Two-Photon Endomicroscopic Imaging with Dielectric Metalens

Two-photon endomicroscopy has become a robust, label-free, high-resolution technique for optical biopsy. Achieving this resolution level in compact probes critically relies on the design of micro-objectives. Conventional micro-objectives, including gradient-index lenses and microlens assemblies, are limited by their bulky packaging and low numerical aperture, ultimately constraining their performance. As flat dielectric optical elements, metalenses provide a promising pathway toward miniaturized endomicroscopic probes while maintaining high-resolution imaging capability. In this work, a high-aspect-ratio titanium dioxide dielectric metalens was designed and fabricated to operate at 780 nm. A metalens-based two-photon endomicroscopy platform was developed, featuring a compact probe that enabled label-free imaging of two-photon fluorescence and second-harmonic generation in unstained skin sections. This flat dielectric metalens approach offers a promising pathway for developing advanced multimodal endoscopic and endomicroscopic imaging platforms.