Flexible trajectory control of Bessel beams with pure phase modulation

On-demand generation of nondiffracting Helmholtz-Gauss laser beams

Nondiffracting beams have gained significant interest because of their ability to propagate over long distances without divergence, making them highly valuable in various laser applications. Historically, laser sources for nondiffracting beams were constrained by their symmetry in the cavity's coordinate system and intracavity elements, which restricted the types of beams that could be directly generated from the cavity. This study presents the first direct generation of nondiffracting Parabolic-Gauss beams, as well as other Helmholtz-Gauss beams with helical wavefronts, directly from a laser cavity. The key technique involves controlling the two end-phase boundaries of a dual-modulation digital laser resonator with a concentric configuration, thereby ensuring stable round-trip conditions for generating various nondiffracting beams. The experimental results demonstrated that the dual-phase modulation digital laser could generate Parabolic-Gauss, Bessel-Gauss, Mathieu-Gauss beams, and even vortex nondiffracting beams. This laser source enables dynamic, real-time adjustment of beam properties, which is highly beneficial for applications requiring nondiffracting beams.

On-Chip Meta-Optics for Engineering Arbitrary Trajectories with Longitudinal Polarization Variation

On-chip integrated meta-optics promise to achieve high-performance and compact integrated photonic devices. To arbitrarily engineer the optical trajectory along the propagation path in an on-chip integrated scheme is of significance in fundamental physics and various emerging applications. Here, we experimentally demonstrate an on-chip metasurface integrated on a waveguide to enable predefined arbitrary optical trajectories in the visible regime. By transformation of the transverse phase to generate longitudinal mapping, the guided waves are extracted and molded into any different optical trajectories (parabola, hyperbola, and cosine). More intriguingly, predefined polarization states with longitudinal variation are also successfully imparted along the trajectory. Owing to the on-chip propagation scheme, the trajectories are uniquely free from zero-order diffraction interference, naturally having a higher signal-to-noise ratio beyond conventional free-space forms. Overall, such on-chip optical trajectory engineering allows for miniaturized integration and can find paths in potential applications of complex optical manipulation, advanced laser fabrication, and microscopic imaging.

Simple algorithm for the design of accelerating Bessel-like beams with adjustable features along their propagation

We present an extremely simple method for designing self-accelerating non-diffracting beams having arbitrary trajectories while their intensity, width and orbital angular momentum are modulated in a prescribed way along their propagation. Different beams constructed with this method are demonstrated experimentally in the paraxial regime and numerically in the non-paraxial regime.