  This paper presents an analytical formulation for correcting the diffraction
associated to the second harmonic of an acoustic wave, more compact than that
usually used. This new formulation, resulting from an approximation of the
correction applied to fundamental, makes it possible to obtain simple solutions
for the second harmonic of the average acoustic pressure, but sufficiently
precise for measuring the parameter of nonlinearity B/A in a finite amplitude
method. Comparison with other expressions requiring numerical integration, show
the solutions are precise in the nearfield.
