Nonlinear optical microscopy: Endogenous signals and exogenous probes

Abstract

Nonlinear optical microscopy (NLOM) relies on nonlinear light-matter interactions to provide images from larger depths within biological structures compared to conventional confocal fluorescence microscopy. These nonlinear light-matter interactions include multiphoton excitation fluorescence (MPEF), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and stimulated Raman scattering (SRS). This review discusses the theories of and instrumentation for various NLOM techniques, with a particular focus on endogenous signals and exogenous probes. These signals and probes expand the breadth of information that optical imaging can provide. We also discuss the application of NLOM in biomedical research, including tissue engineering, drug delivery and clinical diagnostics. Current technological limitations are also discussed.