Optical focusing based on the planar metasurface reflector with application to trapping cold molecules

Abstract

We demonstrate theoretically a 2D subwavelength silicon-grating reflector with strong focusing capability and the potential application to an optical dipole trap of cold molecules such as MgF. We study the dependence of the focusing properties of this reflector on its structural parameters, numerical aperture, and fabrication-error tolerance. Our study shows that the reflector delivers high reflectivity and strong focusing performances with the maximum intensity at the focal point over 200 times the incident one. Such a focusing field on the reflector can provide a deep potential to trap cold MgF molecules from a standard magneto-optical trap.

Chip-scale molecule trapping by a blue-detuned metasurface hollow beam

“…In the past, our group proposed the planar silicon grating with the focusing phase, and studied the dependence of the focusing properties on its structural parameters. We found that the focusing effect is impressive-with the maximum intensity at the focal point over 200 times than that obtained at the same point in the absence of the planar silicon grating [31]. Herein, we present a new scheme for generating a FHB on the subwavelength silicon-grating metasurface with a potential application as an optical dipole trap for cold molecules.…”

“…In order to generate the FHB, the hybrid phase of the grating is designed to have focusing and completely destructive interference functions. From recent research, we studied the subwavelength silicon metasurface grating with the strong focusing capability [31]. Here, we used the phase distribution of the focusing lens in figure 2(a) to converge the light to one point, then combine the phase of figure 2(a) with an π-phase plate, which is a ring in figure 2(b) with an inner radius a (grey area) and an outer radius R (white area).…”

Generation of a blue-detuned optical storage ring by a metasurface and its application in optical trapping of cold molecules

“…Since a phase-transmitting-type metasurface is nearly two-dimensional and the thickness d is generally kept unchanged in the manufacturing process, the phase accumulation φ is realized by changing the effective refractive index n eff at different positions. [20,22] Change in n eff is generally achieved by constructing a material microstructure of a higher refractive index on a substrate of a lower refractive index.…”

“…In contrast, an all-optical storage ring of cold molecules does not require the molecule to possess a permanent electric or magnetic dipole moment but induces an electric dipole moment to generate gradient forces to confine molecules into a potential trap. [20,22] Moreover, it is naturally immune to Majorana-type spin flips, which lead to the loss of trapped molecules. Therefore, the optical storage ring could have a broader range of applications.…”

“…[14][15][16][17][18] Previously, our group proposed a two-dimensional subwavelength silicongrating reflector with strong focusing capability, resulting in an intensely focused spot and ring at the focal plane of the metalens. [19][20][21] The molecules were drawn to the maximum in the red-detuned light field under the influence of the optical dipole force, which serves as a dipole trap. In comparison, when the light field is blue detuned, the interaction potential is repulsive, and the molecules will be repelled to the minimum in the light field.…”