Colored conical emission in BBO crystal induced by intense femtosecond pulses

We present the experimental and theoretical study of colored conical emission (CCE) during intense femtosecond pulses propagating in a β-barium borate (BBO) crystal. CCE revealed special nonlinear dynamics of the strong coupling between the fundamental and second harmonic pulses due to the spatiotemporal modulation instability (MI). The underlying physics of CCE involve three three-photon processes, according to which the beam angular spectra was calculated on the phase-matching conditions and accords with the experimental observation.