Spatially controllable focal fields play a pivotal role in modern optical engineering, offering opportunities for precise manipulation of light-matter interactions in various applications. Double-helix focal fields, in particular, have gained attention due to their unique helix structure that exhibit distinct optical properties. In this paper, we propose a method for generating a controllable spatial double-helix focal field without optimization. This is accomplished by utilizing the radiation pattern of a virtual helix antenna consisting of magnetic units, which is reverse-focused in a 4π-system. Numerical results indicate that the double-helix focal field can be flexibly customized by selecting the shape and parameters of the helix antenna. The novel and customizable double-helix focal field expands the applications of optical engineering in complex opto-fluidics and optical lithography.
The 3D quasi-spherical focal spot and optical ring may find potential application value in fields like arbitrarily oriented particle capture and guidance, super resolution microscopy and optical capture. On the basis of the radiation pattern of the orthogonally superimposed dipoles antenna in a 4Pi focusing system, this paper firstly proposes an approach to create a central pure circular polarization three-dimensional (3D) quasi-spherical focal spot with higher longitudinal resolution. In addition, we also use the radiation pattern of the ring array antenna composed of orthogonally superimposed dipoles antenna elements to flexibly generate a pre-parameterizable and uniformly distributed optical ring. The simulated numerical results show that the method achieves a quasi-spherical focal spot with a slightly smaller longitudinal size (~0.31λ) than the transverse size (~0.41λ), and with the smallest volume (~0.0273λ3 ). The position, radius, ring number and layer number of the constructed optical ring can be adjusted arbitrarily, determined by the parameters of the ring array antenna.
We propose an optimization-free method for creating a two-dimensional (2-D) identical focal spot array with a prescribed number, tunable interval, and controllable position. This can be realized easily by backward focusing of the field radiated from a planar antenna array situated at the foci of two high-numerical-aperture objective lenses. It is demonstrated here that the number of spots in the focal field array is equal to the number of elements in the planar antenna array; the intervals between the two adjacent spots along the x and y directions depend solely on the gaps between the two corresponding elements, and the position for each spot is determined totally by the location of the corresponding element. Furthermore, the intensity distribution of each spot in the 2-D focal array is identical. These kinds of 2-D focal spot arrays with controllable characteristics may find applications in parallel optical micromanipulation, multifocal multiphoton microscopy, and multiparticle parallel acceleration.
A simple and flexible method is presented for constructing a dark spherical spot array with the prescribed spot number and interval along the optical axis. Through reversing the field radiated from a uniform magnetic current line source in combination with an electric current line source having a cosine-squared taper, the desired focal field can be realized in the 4Pi focusing system. The required incident field on the pupil plane can be obtained by solving the inverse problem and is found to be an amplitude-modulated radially polarized beam.
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