Shun Fujii

The nucleus of a thorium-229 atom is like a taut guitar string: it vibrates at a strictly defined frequency. To 'pluck the string', a precise strike is needed — a laser beam of a very specific color.

A theater spotlight keeps the actor in its beam no matter where they step. The terahertz radar we are about to describe does the same with a short light pulse reflected off a moving object. Terahertz waves sit between microwaves and infrared light.