Multiple filaments generation and manipulation are crucial to numerous applications. The refractive index of medium has essentially influenced nonlinear effects in the ultrafast optical process of femtosecond laser filamentation, which is an effective method to tailor and manipulate filamentation. We have proposed a new method that using a periodic gas lattice as transmission medium to generate multiple filaments of femtosecond laser pulse. The periodic gas lattice is consisted of air waveguides, which has the special refractive index change distribution with alternating positive and negative. Our results show that the properties of multi-filament can be well controlled by changing the parameters of the gas lattice. A multi-filament array is formed by the gas lattice along the beam propagation direction, which are systemically investigated with different parameters of lattice at filamentation stages. The underlying physical mechanism of the multi-filament array formation is discussed, which has been demonstrated that the effects of extra focusing and discrete diffraction introduced by the gas lattice medium to promote a new competition and balance in the nonlinear filamentation process. The findings in this work provide a new way for many potential and promising applications that based on the controlled and optimized the femtosecond laser multi-filament array.
Turbulence is ubiquitous in ambient air and has always posed a great challenge for realizing optical applications in the atmosphere. The refractive index of turbulent air fluctuates randomly has obviously influences on the nonlinear process and characteristics of filamentation, which is a crucial role for many practical applications in free-space atmosphere. In the numerical simulation, we have investigated the filamentation and supercontinuum generation of femtosecond laser pulse with strong atmospheric turbulence in the path of whole the propagation distance. The spatial profile of intensity is analyzed in detail by changing perturbation strength of turbulence. The results show that the laser energy flow distribution presents stronger optical modulation instability with the increase of turbulence intensity in air. Complex spatial multifilament structures are generated by nonlinear propagation in strong turbulent air. The optical intensity along propagation distance significantly decrease as the strength of turbulence increases. The supercontinuum spectrum of filamentation in different strengths turbulence is also investigated. The physical mechanism of supercontinuum intensity change with different strengths of turbulence is discussed. Our results are valuable for realizing the free-space applications based on filamentation and supercontinuum in extreme weather with strong turbulence.
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