Optical microscopy using a glass microsphere for metrology of sub-wavelength nanostructures

• Super-resolution imaging of nanostructures by using a glass microsphere.
• High-refractive index microsphere is put on a nanostructure and immersed in oil.
• Microsphere transforms sample’s near-field evanescent wave into propagating wave.
• A magnified image is recorded by an oil-immersion microscope objective in far-field.
• A resolution between λ/4 and λ/7, λ as illumination wavelength, is achieved.

A technique that allows direct optical imaging of nanostructures and determines quantitatively geometric nanofeatures beyond the classical diffraction limit by using high-refractive index glass microspheres is introduced. The glass microsphere is put on a nanostructure that is immersed in oil and collects the sample’s near-field evanescent wave and transforms it into a propagating one, thereby generating a magnified image in the far-field which is recorded by a conventional oil-immersion microscope objective. Experimental results on nanostructures demonstrates a resolution of ∼λ/4–λ/7, where λ is the illumination wavelength, by using a 60 μm glass microsphere and a normal wideband halogen lamp as illumination source. A two-dimensional numerical study of the light propagation through a glass microsphere using finite element method (FEM) is performed, providing key insight into the microsphere’s superior imaging capability.

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