纳米Si镶嵌SiNx薄膜实现Nd∶YAG激光器被动锁模

采用射频磁控溅射技术和热退火处理技术制备了石英衬底的纳米Si镶嵌SiNx薄膜(nc-Si-SiNx),薄膜厚度为200 nm.由X射线衍射(XRD)谱计算得出,经800℃连续3 h退火的薄膜中的Si晶粒平均尺寸为1.7 nm.把纳米Si镶嵌SiNx薄膜作为可饱和吸收体插入闪光灯抽运的平凹腔Nd∶YAG激光器内,实现1.06μm激光的被动锁模运转.当激光器腔长为120 cm时,获得平均脉冲宽度32 ps,输出能量25 mJ的单脉冲序列,脉冲序列的包络时间约480 ns,锁模调制深度接近100%.量子限域效应使得纳米Si的能隙宽度大于1.06μm光子能量,所以双光子饱和吸收和光生载流子的快速能量弛豫是导致纳米Si镶嵌SiNx薄膜实现1.06μm激光被动锁模的主要原因.

Passive Mode-Locking in Nd:YAG Laser Using Nanocrystalline Silicon Embedded in SiNx Film

The nanocrystalline silicon embedded in SiNx (nc-Si-SiNx) film was prepared by radio-frequency (RF) magnetron sputtering technique and thermal annealing. The film of 200 nm thick was deposited on silica glass slice. The average diameter of nanocrystalline silicon in the film annealed at 800 ℃ for three hours was about 1.7 nm according to X-ray diffraction (XRD) spectrum. The passive mode-locking operation of a flash-lamp pumped Nd∶YAG laser was achieved by inserting the nc-Si-SiNx film as the saturable absorber into the plane-concave resonator. A single pulse train with average pulse duration of 32 ps and energy of 25 mJ was obtained when the cavity length was 120 cm. The sustained time of a single pulse train was about 480 ns and the modulation depth of mode-locking was nearly 100%. The nc-Si-SiNx film passive mode-locking at 1.06 μm laser was mainly ascribed to two-photon saturable absorption and fast energy relaxation processes of carriers excited by laser in the nanocrystalline silicon since the energy band gap of the nanocrystalline silicon affected by the quantum confinement related effects was larger than the photon energy of 1.06 μm laser.