Degenerate minima in momentum space—valleys—provide an additional degree of freedom that can be used for information transport and storage. Notably, such minima naturally exist in the band structure of transition metal dichalcogenides (TMDs). When these atomically thin crystals interact with intense laser light, the second harmonic generated (SHG) field inherits special characteristics that reflect not only the broken inversion symmetry in real space but also the valley anisotropy in reciprocal space. The latter is present whenever there exists a valley population imbalance (VPI) between the two valleys and affects the polarization state of the detected SHG. In this work, it is shown that the temperature-induced change of the SHG intensity dependence on the excitation field polarization is a fingerprint of VPI in TMDs. In particular, pixel-by-pixel VPI mapping based on polarization-resolved raster-scanning imaging microscopy was performed inside a cryostat to generate the SHG contrast in the presence of VPI from every point of a TMD flake. The generated contrast is marked by rotation of the SHG intensity polar diagrams at low temperatures and is attributed to the VPI-induced SHG.

动量空间中退化的极小值（谷）提供了可用于信息传输和存储的附加自由度。值得注意的是，这种极小值自然存在于过渡金属二硫化碳（TMD）的能带结构中。当这些原子薄的晶体与强激光相互作用时，产生的二次谐波（SHG）场将继承特殊的特征，这些特征不仅反映了实际空间中破碎的反转对称性，而且还反映了倒数空间中的波谷各向异性。每当两个波谷之间存在波谷种群失衡（VPI）并影响检测到的SHG的极化状态时，就会出现后者。在这项工作中，表明SHG强度的温度诱导变化取决于激发场极化是TMD中VPI的指纹。特别是，在低温恒温器内部进行了基于偏振分辨光栅扫描成像显微镜的逐像素VPI映射，以在TMD薄片每个点都存在VPI的情况下生成SHG对比度。所产生的对比度通过低温下SHG强度极坐标图的旋转来标记，并且归因于VPI诱导的SHG。