A green laser that “unprints” toner from printed paper

Researchers at the University of Cambridge have developed a laser “unprinter”, a laser configuration that can gently remove toner from a printed sheet of paper enabling its reuse. After the “unprinting” process, the paper remains undamaged – at least for the first three times.

Building up on the work already done in the field, the British researchers tried several laser setups before finding the right one: their testing work with different wavelengths and pulse speeds resulted in a prototype capable of vaporizing toner particles from microscopic layers of the paper substrate.

The Cambridge research, “Toner-print removal from paper by long and ultrashort pulsed lasers” explains that the right configuration for an optimal toner unprinting process uses a laser with a 532 nanometers wavelength – the same of the green-toned visible light – and 4 nanoseconds-long pulses.

The method, however, isn’t perfect: “We have repeated the printing/unprinting process three times on the same piece of paper with good results”, the researchers stated, warning that “the more you do it, the more likely it is for the laser to damage the paper, perhaps yellowing it”.

And yet the already gained results – the chance of reusing a laser-printed sheet of paper for at least three times – encourage the researchers to go on with further testing: developing a “perfect” method for toner unprinting would mean concrete and huge benefits for users, companies and the environment overall.