Home – Home – Jornals – Atmospheric and Oceanic Optics 2012 number 11

The results of atmospheric experiments on propagation of femtosecond IR-pulses with complex initial transverse profile of intensity under self-focusing and filamentation conditions are presented. The effect of initial geometric divergence of radiation on transverse structure of light energy of a beam at the end of the path is studied. Numerical simulation of the problem is carried out and parameters of the generated filaments and plasma channel are determined. It is shown that geometric focusing or defocusing of radiation allow the transfer of the nonlinear focus and filamentation region connected with it along the path in sufficiently wide range.

The influence of the coherence degree of the transmitting beam on the bit error rate (BER) for free space optics (FSO) communication systems is investigated. It is found that for all types of propagation paths (horizontal, vertical or inclined), and various degrees of the turbulence strength there are the optimal value of the output power and the optimal degree of coherence of the optical transmitter beam defined by the Fried parameter. The optimal coherence degree can be determined by the minimum of BER.

The intensity of broadband optical pulses propagating in the free space is calculated in the approximation of the envelope of narrowband signal and based on the complex analytic signal. It is shown that the narrowband-signal envelope approximation can be used to calculate the diffraction of pulsed optical beams regardless of the pulse duration and its coherence in space and time.

A modified spectral-phase algorithm for computer generation of time-evolving random processes and fields has been developed. Use is made of a combined autoregressive moving-average model, described by a discrete difference equation. The implementation of the algorithm is shown to be simple and efficient in simulations of dynamic problems of atmospheric and adaptive optics.

This paper considers the results of 12-year long investigations of dependencies of the aerosol scattering coefficient on relative humidity at its controlled growth (hygrograms). It is revealed that this function cannot be always represented in single-parameter form in the entire range of variations of the relative humidity. The well-pronounced phase transition is sometimes observed at its certain value. The frequency of occurrence of hygrograms with phase transition in different seasons and in various air masses is analyzed. The substances are determined, the presence of which in aerosol particles can cause the appearance of the phase transition.

We consider specific features in the spatial distribution and seasonal variations of the atmospheric aerosol optical depth (AOD) in a wavelength region of 0.55 mm on the territory of Povolzhye, Urals, and Western Siberia according to many-year data of satellite (MODIS/TERRA and AQUA) observations. The satellite values of AOD for particular regions of the Middle Urals are compared with AERONET observations in the region of Kourovka Astronomical Observatory. It is shown that the annual AOD variations from April to December are similar in all regions: with turbidity maxima, observed in spring and summer (August), and with minima in June and fall. On the average, the AOD values are larger in the south of the Western Siberia and Povolzhye and minimal in the Northern Urals. A high interrelation in the monthly AOD variations between individual regions is noted.

Measurements of the atmospheric aerosol microphysical characteristics were carried out in April–December, 2009 and January–December, 2011 at the Vostok continental station in the framework of the 54th and 56th Russian Antarctic Expeditions. The instrumentation complex consisted of a modified nephelometer FAN, AZ-10 photoelectric counter and the aethalometer, designed at Institute of Atmospheric Optics. The aerosol number and mass concentrations N _a (cm ^–3) and M _a (mg × m ^–3), aerosol disperse composition in the particle size range d = 0.3–10 mm and the mass concentration of black carbon M _BC (mg × m ^–3) were recorded with the period of 1–2 hours. Temporal variability of the measured aerosol parameters is determined. Seasonal variations of the aerosol parameters are revealed as maximal in the period from November to April and minimal from June to August. It is shown that seasonal differences in the disperse composition of Antarctic aerosol are observed mainly in submicrometer size range. The results obtained are compared with the data of other researchers for high-latitude regions of the Antarctic.

This work contains results connected with boundary layer structure and dynamics in Far East ocean–continent zone in summertime by means of aerosol lidar. Mean values of PBL height, top of the convective layer and mean height of the nocturnal layer are presented. As the example of several summer days, specific features of the PBL structure and dynamics are identified, presented and analyzed. Maximal values of breeze circulation heights are also presented.

The paper analyzes experimental data on variations of vertical-temporal structure of aerosol, which were obtained using lidar complex of the small station of high-altitude atmospheric sensing (SSHAS) IAO SB RAS for the period 2010–2011. A characteristic feature of this period was almost no volcanic activity with emissions to the stratosphere. This made it possible to study the behavior of the vertical structure of the background aerosol in the stratosphere on a monthly basis for certain nights during two years. The analysis of the results revealed differences in the vertical stratification of aerosol between 2010 and 2011. For 2010, the aerosol loading was maximal in January up to heights of 30 km, it diminished starting from February until almost no decrease in March–August, and showed a steady growth since September. In 2011, the aerosol loading of the stratosphere was more intense and longer-term. For instance, the height of the extension of the aerosol component reached 40 km in January–March, and the aerosol was absent in the stratosphere within three months (May–July).

The results of experimental researches of fluctuations of the laser beam intensity extending through a supersonic flooded jet are presented. The work is executed at the stand of Institute of applied and theoretical mechanics of the Siberian Branch of the Russian Academy of Science. The laser beam passed across a jet on various distances from Vitochinskogo nozzle. The experiment was spent at pressure in Ejfelja chamber from 1,7 up to 7 at two modes of the expiration of a jet: with the use of chevrons on the day off nozzle and without chevrons. Dependences of a dispersion and spectra of fluctuations on pressure and distances from the nozzle are found. The internal optical scale of the turbulence is estimated.

The equation for light intensity in maximum, analogous to the equations of strong theory and Kirchhoff formula, is obtained on a basis of experimentally determined existence of deflection of light beams in the range of screen edge and regularity determining it and formation of diffraction fringes by a slit owing to interference of the beams propagating from the ranges near opposite edges of the slit.

In order to show that the presence of nonresonant optical fields near the surface of the agglomerates of nanoparticles may lead to decrease of lasing dye energy threshold of superluminescence and increase its efficiency. The superluminescence was studied experimentally in a thin layer of laser dye R6G with nanoparticles of Ag, Al, Ni, without manifestations of random laser medium and the effect of the plasmon resonance.

The paper presents the results of experimental study of middle scale CuBr laser performance with longitudinal capacitive discharge excitation. Lasing power dependences on various operating conditions were investigated including the influence of equivalent electrode capacitance value. Maximum average output power of 12 W with ~0,5% efficiency was reached in CuBr laser excited by longitudinal capacitive discharge. These results were obtained with total calculated electrode capacitance of 1190 pF on the each side of a gas discharge active region. Linear growing of lasing power with increasing of input power is observed at all values of electrode capacitances and indicates the perspective of further increasing of output power of capacitively excited CuBr lasers.

The experimental measurements of CO ₂ and H ₂O in disc tree-rings of some coniferous from regions with different climates have been obtained, the results were compared with the tree-ring widths, some conclusions were made about climatic response of annual CO ₂ and H ₂O distributions. The hypothesis was put forward that the appearance of long-period cyclicities in annual CO ₂ tree-ring distribution is a tree's response to the environmental change.

A stimulating effect of sunlight transformed by a photoluminescent polymer films on the abundance dynamics, fermentation and respiration of indigenous microflora in oil-contaminated soils was investigated. The extents of biodegradation of petroleum hydrocarbons within 60 days were up to 60–70% and 26% of the overall background pollution level for the experimental and control site, respectively. Residual hydrocarbons extracted from samples of the contaminated soils were analyzed by infrared spectroscopy to show the appearance of additional absorption bands at 3350, 1600, and 1710 cm ^–1, thus indicating the formation of metabolites during enzymatic oxidation of oil. Chromatographic data corroborated the occurrence of intense oxidation.