Re: Laser snipers

On Mon, Sep 17, 2001 at 03:57:59PM -0400, Chris DeBoe wrote:
>> An infra-red laser wouldn't necessarily leave an obvious trail;
that's
>> about all I can think of.
>Does this depend on how much energy you're putting on the target?
>(with the implied question: how much is enough?)

I suspect so. I don't have that information, alas.

>> Trivial. A laser-drive uses _huge_ amounts of energy.
>To move a thousand ton ship, yes.  I'm only talking about moving a
100kg
>trooper.

OK. How much damage does a man-portable laser need to do? An M60 machine
gun firing 7.62NATO (about 3kJ/round) at 100 RPM (recommended cyclic
rate) gives a sustained energy transfer of about 5kW. Let's be generous
and scale that up by ten, to burn through armour and so on; 50kW it is,
for a fairly hefty laser support weapon.

Momentum of a photon = E/c where E is its energy and c is the speed of 
light. A 50kW beam gives about 167 microNewton - which will accelerate 
the 100kg trooper at 1.67 micrometres per second per second. After nine 
days of continuous fire he'll be moving at walking pace.

(For comparison - the M60 fires a 10g round at about 770m/s. Momentum
per round = 7.7 Ns for a force of 13 Newton on full-auto.)