ABSTRACT
This chapter introduces basic mechanism of two-photon absorption (2PA) and its unique feature of spatial resolution with near-infrared (NIR) excitation. Principles of designing materials to exhibit large two-photon absorptivities are explained. Difference in excitation selection rule between one-photon and two-photon excitation (2PE) for these materials is discussed. Potential applications for 2PA, such as three-dimensional (3D) data storage, fluorescent imaging, 3D microfabrication, photodynamic therapy (PDT) and optical power limiting are briefly described. Requirements of material optimization for the particular applications are also discussed. The chapter concludes with a brief introduction of future challenges.
