  A new scheme for non-destructive characterization of quasi-phase-matching
grating structures and temperature gradients via inverse Fourier theory using
second-harmonic-generation experiments is proposed. We show how it is possible
to retrieve the relevant information via measuring only the power in the
generated second harmonic field, thus avoiding more complicated phase
measurements. The potential of the scheme is emphasized through theoretical and
numerical investigations in the case of periodically poled lithium niobate bulk
crystals.
