The propagation of high-power femtosecond laser radiation through an aerosol is studied experimentally and theoretically. In the course of experimental studies, the effect of aerosol on the characteristics of the radiation filamentation region was shown. On the basis of experimental data, the time dependence of the degree of inhomogeneity of the high-power femtosecond laser radiation field due to the spreading of the aerosol cloud is found. A theoretical model is proposed that makes it possible to reproduce experimental patterns not only qualitatively, but also quantitatively.
The influence of the type of the initial beam profile on the beginning and end of filamentation in a turbulent medium is considered based on a numerical experiment. It is shown that the beginning and length of filamentation can both move away and get close depending on the initial profile of the laser beam amplitude with topological charge increasing. In addition, the filamentation length decreases with increase of a topological charge. The statistical dispersion of the spread of the longitudinal filamentation boundaries decreases monotonically with an increase of the topological charge; in turn, the dispersion of lateral spread does not have a unique dependence on the topological charge value.
The propagation of high-power femtosecond laser radiation through an aerosol is considered. The propagation of high-power femtosecond laser radiation is simulated by passing through flat phase screens that simulate the passage through an aerosol. They have effective optical parameters corresponding to the properties of aerosol, which are found, respectively, for different values of intensity levels in the case of nonlinear interaction from the solution of the direct problem.
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.
Evolution of local instability in a ring vortex beam propagating in the turbulent atmosphere with highest nonlinearities of the refractive index as well as in uence of the effective characteristics of the light beam is investigated based on numerical calculation of the nonlinear Schrodinger equation with high-order nonlinearities. Propagation of high-power femtosecond laser radiation (HPFLR) with topological charge in the random medium under overlap of an amplitude-phase mask and an original beam is considered. Depending on the mask configuration and initial radiation power, rotation of the beam can lead both to converge and growth more distant of filamentation beginning as well as extension of filamentation area by two and more times.
Based on time-independent Helmholtz equation and its solution in frame of inhomogeneous approximation a hybrid computational method for imitation of propagation of bounded laser beam focused into biological tissue is introduced. The biological tissue is simulated as a semi-infinite randomly inhomogeneous medium. The developed approach is intended to model laser beams in the super-sharp focusing mode. The results of modeling of laser light focusing into the turbid tissue-like scattering medium with lenses of various shapes are presented.
We present a computational modeling approach for imitation of the time-domain optical coherence tomography (OCT) images of biotissues. The developed modeling technique is based on the implementation of the Leontovich–Fock equation into the wave Monte Carlo (MC) method. We discuss the benefits of the developed computational model in comparison to the conventional MC method based on the modeling of OCT images of a nevus. The developed model takes into account diffraction on bulk-absorbing microstructures and allows consideration of the influence of the amplitude–phase profile of the wave beam on the quality of the OCT images. The selection of optical parameters of modeling medium, used for simulation of optical radiation propagation in biotissues, is based on the results obtained experimentally by OCT. The developed computational model can be used for imitation of the light waves propagation both in time-domain and spectral-domain OCT approaches.
The method of laser IR radiation propagation simulation in a case of randomly inhomogeneous media based on Leontovich – Fock equation in the application of optical coherent tomography modeling in biotissues is proposed. We describe the proposed methodology and demonstrate its implementation on a test case.
We applied the method of statistical trials to the parabolic equation of laser radiation propagation in biotissue to perform a new method of optical coherence tomography modeling. Results of modeling tests show the efficiency of the developed approach.
An equation is formulated for the Wigner function of the light field from the nonlinear Schrdinger equation in the weak nonlinearity approximation of the transfer equation type. Various numerical approaches used to solve this equation for the Wigner function are analyzed.
The fulfillment of the conditions for the complete conservatism of various numerical schemes that are most widely used in the numerical study of the nonlinear Schrödinger equation(NLSE) in the filamentation problem is analyzed, that the use of standard procedures for the numerical realization of NLSE with higher nonlinearities leads to a significant violation of the law of conservation of the Hamilton function in the filamentation process. The solution of this problem is proposed.
Approach to the description of effect of a clustering in air is offered. This effect can be described as an impurity clustering in the squeezed streams. On the basis of the diffusive equations for density of number of filament estimates of the sizes cluster from the size of average intensity are carried out. The equations for density of number of filament were formulated by authors for the description of a multiple filamentation in air earlier.
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