A New Continuous Wave 2500W Semiconductor Laser Vertical Stack Xiaoning Li 1,2 , Chenhui Peng 1 , Yanxin Zhang 1 , Jingwei Wang 1 , Lingling Xiong 1 , Pu Zhang 1 , Xingsheng Liu 1,3 1 State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics Chinese Academy of Sciences No. 17 Xinxi Road, New Industrial Park, Xi'an Hi-Tech Industrial Development Zone, Xi'an, Shaanxi, 710119, P.R. China , tel. 8629-88880786, fax.8629-88887075, smto@opt.ac.cn 2 Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique, Xi’an Jiaotong University, No.28, Xianning West Road, Xi'an, Shaanxi, 710049, P.R. China 3 Xi’an Focuslight Technologies Co., LTD No. 60 Xibu Road, New Industrial Park, Xi'an Hi-Tech Industrial Development Zone, Xi'an, Shaanxi, 710119, P.R. China Abstract With the increasing applications of high power semiconductor lasers in industrial, advanced manufacturing, military, aerospace, medical systems, display, entertainment. etc., semiconductor lasers with high power and high performances are required. The performance of semiconductor lasers is greatly affected by packaging structure, packaging process and beam shaping. In this work, a high power semiconductor laser vertical stack was successfully fabricated. A series of techniques such as spectrum control and beam control were used to achieve marrow spectrum and high beam quality. The performances of the semiconductor laser vertical stack were characterized. A high power of 2500 W, a narrow spectrum of 3.11 nm and an excellent rectangular beam shape were obtained. The lifetime of the vertical stack laser was tested as well. Introduction High power semiconductor lasers have been found increasing applications in pumping of solid state laser systems and fiber amplifiers, frequency doubling, medical systems and material processing, such as welding, cutting and surface treatment [1]. Although the output power of a single emitter has been improved significantly in recent years, the power is still generally limited to below 20 watt for a 9xxnm laser, which is unable to satisfy new applications with higher power demands obviously. Laser bar can provide a magnitude of output power of single emitter by integrating the multiple individual emitters. To further increase the output power, several packaging technologies have been developed, including multiple single-emitter modules, horizontal bar arrays, and area bar arrays [2]. Naturally, integration of single bar unit as a vertical stack is another choice to increase the output power. The multiple bars are electrically connected in series and can be operated at continuous wave (CW) or quasi- continuous wave (QCW) mode. In this work, the traditional packaging structure has been optimized and improved. Based on the new packaging structure, a new 976 nm semiconductor laser vertical stack with 2500 W in CW mode was fabricated and its performances were characterized. A series of techniques such as spectrum control and beam control was used to improve the performance of the vertical stack. Structure design of single bar The performance and reliability of a semiconductor laser are greatly affected by its packaging structure and thermal properties. Since the vertical stack is assembled by single bars, the structure of the single bar has a significant impact on the performance of the vertical stack. Therefore, not only the structure of the vertical stack but also that of the single bar should be considered. Fig. 1 The traditional (a) and double-sided (b) cooling package structure Fig. 1(a) shows a traditional packaging structure. The heat generated from the laser bar is one-sided conducted to heat sink with a low cooling efficiency. Fig. 1 (b) shows the double-sided cooling packaging structure we designed. The heat can be conducted through both the anode and cathode; therefore, the thermal dissipation efficiency is improved significantly. The transient thermal behavior of double-sided cooling packaging was studied using finite element analysis (FEA), as shown in Fig. 2. The simulation result shows that the heat is not only conducted to the heat sink from bottom directly, but also conducted by the cathode, which improves the cooling efficiency. Moreover, according the double-sided cooling packaging design, the heat dissipation efficiency from the cathode can be up to 20%.