Research on Multilayer Dielectric Gratings with High Laser Induced Damage Threshold

Increasing of industrial and military applications needs the high Power and high Beam Quality Laser. Single-mode optical fiber has been limited to a few million watts for its own limitations. Therefore, it is necessary to use multi-unit beam combination method to get higher power laser. At present, the most widely used method is multilayer dielectric grating in spectral beam combining, which requires high beam-forming efficiency and high laser induced damage threshold. However, there is a lack of high laser induced damage threshold coating technology in Taiwan. In order to have the key technologies of high-power laser applications. This project optimizes thin film manufacturing process and establishes relevant experimental data to grasp the key technical parameters based on the past research. Using two way to increase laser induced damage threshold, the first is to establish the process parameters for the ultra-low absorption thin film material, from the plating growth mechanism, substrate temperature, material selection, substrate flatness selection, and substrate cleaning proceed. The second approach is design the electric field to match the film structure to move the peak of the electric field out of the boundary of the film surface to increase the resistance to high energy, and to control the film thickness error. The FDTD calculation software will use to improve the efficiency of the beam combination. Multilayer dielectric grating with high beam-forming efficiency and high laser induced damage threshold will fabricate to provide high-power laser. The reflectance of high reflection mirror is 99.99% and laser induced damage threshold is more than 10 J / cm2 at 532 nm pulsed laser. The beam-forming efficiency of multilayer dielectric gratings will more than 90% and laser induced damage threshold is more than 6 J / cm2 at 1064 nm pulsed laser.