Multiphoton Excitation and Microscopy

Abstract

The phenomenon of multiphoton excitation can be depicted in a Jablonski diagram (Figure 18.1). For one-photon ab- sorption a single photon elevates the fluorophore to the excited state. Depending upon the absorption spectrum and the excitation wavelength the fluorophore may be excited to higher vibration levels of the S1 state or even to the S2 state. Irrespective of the excitation wavelength the fluorophore has reached the excited state by absorption of a single pho- ton. Almost all fluorophores emit from the lowest energy level of the relaxed S1 state.