Multi-dimensional control of femtosecond laser filaments by inserting a wedge plate in the forced focusing region

Abstract

Modulating the length and position of plasma filament is desired for many filament-based applications. We proposed a novel method to manipulate the properties of filament along the propagation direction by introducing asymmetric focusing with a wedge plate in the forced focusing region. By simply varying the inclination degree of a wedge and the distance between the wedge and lens, a plasma filament can break into two sub-filaments along the propagation direction, and the separation between sub-filaments can be controlled. The experiment results are in agreement with the results of simulation by the ray-tracing method. Furthermore, the effect of the wedge angle and rotation angle on the control of the filament is studied. It is found that the separation of the sub-filaments and the azimuth angle of the filament around the original optical axis can be controlled by the wedge angle and rotation angle of the wedge, respectively. When combined with a phase plate, the control method also shows the ability to modulate the multi-filament array with wavefront modification. Our research provides a simple and flexible method for 3-D control of femtosecond laser filaments for practical applications.

Supercontinuum Induced by Filamentation of Bessel-Gaussian and Laguerre-Gaussian Beams in Water

“…Research Content 0-order BG control of filament [27][28][29][30] accompanied nonlinear phenomena [30][31][32] Higher-order BG control of filament [37] nonlinear propagation and filamentation [38] Higher-order LG multiple filaments [33][34][35][36] Coherence of SC [39] Due to the different geometries (i.e., focal spot shape and size, etc.) of BG and LG beams, the filaments generated by BG and LG beams exhibit different shapes.…”

“…For example, Bessel beams have propagation invariance compared with Gaussian ones; that is, they have the ability to maintain their shape and peak power at the extended focal region (Bessel region), which makes them have promising application prospects in many fields, especially for micro-processing. Using the Bessel beams, the length, plasma density and laser intensity of the femtosecond filament can be well controlled [27][28][29][30], see Table 1. For example, Wang et al tailored the profile of the annular Bessel beams by placing an amplitude mask and iris diaphragm, respectively, before the axicon, and thus the onset and terminal positions of femtosecond laser filament in the fused silica can be arbitrarily controlled [28].…”

“…For example, Wang et al tailored the profile of the annular Bessel beams by placing an amplitude mask and iris diaphragm, respectively, before the axicon, and thus the onset and terminal positions of femtosecond laser filament in the fused silica can be arbitrarily controlled [28]. Once the parameters of femtosecond filament are controlled, they are accompanied by several nonlinear phenomena such as photoionization and supercontinuum (SC) generation; fluorescence emission is also affected [30][31][32]. For example, Dota et al studied the filamentation of Bessel beams in BaF 2 by measuring the side emitted fluorescence and transmitted SC [32].…”