A single-shot approach for measuring two-photon action cross-section of fluorescent markers

We report on a novel method designed for measuring two-photon action cross sections spectra in a single shot without tuning the excitation wavelength. Our technique is based on (i) using a nonlinear photonic crystal fiber to broaden the spectrum of the femtosecond excitation pulses and (ii) exploiting angular dispersion to focus different wavelengths to different lateral positions. As a result, two-photon fluorescence signal at different excitation wavelengths can be obtained simultaneously. As a proof of principle, the relative two-photon action cross sections of rhodamine green and DiI-C₁₈ are measured over 740 - 860 nm range using fluorescein as a reference. Our results are in good agreement with that obtained using conventional tunable mode-locked laser.