Efficient Forward Second-Harmonic Generation from Planar Archimedean Nanospirals

TL;DR

This paper demonstrates efficient forward second-harmonic generation from planar Archimedean nanospirals, leveraging their unique asymmetry to produce polarization-selective harmonic signals suitable for metasurface applications.

Contribution

It introduces a novel nanospiral geometry that enables efficient SHG without relying on non-centrosymmetric materials or asymmetric particle arrangements.

Findings

Achieved SHG efficiencies up to 1.3×10^-8 for right-handed circular polarization

Demonstrated polarization-selective conversion between states

Nanospirals remain stable under continuous laser illumination

Abstract

The enhanced electric field at plasmonic resonances in nanoscale antennas can lead to efficient harmonic generation, especially when the plasmonic geometry is asymmetric on either inter-particle or intra-particle levels. The planar Archimedean nanospiral offers a unique geometrical asymmetry for second-harmonic generation (SHG) because the SHG results neither from arranging centrosymmetric nanoparticles in asymmetric groupings, nor from non-centrosymmetric nanoparticles that retain a local axis of symmetry. Here we report forward SHG from planar arrays of Archimedean nanospirals using 15 fs pulse from a Ti:sapphire oscillator tuned to 800 nm wavelength. The measured harmonic-generation efficiencies are 2.6*10-9, 8*10-9 and 1.3*10-8 for left-handed circular, linear, and right-handed circular polarizations, respectively. The uncoated nanospirals are stable under average power loading of as much as 300 uW per nanoparticle. The nanospirals also exhibit a selective conversion between polarization states. These experiments show that the intrinsic asymmetry of the nanospirals results in a highly efficient, two-dimensional harmonic generator that can be incorporated into metasurface optics.