In this work breathers are obtained in a hollow-core photonic crystal fiber (HC-PCF) for the first time. The nonlinear Schrödinger equation describing the propagation of pulses in a HC-PCF is investigated using the Hirota bilinear method and the auxiliary function method. Analytic breather solutions are derived by an appropriate choice of parameters. Dynamical behavior of breathers is exhibited, and the influences of different parameters on the characteristics of breathers are discussed. The presented results could be used in fiber lasers, nonlinear optics and Bose-Einstein condensates.
The robustness and prolongation of multiple filamentation (MF) for femtosecond laser propagation in air are investigated experimentally and numerically. It is shown that the number, pattern, propagation distance, and spatial stability of MF can be controlled by a variable-aperture on-axis pinhole. The random MF pattern can be optimized to a deterministic pattern. In our numerical simulations, we configured double filaments to principlly simulate the experimental MF interactions. It is experimentally and numerically demonstrated that the pinhole can reduce the modulational instability of MF and is favorable for a more stable MF evolution.
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