Experimental upper bounds for resonance-enhanced entangled two-photon absorption cross section of indocyanine green.

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.

Entangled Photon Correlations Allow a Continuous-Wave Laser Diode to Measure Single-Photon, Time-Resolved Fluorescence.

Fluorescence lifetime experiments are a standard approach for measuring excited-state dynamics and local environmental effects. Here, we show that entangled photon pairs produced from a continuous-wave (CW) laser diode can replicate pulsed laser experiments without phase modulation. As a proof of principle, picosecond fluorescence lifetimes of indocyanine green are measured in multiple environments.

Single-Photon Scattering Can Account for the Discrepancies among Entangled Two-Photon Measurement Techniques.

Entangled photon pairs are predicted to linearize and increase the efficiency of two-photon absorption, allowing continuous wave laser diodes to drive ultrafast time-resolved spectroscopy and nonlinear processes. Despite a range of theoretical studies and experimental measurements, inconsistencies in the value of the entanglement-enhanced interaction cross section persist. A spectrometer that can temporally and spectrally characterize the entangled photon state before, during, and after any potential two-photon excitation event is constructed.