Three-dimensional orientation measurement of a single fluorescent nanoemitter by polarization analysis

TL;DR

This paper presents a comprehensive theoretical and experimental method for determining the three-dimensional orientation of a single fluorescent nano-emitter using polarization analysis of emitted light, applicable in various microscopy configurations.

Contribution

It develops a detailed model for orientation measurement considering experimental parameters and demonstrates its application on nanocrystals near a gold film.

Findings

Nano-emitter orientation can be determined by polarization analysis.

Nanocrystals can be approximated by two orthogonal degenerated dipoles.

The method works near metallic surfaces where defocused microscopy fails.

Abstract

We demonstrate theoretically and experimentally that the three-dimensional orientation of a single fluorescent nano-emitter can be determined by polarization analysis of the emitted light (while excitation polarization analysis provides only the in-plane orientation). The determination of the emitter orientation by polarimetry requires a theoretical description including the objective numerical aperture, the 1D or 2D nature of the emitting dipole and the environment close to the dipole. We develop a model covering most experimentally relevant microscopy configurations and provide analytical relations useful for orientation measurements. We perform polarimetric measurements on high-quality core-shell CdSe/CdS nanocrystals and demonstrate that they can be approximated by two orthogonal degenerated dipoles. Finally, we show that the orientation of a dipole can be inferred by polarimetric measurement even for a dipole in the vicinity of a gold film, while in this case the well-established defocused microscopy is not appropriate.