Originally posted by Silver Shadow
And a polished mirror finish finish on your missile will completely reflect and scatter any infrared laser pulse of any power..
Regarding mirrored surfaces and their effect on weapons grade Lasers - A few things to consider (this does apply more to megawatt lasers than kilowatt
lasers however):
1.) No surface is 100% reflective.
The energy that is not reflected is dissipated by the surface as heat. As heat builds up, the reflectivity of the surface will decrease, and it
decreases exponentially from that first contact. Obviously this will increase the time it takes for a laser to inflict damage on a target, but at the
power levels we're talking about, it would be measured in nano or milliseconds as opposed to seconds.
It bears mentioning that mirrors for industrial lasers need to be water cooled, in spite of being over 99.5% reflective for this reason.
2.) For a surface to remain highly reflective, it has to be kept incredibly clean.
A $600 germanium mirror for a 500 watt CO2 laser can be easily destroyed in a fraction of a second if it has so much as the residue of a finger print
that has been wiped off with a lens cloth without benefit of cleansing solvent.
For in-flight missiles to be able to reflect enough of a weapons-class laser beam to be impervious, they'd need to be polished to an optical grade
and wiped off up to clean-room specs. Not the sort of thing that's practical in combat.
You must also consider that as the projectile flies through the air/atmosphere the heat generated, the humidity, air pollution, dust particles and
general oxidation cause surface anomalies imediately upon being launched - this spotting on the projectile gives the attacking DEW ample nonreflective
surface area to heat and thereby neutralize said missile.
3.) A surface is only reflective to a certain range of wavelengths.
As an example, the germanium mirror I talked about above is reflective to CO2 lasers in the far infrared wavelengths (10.6 microns), it is glossy
black and completely unreflective to other wavelengths including visible light which as a reference centers around .4 microns.
On the other hand, a mirror for a Ruby laser, which outputs radiation at .69 microns is standard silver. If you switch the two mirrors with their
respective lasers, each will shatter immediately.
.............
If an enemy were to armor their missiles with a reflective coating, provided they could keep it clean and polished throughout it's flight trajectory
(impossible unless in a particle free perfect vacuum), the resonant cavity optics of the laser could theoretically be changed to amplify a wavelength
that the shell or missile would be vulnerable to.
The ultimate laser weapons goal in the future is to have a free electron solid state laser - the laser operator could select any wavelength desired at
the push of a button neautralizing the effectiveness of reflectivity and therefore decreasing the power needed to accomplish what is now accomplished
with multiple megawatt devices.
[edit on 7-29-2009 by intelgurl]