
Second Harmonic Generation Imaging18
components also inverts. However, the SHG response scales with the square of the fundamental eld,
which does not invert. Consequently, the Guoy phase shi results in a net 180° phase walk between the
doubled light and the square of the fundamental beam. is sign inversion arises smoothly across the focal
volume manifest as a phase shi described by the
z z−
tan ( / )
0
term derived from Equation 1.15. e Guoy
phase term is summed in the exponent, such that it can be treated additively to other phase-shi contribu-
tions, including those arising from dispersion. e Guoy coherence length is given by the follo ...