ABSTRACT
Second-harmonic generation (SHG) microscopy has mostly been developed alongside of incoherent nonlinear 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 scattering). One particularity of coherent nonlinear microscopy is that the detected signals originate from instantaneous 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 absorption of light by the specimen. As a consequence, the light source for nonlinear microscopy does not need to be limited to a narrow absorption band, as it is the case in uorescence, and can be, oppositely, selected to match a spectral window of transmission for the specimen, thus avoiding photo-damage.
