Fig. 4
From: Generating high-order optical and spin harmonics from ferromagnetic monolayers
Crystal-momentum-resolved high-harmonic generation and spin harmonic generation. a Crystal-momentum-resolved harmonic signal from the Z to Γ point on a logarithmic scale. The laser is linearly polarized along the y axis, and the signal is from the x axis. Except the one at Z, all the curves are shifted vertically. Top inset: Zoomed-in view of the 5th harmonic at a different k point. b Band dispersion along the Γ–Z direction for the Fe(110) monolayer. The 5th harmonic corresponds to several crucial transitions from conduction states between 8 and 9.36 eV above the Fermi level (see the horizontal dashed line) to a state at −1.87 eV below the Fermi level. The arrow denotes this radiation. c Spin harmonic generation spectrum. Its zeroth order denotes the demagnetization, while higher orders represent the oscillation. The harmonic only appears at even orders, due to SU(2). The laser field has to interact with the system an even number of times to affect spins. These signals are normally weaker than the emission from the electric dipole
