
Second Harmonic Generation (SHG) 183
The set of equations (3.120) can easily be written for the spectral field envelopes
defined in Eq. (3.123).
The set of coupled equations (3.120) with (3.123) is convenient for a numerical
treatment. No other assumption or approximation has been made, except that the
spectra of the fundamental and second harmonic do not overlap, to be able to
split a single Maxwell’s second-order propagation equation into three coupled
differential equations. The dispersion of the material is contained in the frequency
dependence of the wave vectors k
2
q
() =
2
n
2
()/c
2
. The second derivative of
the envelope with respect to z can generally ...