Catenary metasurface has been widely used in fields such as wild-angle imaging, spectral detection, and broadband absorbers, due to its advantages of high efficiency and broadband. In our previous studies, perfect wavefront control of catenary metasurface is achieved via field-driven optimization (FDO). However, the proposed method focuses solely on the performance of catenary metasurfaces at a specific wavelength. Here, considering the broadband and multifunctional of the catenary and catenary-like metasurfaces, multi-objectives FDO is proposed. With 30 iterations, the average diffraction efficiency of the catenary metasurface increases to ~96% at the wavelength of 9-13 μm. In addition, considering the functionality, the catenary and catenary-like metasurfaces are optimized with a pair of orthogonal polarized light incidences. The optimization process preserves the chiral nature of the catenary metasurface. After 30 iterations, the diffraction efficiency of the catenary metasurface is improved from 96.4% to 99.2%. For catenary-like metasurfaces, the diffraction efficiencies exceed 90% for both left-handed and right-handed elliptically polarized light incidences. Our work provides a methodology for designing multifunctional complex continuous metasurfaces, which may further promote catenary optics.
With orbital angular momentum, tightly focused vortex beams can impose optical torque on particles through momentum transfer. In this paper, based on the Richards-Wolf vector diffraction theory, we examine the forces and moments exerted on Mie particles by a tightly focused beam, including the impact of the beam's intensity distribution and the topological charge (TC) number on particle trapping stability. Numerical calculations are conducted to assess the effects of corresponding parameters on the characteristics of the optical radiation force and the tight focusing properties. Our results show that the direction of the particle’s rotation is determined by the sign of the TC numbers and that there is a direct relationship between the magnitude of the induced torque and the TCs. Furthermore, the stability of particle control can be improved by OAM beams with small TCs. These results have potential applications in light capture, optical storage, and optical imaging.
As an important means of contactless manipulation of targets, optical force has significant application prospects in areas such as light sail propulsion and orbital intervention of space debris. Precise measurement of the optical force generated by spatial targets in complex optical fields is crucial for establishing their spatial dynamics model. The torsion balance can be used to measure the optical torque. We use a 5 μm tungsten fiber to build a torsion balance system to measure the extremely weak optical torque less than 1×10-15 Nm, which can help to establish an accurate model of the interaction between objects and optical forces. At the same time, it provides experimental data for the study of spacecraft orbit control and light sail navigation.
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