Theoretical And Experimental Investigation Of Manipulating Ellipsoidal Micro-particles By Femtosecond Vortex Laser Tweezers

With the development of the optical tweezers, non-contact, no invasionmicromanipulation, and measurement radiation in Pico newton order are realized. Asthe femtosecond vortex beams carry angular momentum, when the femtosecond vortexlaser interacts with particles, the transfer of orbital angular momentum from the vortexfemtosecond laser to micro-particles, thus the femtosecond vortex tweezers can controlthe rotation of the particles. In this thesis, on the basis of previous work, we work on theexperimental and theoretical investigation of rotating ellipsoid particles by femtosecondvortex laser. In the experiment, stable optical rotating of ellipsoid particles was achieved.When changing the power of the femtosecond vortex laser, we can measure the differentangular velocity of the rotating ellipsoid particles. In the theory, we use the ray tracingmethod and the full absorption method to explain the relationship between the power ofthe femtosecond vortex laser and the angular velocity of the rotating ellipsoidal particles.The thesis can be summarized in detail as follows:(1) The main background and significance of manipulating micro-particles byfemtosecond vortex laser tweezers are reviewed. Firstly, the overview of laser opticaltweezers is briefly expounded, that experimental and theoretical study of opticaltweezers is introduced. Secondly, we discuss the theoretical model of trappingmicro-particles by femtosecond laser tweezers and the stability condition. Finally, weintroduce the mechanism of rotating CuO micro-particles by femtosecond vortex lasertweezers. The optical vortex has the unique characteristics, which presented “spiraldefect”. We can improve the femtosecond laser tweezers. In addition, the main contentsof this thesis are given.(2) We achieve the experimental investigation of manipulating ellipsoidmicro-particles by femtosecond vortex laser. In the experiment, we generatecomputer-generated hologram (CGH) by femtosecond laser pulses. After severalexperiments, we can greatly improve the efficiency of CGH. Furthermore, we use thefemtosecond seed laser as the light source, and vertically incident on the CGH core togenerate the vortex beams. We use the vortex beams to trap and rotate the CuO particlesand red blood cells. We also study the relationship between the power of thefemtosecond vortex laser and the angular velocity of the rotating ellipsoidal particles.(3) Based on the ray tracing method and the full absorption method, the theoreticalmodel of rotating ellipsoid micro-particles by femtosecond vortex laser tweezers is built. By the ray tracing method, when the femtosecond vortex laser is incident to themicro-particles, as it reflects and refracts at the micro-particle surface, it can transfer theangular momentum from light to micro-particles. We can obtain the relationshipbetween the power of the femtosecond vortex laser and the angular velocity of therotating ellipsoidal particles. By the full absorption method, the micro-particles canabsorb the entire vortex femtosecond laser carrying the angular momentum to achievethe smooth rotation.(4) We simulate the impact of the power change of the femtosecond vortex laser onthe angular velocity of the rotating ellipsoidal particles. Above all, we simulate the crosssection and the intensity distribution of the vortex optical beams. As shown in thesimulation graph, we can draw that the phase distribution of the vortex beams is spiral,and the intensity of the vortex beams is zero at the center. In this thesis, theTEM01*Doughnut beams are used as the incident beam. Then, according to the differentproperties of the trapped particles, we found the ray tracing model and the fullabsorption model in simulation. We analyze the factors that affect the relationshipbetween the power of the femtosecond vortex laser and the angular velocity of therotating ellipsoidal particles. Finally, it can be seen from the comparison that thesimulation results of the full absorption method agree well with the experiments fittingresults.