Disordered Nonlinear Metalens for Raman Spectral Nanoimaging.

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Far-field optical imaging faces limitations due to the diffraction limit.
• Existing super-resolution techniques often require slow scanning or post-processing with prior image information.
• A perfect far-field superlensing system for real-time color imaging with subwavelength resolution remains elusive.

Purpose of the Study:

• To propose and demonstrate a proof-of-concept for a far-field nonlinear metalens.
• To achieve real-time super-resolution color imaging beyond the diffraction limit.
• To overcome limitations of current super-resolution imaging methods.

Main Methods:

• Fabrication of a nonlinear metalens from a disordered metal-dielectric nanocomposite (titanium nitride and titanium oxynitride).
• Utilizing the double epsilon-near-zero behavior of titanium oxynitride for enhanced light coupling to surface plasmon resonance.
• Employing stimulated Raman scattering (SRS) and enhanced third-order optical nonlinearity for point spread function narrowing.
• Integrating the metalens with a confocal optical microscope for imaging.

Main Results:

• Demonstrated subwavelength resolution of λ/6NA at visible wavelengths using multiwalled carbon nanotubes as a test sample.
• Achieved supercoupling of light to surface plasmon resonance in the visible and near-infrared range.
• Showcased enhanced optical nonlinearity and Anderson localization effects contributing to resolution enhancement.

Conclusions:

• The developed nonlinear metalens offers a promising approach for far-field super-resolution imaging.
• This technology advances the development of robust and versatile real-time color imaging systems.
• The findings pave the way for future applications such as "eye-on-a-chip" technology.