In this study, the heat deposition characteristics of laser filaments formed by femtosecond laser pulses with different initial energy under influences of external focusing are numerically investigated by means of (3D + 1)-dimensional numerical simulations. The results indicate that the numbers and intensity of filaments increase with growth of the input energy. The formation of multiple filaments limits the increase of filament length. When fixing the input energy, radius of the filament becomes narrow while its numbers and intensity are both enhanced under strong focusing. Under stronger focusing, the filaments can also deposit higher laser energy and result in larger energy deposition rate for laser beams with a given input energy, which further leads to dramatic increase in local temperature and pressure. These are likely to affect the filament induced airflow velocity and eventually the mass of formed snow in the cold supersaturated cloud chamber.
The nonlinear propagation of femtosecond Airy laser filaments in water is numerically investigated in this paper. We mainly consider the influences of confinement parameter, pulse duration and beam waist on the deposited energy of filaments. The values of confinement parameter are found to have a significant impact on the temporal and spatial dynamics of the pulse. The characteristics of energy deposition also differ widely for Airy beams with different confinement parameters. The less the confinement parameter, the more energy deposited by filamentation. However, the relative deposited energy evolves relatively small changes under different confinement parameters. We also found the longer pulse duration and longer beam waist are beneficial to the total deposited energy increase.
During recent years, the filamentation of femtosecond laser in the atmosphere has contributed considerable interest to researchers. However, the actual atmosphere can result in different scattering medium, which are adverse to the application of filamentation in the atmosphere. In order to study the propagation of femtosecond laser in real scattering medium, the propagation of 800 nm femtosecond laser in ice cloud, water cloud, fog, aerosol and rainfall is simulated numerically. Combined with the theory of stratified medium model and Mie scattering theory, we constructed a scattering model with a changeable size distribution function in the nonlinear laser model. The results indicated that the different size distribution and phase state of particles have different influence on the propagation properties of the filaments. As the rainfall was dominated by large raindrops, the scattering on filament was the strongest, resulting in the lowest peak intensity and energy. In the case, the distribution of filament energy was extremely inhomogeneous, causing the shortest length of filament and generation of multi-filament. In the image of fluence distribution, a diffraction ring can be observed clearly in the rainfall but was blurred in other medium. The propagation properties of filaments in water cloud and fog were similar because of the same size distribution. However, due to the size of particle in fog was smaller than that in water cloud, the filaments had more higher energy and more concentrated distribution in fog. In addition, the scattering of ice particles was stronger than that of liquid droplets, so the energy of filament in ice cloud was lower than that in water cloud, resulting a reducing of the length and number of filaments in ice cloud. The size of aerosols was the smallest, which had the weakest influence on the filament. Accordingly, in the early of propagation, there had little perturbance on the filament and the beam was transmitting with a stable single filament, and results in the highest peak intensity and energy. With the propagation increasing, the accumulation of scattering attenuation produced the perturbation on filament at a position after the onset of filamentation.
The crucial role of nonlinear propagation effects in the self-guiding of femtosecond laser pulses required accurate representation of nonlinearities to describe them. In this paper, an improved theoretical model has been proposed to study the height distribution of the atmospheric nonlinear refractive index. The results show that the revised model obviously improves accurate estimation of nonlinear index at the long wavelength band. Based on the model, we also found the atmospheric nonlinear refractive index differs much from the lower atmosphere to the upper atmosphere. Our results are essential for engineering applications based on the long-distance ultrashort laser pulses’ transmission in diverse atmosphere.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.