18 June 2015

Mode-coupling instability in monolayer dusty plasma crystal

In the frames of joint cooperation with the Research-Educational Center "Ion-Plasma Technology" we study dusty plasma crystals.

This movie illustrates two amazing phenomena - a heavy particle flies over 2D crystal, and a special kind of dusty plasma instability - mode-coupling instability (MCI).

Experiments by: L. Couedel, A. Lipaev, E. Yakovlev, and E. Vorobiev.

Analysis and visualization by: A. Kislov, K. Zaytsev, and S. Yurchenko.

Special thanks to A. Ivlev for MCI prediction.

30 August 2014

FDTD simulation of interaction between a light and a photonic crystal structure

FDTD simulation of interaction between a plane electromagnetic wave and a globular PC, during pumping in its band gap

Various fundamental phenomena, such as electromagnetic wave interaction with structured optical media, photonic crystal (PC) structures, metamaterials, can be investigated by means of numerical solution of Maxwell equations using finite-difference time-domain method (FDTD). It is very useful in case of studying some special features of wave interaction with PC: wave propagation in complex media, band gap structure, optical field localization in PC volume and near its surface due to structural focusing phenomena. The last one leads to the strong localization of electric field near the PC surface during pumping in its band gap. This effect is of fundamental importance, since it exists not only in 2D and 3D PC structures, but also in acoustic and quasi-crystalline structures of different nature. It can be useful for making new high-efficient laser materials and nonlinear media based on PC structures, and also for new high-sensitive spectroscopic methods.

FDTD simulation
Spatial distribution of light intensity inside the medium, reconstructed from the FDTD simulation

Evidently, the strong localization of optical field takes place near the PC surface, which is connected exactly with the structural focusing effect. Meanwhile, structural focusing cannot be explained by the Bloch theory of light-crystal interaction, because the wave front, interacted with PC, is considered to remain plane in this theory, whilst namely the coherent deformation of the wave front leads to structural focusing.

Transverse localized modes in PC fiber as the result of FDTD simulation

As it can be seen, light interaction with PC fiber also leads to the effects of optical field localization. These effects can play the significant role in nonlinear conversion in PCF, including supercontinuum generation.

30 August 2014

Monte Carlo simulation

Monte Carlo simulation

Monte Carlo numerical simulation is used in order to solve scattering, radiation transfer and light diffraction in random or ordered medium problems, when it is difficult to find an analytical solution. Using statistical averaging of the numerous realizations of photon trajectories in the considered medium, the demanded characteristics can be determined.

Monte Carlo simulation

3D Monte Carlo simulation was used for finding the light intensity from single source propagated through volume of ordered spheres. In this figure the selected directions of light propagation are clearly seen. The trajectory color is changed accordingly to the overall time, which each photon spends inside the structure. When photon crosses the air-sphere border, its color is changed to yellow-red (yellow corresponds to earlier time moment), conversely, crossing sphere-air border is shown by green-blue (blue corresponds to later time moment, green – earlier time moment). Thus, it is possible to find light intensity and other parameters of interest in different time-moments.

30 August 2014

Molecular dynamics method modeling

Heating of nanoparticle

Molecular dynamics (MD) is the group of methods and algorithms, used for modeling of different systems with single particle-resolution. MD is a powerful tool, which helps to estimate the connection between different regularities in micro and macro world.

Melting of crystal plane

Modern computational capacities allow to successfully use MD methods for different tasks of rather fields of science and technology: condensed matter physics, nanotechnology, material science, biophysics, pharmaceuticals, etc.

Liquid drops and gas formation

MD methods became popular especially in study of various structures (e.g. water, amorphous states, organic macromolecules such as proteins). Using MD it is possible to find out the essence of phenomena, when experimentally study is difficult. For example, it concerns investigation of material properties in the nano-confinement condition, fast processes, and processes in the extreme conditions.

2D dipole system at low temperature

Nowadays, MD modeling is a rapid developing field of the computer science. Moreover, computer technology’s achievements result in using of MD modeling for a wide range of different tasks.

Stratification of particles while decreasing of the system temperature

By the use of MD simulation it is possible to observe changes of particle dynamics in case of phase transitions in the system. In both cases gas phase formation, which is in equilibrium with the liquid, is well noticed. MD methods can be also used for observation of the inverse processes.

Movement of particles

Using MD simulation, it is possible to observe structure changes at the single molecule level in case of nonequilibrium phase transition. Laning is a phenomenon which can be observed in systems where two different types of particles (A and B) are forced to move toward each other, for example, particles of opposite sign which are presented in electric field.

Straightening in strips

In the absence of laning, A particles will be randomly squeeze in their initial direction through moving in the opposite direction stream of particles B. However, under certain conditions, there is a fundamental change in the mechanism of the particles flow: particles of type A will begin to line up in long strips, analogously for the particles B. Eventually the whole system breaks down into a set of long chains of similar particles.

Membrane

Such chains are moving towards each other almost without resistance from the particles of the other type. Laning possibly occurs in colloids, plasma, and other systems, which are rather important for fundamental and applied fields of science.