Ultrabroadband flying-focus using an axiparabola-echelon pair

Flying -focus pulses promise to revolutionize laser -driven secondary sources by decoupling the trajectory of the peak intensity from the native group velocity of the medium over distances much longer than a Rayleigh range. Previous demonstrations of the flying focus have either produced an uncontrolled trajectory or a trajectory that is engineered using chromatic methods that limit the duration of the peak intensity to picosecond scales. Here we demonstrate a controllable ultrabroadband flying focus using a nearly achromatic axiparabola-echelon pair. Spectral interferometry using an ultrabroadband superluminescent diode was used to measure designed super- and subluminal flying -focus trajectories and the effective temporal pulse duration as inferred from the measured spectral phase. The measurements demonstrate that a nearly transform- and diffraction -limited moving focus can be created over a centimeter-scale-an extended focal region more than 50 Rayleigh ranges in length. This ultrabroadband flyingfocus and the novel axiparabola-echelon configuration used to produce it are ideally suited for applications and scalable to >100 TW peak powers. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement