研制了一套微通道封装结构半导体激光器的低温测试表征系统, 实现了对高功率半导体激光器在－60℃~0℃低温范围内的输出功率、电光转换效率和光谱等关键参数稳定可靠的测试表征. 采用计算流体力学及数值传热学方法, 模拟了无水乙醇、三氯乙烯以及五氟丙烷三种载冷剂的散热性能. 模拟结果表明, 压降均为0.47 bar时, 采用无水乙醇作载冷剂的器件具有最低的热阻(热阻为0.73 K/W)和最好的温度均匀性(中心和边缘发光单元温差为1.45℃). 低温测试表征系统采用无水乙醇作为载冷剂, 最大可实现0.5 L/min的载冷液体流量, 最多能容纳5个半导体激光器巴条同时工作. 基于该低温测试表征系统, 对微通道封装结构976 nm半导体激光器巴条在6%占空比下的低温特性进行了研究. 测试结果表明, 载冷剂温度由0℃下降到－60℃, 半导体激光器的输出功率由388.37 W提升到458.37 W, 功率提升比为18.02%; 电光转换效率由60.99%提升到67.25%, 效率提升幅度为6.26%; 中心波长由969.68 nm蓝移到954.05 nm. 器件开启电压增加0.04 V, 阈值电流降低3.93 A, 串联电阻增加0.18 mΩ, 外微分量子效率提高11.84%. 分析表明, 阈值电流的减小及外微分量子效率的提高, 是促使半导体激光器在低温下功率、效率提升的主要因素. 研究表明, 采用液体微通道冷却的低温工作方式, 是实现半导体激光器高输出功率、高电光转换效率的一种有效手段.

A set of cryogenic measurement system for semiconductor lasers with microchannel structure was developed. The stable measurement of some vital parameters such as output power, electrooptic conversion efficiency and spectra of high power semiconductor lasers in the range from －60℃ to 0℃ were realized. Based on computational fluid dynamics and numerical heat transfer methods, the heat dissipation performance of three cryogenic coolants, anhydrous ethanol, trichloroethylene and pentafluoropropane was simulated. The simulation results show that semiconductor laser bar with anhydrous ethanol as the coolant has the smallest thermal resistance(0.73 K/W) and the best temperature uniformity(temperature difference between emitters is 1.45℃) when the pressure drop is 0.47 bar. Anhydrous ethanol was used as system coolant, the maximum of ethanol flow rate was up to 0.5 L/min, and 5 semiconductor laser bars could work simultaneously in the system. Based on the cryogenic measurement system, the cryogenic characteristics of 976 nm semiconductor laser bar with microchannel structure at 6% duty cycle were investigated. The experimental results show that the output power of semiconductor laser bar is increased from 388.37 W to 458.37 W which the powerup ratio is 18.02%, the electrooptic conversion efficiency is increased from 60.99% to 67.25%, the efficiency is increased by 6.26%, and the central wavelength is shifted from 969.68 nm to 954.05 nm when the coolant temperature decreases from 0℃ to －60℃. The turnon voltage increases by 0.04 V, the threshold current decreases by 3.93 A, the series resistance increases by 0.18 mΩ, and the external differential efficiency increases by 11.84%. The analysis shows that the decrease of threshold current and the improvement of external differential efficiency are the main factors that promote the power and efficiency of semiconductor lasers at low temperature. This investigation shows that the cryogenic working mode of liquid microchannel cooling is an effective means to achieve high output power and high electrooptic conversion efficiency of semiconductor lasers.