Fig. 2
Ellipticity dependence of the harmonic yield for different harmonics of bulk MgO. a–d Computed ellipticity dependence of the harmonics 21 (black lines) and 23 (red lines) generated from bulk MgO (a, b) vs. the experimentally observed ellipticity dependence of harmonic 19 (c, d) taken from ref. 36. As in Fig. 1, θ = 0° corresponds to the \(\overline {\Gamma X}\) direction. Vertical lines in b, d showing the case of the Mg–O direction (θ = 45°) indicate the positions of \(\epsilon\) = ±0.5 and \(\epsilon\) = ±0.65. e–h Ellipticity dependence of various harmonics, for the major axis of the polarization ellipse at θ = 0° (e, f) and θ = 45° (g, h). The harmonics are divided into a group of mostly atomic-like (e, g) and non-atomic-like harmonics (f, h), the latter exhibiting a pronounced increase of the harmonic yield at non-zero values of ellipticity
