Abstract
It is shown theoretically that filamentation can lead to sizable second harmonic generation. The 2ω0 radiation is emitted into a forward‐directed cone, its angle determined by the wavelength of the fundamental radiation in the plasma waveguide. Experimental observations confirm the theoretical predictions. Aside from the forward‐directed emission cone, non‐negligible 2ω0 power is detected over a broad angular range in the backward direction showing a broadened red‐shifted spectrum.