U.K. Scientists Developed an “Anti-printer”

On the left an erased latter on the right a close up of the vaporized spot (Credit: Cambridge University)
A new method for removing toner from paper was developed by researchers from Cambridge University. The technique which was demonstrated by the researchers can allow printed paper to be reused 5 times before it needs to be recycled. This method opens the door to a new and greener use of paper as well as reduced printing costs.
A conventional laser printer uses heat (from the laser) to convert toner particles into ink which is deposited in turn on the paper. The "unprinting" process, developed by Dr. Julian M Allwood and research student David Leal-Ayala, works by using extremely short (nanoseconds-long) pulses of green laser to heat the toner on the paper and remove it by vaporizing it. Toner is composed of both carbon and a plastic polymer and the green laser vaporizes the polymer in the toner allowing the paper to be reused.
The researchers tested an entire range of  lasers including: ultraviolet, infra-red and visible lasers at different wavelengths and discovered that the bset wavelength is 532 nanometers (green visible laser) with a pulse of about 4 nanoseconds (otherwise the paper itself can be damaged or even catch on fire).
Unknown to many, there is an existing huge industry devoted to removing ink from paper as part of recycled paper processes. However, recycling paper is an energy intensive procedure and the ability to reuse paper several times before recycling it can cut energy costs and reduce greenhouse emissions.  
Japanese manufacturer Toshiba have been selling a special toner called "e-blue" which, just like old thermal fax paper, fades away under the right type of light (you can watch the following video demonstration on YouTube). However unlike the Toshiba invention, the technology developed by the Cambridge researchers can work with any toner or paper.
One of the current unknowns about the research is how exactly will the unprinting process be integrated into future laser printers. Although both processes use heat (to print and unprint ), the new unprinting process requires higher temperatures and so it still remains to be seen whether or not the same laser can be used for both processes.  The researchers have already demonstrated the technique in the lab but now they are planning to develop a prototype device suitable for an office. They are estimating that building the first unit will cost about $30,000.
In 2007 TFOT covered the "Xerox Inkless Printer" – a new printing technology which does not require ink of any kind. Similar to the technology currently on sale by Toshiba, the Xerox technology can be printed and erased dozens of times.