Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. Advanced functionalities are enabled by modulation of the harmonic generation efficiency, which can be achieved with electrical or all-optical triggers. Electrical control of the harmonic generation efficiency offers large modulation depth at the cost of low switching speed, by contrast to all-optical nonlinear devices, which provide high speed and low modulation depth. Here we demonstrate all-optical modulation of second-harmonic generation in MoS₂ with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration. This result arises from a combination of D_3h crystal symmetry and the deep subwavelength thickness of the sample, it can therefore be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms.

二次谐波的产生在几个科学和技术领域中至关重要，包括频率转换、频率梳的自参考、非线性光谱和脉冲表征。通过调制谐波产生效率可以实现高级功能，这可以通过电或全光触发器来实现。与提供高速和低调制深度的全光非线性器件相比，谐波产生效率的电气控制以低开关速度为代价提供大调制深度。_{在这里，我们展示了在 MoS 2}中产生二次谐波的全光调制，调制深度接近 100%，速度仅受基本脉冲持续时间的限制。这个结果来自于一个组合D _{3 h}晶体对称性和样品的深亚波长厚度，因此可以扩展到整个过渡金属二硫属化物家族，为高速集成变频器、宽带自相关器等高级非线性光学器件的设计提供极大的灵活性用于超短脉冲表征和可调谐纳米级全息图。