Measurement of absolute two-photon excitation spectrum of various fluorophores with Fourier transform nonlinear spectroscopy

In this paper, we present the two-photon excitation (TPE) spectra of various fluorescent proteins measured using Fourier-transform nonlinear spectroscopy with a spectral resolution of 60 cm^-1. By the use of an ultrabroadband pulse with a spectrum ranging from 700 to 1100 nm, the TPE spectra ranging from 350 to 550 nm are measured. We measured the absolute TPE spectrum of various fluorescent proteins whose spectrum ranged from 355 to 520 nm using Fourier transform nonlinear spectroscopy. This technique can be applied not only to the two-photon excitation spectrum but also to the absorption spectrum measured together with the emission spectrum.