Generation of high-order harmonics with hybrid spin and transverse orbital angular momentum from a crystalline solid

The interaction between solid materials and an optical vortex has garnered significant attention in recent years. Here, we study theoretically the high-order harmonic generation (HHG) of crystalline solids under the spatiotemporal optical-vortex light. We develop a quantum-orbit model to describe the intricate electron motion driven by a strong optical vortex, demonstrating the conservation law of spin and transverse orbital angular momenta in the HHG process. Harnessing the bicircular spatiotemporal vortex light field, we generate high-order harmonics with the hybrid spin and transverse orbital angular momentum. The proportions of different orbital angular-momentum components of harmonics in solids can also be tuned by adjusting the intensity ratio of the two light beams.