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.