In this Letter, to the best of our knowledge, we report the first experimental demonstration of a new family of autofocusing beams, circular swallowtail beams (CSBs), based on the high-order swallowtail catastrophe, which were determined by potential functions depending on the state and control parameters. The dynamics of the CSBs is discussed here. These types of CSBs tend to automatically focus without external components. Numerical results showed the focal intensity increased significantly, and it was as much as 110 times in the initial plane when the radius of the main ring was 40. Additionally, in contrast to previous circular Pearcey and Airy beams, these CSBs appeared to have more diversity and tunability due to having more propagation trajectories and intensity distribution structures due to high-order diffraction catastrophe. The numerical simulations were verified by our experimental results. These diverse CSBs could have new applications in flexible optical manipulation. These various CSBs could be beneficial for potential applications in optical trapping, medical treatment, or micromachining.
We demonstrate a universal approach for generating high-order diffraction catastrophe beams, specifically for Swallowtail-type beams (abbreviated as Swallowtail beams), using diffraction catastrophe theory that was defined by potential functions depending on the control and state parameters. The three-dimensional curved caustic surfaces of these Swallowtail catastrophe beams are derived by the potential functions. Such beams are generated by mapping the cross sections of the high-order control parameter space to the corresponding transverse plane. Owing to the flexibility of the high-order diffraction catastrophe, these Swallowtail beams can be tuned to a diverse range of optical light structures. Owing to the similarity in their frequency spectra, we found that the Swallowtail beams change into low-order Pearcey beams under given conditions during propagation. Our experimental results are in close agreement with our simulated results. Such fantastic catastrophe beams that can propagate along curved trajectories are likely to give rise to new applications in micromachining and optical manipulation, furthermore, these diverse caustic beams will pave the way for the tailoring of arbitrarily accelerating caustic beams.
We develop the effective experimental approach to generate multi-twisted beams (MTBs) with twisted intensity lobes by superimposing helical phases consisting of multiple independent sub-phases with different azimuthal shift factors. The MTBs' energy flows and propagation properties are also investigated, indicating that such beams exhibit twisted properties. The azimuthal shift factor determines the twisted intensity distributions, and the number of twisted lobes depends on the sub-phase number. The bright lobes of a MTB possess the shapes of thin spiral lines, and the intensity pattern depends on the topological charge. Diverse MTBs can be generated by flexibly manipulating the azimuthal shift factors and the sub-phase number. Also, various mirror-symmetrical twisted beams are constructed using the matrix flip scheme, further enriching the light structures of MTBs. Numerical simulation and experimental results are consistent. Furthermore, the capture and guide of microspheres via the MTBs are experimentally executed and demonstrate the feasibility and practicability of our generated MTBs. The various MTBs will likely give rise to potential applications in fabricating chiral nanostructures and manipulating microparticles.
The generation of polycyclic chiral beams by inducing annular spiral zone phases that consist of multiple subphases is numerically and experimentally demonstrated. Each subphase is composed of a spiral phase, an equiphase, and a radial phase. The number and twisting direction of the spiral intensity lobes for every layer could be individually controlled. Furthermore, the orientations for the twisting lobes could be tuned by changing the introduced equiphase gradient. More importantly, such optical fields also show rotation property when the equiphases with gradient are dynamically and continuously imposed. This advantage of rotation also brings about the possibility of such chiral beams to rotate particles. Such beams would be advantageous for manufacturing tunable chiral metamaterials and have potential applications in optical tweezers and optical communication.
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