Broadband, High-efficiency Gratings For Laser Pulse Compression: Metal-multilayer Dielectric Gratings And Metal-multilayer-dielectric Coated Gratings

Chirped pulse amplification(CPA) technology has created a revolution in the production and use of high-energy, ultra-short pulse petawatt-class lasers and pulse compression gratings(PCG) are key elements of CPA laser systems. Based on the research status, Metal-multilayer dielectric gratings(MMDG) and Metal-multilayer-dielectric coated gratings are studied in this dissertation. MMDGs with grating structures etched on the metal-multilayer dielectric layer substrates,Metal-multilayer-dielectric coated gratings with metal and multilayer dielectric layers coated on bare grating substrate.In the development process of MMDG, we first theoretically analyzed the grating profile parameters and fabrication tolerance. We fabricated the resist masks based on the theoretical analysis, and we utilized oxygen plasmas ashing method to modify the groove depth and duty cycle of resist masks. We ascertained the relationship between mask duty cycle and MMDG duty cycle. According to experimental results, MMDG duty cycle changes between 0.15 and 0.21 while mask duty cycle changes between 0.14 and 0.18.We investigated the evolution of MMDG profiles in ion beam etching process according to experimental results, and established the on-line monitoring model to monitor the etching process in real time which was insensitive to changes of mask duty cycle and resist depth. Groove depth of fabricated MMDGs was controlled within a range of 310 nm to 320 nm. The control accuracy of etching groove depth was 10 nm.The diffraction efficiency of a fabricated MMDG was measured to have a peak diffraction efficiency value of 95.1% at 810 nm wavelength and the maximum bandwidth was 169nm(705nm to 874nm) with efficiency higher than 90%, the average efficiency in the bandwidth was 93.71%.In the development process of Metal/multilayer-dielectric coated grating, we selected suitable substrate material and etching process based on experimental results.Depending on the etching process, we fabricated the bare grating substrate with different grating parameters. The groove depth ranges from 170 nm to 370 nm while duty cycle ranges from 0.40 to 0.71. Based on experimental results, we choose electron beamevaporation process for gold film coating, and ion beam sputtering process for multilayer dielectric film coating. We analyzed the evolution of grating ridges in coating process according to SEM images. And, we set up the phenomenological model of the evolution of Metal/multilayer-dielectric coated grating profiles in the coating process. Based on the model, we optimized the grating parameters, and analyzed the fabrication tolerance. The calculated bandwidth of efficiency higher than 90% is 100nm(755 nm-855 nm). The peak value of diffraction efficiency is 95.70% at 785 nm.The mean value of diffraction efficiency is 93.21% between 755 nm and 845 nm. The optimized metal/multilayer-dielectric grating could be a good alternative to compression grating with good processibility.