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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). [ABSTRACT FROM AUTHOR]

The steady-state structure of a nonequilibrium discharge maintained in the medium by a focused electromagnetic wave beam is determined based on the physical model treating the discharge as a distributed nonlinear system with a given level of the electric field amplitude self-limitation. In this model, finding the self-consistent spatial distributions of the plasma density and the electric field phase in the ionized region is reduced to some inverse electrodynamic problem, whose solution is found in application to the axially symmetric geometry. The electromagnetic field outside the discharge plasma is found in the approximation of geometric optics with the ray reflection and refraction at the boundary being taken into account. The differential equations determining the form of the plasma-vacuum interface are derived and integrated numerically and the distributions of the plasma density and the electric field within and around the discharge are calculated as applied to the conditions of interest for the microwave and optical discharges in gases and solids. [ABSTRACT FROM AUTHOR]

Based on a simple 1D initial-time model, we have carried out the numerical simulation for the spatio-temporal evolution of femtosecond laser pulse induced breakdown in transparent dielectric (fused silica) at the nonlinear stage of the plasma resonance ionization instability. The instability develops from very small seed perturbations of the medium permittivity and results in, because of the strong mutual enhancement of the electric field and plasma density perturbations in the plasma resonance region, the formation of the subwavelength periodic plasma-field structure consisting of the overcritical plasma layers perpendicular to the laser polarization. The calculation of the timecourse and spatial profiles of the plasma density, field amplitude, and energy deposition density in the medium during one breakdown pulse has allowed us to establish the main possible scenarios of the process considered and to found the laser intensity range where this process can underlie the nanograting modification of the medium by repeated pulses. [ABSTRACT FROM AUTHOR]

Collective multipole oscillations (surface and volume plasmons) excited in a metal nanosphere 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 is found to be in good enough agreement with the data of scanning transmission electron microscopy 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 experiments. [ABSTRACT FROM AUTHOR]

Self-consistent electron density profiles of the plasma stream interacting with the electric field of an ultrashort laser pulse are calculated in the framework of the one-dimensional steady-state model with nonlocal polarizability. These profiles are settled down against the background of a given (linear) ion density distribution as a result of the equilibrium between the averaged ponderomotive force, the static space-charge field, and the electron pressure. The average electron density and the longitudinal (parallel to the density gradient) ac electric field are found to be greatly space-modulated in the region downstream of the plasma resonance point. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of ultra-thin titanium oxide films by plasma-induced surface oxidation. Ellipsometry measurements indicate an oxide thickness of about 2 nm. Electrical characterization was performed on microscale and nanoscale metal-insulator-metal tunneling diodes. Electrical fields up to 22 MV/cm were applied without destroying the titanium oxide films. The current-voltage-characteristic of the diodes are found to be asymmetric with respect to zero bias when employing electrodes with different work functions. The permittivity of the ultra-thin titanium oxide was determined to be less than 6, which is the smallest permittivity that has been reported for titanium oxide. [ABSTRACT FROM AUTHOR]

The resonance phenomena caused by the excitation of the surface and volume plasmons in the metal and ionized atomic clusters are studied in the framework of hydrodynamic and kinetic approaches with the inclusion of radiative, collisional, and kinetic (collisionless) damping mechanisms. The resonances of dipole moment at the frequencies of the volume plasmons are found to be strongly damped by the collision-induced losses, while the field amplitude at the central region of the cluster may exhibit large increase at the resonance of both kind of plasmons. [ABSTRACT FROM AUTHOR]

The evolution of optical discharge induced in the volume of transparent dielectric by a focused fs laser pulse is studied under condition of ionization instability that results in deep small-scale periodic modulation of breakdown plasma parameters in the direction of laser polarization. Laser pulse intensity range is found where the instability evolving from very small seed perturbations leads to formation of the contrast subwavelength periodic structure containing narrow zones with overcritical plasma density and enhanced energy deposition. The latter allows considering this structure as underlying the nanograting formation observed experimentally in the fused silica irradiated by series of repeated fs pulses.