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 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.
Theoretical and experimental study of nonresonance generation of laser radiation by atoms, molecules and ions of matter - superradiation - is an important area of research in the field of femtosecond optics. Narrowly directed (forward and reverse), with an intensity proportional to the square of the number of inverted atoms, molecules and ions, radiation can be used to probe the atmosphere using femtosecond lidars. This paper presents the results of comparative experimental studies of the appearance of superradiance at transitions of molecular nitrogen ion in the atmosphere and at transitions of atomic strontium ion in a mixture with inert gases (He, Ne) in a heated cuvette. For the first time, superradiance was observed in the transition from the resonant electronic state 2Р1/2 / to the ground state 2S1/2 (407.8 nm), when Sr pairs were pumped by radiation at a wavelength of 268.1 nm.
The results of experimental studies aimed at improving the efficiency of the “telescope-deformable mirror” scheme for the purposes of long-range propagation of intense light channels in the air are presented.
The results of lidar measurements of emission spectra of targets and aerosols excited by filamented femtosecond Ti:Sapphire laser pulses are presented.
The results of experimental research of the filamentation of femtosecond laser pulses using a bimorph deformable mirror, which allows controlling the position of the filamentation domain determining localization of filaments and high-intensity channels in the beam cross section. The introduction of distortions into the amplitude profile of the beam with using masks showed the inability to control the number and position of filaments in the beam cross section.
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.
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 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 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.
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.
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.
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 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 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.
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.
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.
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.
We consider the algorithms that implement a broadband (‘multiwave’) radiative transfer with allowance for multiple (aerosol) scattering and absorption by water vapor. In the spectral range of 0.9 – 0.98 μm, a closed numerical simulation of modifications of the supercontinuum component of a probing femtosecond pulse is performed. The ability of water vapor concentration measurements with white-light femtosecond lidar on the path 100–200 m is discussed.
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.
The interaction of high-power terahertz radiation from the Novosibirsk free-electron laser at a wavelength of 130 μm in atmospheric transparency window with a model aerosol cloud having the known droplet size distribution function has been studied experimentally for the first time. The experimental data are compared with theoretical calculations obtained from solution of the lidar equation for conditions of the experiment.
The spectral transparency method has been tested experimentally in the terahertz spectral region. The aerosol particle size distribution spectrum has been reconstructed from measurements of the spectral transparency coefficient by the method of Time-Domain THz spectroscopy. The particle size distribution spectra obtained by the spectral transparency method in the terahertz region and by the method of optical microscopy have been compared.
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.
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.
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