Abstract:AbstractIn this paper, generation of optical vortices with time-varying orbital angular momentum (OAM) and topological charge is theoretically demonstrated based on time-modulated metasurfaces with a linearly azimuthal frequency gradient. The topological charge of such dynamic structured light beams is shown to continuously and periodically change with time evolution while possessing a linear dependence on time and azimuthal frequency offset. The temporal variation of OAM yield… Show more
“…[49][50][51][52][53][54][55] Nevertheless, it is noteworthy that a majority of the related studies in the realm of light-matter interactions with complex resonant meta-atoms were limited to conventional Gaussian light beams. However, in parallel, several approaches including spiral phase plates, [56,57] q-plates, [58][59][60] spatial light modulators (SLM), [61] and optical metasurfaces [33,62,63] have been developed to generate and manipulate more complex beams, which has led to the emergence of a new category of light beams known as structured light. [64][65][66] Structured lights, including beams with a spin and orbital angular momentum (SAM and OAM, respectively), radially and azimuthally polarized vector beams, and spatiotemporal optical vortices have been shown to enable a plethora of distinct lightmatter interactions and applications in optical communication, particle manipulation, quantum information processing, sensing, and microscopy.…”
Structured lights, including beams carrying spin and orbital angular momenta, radially and azimuthally polarized vector beams, as well as spatiotemporal optical vortices, have attracted significant interest due to their unique amplitude, phase front, polarization, and temporal structures, enabling a variety of applications in optical and quantum communications, micromanipulation, and super-resolution imaging. In parallel, structured optical materials, metamaterials, and metasurfaces consisting of engineered unit cells-meta-atoms, opened new avenues for manipulating the flow of light and optical sensing. While several studies explored structured light effects on the individual meta-atoms, their shapes are largely limited to simple spherical geometries. However, the synergy of the structured light and complex-shaped meta-atoms has not been fully explored. In this paper, the role of the helical wavefront of Laguerre-Gaussian beams in the excitation and suppression of higher-order resonant modes inside all-dielectric meta-atoms of various shapes, aspect ratios, and orientations, is demonstrated and the excitation of various multipolar moments that are not accessible via unstructured light illumination is predicted. The presented study elucidates the role of the complex phase distribution of the incident light in shape-dependent resonant scattering, which is of utmost importance in a wide spectrum of applications ranging from remote sensing to spectroscopy.
“…[49][50][51][52][53][54][55] Nevertheless, it is noteworthy that a majority of the related studies in the realm of light-matter interactions with complex resonant meta-atoms were limited to conventional Gaussian light beams. However, in parallel, several approaches including spiral phase plates, [56,57] q-plates, [58][59][60] spatial light modulators (SLM), [61] and optical metasurfaces [33,62,63] have been developed to generate and manipulate more complex beams, which has led to the emergence of a new category of light beams known as structured light. [64][65][66] Structured lights, including beams with a spin and orbital angular momentum (SAM and OAM, respectively), radially and azimuthally polarized vector beams, and spatiotemporal optical vortices have been shown to enable a plethora of distinct lightmatter interactions and applications in optical communication, particle manipulation, quantum information processing, sensing, and microscopy.…”
Structured lights, including beams carrying spin and orbital angular momenta, radially and azimuthally polarized vector beams, as well as spatiotemporal optical vortices, have attracted significant interest due to their unique amplitude, phase front, polarization, and temporal structures, enabling a variety of applications in optical and quantum communications, micromanipulation, and super-resolution imaging. In parallel, structured optical materials, metamaterials, and metasurfaces consisting of engineered unit cells-meta-atoms, opened new avenues for manipulating the flow of light and optical sensing. While several studies explored structured light effects on the individual meta-atoms, their shapes are largely limited to simple spherical geometries. However, the synergy of the structured light and complex-shaped meta-atoms has not been fully explored. In this paper, the role of the helical wavefront of Laguerre-Gaussian beams in the excitation and suppression of higher-order resonant modes inside all-dielectric meta-atoms of various shapes, aspect ratios, and orientations, is demonstrated and the excitation of various multipolar moments that are not accessible via unstructured light illumination is predicted. The presented study elucidates the role of the complex phase distribution of the incident light in shape-dependent resonant scattering, which is of utmost importance in a wide spectrum of applications ranging from remote sensing to spectroscopy.
“…In 1992, Allen et al proposed that an optical vortex with a phase factor exp( i θ) (θ is the azimuth angle) carries orbital angular momentum (OAM) with a value of ℏ per photon, where ℏ is the Dirac constant and can be any integer, known as the topological charge. Since the arbitrary value of topological charge provides a new degree of freedom for manipulating light and its interaction with matter, the research on optical vortices attracts considerable attention and continues to deepen, from conventional spiral phase plates to integrated metasurfaces and microring resonators, from particle manipulation to OAM-based communication and quantum information processing, beyond traditional two-dimensional transverse fields to multidimensional tailored beams, especially the time-space modulation of optical vortices. − …”
Longitudinal orbital angular momentum (OAM) is a fundamental
property
of light that has been the subject of extensive research and applied
to diverse important applications, such as optical tweezers, super-resolution
imaging, and optical information processing. Recently, photons have
been observed to possess transverse OAM, where the OAM vector is orthogonal
to the direction of light propagation. As the carrier for this unique
OAM, the spatiotemporal (ST) optical vortex has attracted considerable
interest. Here, we provide a general overview of recent experimental
and theoretical advances on such vortices, presenting their synthesis
and measurement strategies, highlighting their nontrivial properties
in linear propagation and interaction with nonlinear matter, and discussing
the possible future trends and challenges.
“…26,27 However, such a high-harmonic approach in generating time-varying OAM is not easily applicable to other frequency regimes, hindering further demonstrations. Alternatively, Sedeh et al 28 proposed an optical metasurface with a spiral-staircase profile of modulation frequencies to implement time-varying OAM. In fact, such an approach can be feasible and generalized through a space-time-coding digital metasurface with field-programmablegate-array (FPGA) technology, particularly in the microwave regime.…”
The recently proposed extreme-ultraviolet beams with time-varying orbital angular momentum (OAM) realized by high-harmonic generation provide extraordinary tools for quantum excitation control and particle manipulation. However, such an approach is not easily scalable to other frequency regimes. We design a space-time-coding digital metasurface operating in the microwave regime to experimentally generate time-varying OAM beams. Due to the flexible programmability of the metasurface, a higher-order twist in the envelope wavefront structure of time-varying OAM beams can be further designed as an additional degree of freedom. The time-varying OAM field patterns are dynamically mapped by developing a two-probe measurement technique. Our approach in combining the programmability of space-time-coding digital metasurfaces and the two-probe measurement technique provides a versatile platform for generating and observing time-varying OAM and other spatiotemporal excitations in general. The proposed time-varying OAM beams have application potentials in particle manipulation, time-division multiplexing, and information encryption.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.