The US Department of Energy’s Lawrence Berkeley National Laboratory and the University of California Berkeley have created the world’s smallest three-dimensional optical cavities. Most lasers use optical cavities to produce standing waves from which a laser beam is generated. As optical communications and biosensing advance, the smaller the cavity, the smaller the laser, and the more useful it all becomes. While this is bad for traditional natural material cavities, which lose efficiency with size, it’s good for the new nano-cavities. Made from metamaterials, the nano cavities reverse the efficiency trend, losing fewer photons as their size shrinks due to enhanced light and matter interactions. The cavities are created inside alternating layers of silver and germanium and use hyperboloid iso-frequency contours, allowing them a subwavelength (nm) size and the “highest” ever reported optical refractive indices: -17.4 (compare germanium’s 4.0 and air’s 1.0).