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

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.