From: lwcamp@gmail.com   
      
   On Wednesday, February 14, 2018 at 12:08:18 AM UTC-8, Klaus Meinhard wrote:   
   >    
   > Not counting Star-Trek-like "shields", a simple mirror could deflect   
   > 99.9% of the laser energy   
      
   This is true if the laser is sufficiently diffuse (in fact, modern dielectric   
   mirrors can reach 99.9999% reflectivity at a specific wavelength).  However,   
   mirrors fail if the irradiation is too intense.  At ranges where the beam can   
   be focused to a spot    
   significantly smaller than the aperture, expect the mirror to heat up to the   
   point that its reflectivity decreases, causing additional absorption of   
   energy, resulting in a further decrease in reflectivity, to produce a runaway   
   failure.  For laser    
   machining, even highly reflective aluminum (98 to 99% reflectivity) will still   
   absorb around 50% of the beam energy.  Laser weapons could be expected to   
   operate at similar intensity regimes (or higher, for pulsed lasers).  At high   
   intensities, you get a    
   boundary layer of plasma that mediates between the beam and material.  The   
   plasma absorbs the beam, and transfers the beam's heat to the material.  At   
   this point, the reflectivity of the material becomes irrelevant.   
      
   > while the rest may be spread around by a good   
   > heat spreading design of the hull.   
      
   At the fluences typical of weapons-grade lasers, I find that thermal   
   conductivity is a negligible effect to the ability of the beam to penetrate   
   material.   
      
   > And this energy must be produced and   
   > stored somehow in intervals (I doubt that a death-ray like continuous   
   > laser of sufficient energy is possible because of heat problems).   
      
   Modern laser weapons (typically in the 60 to 150 kW range) are able to fire   
   continuously using the power from Diesel generators, or generators turned by a   
   ship's motor (ship in this case meaning an actual ship - one of those things   
   that goes across the    
   top of the water - not a spacecraft).  It is generally accepted that future   
   lasers in the several MW range can be fired continuously from future ship   
   designs engineered to produce power to directed energy weapons and   
   electromagnetic cannons.   
      
   Luke   
      
   Luke   
      
   --- SoupGate-Win32 v1.05   
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