A 3D controllable diffraction‐limited spot array generated by means of a spaced‐dipole array

Abstract

The creation of an array of three-dimensional (3D) multifocal spots in the focal region has attracted interest due to potential applications in parallel or simultaneous process areas. Based on the theory of pattern synthesis of antenna array and the electromagnetic time reversal technique, an optimisation-free approach is reported to construct a 3D controllable diffraction-limited spot array in the focal volume of a 4pi focussing system formed by two high-numerical-aperture (NA) objectives. The proposed method can be implemented readily by inversely focussing the field radiated from a virtual spaced-dipole antenna array mounted at the focus of the 4pi configuration. By solving the inverse problem, the required illumination in the pupil plane for producing the 3D spot array can be found. It is demonstrated that the 3D diffraction-limited focal spot array owns the properties of controllable polarisation, scheduled number, tunable location, and adjustable interval. This array may find applications in 3D simultaneous optical manipulation and trapping, 3D parallel fabrication, 3D optical data storage, and so on. K E Y W O R D S3D diffraction-limited spot array, 4pi configuration, polarisation, spaced-dipole antenna arrayThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Generation of 3D quasi-spherical multi-focus arrays and optical rings using orthogonally superimposed dipole antenna arrays

“…The full width at half-maximums along the x, y, and z axes are ∼0.41λ, ∼0.41λ, and ∼0.31λ, respectively. As a result, the corresponding 3D volume is ∼0.0273λ 3 , 39% below the spot volume (∼0.045λ 3 ) in literature [8], and smaller than the volume of an ellipsoidal focal point (∼0.0355λ 3 ) formed by a single dipole [22], a 23% reduction. Moreover, the side-lobe height is only 10% of the maximum, as shown in figure 2(e).…”

“…First, we suppose that a single virtual orthogonally superimposed dipole antenna is placed at the confocal point of the high-NA objectives. The quasi-spherical focal point at the center of the focal volume can be easily obtained by substituting equation (7) into equations ( 9) and (10) , which exhibits a more uniform distribution compared to the previously reported linearly polarized focal points [22]. The full width at half-maximums along the x, y, and z axes are ∼0.41λ, ∼0.41λ, and ∼0.31λ, respectively.…”

“…In 2022, Jera et al [21] generated a focal point with a volume below the diffraction limit by collecting the radiation of an oscillating electric dipole in the 4Pi microscope. Yu et al [22] used the radiation field of a single dipole in a 4Pi focusing system to produce a smallervolume (0.0355λ 3 ) focal point, which to our knowledge, is the smallest volume reported in the literature. However, this focal point is elongated longitudinally, resulting in a weaker longitudinal resolution.…”

Creating a spatial quasi-spherical focal spot and optical ring with controllable characteristics based on orthogonally superimposed dipoles antenna

“…Therefore, we propose a non-iterative and optimization-free method that can easily produce a higher longitudinal resolution focal spot with pure circular polarization in the center through the inverse focusing of the radiation field of the orthogonally superimposed dipoles antenna. The volume of the focal spot produced by this method is reduced by 23% (0.0273λ 3 vs. 0.0355λ 3 ) compared to the approach proposed in literature [4] that using a single dipole. Additionally, it is demonstrated how multiple quasi-spherical focal spots can be used to produce optical rings with controlled characteristics.…”

“…Creating a sharp focal spot with an azimuthally polarized Bessel-Gauss beam [3] . Recently, a smaller volume (0.0355λ 3 ) focal spot was produced by reverse focusing the radiation field of a single dipole in the 4Pi focusing system, however, the longitudinal resolution of this focal spot is weak [4] . Therefore, we propose a non-iterative and optimization-free method that can easily produce a higher longitudinal resolution focal spot with pure circular polarization in the center through the inverse focusing of the radiation field of the orthogonally superimposed dipoles antenna.…”