Fig. 2: Structuring of third-harmonic light via addition of total angular momentum projection.

a Optical images of patterns at TH excited with an elliptically polarized pump laser. Here, α and β denote the ellipticity angle and the inclination angle of the polarization ellipse, respectively, for the pump beam entering the objective lens; γ is the angle between the fast axis of the QWP and the polarization direction of the input laser beam. The deviation of the retardance of the used QWP from perfect limits the maximum ellipticity angle of the pump to 43.9°. b Numerical simulation of patterns generated by a thin isotropic layer with χ⁽³⁾ nonlinearity when illuminated with a tightly focused laser beam. Scale bars, 2 μm