Domestically Produced Ceramic YAG Laser Gain Material for High Power SSLs

摘要

High power solid state laser systems are being developed for directed energy weapon applications. Scaling to higher power levels will undoubtedly demand larger sizes and more complex designs for laser gain media used in these systems. Ceramic materials are beginning to-replace single crystals as a preferred laser gain medium. Ceramic laser gain materials such as Nd:YAG, Yb-YAG, Er:YAG and Yb:Y203 are increasingly being used in solid state laser systems such as microchip, rotary disk, and multiple slab high-power lasers [1]. Opticallytransparent ceramics have numerous advantages over single crystals. Ceramic material can be fabricated more quickly and to larger sizes than crystals. Most single crystal YAG is grown according to the Czochralski method, in which a seed crystal is pulled and rotated inside an iridium crucible with molten YAG to form a crystal boule. Large crystals are difficult to fabricate because the growing process introduces significant stress and other index distortions. On the other hand, larger sizes can be fabricated with ceramic materials with more uniform optical-properties and dopant homogeneity. The size of the ceramic is only limited by the hot zone dimensions of the sintering furnace. This attribute permits the construction of long slabs for use in multi-kilowatt laser systems without optical bonding of smaller crystal pieces. The complex geometry formability and the near net shape capability also contribute to the cost competitiveness of ceramic materials. Ceramic material can be fabricated in a few days with the appropriate furnace, whereas growing a large crystal requires several weeks and expensive iridium crucibles at very high temperatures. Ceramic sintering temperatures are well below the melting temperatures required for single crystals. More sophisticated composite laser designs can be realized with the ceramic technology, where Q-switched, Raman shifted, and other types of lasers can be made as a single structure. Dopant gradation and multiple dopant types can directly be incorporated during the cermic fabrication process.