A comprehensive experimental system for measuring molecular two-photon absorption using an ultrafast entangled photon pair excitation source

摘要

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, σ_(e2PA), 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. Prom our measurements we conclude ZnTPP's σ_(e2PA) ≤ 1.7 × 10~(-19) cm~2.