Paul Anderson asked:
Hi Chris and team,
Curtains fade because of sunlight. The world has a problem with graffiti. Has anyone tried inventing a laser light that could be used to shine on the graffiti and fade it in a hurry?
We posed this question to Graeme Hirst from the STFC Central Laser Facility...
Graeme: - Yes it can. They're already used in this application, certainly for cleaning expensive things. The trick is to choose a laser so that the colour of the laser light matches the colour of the graffiti ink. [that can then be used to heat the graffiti ink, and blow it off the wall without heating the wall up.] So, yes, itís a very neat solution for cleaning dirty stuff off expensive things. Unfortunately, itís not always cheap and you do have to make sure thereís no one around.
Ben: - Is it also true that you can use lasers to have a look through the paint and try, and find fraud in paintings?
Graeme: - Yes, you can. Again, you choose the right colour. Now, what you're looking to do is to choose a colour which is not absorbed by the top layer of paint so it goes straight through. Itíll be absorbed by something a bit lower down, itíll bounce back off that and whether itís there or not, you will get bounce-back or not and by mapping out the bounce-back, you can look at the layer below the paint layer.
You would need a laser that could be tuned to operate over a wide range of frequencies. If you had such a laser you wouldn't need to photograph the graffiti separately because you'd be able to use the laser to scan the graffiti and ascertain it's characteristics. Once you'd done that, all you'd then need to do is use the optimum wavelength of light, for the particular dyes you wish to remove, to burn those dyes off. All it needs is a tunable wide-band laser. LeeE, Wed, 24th Dec 2008
Hmm... that must have been a very quite xmas eve, if I was posting stuff here just after 11 pm. LeeE, Wed, 16th Jun 2010