Generation Of Surface Focusing Hollow Beam And It's Application On Optical Trapping Of Cold Molecules

In recent years,the design and application of metasurface is one of the most popular researches in the field of optics.Metasurfaces can achieve the functions of wavefront shaping and polarization controlling by reasonably and skillfully designing their materials and structure which traditional optical can do.In addition,they have some characteristics such as convenient manufacturing,structural integration and negative refraction.Therefore,the practicability of metasurfaces in various fields is increasing day by day.In this paper,a new transmission metasurface based on the ability of the metasurface to regulate the light field is designed to form a focused hollow beam?FHB?,and the characteristics of MgF molecular trapped in this blue-detuned light field is also analyzed.The metasurface has a concentric-ring-silicon-grating structure.Through the different width and height of ring structure configuration on a silica surface,the phase of the incident light can be adjusted at different positions.Mixing the phase distribution of a focusing lens and a 0-?phase plate,metasurface can make the transmission light form a hollow area at the focus point.We study the factors which can affect the size of the hollow area,at the same time the high transmittance and focusing efficiency of the metasurface are guaranteed.When the ring number of the 0-?phase plate or the relative aperture of the metasurface change,the size of the hollow area could be adjusted at range of 300nm.Finally,the characteristics of the molecular movement in the focused hollow beam has been theoretically analyzed.The maximum dipole force on the trapping region is 1.57×10^-19,and the scattering rate at the center of the light trap is low enough to avoid affecting the efficiency of trapping.