Some aspects of wave propagation in quadratic weakly nonlinear media

A theory is developed for the propagation of electromagnetic waves in quadratic weakly nonlinear media. Waves with a narrow-band spectrum are studied as well as periodic waves based upon a Volterra series formalism. Conditions of steady propagation are scrutinized. It is shown that the proper conditions are rather complicated in the present case in comparison with the single harmonic case in a cubic medium.