Laser field modulation of high harmonic generation in single monolayer boron nitride

In this work, laser-induced high-order harmonic generation in monolayer hexagonal boron nitride (hBN) is investigated using the semiconductor Bloch equation in the form of the density matrix, combined with the tight-binding model, employing an accelerated Bloch-like basis in the Wannier gauge. Using a linear-polarized 3-μm femtosecond pulse, the crystal orientation dependence of high-order harmonic (HH) spectra is investigated. The carrier-envelope (CE) phase dependence of HHG spectra in hBN reveals that the minimum period is 2π rad, compared to π rad in the case of HHG in systems with inversion symmetry. Furthermore, we investigate the ellipticity dependence of HHG in monolayer hBN. The parallel and perpendicular emission of HHG to the major axis of elliptically polarized light is affected differently by the ellipticity. By utilizing the strong ellipticity dependence of high-harmonic generation (HHG) in the plateau region of parallel emission, we propose a polarization gate (PG) scheme composed of left- and right-circularly polarized laser pulses. Time-frequency analysis reveals that HHG under PG irradiation is predominantly confined to within half an optical cycle of the driving field, enabling the generation of extreme ultraviolet (XUV) radiation with a natural attosecond timescale.