Dynamical Modulation of Transverse Orbital Angular Momentum in Highly Confined Spatiotemporal Optical Vortex

Spatiotemporal optical vortices (STOVs) have attracted numerous attention from researchers in recent years due to their intriguing characteristics with transverse orbital angular momentum (OAM) in the spatiotemporal domain. In this work, we numerically analyze the tightly focusing characteristics of higher-order STOVs and present a method to dynamically modulate the transverse OAM in highly confined STOVs. Richards-Wolf vectorial diffraction theory was employed to simulate the three-dimensional spatiotemporal distribution of the focused STOV corresponding to the incident wave packet of topological charge of -2. The simulation results show that the higher-order spatiotemporal vortices in the transversely polarized components of the focused wave packets split into two first-order vortices with topological charge of -1 when the waist radius of the incident wave packet was larger than 40% of the pupil radius of the focusing lens, and the spacing of the two split vortices could be tailored by adjusting the waist radius of the incident wave packet. Meanwhile, the incident spatial waist radius also affected the tilt angle of the phase singularity trace in the z-polarized component of the focused field. The presented method provides a flexible way to dynamically engineer the spatiotemporal vortices in the tightly focused wave packet and may find potential applications in nanophotonics, light-matter interaction, quantum information processing, etc.