Inna L. Plastun

Resonant self-focusing of periodically modulated laser beams

On-resonance self-action of a beam with periodically modulated amplitude in a two-level saturable absorber is studied numerically. When the period of modulation is comparable with relaxation times, one cannot describe the medium by means of susceptibility, and the response of the medium to the amplitude variation is not immediate. We solve the Bloch equations in each point of the medium to find this response correctly. Transient behavior followed by stable oscillations of population difference and polarization vector is shown to depend strongly on the frequency and amplitude of modulation. Beam propagation is considered using a simplified model of a thin absorber followed by free space, the propagation distance being small compared with the modulation wavelength. Manifestations of non-stationary response of the medium in the output intensity behavior are analyzed.

Resonance self-action and optical transient nutation in frequency-modulated cw laser beams

By numerical simulation we investigate the non-stationary manifestations and nonlinear dynamics of frequency - modulated cw laser beam propagated in resonance conditions. At modulation periods comparable with the atomic relaxation times the time dependence of the output intensity exhibits the manifestations of the optical transient nutation and resonance self-action effects. In the present paper we analyse the effect of resonance self-action on optical nutation and its dynamical manifestations.

Phase and amplitude near-resonance self-action in periodically modulated laser beams

Full space-time numerical modeling of near-resonance self-action of a beam, whose frequency is harmonically modulated in time, is presented. Maxwell-Bloch equations describing the propagation of the beam through a two-level medium with saturable absorption and refraction are solved using an original stable numerical scheme for multidimensional nonlinear Schrodinger equations. Delayed redistribution of intensity over the beam cross-section due to nonlinear self-focusing and self-phase-modulation effects is shown to affect the phase and the amplitude dynamics of the output signal in a rather nontrivial way, depending on the carrier laser frequency.

Self-action of periodically modulated laser beams in doped waveguides

We report numerical modeling of self-action of a beam, whose amplitude or phase is periodically modulated in time, in a gradient waveguide medium doped with two-level saturable active centers. For frequencies close to the dopant absorption line and modulation periods close to its relaxation time the response of the medium is no more instantaneous, and the description in terms of susceptibility fails. We account for the delayed response of the medium by solving numerically the full set of Maxwell-Bloch equations. In case of modulation wavelength and the diffraction length larger than the propagation distance we also make use of a simplified scheme based oil synchronous interaction approximation. Using these schemes we study the influence of the non-stationary self-action of the beam on the transmission of modulation signal through the doped waveguide. It is shown that in the time dependence of the polarization and population difference the nonlinear distortions of the modulation signal can be much stronger than in the output field intensity.

Nonlinear optical properties of open-ended amichair single-wall carbon nanotubes (SW-CNT)

Summary form only given: Optical properties of carboxylic acid functionalized open-ended armchair single-wall carbon nanotubes (SW-CNT) are studied by numerical simulations and in experiments. The polarizability, extinction, saturated absorbance and non-linear refraction are analyzed in various conditions for different types of SW-CNT and compared with experimental data.

Influence of the resonant self-action and nonstationary coherent effects on the characteristics of a frequency-modulated laser beam

Self-action of a frequency-modulated laser beam, propagating through a two-level saturable absorber, is modeled numerically basing of the direct solution of Maxwell-Bloch equations. Following the common idea of spectroscopy, we plot the output intensity versus the input laser frequency that periodically changes in time. At modulation frequencies comparable with the relaxation rates the hysteresis loop is observed, i.e. the dependence of the transmitted intensity upon the instantaneous frequency depends on the direction of the frequency change. At large amplitudes of modulation coherent transient oscillations of the output intensity are observed.

Diamond-like nanoparticles influence on flavonoids transport: molecular modelling

Intermolecular interaction of diamond-like nanoparticles and flavonoids is investigated by numerical simulation. Using molecular modelling by the density functional theory method, we analyze hydrogen bonds formation and their influence on IR - spectra and structure of molecular complex which is formed due to interaction between flavonoids and nanodiamonds surrounded with carboxylic groups. Enriched adamantane (1,3,5,7 - adamantanetetracarboxylic acid) is used as an example of diamond-like nanoparticles. Intermolecular forces and structure of hydrogen bonds are investigated. IR – spectra and structure parameters of quercetin - adamantanetetracarboxylic acid molecular complex are obtained by numerical simulation using the Gaussian software complex. Received data coincide well with experimental results. Intermolecular interactions and hydrogen bonding structure in the obtained molecular complex are examined. Possibilities of flavonoids interaction with DNA at the molecular level are also considered.

Рolarizing properties of molecular ensembles: new approaches to calculations

Polarizing properties of molecular ensembles with different structures are investigated by numerical simulation. Carbon nanotubes with zigzag configuration and nucleobases are considered. By numerical simulation total polarizability is investigated for different structures of molecules ensembles. New semi-analytical procedure for calculation of total polarizability for ensembles with different configuration is offered and tested by its application to ensembles which contain single-wall carbon nanotubes and nucleobases.

Extrapolation method to calculate the total polarizability of long-chain compounds on the example of single-wall carbon nanotubes

Optical properties of open-ended single-wall carbon nanotubes (SWCNT) are investigated by numerical simulation. Different types of carbon nanotubes - with armchair and zigzag configurations - are considered. By numerical simulation total polarizability is investigated for various lengths and for different structures of SWCNT. The new semi-analytical procedure for calculation a total polarizability for long-chain compounds is offered and tested on examples of single-wall carbon nanotubes.

Numerical analysis of open-ended single-wall carbon nanotubes optical properties

Optical properties of open-ended single-wall carbon nanotubes (SW-CNT) are investigated by numerical simulation. The polarizability tensor, which describes changes in optical properties depending on the propagation direction of electromagnetic radiation, is analysed for different types of single-wall carbon nanotubes with various configurations. IR spectrums are investigated for nanotubes without impurities and nanotubes which contain carboxylic group – COOH.