G. G. Matvienko

Self-action of tightly focused femtosecond laser radiation in air in a filamentation regime: Laboratory and numerical experiments

The influence of self-focusing of strong femtosecond laser radiation on the spatial energy distribution of a laser beam was studied. Experimental data are provided on the transverse energy density distribution of the tightly focused radiation of the Ti-sapphire laser following its filamentation in air. The results are interpreted within the framework of the nonlinear Schrödinger equation model. The best agreement between the theory and the experiment is found in the model that takes into account the change of character of the nonlinear response of the medium induced by high-intensity radiation in the nonlinear focus, which includes the change of the ionization mechanism of molecules from multiphoton ionization to tunnel ionization, the completely instantaneous Kerr nonlinearity, and saturation of the latter due to higher-order nonlinearity. The mechanism of the ionization of molecules can change from purely multiphoton ionization to tunnel ionization.

Modeling of helicopter-borne tunable TEA CO2 DIAL system employment for detection of methane and ammonia leakages

Abstract The characteristics of a helicopter-borne lidar based on tunable TEA CO2 laser and its third harmonic designed for remote detection of methane and ammonia leakages from pipelines are analyzed numerically. The spectral range near 3 μm was shown to be most promising for remote sensing of methane emissions. Parameters of radiation of the tunable pulse-periodic mini-TEA CO2 laser and generators of harmonics to be utilized in the helicopter-borne differential absorption lidar are estimated. Emissions of different gas intensities are analyzed for possible detectability at a distance of up to 1 km. The use of the third harmonic of the TEA CO2 laser allows methane emissions from a pipeline to be detected and measured with mean measurement error from 10% to 15% for methane concentrations varying from the background level to the explosion-hazardous one. The optimal pair and possibilities of the ammonia remote sensing on the base of the first harmonic of TEA CO2 laser were determined as well.

Pan Eurasian Experiment (PEEX) - A research initiative meeting the grand challenges of the changing environment of the Northern Pan-Eurasian Arctic-Boreal areas

The Pan-Eurasian Experiment (PEEX) is a new multidisciplinary, global change research initiative focusing on understanding biosphere-ocean-cryosphere-climate interactions and feedbacks in Arctic and boreal regions in the Northern Eurasian geographical domain. PEEX operates in an integrative way and it aims at solving the major scientific and society relevant questions in many scales using tools from natural and social sciences and economics. The research agenda identifies the most urgent large scale research questions and topics of the land-atmosphere-aquatic-anthropogenic systems and interactions and feedbacks between the systems for the next decades. Furthermore PEEX actively develops and designs a coordinated and coherent ground station network from Europe via Siberia to China and the coastal line of the Arctic Ocean together with a PEEX-modeling platform. PEEX launches a program for educating the next generation of multidisciplinary researcher and technical experts. This expedites the utilization of the new scientific knowledge for producing a more reliable climate change scenarios in regional and global scales, and enables mitigation and adaptation planning of the Northern societies. PEEX gathers together leading European, Russian and Chinese research groups. With a bottom-up approach, over 40 institutes and universities have contributed the PEEX Science Plan from 18 countries. In 2014 the PEEX community prepared Science Plan and initiated conceptual design of the PEEX land-atmosphere observation network and modeling platform. Here we present the PEEX approach as a whole with the specific attention to research agenda and preliminary design of the PEEX research infrastructure.

Angular structure of the light intensity near the angles of mirror reflection from the faces of ice crystalline particles

Relationships are obtained which connect the angular and spectral characteristics of the radiation reflected by faces of ice particles with their concentration, size, and deflection of reflecting faces from the horizontal position (flutter). The possibilities are discussed of using the mirror reflection for estimating the particle size and their spatial orientation.

Filament formation beyond linear focus during femtosecond laser pulse propagation in air

The threshold relation between the strength of laser beam focusing and its peak power is determined for post-focal filamentation on the basis of the experimental data and numerical simulations. The dynamics of the post-focal filamentation can vary (propagating or reconstruction type) depending on the strength of linear beam focusing.

Lidar observations of aerosol occurrence in the middle atmosphere of Kamchatka in 2007–2011

The lidar observations, performed in Kamchatka during period from October 2007 to December 2010, are used to analyze the behavior of the vertical aerosol structure in the altitude interval of 30–80 km. The data obtained revealed a regular occurrence of the aerosol scattering during winter in the upper stratosphere and mesosphere at altitudes of 60–75 km. The aerosol scattering in these regions becomes apparent in late October and disappears in March-April. During the warm season (from April to October), the lidar signals correspond well to Rayleigh molecular scattering.

Filamentation of a sharply focused ultrashort laser pulse at wavelengths of 800 and 400 nm: Measurements of the nonlinear index of air refraction

We present the results of experimental investigations of the filamentation dynamics of high-power ultrashort Ti:Sapphire-laser pulses with wavelengths of 800 and 400 nm with their sharp focusing in air. The dependences of position and dimensions of a plasma channel generated in the nonlinear beam focus zone on the laser pulse power are obtained. The effective value of the nonlinear index of air refraction related to the optical Kerr effect is determined for two laser wavelengths from processing of the dependences when using laser radiation self-focusing theory.

Filamentation of the focused Ti: Sapphire laser pulse in air at two harmonics

The results of experiments on the filamentation dynamics of high-power ultrashort Ti: sapphire laser pulses with wavelengths of 800 and 400 nm upon their sharp focusing in air are presented. The dependences of the position and dimensions of the plasma channel that forms in the region of the nonlinear beam focus on the laser pulse power are obtained. The spectra of the laser pulse during its filamentation are measured.

Interaction between gigawatt laser pulses and liquid media: Part 1. Explosive boiling of large individual water droplets

The results of experiments on femtosecond GW laser pulse interaction with isolated millimeter-size water droplets are presented. The temporal and spatial dynamics of optical breakdown in a liquid particle is investigated. The mechanical fragmentation of the droplet as a result of the evaporation and explosion of superheated areas is also discussed. The spectral characteristics of water particle glow during its explosive boiling are investigated.

Propagation of a high-power ultrashort laser pulse along a horizontal atmospheric path

Experimental results of the study of the evolution of the spatial profile and frequency spectrum of terawatt ultrashort Ti: Sa laser pulses propagating along atmospheric paths in the self-focusing mode are presented. The dependence of the laser radiation energy characteristics at the receiving plane on its initial peak power is determined. The tendency of an increase of the laser beam’s angular size and spectral width when increasing its output power is stated. The obtained regularities have been interpreted qualitatively and quantitatively based on the numerical calculations performed in the framework of the model of the nonstationary self-action of an ultrashort light pulse in air. The ob tained results are compared to the results of the authors’ earlier laboratory experiments on the filamentation of focused laser femtosecond radiation.