Entangled two-photon absorption (e2PA) employs advantages of classical two-photon absorption techniques while operating in a linear excitation regime at low fluxes and potentially having greatly enhanced absorption probabilities. A major challenge in measuring the e2PA cross section, σe2PA, is to discriminate e2PA from one- photon losses. Carefully designed transmittance measurements are required to distinguish the two mechanisms. For example, the e2PA signal should depend on the time delay between photons within an entangled pair (in contrast to one-photon losses). Here we present an experimental system implementing this characterization. We perform transmittance experiments for Zinc-tetraphenylporphyrin (ZnTPP) in toluene solution. We use entangled photons produced via spontaneous parametric downconversion at 810 nm wavelength as an excitation source. We show that the change in transmittance associated with e2PA in the sample is less than 1% in our experiment. From our measurements we conclude ZnTPP's σe2PA ≤1:7 x 10-19 cm2.
Alexander Mikhaylov, Kristen M. Parzuchowski, Michael D. Mazurek, Daniel J. Lum, Thomas Gerrits, Charles H. Camp Jr., Martin J. Stevens, and Ralph Jimenez, "A comprehensive experimental system for measuring molecular two-photon absorption using an ultrafast entangled photon pair excitation source," Proc. SPIE 11295, Advanced Optical Techniques for Quantum Information, Sensing, and Metrology, 112950Q (Presented at SPIE OPTO: February 05, 2020; Published: 28 February 2020); https://doi.org/10.1117/12.2541888.
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