Removing printed toner on paper, similar to how we use an eraser to clear pencil writing, is not something entirely new, but there has never been a feasible approach for the mass market.
According to a paper published in Proceedings Of The Royal Society A, a 532 nm green laser light with a pulse length of 4 nanoseconds can evaporate printed toner from paper without significantly damaging it. The process works two to three times before damage would become apparent via a slight yellow tint of the paper, the scientists said. They do not claim that the process is perfect, but they believe that they are on a promising path to enable an un-printer at some point.
According to a press release released by the University of Cambridge, the print removal would be much more environmentally friendly than recycling and producing new paper. Compared to recycling, the un-printing process would save an estimated 50 to 80 percent of carbon emissions.