Programmable high-harmonic emission in solids through photon pathways

Ultrafast all-optical control of light emission is a central goal of extreme nonlinear optics, with implications for compact short-wavelength sources, petahertz optoelectronics, and label-free superresolution microscopy. High-harmonic generation in solids is a particularly attractive platform for this goal because it is highly sensitive to both the driving field and the material response, yet a generally applicable framework for controlling harmonic emission has remained elusive. Here, we demonstrate programmable control of high-harmonic emission in solids and show that it can be quantitatively described within a photon-pathway framework. We find that harmonic emission can be suppressed or enhanced by tuning two experimentally accessible quantities: the effective nonlinear order and the intrinsic emission phase. Across a wide range of semiconductors and dielectrics, this approach unifies parametric and non-parametric modulation, explains distinct delay-dependent spectral responses, and reproduces strong suppression, enhancement, and higher-order pathway revivals. Semiconductor Bloch equation simulations support the model and provide a complementary time-domain picture in which the control field reshapes the interference of sub-cycle emission events. These results establish high-harmonic generation in solids as a programmable emission process and provide a general route towards ultrafast optical switching, compact coherent short-wavelength sources, and label-free attosecond super-resolution microscopy.