Optical sectioning technique which relies on the simultaneous absorption of multiple photons in a single quantized event. As the likelihood of multiphoton absorption is greatest at the focal plane where photon density is highest, this technique provides optical sectioning without excitation above and below the plane of focus. Multiphoton excitation also enables deeper specimen penetration than linear excitation methods such as confocal microscopy. Consequently, this technique is often used for experiments that require deep penetration into living tissue or intact animal specimens.
Mode-locked pulsed lasers are used for deep tissue imaging and optical sectioning.