All known realizations of optical wave packets that accelerate along their propagation axis, such as Airy wave packets in dispersive media or wave-front-modulated X-waves, exhibit a constant acceleration; that is, the group velocity varies linearly with propagation. Here we synthesize space-time wave packets that travel in free space with arbitrary axial acceleration profiles, including group velocities that change with integer or fractional exponents of the distance. Furthermore, we realize a composite acceleration profile: the wave packet first accelerates from an initial to a terminal group velocity, decelerates back to the initial value, and then travels at a fixed group velocity. These never-before-seen optical-acceleration phenomena are all produced using the same experimental arrangement that precisely sculpts the wave packet's spatio-temporal spectral structure.
Although a plethora of techniques are now available for controlling the group velocity of an optical wave packet, there are very few options for creating accelerating or decelerating wave packets whose group velocity varies controllably along the propagation axis. Here we show that `space-time' wave packets in which each wavelength is associated with a prescribed spatial bandwidth enable the realization of optical acceleration and deceleration in free space. Endowing the field with precise spatio-temporal structure leads to group-velocity changes as high as $\sim c$ observed over a distance of…
Accelerating beams are wave packets which appear to spontaneously accelerate without external potentials or applied forces. Since their first physical realisation in the form of Airy beams, they have found applications on various platforms, spanning from optics to plasma physics. We investigate the dynamics of examples of finite-energy accelerating beams derived from catastrophe theory. We use a Madelung transformation in momentum-space, combined with a wavelet transformed analysis, to demonstrate that the beams' properties arise from a special type of vanishing self-interference. We identify …
We propose and generate a new class of structured light fulfilling quantum-like coherent states based on a set of circular Airy vortex modes. Such coherent-state wave packets possess strong focus with both radial and angular self-accelerations, which exploit more general 3D inhomogeneous velocity control with global spatial symmetry of multilayer rotation akin to galactic kinematics, as termed galaxy waves. Galaxy waves are endowed with new degrees of freedom to control strong focusing and acceleration of 3D structured light, promising numerous applications in optical trapping, manufacturing, …
Space-time (ST) wave packets are propagation-invariant pulsed optical beams whose group velocity can be tuned in free space by tailoring their spatio-temporal spectral structure. To date, efforts on synthesizing ST wave packets have striven to maintain their propagation invariance. Here, we demonstrate that one degree of freedom of a ST wave packet -- its on-axis spectrum -- can be isolated and purposefully controlled independently of the others. Judicious spatio-temporal spectral amplitude and phase modulation yields ST wave packets with programmable spectral changes along the propagation axi…
Topological defects, such as quantum vortices, determine the properties of quantum fluids. The study of their properties has been at the center of activity in solid state and BEC communities. On the other hand, the non-trivial behavior of wavepackets, such as the self-accelerating Airy beams, has also been intriguing physicists. Here, we study the formation, evolution, and interaction of optical vortices in wavepackets at the Dirac point in photonic graphene. We show that even in a non-interacting two-component system the topological excitations appearing in a wavepacket can still be considere…
Metasurface has recently emerged as a powerful platform to engineer wave packets of free electron radiation at the mesoscale. Here, we propose that accelerating waves can be generated when moving electrons interact with an array of bianisotropic meta-atoms. By changing the intrinsic coupling strength, we show full amplitude coverage and 0-to-π phase switching of Smith-Purcell radiation from bianistropic meta-atoms. This unusual property leads to the creation of Airy beams that shifts along a parabolic trajectory during propagation. Experimental implementation displays that evanescent fields bo…
Programmable spatiotemporal shaping for partially coherent structured wave packets
Shandong Normal University（山东师范大学）；University of Shanghai for Science and Technology（上海理工大学）；Tianjin University of Technology（天津工业大学）；Shanghai Jiao Tong University（上海交通大学）；Westlake University（西湖大学）
Self-accelerating beams are fascinating solutions of the Schrödinger equation. Thanks to their particular phase engineering, they can accelerate without the need of external potentials or applied forces. Finite-energy approximations of these beams have led to many applications, spanning from particle manipulation to robust in vivo imaging. The most studied and emblematic beam, the Airy beam, has been recently investigated in the context of the fractional Schrödinger equation. It was notably found that the packet acceleration would decrease with the reduction of the fractional order. Here, I st…
Selective avoidance of multiple line-of-sight obstacles at 130~m using locally bending space-time wave packets
CREOL, The College of Optics & Photonics, University of Central Florida（中佛罗里达大学光学与光子学院）；Materials Physics and Applications - Quantum Division, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室材料物理与应用部量子部门）；Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University（哈佛大学工程与应用科学学院）
The development of ideas about the optical phenomenon called the accelerating matter effect led to the hypothesis of the existence of a very general acceleration effect. Its formulation is that the result of the particle interaction with any object moving with acceleration should be a change in its energy and frequency. The validity of the acceleration effect hypothesis in quantum mechanics has recently been confirmed by numerically solving a number of problems related to the interaction of a wave packet with potential structures moving with acceleration. If these ideas are true, they can be f…
