Second harmonic generation of femtosecond pulses at the boundary of a nonlinear dielectric

Using full vector Maxwell simulations we elucidate a fundamental source of temporal splitting of the second harmonic field generated by a femtosecond fundamental pulse under phase-mismatched conditions. One component of the generated field propagates at the second harmonic group velocity while the other is driven by the fundamental field and propagates at the fundamental group velocity. We analyze the conditions under which the temporal splitting should be observable.