Bending space-time wave packets

Abstract

Optical beams with certain asymmetric profiles, such as the Airy beam, can depart from rectilinear propagation and instead travel along curved (typically parabolic) trajectories. Here we show that sculpting the spatiotemporal spectrum of optical pulses yields self-accelerating beams that have symmetric profiles, remain diffraction-free, and travel along power-law curves with propagation distance having arbitrary positive exponent (integer or fractional). We build upon propagation-invariant space-time wave packets (STWPs), in which each spatial frequency is associated with a single wavelength. A linear tilt in the propagation path of an STWP is produced by a corresponding tilt in the spectral domain. A curved trajectory is then produced through locally changing the tilt direction along the propagation axis, which requires associating a prescribed finite-bandwidth spatial spectrum to each wavelength. Using this approach, we realize symmetric STWPs traveling along curved trajectories that follow linear, quadratic, cubic, or even square-root power laws with an acceleration rate that is independent of the beam spatial scale. These novel bending STWPs open new avenues for realizing target-avoidance with electromagnetic waves.

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