Dynamics of Large Femtosecond Filament Arrays: Possibilities, Limitations, and Trade-offs

Abstract

Stable propagation of large, multifilament arrays over long distances in air paves new ways for microwave-radiation manipulation. Although, the dynamics of a single or a few filaments was discussed in some of the previous studies, we show that the stability of large plasma filament arrays is significantly more complicated and is constrained by several trade-offs. Here, we analyze the stability properties of rectangular arrays as a function of four parameters: relative phase of the generating beams, number of filaments, separation between them, and initial power. We find that arrays with alternating phase of filaments are more stable than similar arrays with all beams in phase. Additionally, we show that increasing the size of an array increases its stability, and that a proper choice of the beam separation and the initial power has to be made in order to obtain a dense and regular array of filaments.PACS numbers: 52.38. Hb, 42.65.Sf, 42.65.Tg, 42.65.Jx High-power femtosecond laser-pulse filamentation is a flourishing field of nonlinear optics due to its numerous applications in remote sensing, lightning protection, virtual antennas, and waveguiding [1][2][3]. Experiments show that a femtosecond laser beams can ionize atmosphere at the kilometer-scale distances [4]. Propagation over such long distances is a result of the dynamic balance between the focusing Kerr nonlinearity, diffraction, and plasma defocusing due to multiphoton absorption. A proper arrangement of plasma channels into arrays built of multiple filaments can lead to control [5] and efficient guiding of electromagnetic radiation in air [6]. Dielectric [7] and hollow-core metallic waveguide configurations [8,9] were predicted theoretically and demonstrated experimentally [10] to guide microwave radiation. Periodic arrays of densely packed high-intensity filaments were shown to create a hyperbolic metamaterial medium, that allows for radar signal manipulation and resolution enhancement [11,12].Formation of desired, regular filament patterns requires precise control of filament distribution and interaction. Multiple filaments can be generated by an intense Gaussian beam [13,14], whose power is much higher than the critical power of self-focusing P cr . However, the distribution of filaments resulting from the breakup of a Gaussian beam is determined by intensity fluctuations [15] and modulation instability [16,17]. Moreover, the density of filaments generated in this way is limited [18,19]. Therefore, this method can not provide the fine control and the high filament density required for the microwave-radiation manipulation. A certain degree of control of the filament distribution can be obtained by special preparation of the Gaussian beam. It was demonstrated experimentally that the predetermined initial phase [20,21], amplitude distribution [15], and geometry of the beam [22] offer a limited control of the filamentation pattern. The filament distribution in an array can be even more deterministic if the position of each beam is managed independent...

Free-Space Nonlinear Beam Combining for High Intensity Projection

“…Arrays of filaments have been shown to enable various guided-wave structures in the free space for visible 4 , infrared 5 , radio and microwave 6 – 8 frequency radiation, depending on their configuration. The generation of large arrays of filaments calls for phase manipulation of the laser pulses as well as precise engineering of intensity/phase distributions and the nonlinear beam interactions 8 – 14 .…”

Controlling optical field collapse by elliptical symmetry hybrid polarization structure

“…However, it is always anticipated for the realization of controllable field collapse and sequent filamentation, due to its practical applications, such as guiding microwave radiation [14], enhancement of terahertz emission [15], generation of millijoule-level supercontinuum in solid media [16], etc. For those purposes, some methods have been proposed by controlling the input power and divergence angle [17], shaping the field profile [18,19], using the amplitude/phase mask [20][21][22][23], and introducing the spatial regularization [24]. In fact, the above methods are to manipulate the spatial structure of scalar optical fields in phase and amplitude, whereas the spatial structure of polarization states was rarely involved.…”