[extropy-chat] LASER: DARPA's HELLADS small laser weapon makes headway

Dirk Bruere dirk.bruere at gmail.com
Mon Sep 5 19:38:28 UTC 2005


On 9/5/05, Mike Lorrey <mlorrey at yahoo.com> wrote:
> 
> 
> 
> --- Dirk Bruere <dirk.bruere at gmail.com> wrote:
> > >
> > > Okay,
> > > 1) MIRACL was vastly larger system than the current MTHEL system.
> > > 2) you've got two quotes there saying "a few inches" NOT "twelve
> > > inches". "A few" is taken as two or three in colloquial US english,
> > > which is far closer to my estimate than to yours.
> >
> >
> > Or as I said, 12cm ie around 4 inches.
> > Still, the figures would apply even if it were only 3 inches.
> > And since we're being picky the power density I was working with was
> > 1320W per sq cm.
> 
> Sorry, I thought you had said 12 inches, not 12 cm. However, you still
> need to scale your 12 cm by one to two orders of magnitude downward for
> a fighter portable unit, which should be 12 mm or less.


That's not possible.
I can't be bothered to list all the problems involved so you'll have to wait 
for some official statement on beam dia.


>
> > > Now that we've disposed with that objection, lets do some realistic
> > > calculations of the effects of 150 kW hitting a missile casing in
> > > an area of less than 20 mm radius.
> > >
> > > No, let's do a realistic calculation of a power density of 1kW per
> > > sq cm.
> 
> Once again, you are cooking the books and spreading the butter thin.
> Firstly, you are ignoring the fact that the HELLADS system is said to
> be utilizing dynamic focusing technology, and applying THEL scaling to
> a device two orders of magnitude smaller. A 12 mm beam would be a power
> density of 1326 kW/ sq mm, not centimeter.


Again, very unlikely. 
There are fundamental problems with the optics at that power density.

Another issue is pulse length. Watts measures beam power in
> Joules/second. However beam pulses are generally fractions of seconds.
> If, for example, the laser is 150 kW with a pulse time of 0.1 sec, the
> energy is delivered at a rate of 1500 kJ/s. The determinant of
> ballistic effect of a laser is more properly expressed by its
> Joules/sec rating.


You need to pulse at much higher power densities than that to get an 
explosive ablation effect.

Dirk
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