Setting bounds on two-photon absorption cross-sections in common fluorophores with entangled photon pair excitation

TL;DR

This study establishes experimental upper bounds on two-photon absorption cross-sections in common fluorophores using entangled photon pairs, revealing values significantly lower than previous reports and clarifying existing ambiguities.

Contribution

The paper provides the first experimental upper bounds on E2PA cross-sections for six fluorophores, resolving discrepancies in the literature with more accurate, lower estimates.

Findings

Upper bounds are up to four orders of magnitude lower than previous estimates.

For Rhodamine 6G and 9R-S, bounds are four and five orders lower than prior reports.

Results clarify the magnitude of E2PA cross-sections, impacting future applications.

Abstract

Excitation with entangled photon pairs may lead to an increase in the efficiency of two-photon absorption at low photon flux. The corresponding process, entangled two-photon absorption (E2PA), has been investigated in numerous theoretical and experimental studies. However, significant ambiguity and inconsistency remain in the literature about the absolute values of E2PA cross-sections. Here, we use a fluorescence-based registration scheme to experimentally determine upper bounds on the cross-sections for six fluorophores. These bounds are up to four orders of magnitude lower than the smallest published cross-section. For two samples that have been studied by others, Rhodamine 6G and 9R-S, we measure upper bounds four and five orders of magnitude lower than the previously reported cross-sections.