Description
Chiral photonics enables control over the handedness of light and underpins applications ranging from optical communications and biochemical sensing to emerging quantum technologies. While most existing approaches focus on engineering strong linear optical activity, nonlinear chiral phenomena remain comparatively underexplored. Here, we demonstrate a fundamentally different route in which a photonic structure that is achiral in the linear regime exhibits a pronounced nonlinear chiral response in third-harmonic generation (THG).
We investigate free-standing silicon membrane metasurfaces supporting resonant nonlinear light–matter interactions. Guided by symmetry considerations, we design structures with four-fold rotational symmetry that suppress linear circular dichroism while enabling symmetry-selective nonlinear processes. Experimentally, we observe a strong cross-polarised THG response from the unperturbed metasurface, resulting in a nonlinear circular dichroism as large as -0.83, despite vanishing linear chirality. By introducing controlled in-plane symmetry breaking, additional nonlinear channels open, including copolarized THG, leading to a reversal of the nonlinear circular dichroism sign and a maximum value of +0.41.
These observations are supported by numerical simulations and group-theoretical analysis, which reveal how rotational and mirror symmetries govern nonlinear optical selection rules. The results demonstrate that linear and nonlinear chirality can be independently engineered, providing a new framework for controlling light at the nanoscale.
This work establishes a general platform for nonlinear chiral photonics and opens new opportunities for chiral harmonic generation, nonlinear imaging, optical information encoding, and chiral-selective sensing in symmetry-engineered dielectric metasurfaces.
The presentation will be focused on our recent work: Tonkaev, P. et al. “Nonlinear chiral response from linearly achiral membrane metasurfaces.” Nano Letters, 25(47), 16643–16649, 2025.
| I am the presenting author | Yes |
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