Novel Dynamic Optical Tweezers Techniques And Applications

Optical tweezers is an indispensable instrument in scientific frontier fields.As a significant technical method for manipulating micro&nano particles,optical tweezers provides a three-dimensional potential well for the trap.Laser tweezers is a lable-free,non-contacting,and scatheless technique with high precision for force and position measurement in real time,which has been widely used in biological and medical sciences.However,traditional laser tweezers is always achieved at far field and not omnipotent for all materials in all cases,especially for Mie metallic particles.Concerning this issue,near field optical tweezers,structure-based surface plasmonic tweezers in especial,was proposed and experienced great developments recently.However,the field is always weak and dynamic manipulation is unprocurable.In this thesis,on the basis of the seniors' research,a dynamic laser tweezers system is constructed and applied for specific biomedical applications.Then,a focused all-optical modulated surface plasmon polaritons(SPPs)tweezers system is proposed to achieve dynamic manipulation of metallic particles,which provides great potential for further applications.The content is divided into the following five main aspects:1.Forces acted on the particles in the laser field and surface plasmonic field are theoretically analysised firstly,which provide theoretical basis for further applications.2.A dynamic laser tweezers system is established for biomedical applications,such as drug screening,cell detection and sorting,etc.In the system,particle will be trapped and moved follow the focused laser beam.As the moving particle/cell is subjected to the viscous resistance,it will escape the trap at a spectial velocity,which reflects the specialities of the particle and the liquid condition.As an important process in drug screening,viscosity of the fluid is measured in the system with great agreement with classical methods.Cell detection and sorting is another research focus in biomedicine science,and slight difference between various cell lines is detected and distinguished successfully.The results demonstrate that the proposed laser tweezers system has great advantages of faster,label-free,low consumption,and high precision,promoting it a more convenient technique for biomedical researches.3.Metallic particles,especially those in micron dimension,are difficult to trap in classical optical tweezers systems,and evanescent field is always weak for trap.As a result,a dymanic all-optical matulated surface plasmon parlitons(SPPs)tweezers system is proposed to solve the challenges.Forces acted on the metallic particles in the SPPs field is calculated theoretically by MST and FDTD methods.To the best of our knowledge,our experiments represent the first demonstration of plasmonic trapping of metallic particles with diameters above 500 nm.Further more,linear polarized laser beam is applied to excite SPPs to trap and rotate Au nanowire on account of the significance of Au nanowire's directivity,and special plasmonic structures are built the on metal film.4.All particles in the SPPs field will be clustered to the center,however.It will break the giant field enhancement between the particle and metallic film.As a result,we proposed and experimentally established a myrmecolous shaped dual plasmonic tweezers system,to precisely manipulate a single metallic nanoparticle on flat metal surface,to achieve a great field enhancement for surface enhanced Raman scattering(SERS)applications.The Raman spectrum of rhodamine-6G molecule is measured in the system,which provides great potential for qualitative detection at molecular level.5.As a foundation for further applications in biometical field,particles above a unilaminar cell membrance is manipulated in this system,which provides a new technique for membrance detection and imaging.