By employing the Z-scan technique, the nonlinear optical (NLO) properties of multi-layered WS₂ nanosheets (WNSs) are investigated using pulsed (10 ns) laser irradiation having wavelength of 532 nm. In the trilayer WNSs, the transformation from saturable absorption (SA) to reverse saturation absorption (RSA) is clearly observed only when the magnitude of incident pump intensity exceeds 0.68 GW/cm². The saturation intensity in the case of SA for the used sample is found to be ~0.53 ± 0.03 GW/cm². The SA behaviour appears at low intensity due to one photon absorption (1PA) originated from the direct transition at B excitonic peak. This is confirmed from the measured photoluminescence properties of trilayer WNSs. Further, with the increase of laser intensity, the transformation of 1PA to two-photon absorption (2PA) occurs only for trilayer WNSs. It is observed that at the highest used intensity of 0.93 GW/cm², trilayer WNSs exhibits a large 2PA. A comprehensive analysis of the experimental data of Z-scan enables us to determine a value of ~1.42 ± 0.01 cm/GW for the highest 2PA coefficient (β_2PA) and this value is ~1.5 times higher than those obtained for the multilayer and penta-layer WNSs. The calculated value of the imaginary part of the third-order NLO susceptibility (Im χ⁽³⁾) of the trilayer WNSs is ~4.24 × 10⁻¹³ esu. The properties of transition from SA to RSA in thinned layered of WNSs make these materials favourable for designing different optoelectronic devices.

通过使用Z扫描技术，使用波长为532 nm的脉冲（10 ns）激光辐照研究了多层WS ₂纳米片（WNSs）的非线性光学（NLO）特性。在三层WNS中，只有当入射泵浦强度的幅度超过0.68 GW / cm ²时，才能清楚地看到从饱和吸收（SA）到反向饱和吸收（RSA）的转变。对于用过的样品，在SA的情况下的饱和强度被发现为〜0.53±0.03GW / cm ^2。。由于一个光子吸收（1PA）源自B激子峰的直接跃迁，因此SA行为在低强度下出现。从三层WNS的测得的光致发光特性可以证实这一点。此外，随着激光强度的增加，仅对于三层WNS发生1PA到双光子吸收（2PA）的转变。可以看出，在最高使用强度为0.93 GW / cm ^{2的情况下}，三层WNS表现出较大的2PA。Z-扫描的实验数据的全面分析使我们能够确定〜1.42±0.01厘米/ GW对于最高2PA系数（的值β _2PA），这个值比多层和五层WNS的值高1.5倍。三阶NLO易感性（虚部的计算值林χ ^（3） ）的三层的WNSs是〜4.24×10 ^-13 ESU。WNS的薄层中从SA过渡到RSA的特性使这些材料有利于设计不同的光电器件。