Enhancing entangled two-photon absorption of Nile Red via temperature-controlled SPDC

Entangled two-photon absorption can enable linear scaling of fluorescence emission with the excitation power. In comparison with classical two-photon absorption with quadratic scaling, this can allow fluorescence imaging or photolithography with a 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. Meanwhile, 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. Furthermore, we compared the results of our theoretical approach to experimental data for Nile Red.