Chalcogenide Microsphere‐Assisted Optical Super‐Resolution Imaging

Abstract

Microsphere‐assisted optical imaging has been proved straightforward and cost‐effective for super‐resolution imaging in material science and biomedical research. Optically transparent microspheres with a high refractive index are critical for achieving superior super‐resolution capabilities yet remain to be further exploited. Here, the use of As2S3 (an optically transparent chalcogenide glass) microspheres, with a refractive index as high as 2.31 (at 600 nm) and diameters ranging from 10 to 215 µm, for optical super‐resolution imaging is reported. Under white‐light illumination (peaked at 646 nm), As2S3 microspheres full‐immersed in polymethyl methacrylate or immersion oil generate super‐resolved virtual images of nanostructures (≈90 nm in minimum feature size) with a magnification up to 8×. The lateral resolution of full‐immersed microspheres, which can be as low as ≈172 nm for a 19 µm diameter As2S3 microsphere, is also investigated. Moreover, super‐resolved real imaging of nanostructures with semi‐immersed As2S3 microspheres is demonstrated for the first time. Compared with the full‐immersion approach (e.g., for a 30 µm diameter microsphere, the image plane is ≈30 µm underneath the specimen with a magnification of 4.3×), the semi‐immersion approach provides an obvious improvement in the magnification (6.6×) and a much longer operation distance to the objective (the image plane is ≈140 µm above the specimen).

Microsphere‐Aided Super‐Resolution Scanning Spectral and Photocurrent Microscopy for Optoelectronic Devices

“…With a 10 µm silica microsphere, the signal intensity distribution along the sample's edge is much more distinct, allowing us to calculate the resolution to be 213 nm (see Section S3, Supporting Information). This resolution exceeds the theoretical diffraction‐limit resolution of the ×100 objective with NA = 0.9 (according to Abbe's formula, [ 31 ] $$\ 0.51\frac{\lambda }{{NA}} \approx 301{\rm{\ nm}}$$) under the excitation of a 532 nm laser. To further verify the experimental realization of “super‐resolution” that exceeds the diffraction‐limit resolution of the original confocal microscopy system, Figure S8, Supporting Information, presents the Raman mapping images of this MoS 2 sample acquired with different objective configurations and corresponding resolutions.…”

Wave optics of imaging with contact ball lenses

“…Despite a tremendous interest in MSI methods developed with wavelength-scale microspheres 5 – 21 , the connection of this field of studies to the standard wave theory of aberrated imaging by macroscopic ball lenses has not been previously established. In this work we developed a comprehensive approach to this problem for ball lenses with diameters varying from (quite often used in MSI studies) up to (reaching the limit of millimeter-scale ball lenses).…”

“…On the other hand, a novel type of microscope imaging based on placing microspheres in direct contact with nanoscale objects has emerged in the last decade and has been termed “microsphere-assisted” or “microsphere superlens” imaging (MSI) 5 – 21 . It has been demonstrated experimentally that such microspheres create magnified virtual images with resolution well beyond the classical diffraction limit.…”

Ball Lens‐Assisted Cellphone Imaging with Submicron Resolution

“…An important direction of these studies is represented by so‐called “microsphere‐assisted” or “microspherical superlens imaging (MSI)” where dielectric microspheres with mesoscale diameters ( D ), typically in a 5 < D / λ < 20 range, are placed in contact with the nanoscale objects. [ 23–43 ] The interest in such imaging is determined by its label‐free nature, inherent simplicity, potential biomedical applications, and extremely high resolution ≈ λ /7 exceeding the classical diffraction limit. The MSI theory is an active area of research with several factors being considered including image magnification with a participation of the optical near‐fields.…”