In this work, a two-photon polymerization(2PP) processing device was built using the femtosecond laser, and femtosecond laser direct writing was performed on SU-8 photoresist. Due to the 2PP effect of the photoresist ...In this work, a two-photon polymerization(2PP) processing device was built using the femtosecond laser, and femtosecond laser direct writing was performed on SU-8 photoresist. Due to the 2PP effect of the photoresist caused by the femtosecond laser, the polymeric line with size less than the focal spot size is obtained. Based on the Raman spectroscopy characterization of SU-8 polymer before and after 2PP, we research the dynamic process of femtosecond laser induced 2PP. In Raman spectra, some scattering peaks with large intensity variation, such as 1 108 cm^(-1) and 1 183 cm^(-1), indicate that the asymmetric stretching vibration of C-O-C bond in SU-8 polymer is increased. By comparison, we can find that 2PP only affects the light absorption of initiator, but does not affect the monomer polymerization. It is helpful to understand the interaction of photoresist and femtosecond laser, and plays an important role in quantitatively controlling the polymerization degree of SU-8 polymer and improving the processing resolution of 2PP.展开更多
The characteristic modifications are reported on the surface of polymeric waveguide film in the process of vol- ume-grating fabrication. The light from a mode-locked 76 MHz femtosecond laser with pulse duration of 200...The characteristic modifications are reported on the surface of polymeric waveguide film in the process of vol- ume-grating fabrication. The light from a mode-locked 76 MHz femtosecond laser with pulse duration of 200 fs and wavelength of 800 nm is focused normal to the surface of the sample. The surface morphology modifications are as- cribed to a fact that surface swelling occurs during the process. Periodic micro-structure is inscribed with increasing incident power. The laser-induced swelling threshold on the grating, which is higher than that of two-photon initiated photo-polymerization （TPIP） （8 mW）, is verified to be about 20 mW. It is feasible to enhance the surface smoothness of integrated optics devices for further encapsulation. The variation of modulation depth is studied for different values of incident power and scan spacing. Ablation accompanied with surface swelling appears when the power is higher. By ootimizing the laser carvinR oararneters, hizhly efficient grating devices can be fabricated.展开更多
The effect of initial fabric anisotropy produced by sample preparation on the shear behavior of granular soil is investigated by performing discrete element method （DEM） simulations of fourteen biaxial tests in drai...The effect of initial fabric anisotropy produced by sample preparation on the shear behavior of granular soil is investigated by performing discrete element method （DEM） simulations of fourteen biaxial tests in drained conditions. Numerical test specimens are prepared by three means： gravitational deposition, multi-layer compression, and isotropic compression, such that different initial inherent soil fabrics are created. The DEM simulation results show that initial fabric anisotropy exerts a considerable effect on the shear behavior of granular soil, and that the peak stress ratio and peak dilatancy increase with an increase in the fabric index an that is estimated from the contact orientations. The stress-dilatancy relationship is found to be independent of the initial fabric anisotropy. The anisotropy related to the contact orientation and contact normal force accounts for the main contribution to the mobilized friction angle. Also, the occurrence of contractive shear response in an initial shearing stage is accompanied by the most intense particle rearrangement and microstructural reorganization, regardless of the sample preparation method. Furthermore, the uniqueness of the critical state line in e-logp＇ and q-p＇ plots is observed, suggesting that the influence of initial fabric anisotropy is erased at large shear strains.展开更多
基金supported by the National Basic Research Program of China(No.2010CB934101)the National Natural Science Foundation of China(No.11404173)
文摘In this work, a two-photon polymerization(2PP) processing device was built using the femtosecond laser, and femtosecond laser direct writing was performed on SU-8 photoresist. Due to the 2PP effect of the photoresist caused by the femtosecond laser, the polymeric line with size less than the focal spot size is obtained. Based on the Raman spectroscopy characterization of SU-8 polymer before and after 2PP, we research the dynamic process of femtosecond laser induced 2PP. In Raman spectra, some scattering peaks with large intensity variation, such as 1 108 cm^(-1) and 1 183 cm^(-1), indicate that the asymmetric stretching vibration of C-O-C bond in SU-8 polymer is increased. By comparison, we can find that 2PP only affects the light absorption of initiator, but does not affect the monomer polymerization. It is helpful to understand the interaction of photoresist and femtosecond laser, and plays an important role in quantitatively controlling the polymerization degree of SU-8 polymer and improving the processing resolution of 2PP.
基金supported by the National Natural Science Foundation of China/the Research Grants Council of Hong Kong Joint Research Scheme a grant for NSFC/RGC(No.50218001)the National Science Foundation of China(No.50173015)
文摘The characteristic modifications are reported on the surface of polymeric waveguide film in the process of vol- ume-grating fabrication. The light from a mode-locked 76 MHz femtosecond laser with pulse duration of 200 fs and wavelength of 800 nm is focused normal to the surface of the sample. The surface morphology modifications are as- cribed to a fact that surface swelling occurs during the process. Periodic micro-structure is inscribed with increasing incident power. The laser-induced swelling threshold on the grating, which is higher than that of two-photon initiated photo-polymerization （TPIP） （8 mW）, is verified to be about 20 mW. It is feasible to enhance the surface smoothness of integrated optics devices for further encapsulation. The variation of modulation depth is studied for different values of incident power and scan spacing. Ablation accompanied with surface swelling appears when the power is higher. By ootimizing the laser carvinR oararneters, hizhly efficient grating devices can be fabricated.
基金The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China （Nos. 51209237, 51428901,41030747） and the Fundamental Research Funds for the Central Universities （No. 131gpy05）.
文摘The effect of initial fabric anisotropy produced by sample preparation on the shear behavior of granular soil is investigated by performing discrete element method （DEM） simulations of fourteen biaxial tests in drained conditions. Numerical test specimens are prepared by three means： gravitational deposition, multi-layer compression, and isotropic compression, such that different initial inherent soil fabrics are created. The DEM simulation results show that initial fabric anisotropy exerts a considerable effect on the shear behavior of granular soil, and that the peak stress ratio and peak dilatancy increase with an increase in the fabric index an that is estimated from the contact orientations. The stress-dilatancy relationship is found to be independent of the initial fabric anisotropy. The anisotropy related to the contact orientation and contact normal force accounts for the main contribution to the mobilized friction angle. Also, the occurrence of contractive shear response in an initial shearing stage is accompanied by the most intense particle rearrangement and microstructural reorganization, regardless of the sample preparation method. Furthermore, the uniqueness of the critical state line in e-logp＇ and q-p＇ plots is observed, suggesting that the influence of initial fabric anisotropy is erased at large shear strains.
