suggests that the production of the two inverse radial charge distributions with an equal average ion charge can be forced by the choice of multiple pulses with different intensities and pulse lengths. At high intensities (10¹⁷?10¹⁸ W cm^?2), where EII is insignificant and CE sets in much earlier, the BSI radial charge ordering and the enhancement of the ion charges beyond the single-atom limit by the ignition effect is observed only for short pulses.     

Generation of fast ions in femto-and picosecond laser plasmas at low intensities of the heating radiation

X-ray spectra from Teflon targets irradiated by laser pulses with a duration of 60 fs to 1 ps have been investigated experimentally. It is shown that, when the contrast of the laser pulse is sufficiently low, the effect of self-focusing of the main laser pulse in the plasma produced by the prepulse can significantly enhance the generation efficiency of fast particles. In this case, ions with energies as high as ～1 MeV are observed at relatively low laser intensities, q _las ≈ (4–6) × 10¹⁶ W/cm².     

Ab-initio electronic structure studies of mobility paths in fast-ion conductors—I: Results for MI4−3 clusters

We report results of minimum-basis Pseudopotential Hartree-Fock studies of MI₄^?3 clusters (M = Na⁺, K⁺, Ag⁺, and Cu⁺), and of HgI₄^?2. The calculations are designed to characterize local-site effects on mobility paths in solid state electrolytes. We observe qualitatively correct behavior, with Ag⁺ predicted to be the most mobile ion. Quadrupolar polarizability of the metal ion, which is produced by s-d mixing, lowers the energy of trigonal transition state, thus accounting for the observation that quadrupole polarizable species are ideal mobile ions in close-packed halide frameworks. Mulliken populations show that there is considerable local covalency, so that electrostatic potential studies must be done very carefully. Expansion of the I₄ tetrahedron lowers the barrier energy.     

Generation of frequency shifted picosecond pulses with low temporal jitter

Transient stimulated Raman scattering is used for the generation of a frequency shifted picosecond light pulse; part of this Raman shifted pulse is subsequently coherently scattered at a material excitation of a second Raman cell. Starting with the second harmonic pulse (t_p = 4 ps) of a mode-locked Nd : glass laser system, both the stimulated and the coherently produced pulses have durations of 2.3 ps at different wavelengths. By the appropriate choice of the Raman medium pulses between 13 000 and 21 000 cm^-1 can be generated. The coherent generation process minimizes the temporal jitter between the two pulses and allows to obtain a high time resolution of better than 0.3 ps in excite and probe experiments.     

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si_xO_yF_z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF_x⁺ (x ≤ 5) and F⁺ ions etching effect, Si_xO_yF_z passivation and ion bombardment.     

Isotope-selective ionization utilizing molecular alignment and non-resonant multiphoton ionization

We demonstrate laser nitrogen isotope separation, which is based on field-free alignment and angular-dependent ionization of ¹⁴N₂ and ¹⁵N₂ isotopologues. A linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) creates rotational wave packets in the isotopologues, which periodically revive with different revival times as a result of different moments of inertia. Another linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) ionizes one of the isotopologues selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio R [=I(¹⁵N₂ ⁺)/I(¹⁴N₂ ⁺)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.     

Optical investigation of charge-transfer transitions in spinel Co3O4

Optical transitions in normal-spinel Co₃O₄ have been identified by investigating the variation of its optical absorption spectrum with the replacement of Co by Zn. Three optical-transition structures were located at about 1.65, 2.4, and 2.8 eV from the measured dielectric function of Co₃O₄ by spectroscopic ellipsometry. The variation of the absorption structures with the Zn substitution (Zn_xCo_3−xO₄) can be explained in terms of charge-transfer transitions involving d states of Co ions. The 1.65 eV structure is assigned to a d-d charge-transfer transition between the t_2g states of octahedral Co³⁺ ion and t₂ states of tetrahedral Co²⁺ ion, t_2g(Co³⁺)→t₂(Co²⁺). The 2.4 and 2.8 eV structures are interpreted as due to charge-transfer transitions involving the p states of O²⁻ ion: p(O²⁻)→t₂(Co²⁺) for the 2.4 eV absorption and p(O²⁻)→e_g(Co³⁺) for the 2.8 eV absorption. The observed gradual reduction of the 1.65 and 2.4 eV absorption strength with the increase of the Zn composition for Zn_xCo_3−xO₄ can be explained in terms of the substitution of the tetrahedral Co²⁺ sites by Zn²⁺ ions. The crystal-field splitting Δ_Oh between the e_g and the t_2g states of the octahedral Co³⁺ ion is estimated to be 2 eV.     

Circularly polarised attosecond pulses: generation and applications

ABSTRACT

Molecular high-order harmonic generation(MHOHG) is simulated for H⁺₂ in the nonlinear nonperturbative regime of laser-molecule interactions with ultrashort intense circularly polarised laser pulses. It is shown that combinations of co-rotating or counter-rotating pulses produce laser-induced Coriolis forces with electron-parent ion recollisions, thus enhancing circularly polarised MHOHG, the source of circularly polarised attosecond pulses. Such pulses can be used to induce electron attosecond currents for the generation of attosecond magnetic field pulses, new tools for molecular attomagnetism.     

Electrochemical luminescence of Mg1−xCaxIn2O4:Er electrodes

Improvement for electrochemical luminescence (ECL) property of MgIn₂O₄ is attempted by partial exchange of Mg²⁺ ion in MgIn₂O₄ to Ca²⁺ ion. Mg_1−xCa_xIn₂O₄ solid solution was obtained in the region 0<x<0.4. Efficiency for ECL per unit current for Mg_1−xCa_xIn₂O₄:Er³⁺ increased with the increase in the ratio of Ca²⁺ ion, and showed a peak at x=0.25 and then decreased steeply. ECL efficiency for other rare-earth ion-(RE:Sm, Eu, Ho) doped Mg_1−xCa_xIn₂O₄ also increased comparing with those for MgIn₂O₄:RE. This Ca²⁺ addition effect on the ECL efficiency seems to be caused by the improvement of the efficiency for the impact activation.     

Constants of quenching of 5s 22 D 5/2, 3/2 CdII levels by argon

Constants of quenching of the CdII ion Beutler levels by argon were experimentally determined. Excited cadmium ions in the 5s ^{2 2} D _{5/2, 3/2} states were produced by sputtering metal cadmium with alpha-particles at a temperature of 240°C. The quenching constants for the 5s ^{2 2} D _5/2 and 5s ^{2 2} D _3/2 CdII ion levels were found to be 1.3×10^?10 and 1.8×10^?10 cm³ s^?1, respectively.     

Using ion imaging to analyze higher-order moments of the angular distributions of photofragments

We investigate the effect of the hexadecapole (K=4) polarization moment on the spatial distributions of angular momenta for atoms produced during the photodissociation of diatomic or triatomic molecules by polarized radiation. We derive general expressions for the angular distributions of the atomic density matrix for K = 2, 4 and expressions for the corresponding anisotropy parameters that contain all information on the photodissociation dynamics. We show that these anisotropy parameters can be experimentally determined by using ion imaging. We consider oxygen atoms in the ¹ D ₂ state aligned with respect to the orbital angular momentum as an example and provide ion images of the signals that correspond to the population of the atomic magnetic sublevels ¦m¦ = 0, 1, 2. We show the contributions from the second-and fourth-rank state multipoles to the angular distributions of the atomic density matrix to be comparable in magnitude and significantly different in form.     

EPR investigation on exchange coupled Mn2+ pairs in (CH3)4NCdCl3

EPR experiments were performed at Q-band and 300 K on Mn²⁺ doped (CH₃)₄NCdCl₃. Beside the single ion resonance many weak lines could be observed which can be attributed to nearest neighbour pairs of Mn²⁺ lying along the crystallographic c-axis. The spectra can be described using a Hamiltonian for strongly exchange coupled pairs. The obtained data show that the ionic separation varies in the different spin states. So an additional interaction occurs on the Mn²⁺ dimer, which can be interpreted as an exchange striction effect.     

Stoßdissoziation von H 2 + - und D 2 + -Ionen

The angular and energy distribution of protons produced by collision-induced dissociations of H ₂ ⁺ ions with energies of 10 and 20 keV were measured in a parabola spectrograph. From these measurements the velocity distribution of the protons in the center of mass system of the H ₂ ⁺ ion can be calculated. This gives information about the type, the abundance, and the anisotropy of the processes involved. The most frequent transitions leading to dissociations are the excitation of the 2pσ_u state, the ionisation of the H ₂ ⁺ ion, the transition into the vibrational continuum, and the electron capture into the 1³ σ _u ⁺ state of the hydrogen. It is shown that the cross section for an electronic transition depends on the velocity of the ion, the distance of the nuclei in the ion, the angle between the internuclear axis and the direction of the primary ion beam, and the excitation energy of the target. The fraction of protons produced by vibrational excitation increases with increasing atomic number of the target. Concerning electronic transitions D ₂ ⁺ ions equal H ₂ ⁺ ions of the same velocity.     

Controlled Cu content of electrodeposited CoCu nanowires through pulse features and investigations of microstructures and magnetic properties

CoCu alloy nanowire arrays embedded in anodic alumina template were fabricated by ac pulse electrodeposition. Different off-times between pulses in an electrolyte with constant concentration of Co⁺² and Cu⁺² and acidity of 4 were employed. The effect of deposition parameters on the alloy contents, microstructures and magnetic properties of Co_xCu_1−x nanowires were studied. It is shown that Co content decreased by increasing the off-time between pulses in a wide range (x = 0.53-0.07). These results are in consistence with saturation magnetization, which was reduced with increase in the off-time between pulses. It was also found that by optimizing the off-times, it is possible to fabricate CoCu nanowires with mixed phase of hcp Co, fcc Cu and fcc CoCu crystal phase.     

Theoretical explanations to the EPR g factors for Er3+ ion in La2−xSrxCuO4 superconductor

The electron paramagnetic resonance (EPR) g factors g_∥ and g_⊥ for Er³⁺ ion in La_2−xSr_xCuO₄ superconductor are theoretically explained by using the perturbation formulas of g factors for a 4f¹¹ ion in tetragonal symmetry. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of different states are included. The related crystal field parameters are calculated from the superposition model and the local structural parameters of the impurity Er³⁺ occupying the host La³⁺ site, and the superposition model parameters used in this work are comparable with those for similar tetragonal Er³⁺ centers in some zircon compounds in the previous work. The theoretical studies on g factors of Er³⁺ ion in this work would be of some use to experimentalists doing EPR on La_2−xSr_xCuO₄ (or other superconductors) with Er dopants.     

Pulse-induced mechanoluminescence of ultraviolet-irradiated SrAl2O4:Eu,Dy phosphors

The SrAl₂O₄:Eu,Dy phosphors prepared by solid state reaction technique in a reduced atmosphere of 95% Ar+5% H₂ exhibit very intense mechanoluminescence (ML) which can be seen in daylight with naked eye. When the phosphors are deformed by the impact of a low-power electric hammer, initially the ML intensity increases with time, attains a maximum value and then decreases with time. After the threshold pressure, the peak of ML intensity I_m and the total ML intensity I_T increase with the increasing value of the impact pressure. For the ML excited by the pressure pulse of short duration, two decay times of ML are observed; however, for the ML excited by the pressure pulse of long duration, only one decay time is observed. The ML intensity decreases with successive applications of pressure on SrAl₂O₄:Eu,Dy phosphors. For the low applied pressure in the range below the limit of elasticity recovery of ML intensity takes place when the sample is exposed to ultraviolet (UV) light. This fact indicates that the vacant traps produced during the application of pressure pulses get filled during the exposure of the sample to UV light. The ML in the elastic region of SrAl₂O₄:Eu,Dy phosphors can be understood on the basis of the piezoelectrically induced detrapping model. The non-irradiated SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors exhibit ML during the fracture of the compact mass of phosphors whose ML intensity is less when compared to that of the UV-irradiated compact masses. The ML induced by pressure pulses may be useful for determining the magnitude and rise time of unknown pressure pulses and to determine the lifetime of charge carriers in shallow traps.