Colorless movement of focal spot with arbitrary velocity based on mirrors with special shape

Abstract

Abstract Focal spot with moving speed is a new concept proposed in recent years, which has many applications in physics of intense field. The current method is to control the moving speed of focal spot by chirped pulse technique and chromatic aberration focusing, which suffers from the change of frequency components with the movement of focal spot. In this paper, we propose a method to realize the colorless movement of focal spot at arbitrary speed by using two kinds of mirrors. One is an aspherical mirror with long focal depth and the other is a stepped mirror. For a specific moving speed, we derive the relationship between the surface of aspherical mirror and the wavefront of laser by the geometrical optics. The stepped mirror is used to form stepped wavefront to separate the relationship between the shape of wavefront and the direction of laser. Time-dependent simulations are carried out to verify the real focusing property after considering diffraction effects, and focal spots with moving speed of 0.5c, 2c and −c are obtained.