Multiphoton microscopy, a concept first introduced by Maria Goeppert-Mayer in 1931,  uses pulsed-high power far red and infrared wavelengths to excite femtoliter sized volumes in live and fixed samples. Multiphoton excitation provides high 3D optical sectioning and very low out of focus photodamage. Moreover, the longer excitation wavelengths allow for deeper tissue penetration (up to ~ 1.5mm) compared to confocal microscopy.