Dynamics of femtosecond synthesized coronary profile laser beam filamentation in air

Abstract

Multiple filamentation in air of high-power ultrashort laser radiation with transverse intensity profile resembling a "corona" composed by incoherent combining of several annularly distributed independent top-hat sub-beams is theoretically studied. Through the numerical solution of timeaveraged nonlinear Schrodinger equation, we study the spatio-angular dynamics of synthesized near-infrared "corona-beam" (CB) along the optical path by varying the number and power of the beamlets (corona-spikes). For the first time to our knowledge, the evident advances in the multiplefilamentation region manipulating of synthesized CB are demonstrated. Particularly, by adjusting the number and aperture of the constituting sub-beams it makes possible to significantly delay the CB filamentation onset distance and increase the filamentation length in air. In addition, at the postfilamentation stage of femtosecond pulse propagation under certain conditions the synthesized corona-beams exhibit significantly lower angular divergence of its most intense part (postfilamentation light channel) compared to the beams with regular unimodal intensity profiles (Gaussian, plateau-like) that provides enhancing of laser power delivered to the receiver over the atmospheric links.

Numerical simulations of self-channeling and filamentation of spatially pre-modulated high-power femtosecond laser pulse in air

“…The reduced version of NLSE was obtained after integrating the original (3D+1) NLSE over the temporal coordinate. The issues of the admissibility of using such an approach are considered, e.g., in [12]. It is established that such an approximation makes it possible to adequately simulate the main regularities of high-power laser pulses filamentation at moderate propagation distances (several Rayleigh ranges), when the effects associated with the intra-pulse dynamics of the optical field intensity (light shock wave, time front collapse, electron density kinetics) and temporary "memory" of the medium (pulse group-velocity dispersion, molecular Raman scattering) can be assumed of less importance.…”

“…Following [12], the time profile U of a real (Gaussian) laser pulse with a duration tp was replaced by a probe stepwise pulse with a certain effective duration t0:…”

“…laser beams with non-Gaussian transverse intensity distribution. Examples of such beams are an annular [10] and quasi diffraction-free Bessel-Gaussian beams [11], a necklace "corona-beam" [12], and a "dressed" beam (a superposition of Gaussian and annular profiles) [13,14]. The results of works [10][11][12] showed the possibility of forming a spatially remote and extended filamentation region.…”

“…Examples of such beams are an annular [10] and quasi diffraction-free Bessel-Gaussian beams [11], a necklace "corona-beam" [12], and a "dressed" beam (a superposition of Gaussian and annular profiles) [13,14]. The results of works [10][11][12] showed the possibility of forming a spatially remote and extended filamentation region. Using the structured optical radiation is associated with the specific diffraction dynamics of such beams, which in some cases leads to increasing the coordinate of the beam nonlinear focus and the laser filamentation beginning.…”

Численное Моделирование Филаментации Фазомодулированных Фемтосекундных Лазерных Импульсов В Воздухе

“…Среди них приоритетными для атмосферной оптики являются координата начала и протяженность филаментов, их количество и сплошность (продольная непрерывность). В этом плане перспективным методом решения указанной задачи является использование специально профилированного лазерного излучения, о чем свидетельствуют результаты, полученные в [1][2][3][4]. Одним из примеров преимуществ, проявляющихся при распространении такого структурированного излучения, являются результаты работы [5], в которой экспериментальные исследования выполнялись с использованием фазомодулирующих дифракционных элементов.…”