Hello (again),
A conversation with Devin the Canadian laser physicist this afternoon revealed an interesting phenomenon: while infrared lasers cause 'heat' burns to skin, UV lasers cause 'sun' burns to skin and green lasers vaporise cardboard, apparently 400 nm (violet) lasers stimulate one's nerve endings, causing pain (much like a green-ant bite) but no damage to cells. I thought that this was a very interesting phenomenon and I didn't immediately see any direct cause. It seems unlikely that human nerve endings have channel rhodopsins (otherwise we would feel sensations depending on the lighting we are in! Perhaps good for parties...), so is the light directly affecting cells? Perhaps there is a protein that is directly affected by violet light, and the high intensities of lasers in the laboratory are high enough to cause an effect (this may be why the average party elicits no stinging sensations)?
Perhaps those of use with access to laser laboratories could investigate this phenomenon first hand (James...)? I think it would be worth the sting (which doesn't appear to have long term effects, other than those normally experienced by physicists) to be able to say, "I was stung by light!"
Josh H
PS: This would also offer a way to 'humanely' torture victims without causing any physical damage (and so leaving no hard evidence). This would mean that the phenomenon is well known and that it is currently in use....
Josh, I don't have access to any ultraviolet lasers... we use two-photon polymerisation and a pulsed 800nm laser to activate UV-sensitive gels (since the resolution can be much better if you use two-photon processes).
ReplyDeleteI can tell you first-hand that infrared lasers definitely burn humans: I have burnt my hand with one (it was a fairly delayed reaction, going red and nasty looking about ten minutes after exposure). Thankfully my eyes are still fine: human cornea and retina absorb IR really well, so without laser goggles it is possible to cook your cornea pretty rapidly.
Does anyone know how nociceptors actually work? Maybe this is the physical analogue of the reason why chillies taste hot (they activate TRPV1 receptors, which cause the release of a neuropeptide called 'substance P' in small, unmyelinated nerve fibres innervating the mouth).
Yet another career option for the trained biophysicist: coercive Interrogator for the CIA.
ReplyDeleteHey James,
ReplyDeleteJust quickly, Devin said it was a violet visible light laser and not ultraviolet that caused the stinging sensation: UV just burns in the usual sun-burn way (only at one frequency...). How long did it take for you to get burnt with the IR laser? Devin was saying that you can feel them and your pain reflexes aren't too bad for IR damage. The chilli analogue is an interesting comparison but I'm not sure if there are any light sensitive proteins (aside from melanin and other protective pigments) in skin. Maybe some other thingy is excited and it passes energy to the pain receptors? Also, Devin said the pain was akin to a green ant sting: does anyone know the which mechanisms are involved in ant stings?
For Dr Seth: Coercive Interrogator of Australia, CIA. It was made for this job...!
Josh H
Ant stings are due to formic acid right?
ReplyDelete