Cover Story：Liu ML, Wu HB, Liu XM, Wang YR, Lei M et al. Optical properties and applications of SnS2 SAs with different thickness. Opto-Electron Adv 4, 200029 (2021).

Saturable absorber (SA) is a kind of optical device based on two-dimensional materials for the generation of laser. Due to its low cost, strong optical absorption, fast relaxation time and high nonlinearity, the SA offers outstanding advantages in high-performance pulsed fiber laser. Recently, Professor Wenjun Liu of Beijing University of Posts and Telecommunications, cooperates with Professor Zhiyi Wei of Institute of Physics of Chinese Academy of Sciences and Professor Wei Guo of Beijing Institute of Technology, have reported the Q-switched fiber laser based on the SnS₂ SA. By changing the thickness of SnS₂ SAs, the nonlinearity of them has been adjusted. At the same time, the stability, output power, starting threshold and pulse duration of the fiber laser based on different SAs have been analyzed. Through theoretical calculations, the variation law of carrier mobility and electronic structure of different SnS₂ SAs changing with material thickness and defect state has been further revealed, which explains the influence of material thickness on nonlinearity and absorption. The effective nonlinearity control of SA can not only engineer the parameters of optical devices, but also improve the machining accuracy and efficiency of corresponding lasers. This research has opened up new avenues for the future research of nonlinear optical devices and the development of high performance fiber lasers.