Time-Frequency Integrals and the Stationary Phase Method in Problems of Waves Propagation from Moving Sources

The time-frequency integrals and the two-dimensional stationary phase method are applied to study the electromagnetic waves radiated by moving modulated sources in dispersive media. We show that such unified approach leads to explicit expressions for the field amplitudes and simple relations for the field eigenfrequencies and the retardation time that become the coupled variables. The main features of the technique are illustrated by examples of the moving source fields in the plasma and the Cherenkov radiation. It is emphasized that the deeper insight to the wave effects in dispersive case already requires the explicit formulation of the dispersive material model. As the advanced application we have considered the Doppler frequency shift in a complex single-resonant dispersive metamaterial (Lorenz) model where in some frequency ranges the negativity of the real part of the refraction index can be reached. We have demonstrated that in dispersive case the Doppler frequency shift acquires a nonlinear dependence on the modulating frequency of the radiated particle. The detailed frequency dependence of such a shift and spectral behavior of phase and group velocities (that have the opposite directions) are studied numerically

The solitons redistribution in Bose-Einstein condensate in quasiperiodic optical lattice

We numerically study the dynamical excitations in Bose-Einstein condensate (BEC) placed in periodic and quasi-periodic 2D optical lattice (OL). In case of the repulsive mean-field interaction the BEC quantum tunnelling leads to a progressive soliton's splitting and generating of secondary solitons, which migrate to closest trapping potential minima. A nontrivial soliton dynamics appears when a series of pi-pulses (phase kicks) are applied to the optical lattice. Such sudden perturbation produces a dynamic redistribution of the secondary solitons, leading to a formation of an artificial solitonic superlattice. Different geometries of OL are analyzed.Comment: 16 pages, 6 figure