Spatiotemporal steering of non-diffracting wavepackets

We study the dynamics of space-time non-diffracting wave packets, commonly known as light bullets, in space-time-varying media. We show that by spatiotemporal refraction, a monochromatic focused beam can be converted to a propagating light bullet. By further designing the index profile of the spatiotemporal boundary, the group velocity and the propagation direction of the light bullet can be engineered in a programmable way. These findings provide unique control of electromagnetic waves in space-time, and may lead to applications in the spatiotemporal control of material properties, or for use as a way to emulate relativistic physics in the laboratory.