Superlenses were previously made from elaborate artificial constructs known as metamaterials, which are difficult to be fabricated and tend to absorb a relatively high percentage of photons that would otherwise be available for imaging.
Now, an Indian-origin scientist with the U.S. Department of Energy ‘s Berkeley Lab and his colleagues have fabricated superlenses from materials that are simpler and easier to fabricate than metamaterials.
The superlenses, fabricated from perovskite oxides, are ideal for capturing light in the mid-infrared range, which opens the door to highly sensitive biomedical detection and imaging, according to Ramamoorthy Ramesh, a materials scientist with Berkeley Lab’s Materials Sciences Division.
It is also possible that the superlensing effect can be selectively turned on/off, which would open the door to highly dense data writing and storage.
“A superlens made out of a metamaterial focuses propagating waves and reconstructs evanescent waves arising from the illuminated objects in the same plane to produce an image with sub-wavelength resolution,” said co-author Susanne Kehr at the University of Saint Andrews in the UK.
“Our perovskite-based superlens doesn””t focus propagating waves, but instead reconstructs evanescent fields only. These fields generate the sub-wavelength images that we study with near-field infrared microscopy,” she added.
The perovskites used to make the superlens — bismuth ferrite and strontium titanate — feature a low rate of photon absorption and can be grown as epitaxial multilayers with a highly crystalline quality that reduces interface roughness so there are few photons lost to scattering.
This combination of low absorption and scattering losses significantly improves the imaging resolution of the superlens.
The combination of near-field infrared microscopy with a tunable free-electron laser provided a first of its kind highly detailed study of the spatial and spectral near-field responses of the superlens.
This study led to the observation of an enhanced coupling between the illuminated objects – rectangles of strontium ruthenate on a strontium titanate substrate – and a near-field scattering probe – a metal-coated atomic-force microscope tip with a typical radius of 50 nanometers.
“At certain distances between the probe and the surface of the object, we observed a maximum number of evanescent fields,” said Ramesh.
“Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy and thermal sensors,” he added.
The finding is detailed in the journal Nature Communications.