Using very short pulses of green laser light, printed ink is selectively vaporised (OK, 'ablated' technically), leaving the paper undamaged and ready to reuse.
Manufacturing and recycling paper is a very inefficient, carbon-footprint-heavy process. Cambridge University calculates that worst-case, 'unprinting' uses half the carbon emissions of recycling - best-case, it is 20 times more efficient. If the technology can be fed into commercial devices, this could be an astonishing development.
More here.
