Articles you may be interested inSimulation of resonance hyper-Rayleigh scattering of molecules and metal clusters using a time-dependent density functional theory approach J. Chem. Phys. 141, 124305 (2014); 10.1063/1.4895971Inter-channel effects in monosolvated atomic iodide cluster anion detachment: Correlation of the anisotropy parameter with solvent dipole moment

Collective multipole oscillations (surface and volume plasmons) excited in a metal cluster by moving electron and corresponding inelastic scattering spectra are studied based on the hydrodynamic approach. Along with the bulk (dielectric) losses traditionally taken into account, the surface and radiative ones are also considered as the physical mechanisms responsible for the plasmon damping. The second and third mechanisms are found to be essential for the surface plasmons (at small or large cluster radii, respectively) and depend very differently on the multipole mode order. The differential equations are obtained which describe the temporal evolution of every particular mode as that one of a linear oscillator excited by the given external force, and the electron energy loss spectra are calculated. The changes in spectrum shape with the impact parameter and with the electron passage time are analyzed; the first of them are found to be in good enough agreement with the data of scanning transmission electron microscopy (STEM) experiments. It is shown that, in the general case, a pronounced contribution to the formation of the loss spectrum is given by the both surface and volume plasmons with low and high multipole indices. In particular, at long electron passage time, the integral (averaged over the impact parameter) loss spectrum which is calculated for the free-electron cluster model contains two main peaks: a broad peak from merging of many high-order multipole resonances of the surface plasmons and a narrower peak of nearly the same height from merged volume plasmons excited by the electrons that travel through the central region of the cluster. Comparatively complex dependences of the calculated excitation coefficients and damping constants of various plasmons on the order of the excited multipole result in wide diversity of possible types of the loss spectrum even for the same cluster material and should be taken into account in interpretation of corresponding electron energy loss spectroscopy (EELS) experiments.

The initial stage of the small-scale ionization-induced instability developing inside the fused silica volume exposed to the femtosecond laser pulse is studied as a possible initial cause of the self-organized nanograting formation. We have calculated the spatial spectra of the instability with the electron-hole diffusion taken into account for the first time and have found that it results in the formation of some hybrid (diffusion-wave) 1D structure with the spatial period determined as geometrical mean of the laser wavelength and characteristic diffusion length of the process considered. Near the threshold of the instability this period occurs to be approximately equal to the laser half-wavelength in the silica, close to the one experimentally observed.Formation of periodic nanostructures ("nanogratings") inside the volume of the transparent dielectric by the series of the femtosecond laser pulses of the moderate intensity has attracted considerable attention in the last two decades as a perspective method for the high density optical information writing and storage [1][2][3][4][5][6][7]. The carried out experimental and theoretical studies have allowed to reveal some important features, dependences, and application conditions of this phenomenon (mainly for the structures formed in the fused silica).Nevertheless, the physical mechanisms responsible for the creation of the observed selforganized bulk nanostructures is still under discussion [6,7]. In particular, up to now, there are no theoretical models that would allow to explain clearly the high enough degree of regularity of this structure and calculate its spatial period (measured experimentally as some part of the optical wavelength λ ) as function of external conditions and parameters. Meanwhile, the main mechanisms governing the periodicity of the ionization structure in the every unit laser pulse (that determines ultimately the periodicity in the induced nanograting) can likely be understood and described in a consistent and non-contradictory manner within the framework of known approach developed in studies of small-scale (subwave) ionization-field instabilities of electromagnetic wave in gases [8][9][10][11][12]. In the model we propose below, the instability arises at the stage of ionization (or its saturation at the undercritical plasma density level) due to mutual enhancement of small (seeding) 1D periodic perturbations of the electric field amplitude and the

No abstract

The theory of ionization-field instability in a continuous homogeneous medium is generalized to the heterogeneous nanoporous one with the purpose to clear and analyze the mechanism of nanograting formation during the optical breakdown process in a transparent dielectric (fused silica) containing multiple small inclusions (nanobubbles) with a lowered ionization threshold. Based on the Maxwell Garnett approximation extended to include the size effect caused by the finite ratio of the bubble sizes to the scale of unstable perturbations, we have obtained the equation system describing the spatiotemporal evolution of the plasma density, average field, and effective dielectric permittivity and have derived the characteristic equation connecting the temporal growth rate of these perturbations with their spatial period. Analysis of the roots of this equation shows that the unstable periodic perturbation structure having the maximal growth rate is close in character to the nanogratings observed experimentally (modulation in the direction of the pump wave polarization with the period approximately equal to the half-wavelength in the host material).