(a) Total harmonic yield emitted at the exit of the hollow waveguide and (b) harmonic yield integrated within 1 mrad using an aperture in the far field for two-color (1.6 + 0.533 μm) waveform (WF) and single-color (SC) laser. The corresponding harmonic divergence in the far field for WF (c) and for SC (d). Length and radius of the waveguide are 5 mm and 125 μm, respectively, and gas pressure is 50 Torr. Adapted from Ref. [129].