Light with spatiotemporal orbital angular momentum (ST-OAM) is a recently discovered type of structured and localized electromagnetic field. This field carries characteristic space–time spiral phase structure and transverse intrinsic OAM. Here, we present the generation and characterization of the second harmonic of ST-OAM pulses. We uncover the conservation of transverse OAM in a second-harmonic generation process, where the space–time topological charge of the fundamental field is doubled along with the optical frequency. Our experiment thus suggests a general ST-OAM nonlinear scaling rule, analogous to that in conventional OAM of light. Furthermore, we observe that the topology of a second-harmonic ST-OAM pulse can be modified by complex spatiotemporal astigmatism, giving rise to multiple phase singularities separated in space and time. Our study opens a new route for nonlinear conversion and scaling of light carrying ST-OAM, with the potential for driving other secondary ST-OAM sources of electromagnetic fields and beyond.

具有时空轨道角动量 (ST-OAM) 的光是最近发现的一种结构化和局部化电磁场。该场具有特征性的时空螺旋相结构和横向固有OAM。在这里，我们介绍了 ST-OAM 脉冲的二次谐波的产生和表征。我们揭示了二次谐波产生过程中横向 OAM 的守恒，其中基本场的时空拓扑电荷与光频率一起加倍。因此，我们的实验提出了一个通用的 ST-OAM 非线性缩放规则，类似于传统的光 OAM。此外，我们观察到二次谐波 ST-OAM 脉冲的拓扑结构可以通过复杂的时空像散来修改，从而产生在空间和时间上分离的多个相位奇点。