Interpretation of the data from lidar studies of high-level clouds requires information on the vertical profiles of meteorological quantities. The nearest aerological stations to Tomsk are located at about 250 km away from the city and launch radiosondes only twice a day. The ERA5 reanalysis was considered as a source of vertical profiles, which provides higher spatial and temporal resolution. It is compared with the aerological data, and the possibility of its using was evaluated in this research.
The propagation of ultrashort laser pulses in the atmosphere is accompanied by nonlinear effects. The most low-threshold of them is the effect of cubic nonlinearity along with nonlinear absorption manifesting in aerosol. This effect should lead to the transformation of the scattering phase function formed in a liquid droplet aerosol. To study this effect, numerical and experimental studies on droplets of various sizes and geometries were carried out. As expected, the cubic nonlinearity inclusion should lead to an increase in the effect of backward scattering.
The results of experimental and theoretical studies of the filamentation of femtosecond laser pulses using a bimorph deformable mirror, which allows controlling the position of the filamentation domain throughout a model path due to phase distortions of different parts of a laser beam, determining localization of filaments and high-intensity channels in the beam cross section.
The results of experimental studies of filamentation of focused laser pulses of nanosecond megawatt duration in a medium with strong cubic nonlinearity are presented. It was shown that multiple small-scale beam self-focusing is observed, the nonlinear focus is much closer to the source than the geometric one, and this distance increases with an increase in the pulse energy (power). Long tracks are observed that are uncharacteristic of linear spatial focusing.
The goal of the work was the experimental study of femtosecond filamentation laser pulses using a bimorph deformable mirror (DM). Phase distortions of different parts of the laser beam make it possible to control the position of the filamentation domain along the entire length of the model path. The use of a bimorph deformable mirror makes it possible to determine the localization of filaments and high-intensity channels in the cross-section of the beam. The mode of formation of long (> 100 m) high-intensity (1011-1012 W/cm2 ) weakly converging non-filamentary channels was detected.
The report presents the results of experiments on plasma inducing on aerosol particles containing metals placed in the filamentation area of the beam and identification of the elemental composition from the emission spectra.
The transverse structure formation processes of a laser beam after multiple filamentation were investigated. It is shown that the spectra of post-filamentation light channels (PFC), rings and beam differ substantially. The spectrum of PFC has a significant and symmetrical spectral broadening and covers a range of 600-1100 nm. The broadening of the spectrum of the rings is asymmetric and is directed mainly to the short-wavelength region of the spectrum. The broadening data are stable and do not change when moving away from the multiple filamentation zone. The annular structure of radiation in the cross section of the beam is formed around individual filaments within the region of multiple filamentation, and at a distance of tens of meters from it begins to form a common ring structure surrounding postfilamentation channels.
The transverse structure formation processes of a laser beam after multiple filamentation were investigated. It is shown that the spectra of post-filamentation light channels (PFC), rings and beam differ substantially. The spectrum of PFC has a significant and symmetrical spectral broadening and covers a range of 600-1100 nm. The broadening of the spectrum of the rings is asymmetric and is directed mainly to the short-wavelength region of the spectrum. The broadening data are stable and do not change when moving away from the multiple filamentation zone. The annular structure of radiation in the cross section of the beam is formed around individual filaments within the region of multiple filamentation, and at a distance of tens of meters from it begins to form a common ring structure surrounding postfilamentation channels.
The results of experimental studies of postfilamentation channels controlled by the track length of 150 meters for collimated beams of different diameters. It is shown that the divergence of the laser beam after the filamentation area is much greater than the divergence postfilamentation channels. It is shown that at distances from the end of the field filamentation, significantly exceeding the length of the field filamentation, postfilamentation channels contain sufficient intensity to generate multiple filamentation in the optical elements and enables us to provide a functional effect on the optical elements of the matrix.
The results of experimental studies of the spatial characteristics of multiple filamentation terawatt femtosecond Ti:Salaser in water are presented. With an increase in initial power laser pulses increases the number of filaments, the length of the field is increased filamentation and reducing the length of the filaments have been shown. The distribution of the filaments in the longitudinal direction of the field of multiple filamentation has a maximum cross-sectional filament is shifted from the center to the periphery of the beam at the end region of filamentation. The minimum diameter of the beam on the track corresponds to the position of the maximum number of filaments. After the point of maximum impulse essentially loses energy in the initial direction of propagation. Upon reaching the pulse power 2 104 Pcr of multiple filamentation area is formed of a hollow cone, the apex directed to the radiation source.
Results of experiments on controlling the position and length of the filamentation zone of femtosecond laser pulses in atmospheric path length 150 m using different initial spatial focusing and defocusing. The obtained distribution of filaments along the filamentation zone, measured dependence the length of the filamentation zone of the numerical aperture of the beam, its initial radius and pulse power.
The results of experiments to study the spatial characteristics of multiple filamentation gigawatt laser pulses in the glass are presented. It is shown that with increasing pulse power multiple filamentation region increases in length and diameter, the distribution of filaments within the region has a maximum value when the power > 105 Pcr area filamentation takes the form of a hollow cone, the apex directed to the source of the laser radiation.
The results of natural experiments of the propagation of powerful femtosecond laser radiation in glass and water, accompanied by multiple filamentation, and the results of numerical simulation of the process are presented. Based on the diffusive equations for density of the number of filament estimates of the positions of maxima in the number of filaments were obtained. Sufficient criterion of macroscopic refocusing for density of the number of filaments was established.
Experimental results of investigations into the transformation of the spectral and spatial characteristics of femtosecond collimated and focused Ti:Sapphire-laser beams with wavelengths of 800 and 400 nm upon filamentation in continuous liquid media are presented. It is shown that broadening of the laser pulse spectrum due to phase self-modulation in the medium with a cubic nonlinearity depends on the pulse power and beam diameter. Dependences of the number of filaments, width of laser radiation spectrum, nonlinear focusing distance, and diameter of the filamentation region on the laser pulse power are measured. The existence of a relative power interval in which the explosive growth of the number of filaments occurs, is established.
The results of experiments to study the spatial characteristics of multiple filamentation gigawatt laser pulses in the glass are presented. It is shown that with increasing pulse power multiple filamentation region increases in length and diameter, the distribution of filaments within the region has a maximum value when the power > 105 Pcr area filamentation takes the form of a hollow cone, the apex directed to the source of the laser radiation.
The results of numerical simulation of multiple filamentation of terawatt femtosecond pulse Ti:Sapphire laser performed on the experimental data obtained in the airway of a length of 106 m when changing the initial spatial focusing and laser power.
Results of experiments on controlling the position and length of the filamentation zone of femtosecond laser pulses in atmospheric path length 110 m using different initial spatial focusing and defocusing. The obtained distribution of filaments along the filamentation zone, measured dependence the length of the filamentation zone of the numerical aperture of the beam, its initial radius and pulse power.
The results of experimental studies of the spatial characteristics of multiple filamentation terawatt femtosecond Ti:Salaser in water are presented. With an increase in initial power laser pulses increases the number of filaments, the length of the field is increased filamentation and reducing the length of the filaments have been shown. The distribution of the filaments in the longitudinal direction of the field of multiple filamentation has a maximum cross-sectional filament is shifted from the center to the periphery of the beam at the end region of filamentation. The minimum diameter of the beam on the track corresponds to the position of the maximum number of filaments. After the point of maximum impulse essentially loses energy in the initial direction of propagation. Upon reaching the pulse power 2 104 Pcr of multiple filamentation area is formed of a hollow cone, the apex directed to the radiation source.
Experimental results on the position and length control of the femtosecond laser pulses filamentation area on the atmospheric path of 30 m length using a different initial spatial focusing are presented. The dependence on the filamentation area length of numerical beam aperture value was obtained. Obtained data comparison on filamentation area length and quantity of filaments with previously conducted experiments results and the other authors’ data carried out.
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.
The results of experimental studies of filamentation of femtosecond laser pulses in water is presented. Measured the number of filaments, the spectral width of the laser radiation, nonlinear focusing distance, the diameter of the field of filamentation power laser pulses. Noted the existence of plot on the scale of the relative power in passing which the explosive growth in the number of filaments.
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