State Key Laboratory of Luminescent Materials and Devices, School of Materials Science and Engineering, South China University of Technology, Wushan Road 381, Guangzhou, 510641, P. R. China.
Department of Physics, Zhejiang Normal University, Jinhua, Zhejiang, 321004, P. R. China.
Adv Mater. 2018 Jul;30(28):e1801638. doi: 10.1002/adma.201801638. Epub 2018 May 23.
In materials showing reverse saturable absorption (RSA), optical transmittance decreases at intense laser irradiation. One approach to application of these materials is to protect the sensors or human eyes from laser damage. To date, research has mainly concentrated on thin films and suspensions of graphite and its nanostructure (including nanotubes, graphene, and graphene oxides), which are mainly used as an optical limiter for nanosecond laser pulses. Moreover, thin individual pieces of semiconductor usually exhibit increased transmittance due to saturable absorption when the laser energy (E ) is higher than the band gap (E ). Here, it is shown that indirect gap semiconductor WSe exhibits high RSA on exposure to a femtosecond laser under E > E near band gap excitation, which is attributed to the longitudinal optical phonon-assisted anti-Stokes transition by the annihilation of phonons and the absorption of photons. An optical limiting threshold (≈21.6 mJ cm ) lower than those reported for other optical-limiting materials currently for femtosecond laser at 800 nm is observed.
在表现出反向饱和吸收（RSA）的材料中，在强激光辐照下光透射率会降低。将这些材料应用于实际的一种方法是保护传感器或人眼免受激光损伤。迄今为止，研究主要集中在石墨及其纳米结构（包括纳米管、石墨烯和氧化石墨烯）的薄膜和悬浮液上，这些材料主要用作纳秒激光脉冲的光限幅器。此外，当激光能量（E）高于带隙（E）时，通常较薄的半导体片由于饱和吸收而表现出增加的透射率。在这里，研究表明，在近带隙激发下，间接带隙半导体 WSe 在暴露于飞秒激光时表现出高 RSA，这归因于通过声子的湮灭和光子的吸收来实现的长光学声子辅助反斯托克斯跃迁。观察到的光学限制阈值（约 21.6 mJ cm）低于目前用于 800nm 飞秒激光的其他光限制材料的报告值。
