Selective avoidance of multiple line-of-sight obstacles at 130~m using locally bending space-time wave packets

Abstract

Self-accelerating optical beams follow curved trajectories rather than propagating rectilinearly, which raises the prospect for avoiding line-of-sight (LoS) obstacles blocking the beam path. However, if a conventional laser beam is intercepted by an obstacle en route to an intended LoS target, then replacing this beam with a bending beam is not adequate: the obstacle is avoided but the target cannot be concomitantly reached. Rather, a laser beam that \textit{locally} bends around the obstacle -- before continuing along its rectilinear path -- is needed. Here we show that engineering the spatiotemporal spectrum of a pulsed beam yields a space-time wave packet whose propagation dynamics can be tuned at will to locally bend around one or multiple obstacles, thereby avoiding them, to selectively reach a designated target. We carry out our experiments over distances extending to 130~m from the source, carried out in an open-air environment. In one scenario, the beam is incident on a target placed between two LoS obstacles, one preceding it and one following it -- both of which are avoided. In a second scenario, the locally bending beam avoids one and then two LoS obstacles preceding the intended target. These results may contribute to applications requiring selective incidence on targets in remote sensing, stand-off detection, directed energy, for optical and radio-frequency communications in presence of LoS obstacles, and for selectively delivered radiation therapies.