About two-photon microscopy

Ben Hom Chen

I know two-photon microscopy use the longer wavelength laser,but with more photon density.To my knowledge,the laser with more photon density means it is very strong(High Power?).But articles always say that two-photon microscopy only damage on focus point and is suitable to investigate biologic sample,while one-photon confocal microscopy will damage the sample everywhere that light can reach.

But I really wonder,if two-photon microscopy have a stronger laser(more photon number in short time),why wouldn't it damage the sample everywhere?

Is the laser harmful only after the sample is excited?

Thx>.<