Abstract
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.
Highlights
Far-field optical super-resolution microscopy has been routinely adopted for biological imaging with extraordinary resolution beyond the diffraction limit [1,2]
The proposed super-resolution saturated TA nanoscopy (STAN) system is modified on the conventional saturated transient absorption (TA) microscope
The diagram depicting the optical transitions of STAN and other super-resolution NIR systems is shown in Fig. S1, Supplement 1
Summary
Far-field optical super-resolution microscopy has been routinely adopted for biological imaging with extraordinary resolution beyond the diffraction limit [1,2]. We found that the saturation laser with higher photon energy relative to that of the pump and probe lasers is the most key factor responsible for improved spatial resolution, other than the saturation intensity. Both the STA and TA signals are proportional to the probe and pump lasers (Fig. S6, Supplement 1).
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