Ultrafast Single-Molecule Fluorescence Measured by Femtosecond Double-Pulse Excitation Photon Antibunching

Area of Science:

• Single-molecule spectroscopy
• Ultrafast physical chemistry
• Nanophotonics

Background:

• Avalanche photon diodes (APDs) limit fluorescence lifetime measurements due to slow response and energy dependence.
• Accurate fluorescence lifetime measurements are vital for understanding energy transfer and optimizing plasmonic nanostructures.

Purpose of the Study:

• Introduce a novel femtosecond double-excitation (FeDEx) photon correlation technique.
• Achieve ultrafast time resolution in single-molecule fluorescence independent of detector limitations.
• Demonstrate FeDEx for precise lifetime measurements in complex nanophotonic systems.

Main Methods:

• Femtosecond double-excitation (FeDEx) photon correlation.
• Boxcar integration measuring photon antibunching versus time delay.
• Utilizing DNA origami for precise positioning of molecules between nanoparticles.

Main Results:

• FeDEx technique achieves time resolution limited only by laser pulse length.
• Demonstrated measurements on donor-acceptor complexes and single molecules in plasmonic antennas.
• Observed ~75-fold radiative rate enhancement and 19 ps lifetimes in nanoparticle-molecule systems without reconvolution.

Conclusions:

• FeDEx offers a powerful, reconvolution-free method for ultrafast single-molecule fluorescence lifetime measurements.
• Enables accurate characterization of nanoscale light-matter interactions.
• Facilitates optimization of plasmonic antennas for enhanced light emission and energy transfer.