Some things are printed for long-term use or storage, but plenty of pages are read once before being thrown out. Now, engineers at the University of Cambridge have found a way to wipe these printed pages clean and reuse them. The team, led by David Leal-Ayala, created an 'unprinter' that sends lasers in short pulses towards the paper. The lasers don't affect the white cellulose fibers, but the darker toner absorbs them, generating heat that vaporizes the ink from standard printers in several thin layers. The team tried a number of different colors and pulse lengths to determine the optimal laser type, eventually settling on green light with a relatively long pulse rate of four nanoseconds. With this laser, they were able to print and erase a page three times without noticeable damage.
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