High-harmonic generation from strain-engineered graphene for polarization tailoring

Strain engineering is a versatile method to boost the carrier mobility of two-dimensional materials-based electronics and optoelectronic devices. In addition, strain is ubiquitous during device fabrication via material deposition on a substrate with a different lattice structure. Here, we show that the polarization properties of the harmonics in graphene under uniaxial strain are strongly, yet differently affected in the lower and higher orders. The polarization plane of the lower-order emitted harmonics is rotated-a manifestation of Faraday rotation due to the broken symmetry planes. In contrast, we observe elliptically polarized higher-order harmonics due to the intricate interplay of the interband and intraband electron dynamics. The implications of these findings are twofold: First, we show how the rotation of the polarization plane of the lower-order harmonics can be used as a probe to characterize the strain's nature, strength, and angle. Second, we demonstrate how strain engineering can be used to alter the polarization properties of higher-order harmonics, relevant for applications in ultrafast chiral-sensitive studies. Our research opens a promising avenue for strain-tailored polarization properties of higher-order harmonics in engineered solids.