To enhance the optical pressure on a thin dielectric sample, a resonance structure using graphene layers coated over a metal film on a high index prism sputtered with MgF2 was theoretically analyzed. The number of graphene layers and the thicknesses of metal and MgF2 films were optimized to achieve the highest optical pressure on the sample. Effects of three different types of metals on the optical pressure were investigated numerically. In addition, simulations were carried out for samples with various thicknesses. Our numerical results show that the optical pressure increased by more than five orders of magnitude compared to the conventional metal-film-base resonance structure. The highest optical pressure was obtained for 10 layers of graphene deposited on 29-nm thick Au film and 650 nm thickness of MgF2 at 633nm wavelength, The proposed graphene based resonance structure can open new possibilities for optical tweezers, nanomechnical devices and surface plasmon based sensing and imaging techniques.
The optical force of an evanescent field is useful for trapping individual proteins and molecules. We theoretically investigate the optical pressure exerted on an attached and wellspread cell on a waveguide in the vicinity of an evanescent field. To do this, the cell is modeled as a three-planar-layer (membrane-cytoplasm-membrane). These layers and a gap of water are used as a stratified cover medium for the waveguide. Then, the mode equation of a slab waveguide with a simple and semi-infinite cover medium is modified and solved graphically. The effects of the cell cytoplasm and membrane thicknesses and their refractive indices and the sample-waveguide separation distance on the optical pressure are numerically studied. The results show that the optical pressure increases when the cytoplasm thickness increases, but decreases when the cell membrane thickness is increased. Furthermore, the optical pressure does not significantly change when the sample film thickness increases to more than 0.2 of a wavelength. The optical pressure decreases when the waveguide-sample distance for a specific mode is increased, but can be attractive or repulsive depending on both the cytoplasm refractive index and the mode number.
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