I think you are thinking of oil immersion (microscopy) there. They are using a meta material as a superlens though which allows to work around the diffraction l

I think you are thinking of oil immersion (microscopy) there. They are using a meta material as a superlens though which allows to work around the diffraction limit. Edit: they seem to be improving an already known technique called "structured illumination microscopy". For that, the sample is illuminated with a light pattern (here: a speckle pattern) and the phase of the light is shifted in the process. After collecting various images, an image of better resolution can be computed. Their improvement seems to be to use a particular meta material that allows to capture far more spatial detail than otherwise. Links: https://en.wikipedia.org/wiki/Oil_immersion https://en.wikipedia.org/wiki/Oil_immersion , https://en.wikipedia.org/wiki/Superlens https://en.wikipedia.org/wiki/Superlens , https://en.wikipedia.org/wiki/Plasmonic_metamaterial#Hyperbolic https://en.wikipedia.org/wiki/Plasmonic_metamaterial#Hyperbo... , https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system , https://en.wikipedia.org/wiki/Super-resolution_microscopy#Structured_illumination_microscopy_(SIM) https://en.wikipedia.org/wiki/Super-resolution_microscopy#St...