Experimental results of measurements of the threshold power density of stimulated radiation in solutions of the coumarin-30 dye with ZnO nanoparticles irradiated with femtosecond laser pulses are presented. It is shown that the thresholds of stimulated emission in solutions of the coumarin-30 dye with ZnO nanoparticles are approximately three orders of magnitude higher than the thresholds of stimulated emission in solutions of the coumarin-30 dye with ZnO nanoparticles irradiated with nanosecond laser pulses.
The results of measure of the duration of a femtosecond laser pulse propagating in a mixture of dry air and water vapor (atmosphere) on a hundred-meter atmospheric track have been presented. Measurements have been made for a spectrally limited pulse and a pulse with initial frequency-phase modulation. A model for calculating the humidity and refractive index of a multicomponent medium for estimating the dispersion spread of an ultrashort pulse in the atmosphere has been discussed.
One of the actual problems of the multi-frequency laser remote sensing is the using of the self-action phenomena of pulsed femtosecond laser radiation. When femtosecond laser radiation propagates in the atmosphere, both the transformation of the spectral and spatial characteristics of the radiation dispersion and the pulse duration occurs. The effect of atmospheric air dispersion on the duration of a femtosecond pulse propagating in the atmosphere is discussed via the results of experiments. The fact of compensating of the dispersion spreading of the pulse duration in air by its temporary “compression” under the influence of a change in the phase modulation index in an optically active impurity is not excluded.
The problem of the propagation of a femtosecond laser radiation in the atmosphere remains relevant in the application to the problems of remote sensing. When radiation propagates in a multi-component dispersive medium, for example, atmosphere, two important facts are occurred. The first is the transformation of the spectral and spatial characteristics of the radiation. The second is the dispersion modification of the duration. The results of experiments to take into account the dispersion effect of a multi-component medium (atmospheric air) on the duration of a femtosecond wave packet propagating in the atmosphere are discussed.
A series of laboratory and full-scale experiments on the propagation of high-power terawatt radiation on the basis of a femtosecond stand of the IAO SB RAS have been carried out. The problem of the spreading of femtosecond pulses in air is considered. The results of the investigation of dispersion spreading of pulses of femtosecond duration are presented.
A brief description of the unique femtosecond lidar is presented. A number of experiments were conducted on inclined
remote sensing of the atmosphere above Akademgorodok, Tomsk (56 ° N, 85 ° E) via this lidar. Questions on the
features of the propagation of femtosecond laser radiation, for example filamentation, generation of conic emission of a
supercontinuum (SC) are considered. The most important characteristics of the femtosecond lidar system are determined
with reference to the problem of remote sensing of the atmosphere, in particular, low cloud cover. The study has a
pronounced practical additivity to the use of a femtosecond lidar system in remote sensing problems.
A brief review of the development of experimental methods of the monitoring of the environment using femtosecond lidar systems of Institute of atmospheric optics (IAO SB RAS, Tomsk, Russia) has been presented. Spectrums if lidar returns for the distance 110 m which has been detected via femtosecond laser-induced breakdown spectroscopy method (FS-LIBS) has been discussed. It has been shown that as spectral distribution of the energy of the supercontinuum emission, as results of the interference of the emission of “near” filaments are detected in the case of multiple filamentation of lidar signals.
The results of laboratory experiments and numerical calculation of propagation of high-power terawatt femtosecond laser radiation via different media (air, glass and water) are represented. The experiments have been made on femtosecond Ti:Sa-laser system of IAO SB RAS. The spatial features of high-power terawatt femtosecond laser radiation are presented also. The ability of control of the position of the beginning of the field filamentation and angle of divergence of supercontinuum on high-power terawatt femtosecond laser radiation via plane parallel plate (glass) are found. The values of the location of the high value of the backscattering depending on filamentation conditions and the characteristics of supercontinuum and lidar system are obtained. The ability of the remote sensing of cirrus clouds with the help of high-power terawatt femtosecond laser radiation is discussed. The results of interactions of high-power terawatt femtosecond laser radiation and ice hexagonal plate crystal depending upon location of this crystal and filamentation conditions are represented.
The experimental results of the filamentation terawatt femtosecond Ti:Sapphire-laser along an atmospheric path of 100- m length atmospheric path using different spatial focusing and pulse power. The high efficiency of controlling the position and length of the filamentation zone using various spatial focusing are presented. The dependences of the length and position of the filamentation of the initial degree of focus and pulse power, number of filaments along the filamentation zone is determined. The data are compared to the length of the field and the number of filaments filamentation with the results of our earlier experiments.
Mueller matrices for ice crystals horizontally and preferably oriented in horizontal plane are calculated with a code
("facet-tracing") based on the geometric optics. For the case of preferably oriented ice crystals particles uniform and
normal distributions of flutter with maximum dimension of 5° are analyzed. The main physical regularities inherent to
the scattering matrices are discussed. Degree of polarization of the scattered light is shown to be a qualitative criterion of
number of photon trajectories that contribute effectively to the scattered light. The inverse scattering problem of
retrieving aspect ratios of the horizontally/preferably oriented hexagonal ice plates from polarization of the scattered
light in the bistatic sounding scheme has been proposed and discussed.
Knowledge of optical properties of ice crystal particles of cirrus clouds is a challenging problem of atmospheric optics.
Cirrus clouds cover, in average, 20%-30% of Earth's surface that leads to their essential impact of climate. Therefore
these optical properties are needed for incorporation in up-to-date models of Earth's radiation budget and, consequently,
they should be used in numerical models of climate prediction or climate change.
The optical properties of ice crystal particles have been calculated for recent 20-30 years by a lot of authors under an
assumption of 3-D orientation. However, the crystals often reveal a tendency to be oriented in the horizontal plane
because of aerodynamic laws.
Phase functions for light scattering by horizontally and preferably oriented hexagonal ice plates and columns are
numerically calculated within the framework of geometric optics. The main quantitative properties of the halos (sundog,
parhelion 120°, suncave Parry arc, sunvex Parry arc, and others) are obtained for a number of both incident light
directions and aspect ratios of the plates and columns respectively. A parameterization of the phase functions in the
parhelic, subparhelic and circumzenithal (circumhorizonthal) circles for the plates and all scattered energy for the
columns are proposed based on the integral contributions of the narrow angular peaks (halos) that are tabulated as the
weight coefficients.
Our results can be used for atmospheric lidar observation for determining of size, shape distributions of the ice crystals
particles in cirrus clouds.
A method for retrieving aspect ratios of the plates by means of polarization measurements is discussed.
The scattering (Mueller) matrices for hexagonal ice plates of various aspect ratios are calculated by the facet tracing method developed earlier. For horizontally oriented plates, the Mueller matrices depending on the incident angle have been obtained. The peculiarities inherent to the scattered light along the parhelic circle have been studied. A generalization of the data for small flatter of these plates relative to the horizontal plane is discussed.
Scattering matrices are calculated for hexagonal ice columns and plates with preferred orientation near the horizontal plane by means of an algorithm based on geometric optics. Distributions of scattered energy among the various arcs inherent to scattering by oriented crystals are obtained. Impact of small orientation deviations from the horizontal plane is discussed.
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