纳米半导体复合薄膜的非线性光学性质及其在激光器中的应用

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。

Nonlinear optical properties of nanometer semiconductor compound films and their applications to lasers

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.