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From: B. Harris)
Subject: Re: Biological Effects of Ultra-Violet Lasers on Brain Chemistry
Date: 26 Apr 1999 03:35:10 GMT

In <> Happy Dog
<> writes:

>"Steven B. Harris" wrote:
>> In <> Happy Dog
>> <> 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?

   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.


From: B. Harris)
Subject: Re: Biological Effects of Ultra-Violet Lasers on Brain Chemistry
Date: 26 Apr 1999 06:58:30 GMT

In <> Bret Wood
<> 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.

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