The Influence Of Gain On The Optical Torque Of Other Material Structures In Optical Twist Settings

Optical micromanipulation technology is mainly used to study the mechanical effects of light on particles of tens of nanometers or micrometers.Since the research began in the 1970 s,it has been found that the optical force generated by it can not only make the object move along the direction of light propagation,but also make the nano particles rotate.For example,it can rotate the cell molecules,and also make the nano crystals rotate in the solution.It has the advantages of easy operation,no damage,and so on,so it provides more choices for the application of nano machinery and the popularization of nano technology in biological science.Therefore,it has become a powerful assistant in biology,medicine,cell molecule,clinical operation and so on.Then,the increase and collection of optical torque has a very practical application significance.However,how to generate large optical torque is still a very difficult task,because the angular momentum of incident light is limited,and the angular momentum must be conserved.In recent years,people have tried some methods to increase the optical torque.For example,some people use the metal material to make a chiral structure,which can increase the optical torque via plasmonic resonance,but the metal material will have a great heat effect,thus affecting the application;some people choose to replace the original single-layer structure by using a double-layer material structure,which recycle light through multiplescattering,and prolongs the capture of light,so as to achieve enhanced optical torque.In addition,it can also produce a larger optical twist between the two layers of materials,so as to rotate the objects.This structure produces a larger torque and less absorption.Thus,it is an effective method to use the double-layer structure to enhance the optical torque.We know that the gain material has the function of amplifying the light,so we guess that the optical torque can be further increased by using the gain material in optical twist settings.Based on the above research background,this paper mainly studies the influence of the gain material layer on the optical torque of other material layers in the double-layer structure,which provides more options for optical micromanipulation.The content of this paper is as follows:The first chapter is the research background,which is divided into three parts: the development overview of optical micromanipulationtechnology,the classification of optical micromanipulation technology,and the last part is the introduction of the structure of this paper.The second chapter is a brief introduction of the theoretical methods in this paper.Firstly,the multiple scattering theory is introduced to calculate the scattering field.Secondly,the extended Mie theory is used to calculate the optical force and the optical torque.And we give the analytical expressions of the optical force and the optical torque.The third chapter is the analysis of the numerical simulation results.Firstly,in the first section,the parameters used in this paper are introduced.Secondly,in section 3.2,it introduces the method to judge whether the numerical results are accurate.Then in section 3.3,the influence of gain material on the optical torque of other materials is analyzed.It is found that,in the double-layer structure composed of multiple spheres,the optical torques of the lossy(lossless)material layer in the gain-loss(gain-lossless)structures are much larger than those of the single lossy(lossless)material layer(one order of magnitude larger),and sharp peaks appear in resonance.As the upper and lower layers rotate in opposite directions,they will also produce large optical twist.In the double-layer structure composed of gain-gain materials,the optical torque generated by the upper and lower gain materials do not have obvious advantage than that of the single-layer structure,and sharp peaks will also occur at the resonance,but the two layers rotate in the same direction,which is different from the law of gain and other material structures.The fourth chapter is a summary of this paper and the future research work.