Micro And Nano Fabrication Using Laser Interference Technology

In this thesis, the approaches of the fabrication of micro and nano structures are investigated. Several technologies of controlling laser beams are developed and applied to generate a series of surface patterns and volume structures. The contents of the thesis are as follows:1. Investigation of the laser and azopolymer interactions.The introduction of azopolymers and their properties are presented. Laser induced isomerization are introduced. The laser induced motions in different scales and the corresponding responsive properties, like photo-induced orientation, mass migration, photo-mechanics effect, are presented. The characterization and the measurement approach are discussed. Finally, azopolymer with different substituent groups, cross-linked degrees and composite polymer (azopolymer doped with Ag nano particles) are investigated by laser induced orientation. The experimental results illustrate that substituent group has strong influence upon the orientation of azopolymer. Cross-linking will suppress mass migration inside azopolymer. Azopolymer doped with Ag nano particle will quicken the orientation of the composite material in low consistency intermingle, while the orientation speed will be slacked off in high consistency intermingles. Ag nanoparticle/azopolymer nanocomposites are prepared with controlled concentration of Ag nanoparticles by in situ reduction of Ag(I)–diketone complexes in an azopolymer matrix. Compared with pure azopolymer, the birefringence of this nanocomposite is more stable.2. Fabrication of periodic and quasi-periodic micro and nano structures via laser interference technologies. The multiple-beam interference technology is used to modulate the intensity distribution and the polarization states in the space by controlling the phase, the polarization and the intensity of the interfering beams. Via two-beam polarization holography, surface relief gratings and refractive index gratings are generated. Simulative results by Matlab illuminate that if the number of the interfering beams is above (including) four, the phase and the polarization of the interference have strong influence upon the interfering field. In three-beam interference case, the phase of the interfering beams will not change the shape of the intensity patterns. However, by controlling the polarization of the interfering beams, we can obtain different patterns in the interfering field, which can be applied to generate different textures. Multiple exposures of two-beam interference and three-beam interference can be utilized to generate quasi-periodic microstructures on different sample surface.3. Investigation of the mechanism laser induced mass migration inside azopolymer materials. Hexagonally distributed circular caps are generated on the surface of azopolymer films by polarization controlled three-beam interference ablation and utilized as the investigated objectives to demonstrate the mechanism of laser induced mass migration inside azopolymer materials. Two beam interference of different polarization arrangements are adjusted and used to expose the circular caps on azopolymers. While the interfering beams are of (P, P) mode, the caps are stretched along the direction of P polarization. If the interfering mode is set to (P, P) and (+45°, -45°), the caps are seldom deformed in the surface plane. When the interfering beams are of (S, P) mode, the caps are deformed in the tilted direction. The experimental results illuminate that only when the intensity gradient exists in the direction of the irradiating polarization, the mass migration happens inside azopolymers.4. Fabrication of dual-scale structure on azopolymer. Dual-scale microstructures can be used as superhydrophobic surface, structural color and high adhesive surface. Based on laser interference technology, dual-scale microstructures can be fabricated on azopolymer surface. Two different materials four amorphous side chain azopolymers with cyano group (AzoCN), methyl group (AzoCH3) are used as investigated objectives. Experimental results illuminate that nano band textures will be formed on the surface of azopolymers with cyano group (AzoCN) when the sample is exposed by single beam exposure. However, only nano cluster structures will be formed on azopolymers with methyl group (AzoCH3). The size of the nano structures is dependent on the laser exposure dose and the laser power. While the sample are exposed to two beam interference of different modes, on AzoCN, dual-scale structures with nano textures in different directions can be formed, and on AzoCH3, dual-scale structures with nano cluster structuresare formed.5. Generation of cylindrical vector beams. Cylindrical vector beams, like radially polarized beams and azimuthally polarized beams are generated by carefully selecting the output light of high birefringence C-cut YVO4 crystal. YVO4 crystal can be used produced cylindrical vector beams with different wavelengths. Based on azopolymer, we designed and produced axisymmetric phase retardation plates (ASPRP). The phase retardation of ASPRP can be easily controlled by materials, the thickness of the sample films and the laser dose. ASPRP can be used to generate cylindrical vector beams.