Measurements of two-, three-, and four-photon excitation action cross sections

We report quantitative measurements of two-, three-, and four-photon excitation action cross sections of several commonly used fluorophores and fluorescent proteins at three different excitation wavelengths of 800 nm, 1300 nm, and 1680 nm.

1. Introduction

Recently, Horton et al. demonstrated deep tissue three-photon fluorescence microscopy of mouse brain in vivo [1]. The combination of the long excitation wavelength and three-photon excitation enabled unprecedented tissue penetration depth, and subcortical structures were visualized directly in an intact mouse brain in vivo. In the past two decades, the two-photon excitation cross sections of many common fluorophores [2]–[5] and fluorescent proteins [6]–[8] were measured. These data provide a reliable database for two-photon fluorescence microscopy.