Characterization of conical emission of light filaments in media with anomalous dispersion

Conical emission featuring a diminishing emission angle with increasing wavelength detuning is observed in ultrashort light filaments in fused silica at a carrier wavelength with anomalous dispersion. In the measured angularly resolved spectrum of the filament, this conical emission appears as an elliptical, or O-like, structure that fits quantitatively to the elliptical spectrum of gain in the Kerr-driven spatiotemporal instability of nonlinear plane wave