Optical Force Induced By An Airy Light-sheet Using Discrete Dipole Approximation

In 2018,half of the Nobel Prize in Physics was awarded to Arthur Ashkin,a scientist at Bell Laboratories,in order to commend his work in the field of optical tweezers and their applications in biological systems.Optical tweezers,tightly and strongly focused lasers,make it possible that scientists are able to have powerful manipulation of micro-nano particles with non-contact control.These tools may reduce physical damage to the particles due to direct contact.Airy light-sheet is one of the non-diffraction beams,that is,two dimensional form of a three dimensional Airy beam.There are many unique characteristics of an Airy light-sheet,including non-diffraction,self-reconstruction and self-acceleration.In this work,discrete dipole approximation method(DDA)is used to solve the scattering of and optical forces on different particles induced by a vector Airy light-sheet,the main works are as follows,1.Based on the vector angular spectrum theory,the mathematical expressions of a vector Airy light-sheet are derived,including TE polarization and TM polarization.The results show that size parameters and modulation parameters of the light-sheet make a significant difference in the complex amplitude distribution of the electromagnetic fields.The larger the size parameter,the wider the main lobe and side lobes of the light-sheet.The larger the modulation parameter the greater the contrast between the main lobe and side lobes.2.DDA and GLMT are used to compute the scattering and radiation pressure of spherical particles induced by vector Airy light-sheets,respectively,in order to verify the feasibility of DDA.Then,the numerical results of the coefficient factors of extinction and absorption,the optical forces in the direction of y-axis and z-axis are computed,when taking into account particles of various shapes,equivalent radius,refractive indices and light-sheets of different wavelength,size parameters and modulation parameters.In this work,the particles are classified into regular and irregular particles.The former includes spherical and ellipsoid particles,and the latter includes square,coated particles and red blood cells.In order to visualize the interaction between particles and Airy light-sheet,internal and near fields are shown in each section.3.Radiation pressure of multi-particles is calculated,including double particles,and triple particles.Firstly,we studied how the parameters of multi-particles and light-sheets make a difference to scattering.Then,optical forces of vector Airy light-sheets on multi-particles are numerically computed,and the influence of particle parameters and beam parameters are taken into account.