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9.1 Introduction
Second-harmonic generation (SHG) microscopy has mostly been developed alongside of incoherent non-
linear microscopy (multiphoton excitation uorescence), and has largely contributed to the emergence of
coherent nonlinear microscopy (e.g., higher harmonic generation or coherent anti-Stokes Raman scatter-
ing). One particularity of coherent nonlinear microscopy is that the detected signals originate from instan-
taneous interaction of incident electromagnetic radiation with the specimen, making ultrafast imaging
possible. is is because these nonlinear interactions are of a scattering nature and, as such, do not involve
absorptio ...