Sculpting ultrafast mid-infrared light for solid-state high harmonic generation

Abstract: The ability to sculpt light in space, time, and polarization has revolutionized studies of light-matter interaction and enabled breakthroughs in optical communication, imaging, and ultrafast science. Among the many degrees of freedom of light, orbital angular momentum (OAM) further expands these capabilities by unlocking new regimes of control in information encoding, particle manipulation, and symmetry-driven selection rules. However, exploiting OAM to drive nonlinear, non-perturbative effects in solids remains challenging, especially in the mid-infrared (MIR) spectral regime, a key region for accessing these effects in ambient air, where spatial light modulators do not operate. Here, we circumvent this limitation by generating femtosecond, few-cycle MIR Bessel-Gauss vortex (BGV) and Perfect optical vortices (POVs), using a robust, static spatial-shaping strategy. Using those beams to drive the high-harmonic generation (HHG) process in solids, we show that the resulting harmonic beams faithfully inherit the structural properties of the drivers: the constant-intensity ring of the POV is preserved across harmonic orders, while the harmonic BGVs retain their intrinsic TC-dependent profiles. Furthermore, by verifying the OAM up-scaling law, we confirm OAM conservation during HHG in solids. These results establish strong-field HHG in solids as a robust platform for synthesizing ultrafast structured harmonic light with controllable, high-value OAM.