Decoding Polarization in a Single Achiral Gold Nanostructure from Emitted Far-Field Radiation

Area of Science:

• Plasmonics and Nanophotonics
• Optical Chirality and Polarization
• Metamaterials and Nanostructures

Background:

• Optical chirality in plasmonic nanostructures is usually attributed to their geometric chirality.
• The potential for achiral structures to exhibit chiroptical far-field responses is often overlooked.
• Understanding near-field interactions is crucial for predicting far-field optical properties.

Purpose of the Study:

• To analyze the polarization state of light emitted from single planar achiral plasmonic nanostructures.
• To investigate the role of coupled plasmon modes and their relative phase in determining optical chirality.
• To demonstrate that near-field interactions dictate the far-field chiroptical response.

Main Methods:

• Numerical simulations of surface charge distribution to understand near-field behavior.
• Polarized single-particle dark-field scattering spectroscopy to analyze chiroptical responses.
• Development of an analytical model to extract polarization information from scattering spectra under unpolarized illumination.

Main Results:

• The polarization state of emitted light is determined by the superposition of fields from multiple plasmon modes, influenced by their relative phase.
• Simulations confirm that near-field charge distributions predict the far-field polarization state.
• An analytical model successfully retrieves polarization information from scattering spectra of achiral and chiral structures.

Conclusions:

• Achiral plasmonic nanostructures can exhibit significant chiroptical responses in the far-field.
• The interplay of plasmon modes in the near-field governs the emitted light's polarization.
• The developed analytical model provides a general framework for analyzing chiroptical responses in both chiral and achiral plasmonic systems.