From: sbharris@ix.netcom.com(Steven B. Harris) Newsgroups: sci.med Subject: Re: Biological Effects of Ultra-Violet Lasers on Brain Chemistry Date: 26 Apr 1999 03:35:10 GMT In <3723BD07.EA938AB9@nospam.sympatico.ca> Happy Dog <happydog@nospam.sympatico.ca> writes: >"Steven B. Harris" wrote: > >> In <372390BF.50C276E@nospam.sympatico.ca> Happy Dog >> <happydog@nospam.sympatico.ca> writes: >> >> >> None, unless the beam is powerful enough to blow a hole in your >> >> head. Which doesn't describe any UV laser known. >> > >> >Huh? A kilowatt CO2 cutting laser won't? >> >> That's far IR. It's much more difficult to make high powered UV >> lasers. Or, perhaps I should say, high energy UV lasers. A >> home-buildable nitrogen laser puts out a respectable amount of power >> for a very short time-- a few 10's of nanoseconds. It's average power, >> not peak power, that does the damage, of course. > >Oops. I have an ion laser that, with the right optics, will do about >7 watts continuous wave @ 275nm - 285nm. That should do it, no? >erf Not to blow a hole in your head, as seven watts of heat just is not enough. Granted, brought to a focus it would certainly smart: it's about what you get from a 3 inch magnifying glass at noon. But you're not going to burn a hole through a skull in any reasonable time with a 3 or 4 inch magnifying glass-- you're just going to provoke a lot of swearing. As an unfocused beam, that much UV might do to give you a very bad sunburn, and certainly would very rapidly take out your corneas and retinas. Good luck grinding those quartz lenses. SBH From: sbharris@ix.netcom.com(Steven B. Harris) Newsgroups: sci.med Subject: Re: Biological Effects of Ultra-Violet Lasers on Brain Chemistry Date: 26 Apr 1999 06:58:30 GMT In <3723CFA7.F00A3A33@cs.uoregon.edu> Bret Wood <bretwood@cs.uoregon.edu> writes: >> A "high-powered" UV laser basically works like a flame-thrower. The energy >> is absorbed by proteins and turned into heat, resulting in exploding water >> vapor and cell death. > >Actually, depending on the UV wavelength, it probably has enough >energy per photon to directly break many types of chemical bonds. >Eventually though, all energy turns into heat. The quick interconversion of electronic transition absorption to heat (atomic vibration) means the primary effect is basically the same for UV lasers as it is for IR lasers (or IR in substances with appropriate IR vibrational absorption bands, ie most heterogeneous stuff like skin plus blood). That's true of UV in non-conductors until you get to frequencies above all such electronic transition energies, which generally happens in the X-ray (In conductors, it happens at frequencies above the effective "plasma cutoff" of the substance you're aiming at-- the plasma here consisting of conduction band electrons. Which transition happens in the UV for many metals. In gold it's starting to happen in the violet, which is why gold foils are violet but can be seen through, yet at the same thickness block and reflect far IR very well (useful for foundry workers and astronauts on the moon). Above this point in frequency, whatever your substance, penetration goes way up, and you've got a very different kind of weapon. It's still nasty because you still deposit energy along the beam by Compton scattering from individual electrons. But the rate of energy deposition is way down, and it's not a surface boiling blowtorch anymore, but a deep-cooker and ion producer. For the human head, not made of metal, that would require not a UV, but rather an X-ray laser, of a type which isn't available except as pumped by a nuclear weapon. And I suppose a certain dose of that would indeed give you, not heating effects, but primarily mental effects from acute ionizing radiation neuronal dysfunction-- just as big dose from a neutron bomb does. |