Objective Recent studies have shown that the optical system that produces the bottle beam is gradually diversifying. However, most optical systems are more complex and the resulting bottle beams are larger in size. This article uses the metasurface to generate a bottle beam. The ultrasurface system is straightforward and well-integrated. The lateral and longitudinal inner diameters of the generated bottle beam are considerably reduced, and the capture of tiny particles is more accurate. This has potential research and application value for multiparticle capture and precise capture.
Methods In this study, to generate multiple bottle beams, an opaque annular obstacle is added to the metasurface with the hyperbolic phase distribution (PB phase). The metasurface is constructed with titanium dioxide (TiO2) nanopillars arranged on a silicon dioxide (SiO2) substrate. To design the working wavelength of the nanopillars to 632.8 nm, the length, width, and height of the super surface nanopillars are designed to be 377, 87, and 600 nm, respectively. Moreover, by varying the relative aperture value (RA) of the metasurface, the lateral and longitudinal inner diameters of the bottle beam are altered. The number of bottle beams produced can be altered by changing the size of the annular obstacle on the metasurface.
Results and Discussions This article produced four micron-level bottle beams [Fig.6(a)]. Further, by increasing the RA value of the metasurface, the lateral and longitudinal inner diameters of the bottle beams are reduced [Fig.7(a)]. Thus, the RA value of the metasurface can be changed to alter the size of the generated light field. We select one of the bottle beams and observe that its transverse and radial full width at half maximum (FWHM) are roughly linear with RA [Fig.7(b)--(c)]. In this paper, the number of bottle beams produced is changed by changing the size of the annular obstacle on the metasurface [Fig.8(a)--(c)].
Conclusions The metasurface method used in this paper generates four bottle beams. Two of the bottle beams are selected. The measured FWHMs of the two bottle beams are 0.47 and 0.61 μm in the transverse direction, respectively, and 0.9 and 1.2 μm in the longitudinal direction. Simultaneously, this paper finds that by changing the RA value of the metasurface, the inner diameter of the multiple bottle beams is variable, and its transverse FWHM and radial FWHM are roughly linear with RA. Therefore, if particles with a specific size need to be captured, the metasurface with a specific RA can be designed to generate a bottle beam with the required size. This paper also found that the size of the outer ring that controls the annular obstacle remains unchanged, and when its size is changed, the number of the bottle beams is changed to 2, 4, and 5, respectively. The size of the multiple bottle beams produced in this paper is considerably reduced, and capturing tiny particles is more accurate, which is of great significance to the study of particle capture.
