Optical Trapping And Manipulation Of Micro-and Nano-Particle With Gaussian And Cylindrical-Vector Beams Optical Tweezers

Optical tweezers are the beam gradient optical traps where micro particles could be trapped by focusing the laser beam using a microscope objective. The gradient force generated by optical tweezers is suitable to trap and manipulate micro- and nano- particles. Optical tweezers had become a versatile tool for researches in many science fields including physics, biomedicine, and fine machining. With the development of these fields, there are new needs to optical tweezers technique. In this thesis, we realized the orientation and angular manipulation of particles, the collective and separate manipulation of multi-particle to meet these increasing requests. We also had introduced new trapping beam mode to optimize system performance.The shape of the optical trap and the polarization of the laser are important factors for the orientating manipulation of particles. Orientating manipulation of particles especially biological particles were performed in three-dimension by optical tweezers. Vertical and horizontal manipulations of cylindrical particles (Escherichia coli and carbon nanotubes) were achieved by dot-shaped and line-shaped optical trap. The particles with the anisotropic electric characters such as carbon nanotubes (CNTs) could be orientated by linear polarized optical trap. CNTs could be oriented and assembled in the two-dimensional plane by controlling the polarization direction. By using of the highly focused heat energy at the optical trap, orientating grown of phenanthrenequinone (PQ) was realized successfully by optical tweezers.The properties of trapping beam are the main factor which influencing the system performance of optical tweezers. Cylindrical-vector beams including azimuthally polarized beam and radially polarized beam were formed by the liquid-crystal polarization converter. The intensity distribution near the focal region of these beams were calculated and analyzed theoretically and then verified experimentally. The azimuthally polarized beam is distinguished by a purely transverse annular focal region, and the radially polarized beam is distinguished by its longitudinal field at high numerical apertures. The focus spot size of radially polarized beam is smaller than the focused Gauss beam. We had constructed a new three-mode optical tweezers system, which consisted of the azimuthally polarized trapping beam, the radially polarized trapping beam, and the Gauss trapping beam. The radial and axial trapping efficiency were measured under these three trapping modes, respectively. In axial direction, the radially polarized trapping beam resulted in the best trapping, followed by azimuthally polarized trapping beam and Gauss trapping beam in the order. On the contrary, the Gauss trapping beam resulted in the best trapping in radial direction. Due to the unique hollow focus spot, the stable trapping of metallic particles and fine controlling of particles were demonstrated by azimuthally polarized trapping beam. In addition, azimuthally polarized trapping beam could improve the trapping effect while reducing the risk heat damage.Angular manipulations of particles were achieved by optical tweezers due to the transfer of angular momentum from light to particles. We had discussed the principle of the light-induced rotation caused by spin angular manipulation. The results showed that the rotation speed depended on the incident laser power, the size and the rotational symmetry of the particles. The rotation speed of particles induced by spin angular momentum of light was higher than that caused by orbital angular momentum. And optical rotation induced by orbital angular momentum could promote multi-particle co-rotating. Then we had proposed a novel method to rotate driven particles via combining it with drive particles. Most importantly, there were no special requirements for the shape of the driven particles. The biological particle (E. coli) and CNTs can be continuous rotated by optical tweezers using this method. Moreover, the Rubrene particles could emit strong fluorescence exciting by the laser at the wavelength of 532nm, and it could provide a potential application to sort and manipulate other particles with the fluorescence characteristics.The collective trapping and manipulation of micro- and nano- multi-particle were achieved by traditional single optical trap system. The molecular polarization and thermal diffusion of nanoparticles played crucial roles in the light-induced agglomeration and diffusion process. Moreover, we had proposed a simple and inexpensive method to achieve one-dimension beam array including Gauss beam, hollow core beam and line-shape beam using a couple of prisms. A novel multi-trap optical tweezers system was constructed by inserting a couple of prisms based on the previous traditional optical tweezers system. The separate optical trapping and manipulation of multi-particle were achieved preliminary by this new system.