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121.
Alfredo De Rossi Gaetano Assanto Stefano Trillo William E. Torruellas 《Optics Communications》1998,150(1-6):390-398
We have identified a family of (2+1)D spatial solitary waves which can stably propagate in bulk media in the presence of coexisting diffraction, self-focusing Kerr and quadratic nonlinearities. In a conspicuous range of excitation conditions close to the stationary solutions, the emerging wavepackets are immune to the detrimental occurrence of filamentation and collapse, typical of pure Kerr media. The presence of a second-order contribution to the cubic nonlinear response is, therefore, able to prevent optical damage in applications relying on self-guidance. We show that the cross-phase modulation plays an important effect on stability. Our estimate shows that the effects of the cubic susceptibility cannot be neglected below a certain beam size in realistic crystals (e.g. KTP or similar). 相似文献
122.
C. Fahlander G. de Angelis D. Bazzacco S. Beghini F. Brandolini D. Cline L. Corradi M. De Poli E. Farnea A. Gadea T. Härtlein S. Lunardi G. Montagnoli D. R. Napoli C. M. Petrache Z. Podolyák C. Rossi Alvarez F. Scarlassara A. M. Stefanini C. Y. Wu 《Acta Physica Hungarica A》1998,7(1):109-110
Two-phonon γ-vibrational states in166Er have been populated using Coulomb excitation. The Kπ=4+ component of the vibration appears to be fragmented over several states, whereas only one Kπ=0+ state is observed. 相似文献
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126.
Theory of power coupling between multimode optical fibres 总被引:1,自引:0,他引:1
In this paper power coupling between two multimode optical fibres is investigated. A formalism (based on a geometrical approach) suitable for analysing any coupling configuration between fibres with any index profile and any radiance distribution is presented. The model is applied to obtain coupling losses both in uniformly excited parabolic- and step-index fibres, in the presence of all kinds of coupling errors. Numerical results of extensive utility are shown and useful asymptotic expressions of coupling efficiency, valid for small values of coupling error parameters, are derived together with some practical rules for error combination. Mention is also made of some experimental results we have obtained, which corroborate some previous assertions. The work can supply a useful tool in the design of joints and connectors between single fibres or optical cables. 相似文献
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Ohne Zusammenfassung 相似文献
129.
Gary D. Bent Ralph H. Bartram Angelo R. Rossi Peter J. Kemmey 《Journal of Physics and Chemistry of Solids》1979,40(7):493-502
The energies of the ground state and low-lying excited states of the N4? defect in KN3 have been calculated using ab initio techniques. A rectangular equilibrium geometry with dimensions X = 2.76 and Z = 2.47 a.u. and ground state symmetry of Γ4+ was determined by calculating N4? as a free radical. For this ground state the unpaired electron is in a π orbital which is consistent with the experimental hyperfine tensor only if one edge of the N4? radical is parallel to the c axis in KN3. These results were used to calculate the X2Γ4+ state of N4? in the crystal field of KN3, yielding an energy of ?217.899 Hartrees. The isotropic hyperfine constant was calculated to be a = 2.1 G and the components of the anisotropic hyperfine tensor as Bxx = ?3.4 G, Byy = 7.0 G and Bzz = ?3.6 G, in good agreement with experimental and INDO results. Several excited states were calculated for the N4? defect in KN3. When an estimate was made of the correlation energy, the transition energy of the X2Γ4+→A2Γ3? transition agreed well with the peak energy of the 780 nm absorption band which has been attributed to N4?. 相似文献
130.
We study the distributions of the number of visits for some noteworthy dynamical systems, considering whether limit laws exist by taking domains that shrink around points of the phase space. It is well known that for highly mixing systems such limit distributions exhibit a Poissonian behavior. We analyze instead a skew integrable map defined on a cylinder that models a shear flow. Since almost all fibers are given by irrational rotations, we at first investigate the distributions of the number of visits for irrational rotations on the circle. In this last case the numerical results strongly suggest the existence of limit laws when the shrinking domain is chosen in a descending chain of renormalization intervals. On the other hand, the numerical analysis performed for the skew map shows that limit distributions exist even if we take domains shrinking in an arbitrary way around a point, and these distributions appear to follow a power law decay of which we propose a theoretical explanation. It is interesting to note that we observe a similar behavior for domains wholly contained in the integrable region of the standard map. We also consider the case of two or more systems coupled together, proving that the distributions of the number of visits for domains intersecting the boundary between different regions are a linear superposition of the distributions characteristic of each region. Using this result we show that the real limit distributions can be hidden by some finite-size effects. In particular, when a chaotic and a regular region are glued together, the limit distributions follow a Poisson-like law, but as long as the measure of the shrinking domain is not zero, the polynomial behavior of the regular component dominates for large times. Such an analysis seems helpful to understand the dynamics in the regions where ergodic and regular motions are intertwined, as it may occur for the standard map. Finally, we study the distributions of the number of visits around generic and periodic points of the dissipative Henon map. Although this map is not uniformly hyperbolic, the distributions computed for generic points show a Poissonian behavior, as usually occurs for systems with highly mixing dynamics, whereas for periodic points the distributions follow a different law that is obtained from the statistics of first return times by assuming that subsequent returns are independent. These results are consistent with a possible rapid decay of the correlations for the Henon map. 相似文献