Damage of a metal spherical nanoparticle by femtosecond laser pulses is analyzed by splitting the overall process into two steps. The fast step includes electron photoemission from a nanoparticle. It takes place during direct action of a laser pulse and its rate is evaluated as a function of laser and particle parameters by two approaches. Obtained results suggest the formation of significant positive charge of the nanoparticles due to the photoemission. The next step includes ion emission that removes the excessive positive charge and modifies particle structure. It is delayed with respect to the photo-emission and is analyzed by a simple analytical model and modified molecular dynamics. Obtained energy distribution suggests generation of fast ions capable of penetrating into surrounding material and generating defects next to the nanoparticle. The modeling is extended to the case of a nanoparticle on a solid surface to understand the basic mechanism of surface laser damage initiated by nano-contamination. Simulations predict embedding the emitted ions into substrate within a spot with size significantly exceeding the original particle size. We discuss the relation of those effects to the problem of bulk and surface laser-induced damage of optical materials by single and multiple ultrashort laser pulses.
The objective of this combined experimental and theoretical research is to study the dynamics and mechanisms of nanoparticle
interaction with ultrashort laser pulses and related modifications of substrate surface. For the experimental effort,
metal (gold), dielectric (SiO2) and dielectric with metal coating (about 30 nm thick) spherical nanoparticles deposited on
glass substrate are utilized. Size of the particles varies from 20 to 200 nm. Density of the particles varies from low (mean
inter-particle distance 100 nm) to high (mean inter-particle distance less than 1 nm). The nanoparticle assemblies and the
corresponding empty substrate surfaces are irradiated with single 130-fs laser pulses at wavelength 775 nm and different
levels of laser fluence. Large diameter of laser spot (0.5-2 mm) provides gradient variations of laser intensity over the
spot and allows observing different laser-nanoparticle interactions. The interactions vary from total removal of the nanoparticles
in the center of laser spot to gentle modification of their size and shape and totally non-destructive interaction.
The removed particles frequently form specific sub-micrometer-size pits on the substrate surface at their locations. The
experimental effort is supported by simulations of the nanoparticle interactions with high-intensity ultrashort laser pulse.
The simulation employs specific modification of the molecular dynamics approach applied to model the processes of
non-thermal particle ablation following laser-induced electron emission. This technique delivers various characteristics
of the ablation plume from a single nanoparticle including energy and speed distribution of emitted ions, variations of
particle size and overall dynamics of its ablation. The considered geometry includes single isolated particle as well a
single particle on a flat substrate that corresponds to the experimental conditions. The simulations confirm existence of
the different regimes of laser-nanoparticle interactions depending on laser intensity and wavelength. In particular,
implantation of ions departing from the nanoparticles towards the substrate is predicted.
Polarization-dependent ripples were formed at silicon surfaces under femtosecond laser irradiation. Proposed theoretical
model describes changes in optical response of semiconductor surface, induced by generation of nonequilibrium
electron-hole plasma, and explains mechanism of surface polaritons and waveguide modes exciatation during
femtosecond laser pulse action.
The results of both analytical and numerical study of the optical damage of a solid nano-size particle, partly ionized by
an ultra-short laser pulse (USLP) are presented. The comparison of the results that has been obtained analytically and
numerically shows that the proposed method allows to describe the main features of nano-particle damage induced by
Coulomb forces, that arise in solid due to the charge equilibrium distortion under USLP action.
The kinetics of energy spectra of the spreading ions has been analyzed taking into account the Coulomb repulsive forces
and the retarding processes that restrict ion motion inside the particle.
The results of theoretical investigation of processes resulting from disturbance of charge equilibrium in a solid nanoparticle,
induced by fast ionization under high-intensity ultra-short laser pulse action are presented. Analytical and
numerical methods were used to study time evolution of space and energy distributions of moving ions during their
spreading away from the particle for various sizes and shapes of the particle as well as various degrees of ionization of
its material. The final aim of the presented study is to analyze the influence of the disturbance of charge equilibrium
induced by high-intensity ultra-short laser pulses in a solid on parameters of laser-induced damage of the material, and
the regularities of the atoms and ions motion of the media in damage area under the action of local laser-induced
Coulomb potential.
The development of new principles for near-field probe design has been crucial for near-field technology progress for the last ten years. Employing surface polaritons gives the new opportunity for near-field probe development. Using this waves it can be provided not only efficient energy channel along near-field probe but good field localization in the tip.
KEYWORDS: Waveguides, Metals, Polaritons, Signal attenuation, Near field optics, Radio propagation, Near field, Near field scanning optical microscopy, Wave propagation, Far infrared
We report the results of the theoretical investigations of the existence of peculiarities of the surface electromagnetic waves (SEW) in a cylindrical three-layer waveguide on the metal-dielectric boundary in far IR range where the electrodynamical characteristics of the metal are described only in the approximation of normal skin effect. We consider the problem of the field structure of SEW, its parameters of attenuation from both sides of the medium boundary, its propagation length along the cylindrical surface. The Leontovich boundary conditions were used. The problem solved has significant value for near-field optics (NFO) in the far IR range where the principles of NFO are only being established.
KEYWORDS: Waveguides, Polaritons, Signal attenuation, Metals, Near field optics, Light wave propagation, Electromagnetic radiation, Dielectrics, Radio propagation, Optical components
It has been considered the transformation efficiency of laser radiation into cylindrical surface plasmon-polaritons on a resonance harmonic grating covered cylindrical waveguide. It has been investigated in detail the case when polaritons propagate along a waveguide. The results are interesting for the development of effective probes for near-field optical devices.
KEYWORDS: Waveguides, Polaritons, Near field, Metals, Cladding, Wave propagation, Near field optics, Numerical simulations, Environmental sensing, Signal attenuation
The propagation parameters and their relation with the medium properties were investigated for surface polaritons excited in coated cylindrical waveguide. The possibility of excitation of symmetric and antisymmetric types of polariton's modes has been demonstrated for a cylindrical three-layer waveguide with a metal cladding. It has ben shown that the near field of cylindrical surface polariton can be theoretically localized to an arbitrarily small space. The conditions for total localization of the near field of the TM0-mode were determined by numerical simulation for three-layer waveguide with a metal core. The result of this analysis can be used for development of more effective probes for IR near-field devices.
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