Trapping Performance Of Plasmonic Optical Tweezers For Silver Triangular Nanoprism Dimer

The trapping performance of isopharon optical tweezers is closely related to the shape of metal nanostructure,incident light parameters,the size and dielectric properties of the object to be trapped,and the surrounding environment.Compared with the circular and linear waveguide nanostructures,the triangular plate structure with three sharp angles is more likely to generate large gradient local field enhancement due to its anisotropy,and the particles to be captured in this structure will be subjected to greater trapping force and potential well.A great deal of research has been done on the factors affecting the enhancement ratio of the triangular structure field,such as the wavelength of incident light,the polarization state and the structural parameters of the triangular plate.In this paper,after simply preparing the nano-triangular plates experimentally,based on the principle of surface plasmon generation,firstly,the surface plasmon properties of the dimer structure,diagonal and laminated dimer,of silver nanoprism were studied.It is found that both structures can produce strong field enhancement when the dipole resonance peak is incident at the corresponding wavelength;when the multipole resonance peak is incident at the corresponding wavelength,the position of the field enhancement is on the outside The apex angle,and as the wavelength changes,the field enhancement position is also constantly changing.By comparison,it is found that the diagonal structure can generate a strong enhanced field on the upper surface and form a symmetrical electromagnetic field area.After that,the difference in light force received by nano-microspheres with different dielectric constants in the nano-triangular structure was studied.The incident laser used is unit intensity,y-polarized Gaussian laser,and the wavelength is 817 nm corresponding to the dipole resonant peak of angular diagonal structure.The surface morphology,size,dielectric properties,etc.of the microspheres to be captured will also affect the degree of capture of the microspheres in the light field.In this paper,the optical force and potential well of gold microspheres,polystyrene microspheres and silicon dioxide microspheres with radius of 10 nm,20 nm,30 nm and 40 nm in angular diagonal dimer are calculated.The light force and potential well received by the microspheres and silica microspheres in the diagonal structure dimer determine the best capture position and the capture degree of different microspheres in the light field.The microspheres at 10 nm and 20 nm could be captured,the microspheres at 30 nm could not be stably captured,and only the gold microspheres at 40 nm could be stably captured.Different optimal capture conditions for different microspheres make particle screening possible.The difference in optimal capture conditions for different microspheres makes particle screening possible.Finally,the influence of external environmental conditions on the capture performance of the dimer structure was studied.The change of surface plasmon characteristics of the dimer with angular diagonal structure was studied when the size of light source spot,the refractive index of external environment background and the substrate were changed.Taking the golden sphere as an example,the effects of different parameters on the structure capture performance of the dimer were compared,in order to obtain the most favorable external environmental parameters for the capture phenomenon and provide some theoretical guidance for the laboratory capture.