> Mike Rosing[SMTP:[EMAIL PROTECTED]] wrote: > > On Thu, 31 Oct 2002, Steve Schear wrote: > > > >Information about the damage such lasers could inflict is classified. > But in > > >general, experts say, a 25-kilowatt laser could blind an enemy sensor > several > > >hundred miles away. It also could put a hole through a sheet of metal > from a > > >distance of several miles. > > A few assumptions and you can estimate the damage. Is that laser power > level or source power level? Peak powers in the terrawatt range are > normal, but energy level is usually only a few joules. If it's CW, then > 25kJ/sec on a 1cm^2 area could do some useful damage to most anything. > This is a game we can all play.
Lasers as weapons have 3 major modes of action. 1. Blinding sensors. This could be temporary, or permanent, depending on the sensor and the power level. Firing 100kW at a Sidewinder, Copperhead, or modern equivalent would probably ruin it. Ditto for laser or video guided precision muntions. (Note that human eyeballs count as sensors for this purpose (ugh!)). 2. Burn-through. If enough energy is absorbed by the target, it heats to the point where it starts to lose structural integrity. This can directly make it useless, set fire to internal components, fuel, or explosives. A missile under thrust is highly stressed, and can buckle. A airframe can lose streamlining, and rip apart. Usually requires a lot of power. 3. Ablative blast. A short, intense hit with a laser can cause the a thin layer of the surface to vaporize. This vapor expands very rapidly away from the underlying surface, and due to conservation of momentum, provides a physical blow to the remaining material. Requires a brief, high-intensity pulse. > > >Correspondingly, a 100-kilowatt solid-state laser -- the Holy Grail for > > >weapons developers -- could deliver a destructive beam to a target > dozens of > > >miles away, making it an effective tactical weapon. > > With the engines of a B2 bomber maybe... > > > >Lasers do have one big drawback. The beam is not very effective in > inclement > > >weather and requires greater levels of energy to pierce thick clouds. > > Use a better wavelength dummy... > Wavelength changing won't help with clouds much (that's why they're white). Suspended droplets of water are going to disperse any wavelength they don't absorb. At higher energies, you could burn a hole through the cloud, but that leads to other problems. For a start, the cloud is moving, so the hole is not stable. Second, a high intensity continuous beam causes 'thermal blooming'. When the laser heats the air within it's beam, that air expands, lowering it's refractive index compared with the surrounding air. This causes the beam to refract outwards, like the bell of a trumpet. At even higher powers, the air itself will ionize. The plasma is highly absorbtive. Some of these problems can be avoided by using very short pulses. Also, if the laser is mounted in an airplane, the beam is, for most of it's path travelling through 'fresh' air. One other trick would be to use a 'target designation laser' of one wavelength, and then have two or more weapon lasers converge on the designated target simultaneously from different locations. Peak power is then reached only on target. > > Because of the relative motion and closing rates of actively engaged > combat > > systems and the ease with which the missile surfaces can be hardened > > against directed energy, I suspect fielding an effective system will be > as > > difficult and expensive as the antimissile systems now under > development. > > Light speed is faster than any mechanical motion we can do for the > forseeable future. 10^4 Joules is needed to do damage, so if that can be > delivered in a millisecond the receiving end is gonna have problems. > An interesting defense would be an easy to ablate surface that ionizes at > low energy so the laser can't penetrate very deep. After 30 seconds, the > receiving end is still gonna have problems. So if the missle can close > the range to the laser in less time than that, the laser has problems. > See 'ablative blast' above. This might work for a ground target, but a airborne one would have real problems. > For every weapon there is a counter :-) Just like crypto... > > Patience, persistence, truth, > Dr. mike > Peter Trei
