Far-field transient absorption nanoscopy with sub-50 nm optical super-resolution

Nanoscopic imaging or characterizing is the mainstay of the development of advanced materials. Despite great progress in electronic and atomic force microscopies, label-free and far-field characterization of materials with deep sub-wavelength spatial resolution has long been highly desired. Herein, we demonstrate far-field super-resolution transient absorption (TA) imaging of two-dimensional material with a spatial resolution of sub-50 nm. By introducing a donut-shaped blue saturation laser, we effectively suppress the TA transition driven by near-infrared (NIR) pump–probe photons, and push the NIR-TA microscopy to sub-diffraction-limited resolution. Specifically, we demonstrate that our method can image the individual nano-grains in graphene with lateral resolution down to 36 nm. Further, we perform super-resolution TA imaging of nano-wrinkles in monolayer graphene, and the measured results are very consistent with the characterization by an atomic force microscope. This direct far-field optical nanoscopy holds great promise to achieve sub-20 nm spatial resolution and a few tens of femtoseconds temporal resolution upon further improvement and represents a paradigm shift in a broad range of hard and soft nanomaterial characterization.