Interaction of argon clusters with intense laser pulses is studied theoretically. Free electrons energy distribution is studied. Differences between infrared and vacuum ultraviolet frequency regimes are pointed out. Clear physical interpretation of the obtained results is given.
The explosion of rare-gas atomic clusters induced by short, intense X-ray pulses generated by a free-electron laser is studied. A numerical approach for an explicitly time-dependent description of small to medium size clusters in 3D is developed within the Thomas-Fermi model. Such an approach, though strongly simplified in comparison to fully quantum-mechanical schemes, is nevertheless expected to yield a qualitatively correct description of the electronic and ionic dynamics of these systems, at a much lower computational cost.
Anderson localization of electromagnetic waves in random arrays of dielectric cylinders confined within a planar metallic waveguide is studied. The disordered dielectric medium is modeled by a system of randomly distributed 2D electric dipoles. An effective theoretical approach based on the method of images is developed. A clear distinction between isolated localized waves (which exist in finite media) and the band of localized waves (which appears only in the limit of the infinite medium) is presented. The Anderson transition emerging in the limit of an infinite medium is observed both in finite size scaling analysis of transmission and in the properties of the spectra of some random matrices. The sound physical interpretation of the obtained results suggests deeper insight into the existing experimental and theoretical work.
The dynamics of small (<55 atoms) argon clusters ionized by an intense, infrared, femtosecond laser pulse is studied using a Bloch-like hydrodynamic model. Evolution of both free electrons and ions formed in the cluster explosion process is examined. Oscillations of the electron cloud in a rare-gas atomic cluster are described as a motion of a fluid obeying Bloch-like hydrodynamic equations. Our theoretical approach includes all possible ionization mechanisms: tunnel (or field) ionization both by an external laser field, and by an internal field due to the space-charge distribution inside the cluster, as well as electron-impact (or collisional) ionization. The results of our simulations are compared both with experimental findings and with predictions of other theoretical models.
We investigate numerically the problem of optimization of directional characteristics of dipole antennas located inside, or in the vicinity of, photonic crystals or more general artificial dielectrics, made of very thin perfectly conducting wires. We concentrate on two-dimensional propagation. Simulated annealing is used to find the distribution of wires which optimizes the directional pattern. It is demonstrated that high directivity can be obtained for systems containing a very small number of elements provided that the size and shape of the unit cell as well as the position of the radiating source with respect to the crystal are optimized. Building up of the radiation pattern is also illustrated with the help of the wave-optical rays.
We studied the spectral properties of the matrices describing multiple scattering of electromagnetic waves from randomly distributed point-like magneto-optically active scatterers under an external magnetic field B. We showed that the complex eigenvalues of these matrices exhibit some universal properties such as the self-averaging behavior of their real parts, as in the case of scatterers without magneto-optical activity. However, the presence of magneto-optically active scatterers is responsible for a striking particularity in the spectra of these matrices: the splitting of the values of the imaginary part of their eigenvalues. This splitting is proportional to the strength of the magnetic field and can be interpreted as a consequence of the Zeeman splitting of the energy levels of a single scatterer.
Localized waves in disordered left-handed materials are studied using a generalized coupled-dipole model. Resonances in an open system consisting of randomly distributed electric and magnetic dipoles are investigated. A new type of long-lived resonance modes localized at the boundary of the system is found. They resemble evanescent waves responsible for a superfocusing phenomenon by a left-handed lens.
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