Optical Focusing Based On The Planar Metasurface With Application To Trapping MgF Cold Molecules

Metasurface is a structural plane composed of metal or dielectric structural units arranged at sub-wavelength intervals.These structures can change the phase of the incident light so that the reflected or transmitted light forms a corresponding wavefront according to the spatial distribution of the structure.By adjusting the geometrical parameters of the structural elements(such as the size and shape of the structural elements),we can control the wavefront of reflected or transmitted light.By controlling the phase of electromagnetic waves,beam deflection,metalens,hyper-holography,vortex generation,coding,stealth,phantom and other functions can be realized,which have great applications in the fields of quantum communication,new energy,and optical imaging.In this paper,metasurface is studied and the metasurface is applied to the field of cold molecules.The main research contents are as follows:Firstly,a new type of metasurface structure is proposed,that is,a metasurface reflector composed of silicon grating elements with different periods,different duty ratios and different heights.We study the law of the focusing characteristics of this metasurface reflector with different numerical apertures.The results show that the metasurface structure we designed has a great focusing characteristic,and the intensity of the light field at the focus is more than 200 times stronger than that of the incident light.Secondly,an optical trapping scheme using a metasurface lens for MgF molecules is proposed.The optical potential and dipole force of the MgF molecule in the focused light field,the van der Waals potential of the grating surface and the scattering rate of the MgF molecule are calculated.The results show that this metasurface lens can achieve loading and surface trapping of MgF molecules.Finally,the aberration of the metasurface lens is discussed.The effects of the aberrations caused by different incident wavelengths on the lens and the magnitude of the lens on the size of the focused spot of the lens are studied.