Ultra-deep two-photon fluorescence excitation in turbid media

An important application of two-photon excited fluorescence (TPEF) microsco py is to provide high-resolution images from deep within scattering media. We investigate strategies to further improve TPEF penetration depth by cons idering the effects of scattering on fluorescence generation and collection separately. In particular, we demonstrate that the redistribution of laser power into higher energy pulses by means of a regenerative amplifier impro ves the TPEF depth penetration by two to three excitation scattering mean f ree paths. (C) 2001 Published by Elsevier Science B.V.