YAG/Nd:YAG/YAG ceramic planar waveguide laser amplifier with 327-mJ output at 100-Hz repetition rate
Schematic of the single-pass Nd:YAG ceramic planar waveguide laser amplifier system.
Electro-optical efficiency is an important parameter for all-solid-state lasers. With higher efficiency, construction of laser devices can achieve miniaturization and reduce weight more easily. As a laser gain medium, a planar waveguide combines the advantages of slabs and fibers, such as high power and high energy conversion efficiency. Bonding is a popular technique for fabricating planar waveguide laser gain media. However, for planar waveguide laser media with large aspect ratios, the necessity of controlling the core thickness and mechanical strength of the bonding interface still restrict the development of this technology.
Tape casting technology, which offers high precision and excellent controls of film thickness and composition, can overcome the difficulties of bonding. By utilizing the methods of tape casting and ceramic sintering, integrated preparation of planar waveguide laser ceramics can be realized.
A YAG/Nd:YAG/YAG ceramic planar waveguide laser amplifier, fabricated by nonaqueous tape casting and solid-state reactive sintering, was jointly presented by the research group led by Prof. Qingsong Gao at Institute of Applied Electronics, China Academy of Engineering Physics, and the research group led by Prof. Jiang Li at Shanghai Institute of Ceramics, Chinese Academy of Sciences. A single-pulse energy of 327 mJ at a repetition rate of 100 Hz was obtained. To the best of the researchers' knowledge, this is the highest reported output energy with such good beam quality achieved with ceramic YAG/Nd:YAG/YAG planar waveguides fabricated by non-aqueous tape casting and solid-state reactive sintering. The report appeared in the Chinese Optics Letters, Volume 14, No. 5, 2016 (J. Liu et al., Diode-pumped composite ceramic Nd:YAG planar waveguide amplifier with 327-mJ output at 100-Hz repetition rate).
The experimental configuration of the Nd:YAG planar waveguide laser consists of three parts: the seeder, beam coupling system, and amplifier. The seeder used in this study was a Nd:YAG laser resonator. The dimensions of the laser medium were 1 mm ×10 mm × 60 mm. The ceramic YAG/Nd:YAG/YAG waveguide structure was formed in the thickness direction, and each end had an undoped YAG end cap. The pump beam from the diode laser array was launched into the planar waveguide from the end facet at a particular angle. A seeder laser was coupled from one end and amplified for a single pass.
Commenting on this development, Prof. Qingsong Gao noted, "Besides the merits of high energy and high efficiency, its extremely small size enables miniaturization and lightweight design of laser systems. So, the ceramic planar waveguide laser is one of the future directions of development of high-energy all-solid-state lasers."
Future research will focus on the development of ceramic planar waveguide lasers, such as further increasing their output power and efficiency and broadening their spectral range.
新工艺制备的增益介质使激光放大器激光输出达国际领先水平
图片说明：单通Nd:YAG陶瓷平面波导激光放大器系统示意图。
电光效率是全固态激光器的一个重要参数。效率越高，激光器更易实现小型化和轻量化。采用平面波导材料作为增益介质的激光器，同时具有块状固体激光器功率高和光纤激光器能量转换效率高的优点。键合技术是实现平面波导激光增益介质的常见技术途径，但针对大纵横比的平面波导材料仍存在芯层厚度控制和键合强度等问题。
流延成型技术是一种精度高、膜厚度和组分可控性强的陶瓷成型工艺。采用流延成型和陶瓷烧结技术可以克服单晶键合技术的缺陷，实现平面波导结构激光陶瓷的一体化制备。
中国工程物理研究院应用电子学研究所高清松研究员课题组联合中国科学院上海硅酸盐研究所李江研究员课题组采用非水基流延成型和固相反应烧结工艺制备的YAG/Nd:YAG/YAG陶瓷平面波导作为激光放大器的增益介质，获得100 Hz重复频率下327 mJ单脉冲能量的激光输出，据该课题组所知，这是国际范围内采用非水基流延成型制备的该种陶瓷平面波导达到的最大单脉冲能量输出。相关研究成果发表在Chinese Optics Letters 2016年第5期上(J. Liu et al., Diode-pumped composite ceramic Nd:YAG planar waveguide amplifier with 327-mJ output at 100-Hz repetition rate)。
整个激光器系统包括三个主要部分：种子源，种子光耦合系统，以及放大器。种子源为双棒串接的Nd:YAG振荡器。放大器增益介质尺寸为1 mm×10 mm×60 mm，1 mm厚度上为陶瓷YAG/Nd:YAG/YAG波导结构，并且两端各有5 mm的非掺杂YAG端帽。抽运源经过慢轴缩束快轴聚焦后，以特定的角度倾斜抽运平面波导介质。种子光从波导一端注入，放大光从另一端输出。
高清松研究员认为，该陶瓷激光放大器不仅具有输出能量高、效率高的优点，而且它的体积非常小能够实现激光器系统的小型化、轻量化，是未来数年高能全固态激光器的主要发展方向之一。
后续工作是陶瓷平面波导激光器的拓宽和发展，通过优化系统，进一步提高效率，提升功率，并拓宽工作光谱范围。