Asymmetric optical second-harmonic generation from chiral G-shaped gold nanostructures

Area of Science:

• Optics and Photonics
• Materials Science
• Electromagnetism

Background:

• Chiral materials exhibit unique optical properties due to their non-superimposable mirror images.
• Second-harmonic generation (SHG) is a nonlinear optical process where two photons interact to create a single photon of double the frequency.
• Distinguishing chirality optically often requires complex experimental setups or specific light polarizations.

Purpose of the Study:

• To introduce and characterize a novel electromagnetic phenomenon: asymmetric second-harmonic generation (ASHG).
• To demonstrate a method for distinguishing the handedness of planar chiral structures using linearly polarized light.
• To elucidate the underlying physical mechanisms, including surface plasmon resonance and multipole interference.

Main Methods:

• Fabrication of planar chiral gold nanostructures.
• Experimental investigation of second-harmonic generation using linearly polarized light.
• Analysis of the angular dependence of SHG intensity upon sample rotation.

Main Results:

• Observed asymmetric SHG from planar chiral nanostructures, dependent on sample orientation.
• Demonstrated the ability to differentiate between left- and right-handed chiral structures.
• Identified surface plasmon resonance and the interference of anisotropic electric/magnetic multipoles as key contributors.

Conclusions:

• ASHG provides a sensitive and straightforward method for chiral material characterization.
• The phenomenon relies on the interplay between plasmonic resonances and multipolar responses in chiral nanostructures.
• This work opens new avenues for optical sensing and chiral photonics.