Spectral tomographic imaging with aplanatic metalens

Tomography is an informative imaging modality that is usually implemented by mechanical scanning, owing to the limited depth-of-field (DOF) in conventional systems. However, recent imaging systems are working towards more compact and stable architectures; therefore, developing nonmotion tomography is highly desirable. Here, we propose a metalens-based spectral imaging system with an aplanatic GaN metalens (NA = 0.78), in which large chromatic dispersion is used to access spectral focus tuning and optical zooming in the visible spectrum. After the function of wavelength-switched tomography was confirmed on cascaded samples, this aplanatic metalens is utilized to image microscopic frog egg cells and shows excellent tomographic images with distinct DOF features of the cell membrane and nucleus. Our approach makes good use of the large diffractive dispersion of the metalens and develops a new imaging technique that advances recent informative optical devices.Bioimaging: metalenses make 3D analysis effortlessAn ultrathin “metalens” that uses semiconductor nanostructures to focus light can help microscopes resolve detailed images of live cells without complex mechanical components. In conventional tomographic imaging, a scanning instrument passes over the sample and takes multiple cross-sectional images, which are then reconstructed into a 3D picture. Tao Li from Nanjing University in China and colleagues have now simplified this technique by fabricating lenses patterned with concentric rings of gallium nitride nanopillars. The lens made of nanopillars has wavelength-dependent properties that enable focusing on different regions of a target simply by sweeping through the visible light spectrum. Experiments with frog egg cells demonstrated this approach could zoom in and obtain detailed, high quality images of the inner membrane and nucleus without harming the sample or moving the metalens.