  Entangled two-photon absorption can enable a linear scaling of fluorescence
emission with the excitation power. In comparison to classical two-photon
absorption with a quadratic scaling, this can allow fluorescence imaging or
photolithography with high axial resolution at minimal exposure intensities.
However, most experimental studies on two-photon absorption were not able to
show an unambiguous proof of fluorescence emission driven by entangled photon
pairs. On the other hand, existing theoretical models struggle to accurately
predict the entangled-two-photon-absorption behavior of chemically complex
dyes. In this paper, we introduce an approach to simulate entangled two-photon
absorption in common fluorescence dyes considering their chemical properties.
Our theoretical model allows a deeper understanding of experimental results and
thus the occurrence of entangled two-photon absorption. In particular, we found
a remarkable dependency of the absorption probability on the phase-matching
temperature of the nonlinear material. Further, we compared results of our
theoretical approach to experimental data for Nile Red.
