Our approach for modeling laser beam propagation through turbulence involves parabolic equation method and results of experimental investigation in laboratory. The analytic solution to the problem of the Gaussian beam propagation through non-uniform gas has been derived. The solution depends on the refracted index, i.e. on the gas density. The density distribution can be found from the Navier-Stokes system. The appropriate solution may be constructed by two ways : (i) as a series in powers of vorticity which is supposed to be small; (ii) with the aid of the parametrix method which includes an iterative procedure. It follows from the solution that acoustic radiation of vortex rings arises. Statistical properties of the propagating beam were found from the solution to the parabolic equation as average over time. In experiments the propagation path was equal to 7 m. The laser beam propagation was accompanied by convection and lateral wind. The frequency of turbulent fluctuations was equal to 2-10 Hz. Phase trajectories were found as well as statistical properties of the beam intensity in turbulent gas flow. The conclusion is as follows. Statistical characteristics traditionally used for the estimation of the laser beam special distortions in the open space transmission channels are to be complemented by the dynamic parameters such as the space of embeddings dimension, characteristic frequencies for the phase trajectories and so on.
The features of the reflection of quasi-monochromatic optical pulse from intensive low frequency few cycle pulse
in various nonlinear media are analyzed. The reflection effects are studied for the interaction of the optical
pulse with low frequency solitons and breathers. A signal pulse experiences frequency shift, and its velocity
changes correspondingly resulting in a time delay. The restrictions on the group velocity detuning and dispersion
parameters are obtained and approved by numerical simulation.
We investigate the interaction of two optical beams at different frequencies in an optical gradient waveguide. The index
has a parabolic profile, and the nonlinearity belongs to a defocusing type. The total reflection of a tilted signal beam
from a negative inhomogeneity induced by pump-beam occurs while both beams are trapped in the refractive index
trough is considered. We derive the equation for the rays, taking into account cubic nonlinearity and transverse
inhomogeneity. Trajectories of the signal beam at different ratios of the values of the nonlinearity, heterogeneity and the
initial angle of inclination are plotted. The critical angle of total reflection in a gradient waveguide with negative
nonlinearity is found. The interaction of co-axis beams is also discussed. The waveguiding propagation of a pump beam
under the balance between defocusing with negative nonlinearity and focusing with parabolic inhomogeneity is
presented. The wide signal beam can split by narrow pump beam.
The total reflection effect of the weak signal pulse from the high-power reference pulse with another frequency is first
demonstrated in the dispersive nonlinear medium. It is shown that as a result of the binary collision, signal pulse
frequency shift occurs, propagation velocity changes and time delay takes place. The conditions of total internal
reflection from moving inhomogeneity induced by pump pulse in nonlinear medium are found. The expression for the
reflected wave frequency shift is obtained. The possibility of pulse reflection from bright solitons in cubic medium is
Novel effects for few-cycle pulses propagation in quadratic media with dispersion management are considered. First, the
process of extraordinary wave generation in uniaxial crystal is tightly related with the process of ordinary wave profile
differentiation. Velocity mismatch limits interaction efficiency and leads to splitting of generated waves into two subpulses.
Such effect can be suppressed in the medium with periodic modulation of quadratic nonlinearity or with velocity
mismatch sign modulation. Second, highly interesting effects arise with the third-order dispersion. Dispersive spreading
can be reduced in layered medium with alternating third-order dispersion coefficients. Quadratic photonic crystals with
modulated dispersion coefficients or with managed dispersion are very promising for few-cycle pulse nonlinear optics.
One- and two-wave soliton trapping and propagation dynamics are also studied in such crystals. The analytical theory is
accompanied with the numerical simulation results.
We first study features of optical periodic lattices generated with mismatched cascade three-wave interaction in
quadratically nonlinear media. We elaborate the theory of parametric waveguides arrays induced by two crossing pump
waves together with exited sum wave. As the signal wave spreads due to the diffraction the induced lattice appears and
its transverse dimension increases. Note the parametric periodic grating becomes apparent since launching any signal
beam. It's likely to be the leading peculiarity of cascaded induced lattices. Parametric inhomogeneity depends on wave
vector mismatch sign, and its modulation depth can be controlled by pump beam intensity. We observed a transformation
from the discrete diffraction into the waveguiding of one or several signal beams with the increasing of pump intensity.
The discrete diffraction dynamics dependence on pump intensity, spatial period, and signal beam tilting is analyzed when
one or few central waveguides are exited at the input. At the certain incidence diffractionless propagation of signal beam
takes place. The similar discrete diffraction effects in 2D cascaded lattices with various pump structure geometries have
been studied. The additional degree of freedom gives novel properties to the effect of discrete diffraction.
Dynamics of powerful femtosecond singular-phase pulsed beams in a dielectric medium under the ionization
conditions is analyzed numerically. The multiphoton ionization is revealed to contribute to the stable (quasi-soliton)
regime of pulse propagation over distances exceeding five diffraction length. Use of the singular beams allows one to
reach the larger densities of the light field and generated plasma.
We offer a model of induced gratings describing a stationary transverse periodical distribution of FF and SH amplitudes
by trigonometrical functions risen to the definite power. Dependences of a lattice contrast, and peak amplitude on the
spatial period of the structure as well as the phase mismatch are found. The least period of the gratings corresponds with
a critical value of period, at which the periodic structure degenerates into a plane wave. We obtain also that such lattices
except the high contrast structures are unstable at long distances of about tens of the diffraction lengths. The modulation
instability of the lattices under the effect of the low frequency amplitude noise was investigated. Moreover, all-optical
switching effects for such structures in the quadratically nonlinear media were obtained.
New effect of mismatched parametric reflection due to noncollinear three-wave interaction in quadratic and cubic medium is studied. Original theory of this phenomenon is developed. Simple expression for the parametric reflection critical angle is found. Theoretical results are confirmed by numerical simulation.
A theoretical model has been developed for multiwave mixing in media with photorefractive nonlinearity, making it possible to describe the process of interaction between the waves in the conditions exhibiting nonlinearities of different orders with due regard for the mixing geometry. Theoretically, the process of <i>N</i>-wave mixing at the <i>N</i> - 1<sup>th</sup>-order nonlinearity has been described with the help of a band model for the photorefractive nonlinearity mechanism that includes the transitions from impurity levels within the band gap and enables description of the diffusion or drift processes in the external electric field. The energy efficiency of multiwave mixing and geometric parameters of spatial solitons in photorefractive Bi<sub>12</sub>TiO<sub>20</sub> crystals in the conditions of pulsed and continuous laser excitation have been studied experimentally. It has been found that switching-on of the photorefractive nonlinearity mechanism with 532 nmwavelength laser pulses requires a time interval in excess of 20 - 50 ns, with saturation beyond 80 ns. The formation dynamics of spatial solitons in photorefractive Bi<sub>12</sub>TiO<sub>20</sub> crystals has been analyzed with the use of continuous-wave radiation of a He-Ne laser. It has been determined that the formation conditions and dynamics are influenced by a number of factors including the geometry of radiation input into a crystal, power of the light beam, orientation of its polarization in the directions of the crystal axes, applied electric field and its direction.
The properties of a novel type of dislocations, called spatio-temporal vortices, are discussed. We propose to registrate them making dynamic interferogram of signal waves. Methods of their generation are suggested as well. It is illustrated that a spatio-temporal dislocation appears due to interaction of two Gauss-Laguerre pulsed beams with half-Pi phase shift. We show that superposition of two non-complanar phase modulated beams gives birth to the train of spatio-temporal vortices, which are periodical in space or time. The dynamics of a spatio-temporal vortex-soliton in defocusing Kerr-like medium is considered.
The influence of microwaves on biological materials, water solutions and pure water is the subject of many experiments and theoretical investigations. Some aspects of this problem include the so-called 'non-thermal' effects and arising of metastable states in liquid water under the action of microwaves. We carried out experimental investigation of the thermal effects of microwave interaction with water solution. These experiments consist of the spectrophotometric investigation of the reaction of non- organic water solution on the influence of 25 GHz microwaves with the thermal intensity. We investigate the optical density of the 12 percent MgSO<SUB>4</SUB> water solution, heated by microwaves to the different temperatures: 40 degrees C, 30 degrees C, and 25 degrees C. Water irradiated by low intensity continuous microwave radiation also exhibits an increase in optical density in near UV region, caused by the excitation of the electronic configuration of water molecule. The results obtained and therefore, indicative of changes in the water molecule itself under the action of microwave irradiation. The optical density spectra show these changes to be long-living.
For the first time the total transfer of pump energy to signal wave has been registered in the optical parametric oscillator with multiple frequencies. Both cases of quadratic and cubic nonlinearities have been investigated. The influence of phase mismatches (Delta) k<SUB>3</SUB> equals k<SUB>3</SUB> - k<SUB>2</SUB> - k<SUB>1</SUB> and (Delta) k<SUB>2</SUB> equals k<SUB>2</SUB> - 2k<SUB>1</SUB> on the operation of OPO is discussed.
A non-stationary reflection of continuous wave beam from a Kerr layer at a small incident angle is proposed based on numerical simulation. The angle of laser beam propagation and it center have a temporal oscillations near the average value at the end of nonlinear layer.
The thin films of fullerene C<SUB>60</SUB> and phtalocyanins (Pc): H<SUB>2</SUB>-Pc, Cu-Pc and Ru-Pc have been evaporated in vacuum on single crystalline quartz and KBr substrates (thicknesses: 0.14 - 2 micrometers ). Infrared reflectivity and transmittance spectra (BOMEM DA3-36, 500 - 5000 cm<SUP>-1</SUP>) were used for optical constants (refractive index and absorption coefficient) and complex dielectric function determination. In the case of fullerene by dispersion analyses of spectra the oscillator parameters for IR bands were obtained too.