'Picocavity' focuses light below atomic scale

The invention has the potential to unlock light-catalysed chemical reactions and to be used in opto-mechanical data storage devices.

Previously, it had been thought that it was not possible to focus light into a spot smaller than its wavelength. The Cambridge-led team used conductive gold nanoparticles to create an optical cavity so small that a single molecule could fit inside it; known as a "pico-cavity" by the researchers, it consists of bump in a gold nano structure the size of a single atom, and confines light to a space less than a billionth of a metre across.

Constructing the pico-cavity involved building a structure with single atom control. The Cambridge team sandwiched a layer of a self-assembling organic molecule, biphenyl-4-thiol, between a film of gold and a gold nanoparticle, with the whole assembly cooled to -260°C to reduce the speed of the atoms' motion, and used lasers to move individual atoms in the nanoparticle, and allowed them to observe the atoms’ motion in real-time.