Nonlinear optical microscopy for the invisible

Nonlinear optical microscopy (NOM) has become increasingly popular in biomedical research in recent years with the developments of laser sources, contrast mechanisms, novel probes and etc. One of the advantages of NOM over the linear counterpart is the ability to image deep into scattering tissues or even on the whole animals. This is due to the adoption of near-infrared excitation that is of less scattering than visible excitation, and the intrinsic optical sectioning capability minimizing the excitation background beyond focal volume. Such an advantage is particularly prominent in two-photon fluorescence microscopy compared to one-photon fluorescence microscopy. In addition, NOM may provide extra molecular information (e.g. second harmonic generation and third harmonic generation) or stronger signal (e.g. stimulated Raman scattering and coherent anti-Stokes Raman scattering compared to spontaneous Raman scattering), because of the nonlinear interaction between strong optical fields and molecules. However, the merits of NOM are not yet fully exploited to tackle important questions in biomedical research. This thesis contributes to the developments of NOM in two aspects that corres