Research On Femtosecond Laser Processing And Applications Of Micro/Nano Gratings

Micro and nanostructures induced by femtosecond laser have caused more and more attention, these structures have a strong application in the field of photonic crystals, optical storage and micro-optoelectronic devices. Research goal of this thesis is to analyze applications for femtosecond laser processing micro/nanograting structures. A method for Circularly Polarized Femtosecond Laser (CPFL) processing is proposed, which can induce multi-color on iron surface. During on modulating the incident angle of white light, diverse colors were displayed on the iron surface which is induced by CPFL. Color brightness and color patterns are not obvious when slowly change the viewing angle. It verifies that CPFL have the same research value on the process of structural color compared with linearly polarized. The study will have great reference value in the field of the color design and color display.Femtosecond laser processing micro/nanograting structures can also be applied in photovoltaic devices. Based on femtosecond laser processing micro/nanograting structures, we use SPPs effect to enhance device performance. We make theoretical modeling and experimental simulation work on grating structure of MSM photodetectors, analyzing the influence of the duty cycle, grating thickness, and subwavelength aperture configuration parameters on detector absorption properties. The thesis including the following research contents:Build a complete system of femtosecond laser micro/nano fabrication corresponding experiments. Introduce the theory of finite difference time domain (FDTD) method and the simulation steps of FDTD solutions software.Femtosecond laser fabricated micro/nano-structures in metallic iron and stainless steel surfaces, treatment zones of metal surface were observed by SEM image. Surface microstructures manufactured by linear polarized femtosecond laser are generally nanoscale NC-LIPSS, while those dealt with circularly polarized femtosecond laser are generally irregular and unevenly distributed. According to different grating structures, we analyzed the absorption properties by FDTD solutions. The results of circularly polarized femtosecond laser processing iron surface color were analyzed. The results verify the circularly polarized laser has a certain unique in the fabrication of structural color.Femtosecond laser processing micro/nanograting structures can be applied in photovoltaic devices. A new type of SPPs enhanced metal-semiconductors-metal photodetector structure employing rectangular-shaped nanogratings is modeled. The sub-wavelength aperture width, the nano-grating height, the duty cycles of metallic nano-gratings have been optimized to minimum the optical reflection of the MSM-PD, by minimizing the reflection from the sub-wavelength aperture. The FDTD simulation tool has been used and the results have shown that the nano-grating assisted MSM-PD structures can theoretically attain a minimum light reflection near 900 nm of about 15% of the conventionally-designed MSM-PDs. The results provide useful information for the design and fabrication of high absorption, nano-scale optoelectronic devices.