| Photonic crystals are a new type of artificial of materials with multi-dimensionality . periodic dielectric structure. They can create a range of forbidden frequencies called photonic bandgap. Photons with energy lying in the gap cannot propagate through the medium. Using self-assembly to produce three-dimensional photonic crystals is the more feasible method. But making perfect crystalline arrays of sphere is not easy. Invariably, random ( bad) defects occur within the lattice . These affect the photonic crystal applications. Much effort has focused on eliminating these unwanted defects from the self-assembled material, and extremely ordered photonic bandgap crystals have been made. However people can't control the defect during the self-assembling. We modify the defect by applications of optical tweezers technology. Structural defects can dictate the properties of photonic bandgap materials, adding intentional defects within the crystal are needed. This experiment is the foundation of the future work. Based on the theories of optical pressure forces, this paper deduce the formula along Z axial, analyze the effects of microscope objective NA laser, profileon trapping force. The results show the light rays nearby the center of the objective back aperture have greater contribution to the transverse forces, while those nearby the edge affect mainly the axis forces. The transverse trapping force can be increased effectively by modifying laser profile, while the axial stability of the system is still assured.We using a He-Ne laser as light source, an optical tweezers with one optical trap was set up. The laser light and the observation light normally incident the objective back aperture. We can always observe and manipulate dielectric spheres at the top layers. Polystyrene beads, silicon dioxide spheres were successfully manipulated with the optical tweezers system. The construction of optical tweezers is the foundation optical micromanipulation of photonic crystals.
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