采用射频磁控溅射技术制备了Ge掺二氧化硅(Ge-SiO2)和Ge, Al共掺二氧化硅(Ge/Al-SiO2)两种复合薄膜, 并进行了热退火处理形成了纳米Ge镶嵌结构。通过紫外-可见吸收谱测量, 确定了两种薄膜中纳米Ge的光学带隙, 并采用皮秒激光Z-扫描技术研究了薄膜的非线性光学性质。测试结果显示, 在1 064 nm激发下得到的Ge-SiO2和Ge/Al-SiO2薄膜的非线性吸收系数分别为-1.23×10-7 m/V和4.35×10-8 m/W, 前者为饱和吸收, 而后者为双光子吸收。把两种薄膜作为可饱和吸收体均可实现1.06 μm激光的被动调Q和被动锁模运转。与Ge-SiO2薄膜比较, 采用Ge/Al-SiO2薄膜可以获得较窄的调Q脉冲和锁模脉冲。最后, 理论分析和实验比较了两种薄膜实现被动调Q和锁模的机理。

The Ge-SiO2 and Ge/Al-SiO2 compound films were prepared by Radio-Frequency (RF) magnetron sputtering technique, and then Ge nanocrystals were obtained in the films by a thermal annealing treatment. The optical bandgaps of the Ge nanocrystals in the two films were calculated by measured UV-visible absorption spectral data, and the nonlinear optical properties of the two compound films were investigated by using picosecond laser Z-scan technique. Experiments show that the nonlinear absorption coefficients of Ge-SiO2 and Ge/Al-SiO2 films at 1 064 nm lasing are -1.23×10-7 m/V and 4.35×10-8 m/W, respectively. The former corresponds to the saturable absorption, while the latter corresponds to the two-photon absorption. Furthermore, both the Ge-SiO2 and Ge/Al-SiO2 films can be as the saturable absorbers to implement the passive Q-switching and mode-locking operation for a 1.06 μm laser. Obtained experimental results demonstrate that Ge/Al-SiO2 film could achieve narrower Q-switched pulse and mode-locked pulse than that of the Ge-SiO2 film. Finally, it discusses the mechanisms of passive Q-switching and passive mode-locking with the two films.