On Feb 7, 8:51 pm, MacFrag...@[EMAIL PROTECTED]
wrote:
> > It can help. It's harder to do than you might think, across the
spectra
> > involved, but yes, it is a plus.
>
> So a mirror that would reflect an infrared laser would not necessarily
> reflect an indigo or UV laser?
> Working from the lesson that "there is no gamma ray mirror", do beams
> get exceedingly more difficult to reflect the shorter the wavelength
> is?
> Or do you simply need different types of mirrors for infrared, visible
> light and UV?
Highly polished metals are fairly good mirrors up through the near
ultraviolet. Gold is best in the infrared but is not terribly
reflective in the visible region, silver works works well at infrared
(but not as good as gold) and visible frequencies but stops working in
the near UV, and aluminum is reflective from IR through near UV but is
not as good as gold or silver in the regions where those metals have a
high reflectance.
Note that fairly good is probably not good enough. A 95% reflectivity
may seem high, but a dielectric mirror optimized for a narrow band of
wavelengths can achieve 99.99% reflectivity and can handle megawatts
per square centimeter. If you know the wavelength of light coming out
of your laser weapon, you can use dielectric mirror coatings optimized
for that wavelength, giving you beam focusing mirrors that can handle
the heat from your weapon far better than any defensive mirror that
must work across a wide band of wavelengths.
> Aaaaaaaand if the latter is the case, I have no idea about the
> feasibility, but could you sort of apply different reflective layers
> to a single surface in order to cover a wider range of wavelengths
> (sort of like multiple coats of paint)?
Dielectric mirrors have sufficiently narrow bands that you would need
a LOT of layers. The optical bandgap materials they are researching
now may have large enough optical bandgaps to make something like this
feasible - as long as the outer layers don't have some absorption
resonance which you would rather reflect. It is interesting to note
that all optical properties in some sense come from absorption(the
real part of the dielectric function is related to reflection, the
imaginary part is related to absorption, and the two are related by a
Kramers-Kronig transform
http://en.wikipedia.org/wiki/Kramers-Kronig_relation
)
so any mirror must have absorption in some part of the spectrum.
> The tactical consequence I see in effective anti-laser mirrors would
> be that lasers become a lot less useful. You'd have to aim at
> vulnerable spots like, for instance, engine nozzles,
Note that one of the thing lasers are really good at is pinpoint
aiming at vulnerable spots.
> Also, lasers would lose a lot of their value as Point Defense weapon:
> coat your missiles and kinetic slugs in sparkling ****niness, and the
> PD laser will just make for a beautiful prism lightshow (exaggerating
> a bit here but you get the idea).
Again, a mirrored surface will help when the incoming kinetics are far
away, but when they get close enough the lasers will burn through
anyway. This will help reduce the time the kinetics are vulnerable,
but is not the uber anti-laser counter defense.
Luke
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