Multiphoton microscopy requires a pulsed infrared light source for excitation of the fluorophores. Titanium:Sapphire (Ti:Sa) lasers are frequently employed as workhorse in many multiphoton setups. They are appreciated for their tunability and output power, but they are also complex systems that require active cooling. A convenient alternative are Erbium-fiber lasers operating at 780 nm. Their benefits are compactness, stability, ease-of-use and a competitive price. Fiber-lasers are ready to replace Ti:Sa lasers in applications that do not require tunability and high output powers, which is true for many multiphoton applications for two reasons:

1. The 2-photon absorption spectra are normally much broader than one would expect from the corresponding 1-photon spectra. Additionally, the peak of 2-photon absorption is frequently blue-shifted thus most dyes can be efficiently 2-photon excited with a laser operating at 780 nm.
2. 2-photon excitation is frequently used for live-cell imaging thanks to a reduced photodamage compared to 1-photon excitation. The nonlinear process confines the photodamage to the focal region. But still multiphoton microscopy is limited by photodamage and phototoxicity at higher power levels. Therefore the excessive power levels of Ti:Sa lasers are not necessarily an advantage. At the lower output powers of currently available fiber lasers still, one has to choose the right imaging-parameters in order prevent photodamage. So for many applications the power levels that fiber lasers can provide are still more than enough.