The comparative study on nonlinear absorption of WS2 nanosheets was performed by using nanosecond Z-scan measurements at 532 nm and 500 nm. It was found that, WS2 nanosheets exhibit saturable absorption (SA) at low excitation intensities, and the saturable intensity at 500 nm is much stronger than that at 532 nm, which implies that resonance plays main role. With the increase of incident intensity, a switch from SA to reverse saturable absorption (RSA) occurs. Besides, ultrafast dynamics of WS2 nanosheets were investigated by using femtosecond pump-probe technique. Photo-dynamics process was found to contain a double exponential energy relaxation with a fast decay component (14 ps) and a slow one (145 ps).

中文翻译：

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WS2纳米片非线性吸收和超快动力学的共振增强

通过在 532 nm 和 500 nm 处使用纳秒 Z 扫描测量，对 WS2 纳米片的非线性吸收进行了比较研究。结果表明，WS2纳米片在低激发强度下表现出饱和吸收（SA），500 nm处的饱和强度远强于532 nm处，这意味着共振起主要作用。随着入射强度的增加，发生从 SA 到反饱和吸收 (RSA) 的转换。此外，使用飞秒泵浦探针技术研究了WS2纳米片的超快动力学。发现光动力学过程包含具有快速衰减分量 (14 ps) 和慢速衰减分量 (145 ps) 的双指数能量弛豫。