
Second Harmonic Generation Imaging76
absence of resonance eects. e linear index mismatches are also neglected, although they may have a
signicant inuence on beam propagation.
Description of Focused Fields
e angular spectrum representation [13] is used to calculate the eld distribution obtained by propa-
gating an initial eld distribution (amplitude and phase) at the back aperture of a microscope objective
under a given set of focusing conditions (NA, index of refraction). In this representation, the eld is
described as a sum of plane waves with variable amplitudes and propagation directions, so that the
excitation eld near focus is c ...