The cover image represents laser light illuminating a densely-spaced, randomly-arranged, 3D-network of a WS₂ polymorph (“nanomesh”), where 2D sheets intersect and twist on top of each other, modifying the energy landscape of the material, as presented by Ventsislav K. Valev and co-workers in article number 2100117. The multiphoton emission is dominated by large second harmonic generation (SHG) that is doubly resonant at the broad C spectral feature of the transition metal dichalcogenide.

中文翻译：

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非线性光学：具有修正能量景观的 WS2 纳米网格多晶型二次谐波产生的双共振增强（激光光子学修订版 15(6)/2021）

封面图片代表激光照亮 WS ₂多晶型物（“纳米网”）的密集间隔、随机排列的 3D 网络，其中 2D 片材在彼此顶部相交和扭曲，从而改变了材料的能量景观，正如 Ventsislav K. Valev 及其同事在文章编号 2100117 中提出的那样。多光子发射主要由大二次谐波产生 (SHG) 主导，它在过渡金属二硫属化物的宽 C 光谱特征处双重共振。