Efficient second harmonic generation by a femtosecond pulse far from phase matching

Highly efficient second harmonic generation by a femtosecond pulse under the condition of group matching in the absence of phase matching was obtained. Second-order dispersion and cubic nonlinearity of the propagation medium were considered. The cubic nonlinearity is necessarily required for the generation to be efficient. The results obtained open up a fundamental opportunity for the efficient cascade generation of optical harmonics to be realized.