Interchannel Interaction Research Articles

Strong impact of the giant resonance on the radiationless decay of the 4d vacancy in Xe: I. Decay of the 4d9np resonances

The influence of the interchannel interaction on the radiationless decay of the Xe 4d9np resonances is found to be extremely large due to the potential barrier effect. Interaction between the 5s5p–4dεf and 5p5p–4dεg decay channels reduces the decay transition amplitude associated with the outgoing g wave by a factor of about 3. The effect is confirmed by the good agreement between computed and measured photoionization cross sections and polarization parameters of the Xe 5p4mp levels.

Fourfold excitations, intra- and inter-shell correlations in the Auger decay of Kr 3d-np resonances

Many-electron effects in the photoionization of Kr near the 3d9np resonances were investigated theoretically. Cross sections for the population of the 4p4(1D)mp states, their alignment and orientation, and angular distribution of the Auger electrons were computed considering the resonance Auger effect as a coherent process. Probabilities of the radiative cascades following the resonant Auger effect were estimated quantitatively within the transition-array technique. The role of intra- and inter-shell correlations was investigated. Lineshapes computed, taking into account interchannel interaction, are in good agreement with the measured ones. Fourfold excitations of the Kr ground state were proposed to influence the resonance population, alignment and orientation of the 4p4np levels.

SURPRISES: when ab initio meets statistics in extended systems

The surface photoelectron and inner shell electron spectroscopy (SURPRISES) program suite performs ab initio calculations of photoionization and non-radiative decay spectra in nanoclusters and solid state systems by using a space-energy similarity procedure to reproduce the band-like part of the spectra. This approach provides an extension of Fano resonant multichannel scattering theory dealing with the complexity arising from condensed matter calculations at a computational cost comparable to that of molecules. The bottleneck of electron spectroscopy ab initio calculations in condensed matter is the size of the Hilbert space where the wavefunctions are expanded and the increase in number of final decay states in comparison to that of atoms and molecules. In particular, the diagonalization of the interchannel interaction to take into account the correlation between the double ion and the escaping electron is impracticable when hole delocalization on valence bands and electronic excitations are included in the model. To overcome this problem SURPRISES uses a 'space-energy similarity' approach, which allows the spreading of the Auger probability over the bands without tuning semi-empirical parameters. Furthermore, a completely new feature in the landscape of ab initio resonant decay processes calculations is represented by including energy loss through a statistical approach. Using the calculated lineshape as electron source, a Monte Carlo routine simulates the effect of inelastic losses on the original lineshape. In this process, the computed spectrum can be directly compared with acquired experimental spectra, thus avoiding background subtraction, a procedure not free from uncertainty. The program can exploit the symmetry of the system under investigation to reduce the calculation scaling and may compute photoemission and Auger decay angular distribution patterns including energy loss for the electrons emitted in resonance-affected photoionization processes. In this paper, we present general methods, computational techniques and a number of numerical tests applied to the calculation of Si K–LL and O K–LL Auger spectra from different SiO2 nanoclusters.

Interchannel interaction in orientation and alignment of Kr 4p4mp states in the region of 3d9np resonances

The interaction between intermediate channels which influence the population of Kr 4p4mp ionic states in the region of the 3d9np resonances by the photon-induced Auger decay was investigated. The most important influence on the investigated process stems from 4p5ϵ′ℓ and 3d9ϵ′ℓ channels.

Fast electron impact ionization of endohedral atoms

The differential generalized oscillator strengths (GOS's) for ionization of the s-subshells of the He and Ne atoms encapsulated inside a fullerene, C60 cage, along with the single differential cross sections for ionization by fast electrons, are calculated. It is shown that the modulation of the wave function of the ejected electron caused by the interference between the direct ejection and the waves scattered by the fullerene shell results in confinement resonances in the GOS's and the resulting impact ionization cross sections. When the energy transfer to the target is close to that of the giant plasmon resonance in C60, the interchannel interaction of the atomic ionization channels with the C60 ionization channels significantly influences the cross section for electron impact ionization of the confined atom.

Alternating-Current Conductivity for a Two-Channel InteractingQuantum Wire

We investigate theoretically the ac conductivity of a cleantwo-channel spinless quantum wire in the presence of bothshort-ranged intra- and inter-channel electron–electroninteractions. In the Luttinger-liquid regime, we formulize theaction functional of the system with an external time-varyingelectric field. The obtained expression of ac conductivity forthe system within linear response theory is generally anoscillation function of the interaction strength, the drivingfrequency as well as the measured position in the wire. Thenumerical examples demonstrate that the amplitude of acconductivity is renormalized by the both interactions, and the dcconductivity of the system with inter-channel interaction issmaller than that without inter-channel interaction.

Interchannel interaction of optical solitons.

We study interaction between two solitons from different frequency channels propagating in an optical fiber. The interaction may be viewed as an inelastic collision, in which energy is lost to continuous radiation due to small but finite third order dispersion. We develop a perturbation theory with two small parameters: the third order dispersion coefficient d(3), and the reciprocal of the interchannel frequency difference, 1/beta. We find that amplitude of the leading contribution to radiation emitted during the collision is proportional to d(3)/beta(2). The source term for this radiation is of the form that would be generated by a variation in the second order dispersion coefficient. In addition, the only other effects up to the combined third order of the perturbation theory are phase changes and position shifts of the solitons. Solitons propagating in a given frequency channel interact via radiation emitted due to collisions with many solitons from other frequency channels. We show that this intrachannel interaction effect, induced by many interchannel collisions, is identical to the radiation mediated intrachannel interaction effect observed for solitons propagating under the influence of disorder in the second order dispersion coefficient.

40-Gb/s x 4-channel all-optical multichannel limiter utilizing spectrally filtered optical solitons

We propose a novel all-optical multichannel limiter that uses spectrally filtered optical solitons. The periodic nonlinear optical fiber described herein can suppress the interchannel interaction caused by four-wave mixing. By applying this all-optical multichannel limiter to a 40-Gb/s /spl times/ 4-channel wavelength-division-multiplexing signal, minimum received optical powers at the bit-error rate of 10/sup -9/ were improved by more than 2 dB in all channels.

Two-steplaser excitation of the even parity 5p1/2np and nf J = 1,2 Rydberg levels of neutral tin

We report new experimental data on the even parity 5p1/2np and nf J = 1, 2 Rydberg series of tin excited fromthe 5p6s(3/2,1/2)1 intermediate level using a two-step laserexcitation technique in conjunction with an atomic beamapparatus. The Rydberg series 5pnf(1/2,5/2)2 (12⩽n⩽46) and 5pnp(1/2,1/2)1 (20⩽n⩽31) arereported for the first time, whereas the 5pnp(1/2,3/2)2(16⩽n⩽56) series have been extended to higherprincipal quantum number. The previously reported threep levels, 5p8p(3/2,3/2)0,2 and 5p8p(3/2,1/2)2, andthree f levels, 5p5f(3/2,5/2)1,2 and 5p5f(3/2,7/2)2,have also been detected. The inter-channel interaction among the5pnf(1/2,5/2)2 and 5p5f(3/2,5/2)2 channels has beenstudied using a two channel quantum defect theory.

Qualitative modification of the high energy atomic photoionization cross section

It is demonstrated that the nonrelativistic high energy omega-->infinity behavior of the photoionization cross section of an nl atomic subshell, sigma(nl)(omega), for l>0 is independent of l and is given by sigma(nl)(omega) approximately 1/omega(9/2), rather than the previously generally accepted sigma(nl)(omega) approximately 1/omega(l+7/2). Furthermore, for l = 1, although the exponent does not change, the coefficient is significantly altered. This modification of sigma(nl)(omega) is due to the interchannel interaction between ns photoionization channels and l not equal0 channels in the atom. As a result, for the photoionization of l not equal0 electrons, the single-particle approximation is never correct in the omega-->infinity limit. This has important consequences for sum rule calculations.

Long-haul WDM transmission using higher order fiber dispersion management

We propose a fiber dispersion management scheme for large-capacity long-haul wavelength division multiplexing (WDM) transmission systems that considers not only second- but also third-order dispersion characteristics using transmission fibers with opposite dispersion signs. It eliminates the waveform distortion of WDM signals that originates from the existence of third-order dispersion, which is a constraint placed on WDM capacity in conventional dispersion management, while reducing the interchannel interaction caused by the interplay of fiber nonlinearity and second-order dispersion. Design concept of the scheme is discussed to show the feasibility of using actual fiber parameters. An experimental investigation on transmission performance regarding the signal pulse format, nonreturn-to-zero (NRZ) and return-to-zero (RZ), and interchannel interaction caused by four-wave mixing (FWM) and cross-phase modulation (XPM) is described for optimizing WDM system performance. It is experimentally shown that RZ pulse transmission is possible without significant spectral broadening over a wide wavelength range in dispersion managed fiber spans. Using these results together with a wideband optical amplifier gain-bandwidth management technique, yields long-distance WDM transmission with the capacity of 25/spl times/10 Gb/s over 9288 km.

Long-haul 16 x 10 Gb/s WDM transmission experiment using higher order fiber dispersion management technique

We propose a dispersion management scheme for long-haul wavelength-division-multiplexed (WDM) transmission systems that considers not only second-, but also third-order dispersion using transmission fibers with opposite dispersion signs; it eliminates waveform distortion due to the existence of third-order dispersion with reducing interchannel interaction caused by fiber nonlinearity. With this technique, WDM transmission with a total capacity of 160 Gb/s is demonstrated over 9412 km.

The 2s 12p 4 autodetachment resonance in the C − negative ion

The calculations of the photodetachment cross section for the C − negative ion has been performed within the newly-developed many-body theory method, the RPAE interchannel interaction and dynamic relaxation and polarization corrections being included. The 2s 12p 4 shape resonance is shifted to a higher photon energy and broadens as compared to the resonance parameters determined earlier within the RPAE, which is consistent with the experimental evidence and the recent R-matrix calculations.

Two-way traffic flow: Exactly solvable model of traffic jam

We study completely asymmetric two-channel exclusion processes in one dimension. It describes a two-way traffic flow with cars moving in opposite directions. The interchannel interaction makes cars slow down in the vicinity of approaching cars in the other lane. Particularly, we consider in detail the system with a finite density of cars on one lane and a single car on the other. When the interchannel interaction reaches a critical value, a traffic jam occurs, which turns out to be of first-order phase transition. We derive exact expressions for the average velocities, the current, the density profile and the k-point density correlation functions. We also obtain the exact probability of two cars being in one lane of distance R apart, provided there is a finite density of cars on the other lane, and show that the two cars form a weakly bound state in the jammed phase.

Two-photon laser-optogalvanic spectroscopy of the odd-parity Rydberg series of krypton

We report new data on the odd-parity bound and autoionized Rydberg series of krypton using single-colour two-photon laser-optogalvanic spectroscopy. These series were excited from the and metastable levels. A total of 10 odd-parity , , , , , and unresolved (or ) Rydberg series are observed. The , , (or ) and Rydberg series have been observed up to n = 49, 44, 39 and 36 respectively. The interchannel interaction among the overlapping Rydberg series has been studied using the multichannel quantum-defect theory. In addition, the two-photon parity-forbidden Rydberg series excited from the level is also observed.

Electromagnetic waves propagation in real multimode waveguide structures

A power flow equation describing the power flow of electromagnetic waves in a real multimode waveguide represented by a linear multichannel trasmission system exhibiting an attenuation, dispersion, and an interchannel interaction is solved in three iterative ways. In the case of constant attenuation and constant propagation velocities in all channels and for the convolution interchannel interaction, a closed analytical solution of the problem is presented. Interesting forms of the solution, transfer function, and impulse response of the system which enable us to separate and compare the attenuation, dispersion, and coupling effects independently of each other are derived. The transfer function, the impulse response, and excitation conditions for their measurements are further discussed. Relations which make it possible to compare different experimental data obtained under specific excitation conditions in various laboratories are determined. Finally, a linear system with memory in time is studied and it is shown that the real multimode waveguide as a linear multichannel transmission system can be considered as a general linear system with memory in space.

Conductivity of an interacting two-channel Tomonaga-Luttinger model.

Conductivity of a coupled two-channel dirty Tomonaga-Luttinger model is calculated from the Mori formalism. We find that the conductivity becomes enhanced as the interchannel interaction is turned on even when the interaction is repulsive. This effect is opposite to those from the 2${\mathit{K}}_{\mathit{F}}$ charge-fluctuation coupling in systems with the channel separation 1/${\mathit{k}}_{\mathit{F}}$, and is considered to come from the suppressed charge-density-wave fluctuations.

Relativistic multichannel calculation of the Ne KLL and Ar L2M2,3M2,3 Auger transition rates.

The multichannel multiconfiguration Dirac-Fock method has been used to study the Ne KLL and Ar ${\mathit{L}}_{2}$${\mathit{M}}_{2,3}$${\mathit{M}}_{2,3}$ Auger-electron transitions. Final-state correlation effects are accounted for by simultaneously including several ionic configurations and ionization channels in the calculation of the final-state many-electron wave functions. Our computational approach is based on scattering theory, which properly accounts for the incoming wave boundary condition. The line intensities from our test calculation for Ne KLL transitions are in good agreement with earlier theoretical results and with experiment. The interchannel coupling is stronger for the final states of the Ar ${\mathit{L}}_{2}$${\mathit{M}}_{2,3}$${\mathit{M}}_{2,3}$ transitions, but the net effect on the line intensities is somewhat smaller than that for Ne. Even the most extensive multichannel calculations are not fully able to reproduce the measured total rate and the ratio of $^{3}$${\mathit{P}}_{0,1,2}$ to $^{1}$${\mathit{D}}_{2}$ transition rates. The remaining discrepancy in the branching ratios of Auger lines is attributed to the omission of initial-state configuration interaction, whereas the discrepancy between the measured and calculated total rates is suggested to be mainly due to the neglect of relaxation. Our results indicate that, in analogy to outer-shell photoionization, the final-state interchannel interaction does not in general affect the strongest Auger lines very much when the kinetic energy of the Auger electrons exceeds about 200 eV.

Reduced L1 level width and Coster-Kronig yields by relaxation and continuum interactions in atomic zinc.

Calculations of the level width \ensuremath{\Gamma}(${\mathit{L}}_{1}$) and the ${\mathit{f}}_{12}$ and ${\mathit{f}}_{13}$ Coster-Kronig yields for atomic zinc have been performed with Dirac-Fock wave functions. For \ensuremath{\Gamma}(${\mathit{L}}_{1}$), a large deviation between theory and evaluated data exists. We include the incomplete orthogonality of the electron orbitals as well as the interchannel interaction of the decaying states. Orbital relaxation reduces the total rates in all groups of the electron-emission spectrum by about 10--20 %. Different, however, is the effect of the continuum interaction. The ${\mathit{L}}_{1\mathrm{\ensuremath{-}}}$${\mathit{L}}_{23}$X Coster-Kronig part of the spectrum is definitely reduced in its intensity, whereas the MM and MN spectra are slightly enhanced. This results in a reduction of Coster-Kronig yields, where for medium and heavy elements considerable discrepancies have been found in comparison to relativistic theory. Briefly, we discuss the consequences of our calculations for heavier elements.

Interchannel Interactions and Relaxation in the 2p Auger Spectra of Mg-like lons

Relativistic Auger rates for the 2p spectra of Mg-like ions have been calculated in the atomic range 13 ⩽ Z ⩽ 36. We used the multiconfiguration Dirac-Fock method but beyond a simple frozen-orbital approach we include also relaxation for the bound electrons and the interchannel interaction between the continuum states. Both effects may alter the individual transition rates remarkably. This is analysed for a few selected states within the isoelectronic sequence. Weak transitions within the 2p spectra can be changed by an order of magnitude because of the continuum coupling. The influence of both effects for higher-Z ions is reduced but still remain visible.