Influence of different scattering medium on propagation characteristics to femtosecond laser pulses

Abstract

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.