1. Experimental upper bounds for resonance-enhanced entangled two-photon absorption cross section of indocyanine green.
- Author
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He, Manni, Hickam, Bryce P., Harper, Nathan, and Cushing, Scott K.
- Subjects
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ABSORPTION cross sections , *INDOCYANINE green , *RESONANT states , *ORGANIC dyes , *PHOTONS - Abstract
Resonant intermediate states have been proposed to increase the efficiency of entangled two-photon absorption (ETPA). Although resonance-enhanced ETPA (r-ETPA) has been demonstrated in atomic systems using bright squeezed vacuum, it has not been studied in organic molecules. We investigate for the first time r-ETPA in an organic molecular dye, indocyanine green (ICG), when excited by broadband entangled photons in near-IR. Similar to many reported virtual state mediated ETPA (v-ETPA) measurements, no r-ETPA signals are measured, with an experimental upper bound for the cross section placed at 6(±2) × 10−23 cm2. In addition, the classical resonance-enhanced two-photon absorption (r-TPA) cross section of ICG at 800 nm is measured for the first time to be 20(±13) GM, where 1 GM equals 10−50 cm4 s, suggesting that having a resonant intermediate state does not significantly enhance two-photon processes in ICG. The spectrotemporally resolved emission signatures of ICG excited by entangled photons are also presented to support this conclusion. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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