Ultrafast 1.8 µm fiber laser system for in vivo three- and four-photon fluorescence microscopy

Abstract

We have developed a fiber laser system that produces 142 fs pulses at 1.8 µm and demonstrated in vivo three/four-photon fluorescence microscopy. We observe cortical neurons at a depth of 0.8 mm from the brain surface by three-photon excitation and astrocytes at a depth of 0.2 mm by four-photon excitation.