ABSTRACT Nonlinear circular dichroism (CD) is of great significance for the research of nonlinear photonics technology. It is typically generated in materials with chiral structures. Van der Waals (vdW) crystals, known for strong optical nonlinearity and single exciton−like effects, have emerged as promising candidates for nonlinear photonics. However, due to the achiral nature, nonlinear CD in vdW crystals has rarely been explored. Here, by transferring the vdW crystal NbOCl 2 onto an anisotropic lithium niobate substrate, we retain the high nonlinear conversion efficiency of NbOCl 2 while substantially enhancing its nonlinear CD. The second harmonic generation CD (SHG‐CD) and third harmonic generation CD (THG−CD) are increased from 0.18 and 0.31 on a silica substrate to 0.58 and 0.89, respectively. Through analysis of the experimental results, we conclude that the observed nonlinear CD is modulated by the anisotropic strain in plane induced by temperature variation. By tuning the anisotropic strain in lithium niobate via temperature changes, dynamic modulation of the nonlinear CD can be achieved. This work provides a novel strategy for manipulating nonlinear CD, with potential applications in chiral sensing, molecular imaging, and the study of ultrafast dynamic processes.
Chen et al. (2026) studied this question.