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Entangled two-photon absorption (ETPA) has recently become a topic of livelydebate, mainly due to the apparent inconsistencies in theexperimentally-reported ETPA cross sections of organic molecules. In this work,we provide a thorough experimental study of ETPA in the organic moleculesRhodamine B (RhB) and Zinc Tetraphenylporphirin (ZnTPP). The goal of thiscontribution is twofold: on one hand, it seeks to reproduce the results ofprevious experimental reports and, on the other, it aims to determine theeffects of different temporal correlations -- introduced as a controllabletime-delay between the photons to be absorbed -- on the strength of the ETPAsignal. In our experiment, the samples are excited by entangled pairs producedby type-I SPDC, with a spectral distribution centered at 810 nm. Surprisingly,and contrary to what was expected, the time delay did not produce in ourexperiments any systematic change in the cross-sections when monitoring theETPA signal using a transmission measurement scheme. As a plausible cause ofthis unexpected result, we argue that the photon-pair flux, typically-used inthese experiments, is not sufficient to promote the two-photon absorptionprocess in these molecules. This suggests that the actual absorptioncross-section values are lower than those previously reported, and therefore donot lead to a measurable ETPA effect for the transmission method.

Experimental study on the effects of photon-pair temporal correlations in entangled two-photon absorption