Reference standards for two-photon absorption cross-section and polarization ratio in the 440-630 nm wavelength range

We present absolute two-photon absorption (2PA) cross-section (σ_2PA) and circular vs. linear polarization ratio (Ω) spectra for 12 solvated fluorophores in the wavelength range, λ_2PA = 440-630 nm. Measurements were performed using a single-beam fluorescence-excitation technique with broadly wavelength-tunable femtosecond pulses. Relative 2PA spectral profiles are corrected for excitation photon flux density by determining, at each wavelength, the laser pulse temporal and spatial widths, with additional absolute σ_2PA measurements at select wavelengths calibrated by preexisting longer-wavelength references using corresponding one-photon excited fluorescence. The estimated accuracy of the resulting σ_2PA is 15-20%, suitable for correcting nonlinear-optical spectra in the blue-green range of wavelengths.