Stupid Laser Questions

[NoXion]

OK, I have some questions about lasers that may seem a bit stupid, but I'll never know if I don't ask, so here goes:

Can lasers be focused? For example, I want my laser to come to a point about 1 light-second away from the aperture.

How do would I express a laser's power in Watts, Joules etc when I currently rate the laser power in tons? For example, how powerful in watts/joules would a laser that imparts 1 Megaton of energy per one-millisecond blast to a target?

Do powerful lasers use any sort of ammunition apart from electricity? I have heard of lasers gaining energy from chemical as well as electrical sources.

[Kuroneko]

Can lasers be focused? For example, I want my laser to come to a point about 1 light-second away from the aperture.

Yes. However, the device would have be incredibly precise. For beam with radius r to focus at distance a>>r, the angle from the edge of the beam at the aperture to the focus point has cosθ=r/sqrt[a²+r²]=1/sqrt[(a/r)²+1] =~ r/a. Since for t>0, acos(t) = π/2 - t - t²/6 - O(t^5), the angle is only about r/a radians short of a right angle.

How do would I express a laser's power in Watts, Joules etc when I currently rate the laser power in tons? For example, how powerful in watts/joules would a laser that imparts 1 Megaton of energy per one-millisecond blast to a target?

Power in watts is (MT/s)*(4.184e15J/MT). Consequenty, 1MT/1ms = 1e3MT/s = 4e18 watts.

Do powerful lasers use any sort of ammunition apart from electricity? I have heard of lasers gaining energy from chemical as well as electrical sources.

Yes, but chemical energy storage won't be capable of operating this device for even a nanosecond, even ignoring the problem of the device simply melting itself if it operates for that long.

[Admiral Valdemar]

The trend is towards solid-state diode lasers like the Nd-Yag system or even more exotic crystal based devices. We've had expensive and dangerous chemical lasers for years (the ABL on a modified 747 is such a thing) but they are simply too inefficient and bulky.

[NoXion]

Just out of curiosity, what would be the effect of such a weapon? I plan to mount 4 of them in an interceptor for hunting down fighter-bombers.

Power in watts is (MT/s)*(4.184e15J/MT). Consequenty, 1MT/1ms = 1e3MT/s = 4e18 watts.

And if I remember my scientific notation correctly that's 4 thousand petawatts What's the power output of a typical nuclear power station, for comparison?

However...

Yes, but chemical energy storage won't be capable of operating this device for even a nanosecond, even ignoring the problem of the device simply melting itself if it operates for that long.

It seems that cooling is going to be a major problem

[AMX]

Somewhere around 1000MW, IIRC.
Luckily, we're comparing apples and oranges here, since the power station works continuously, while the laser is pulsed.

So, trying not to make any stupid errors...

4*10^18W for 10^-3s means, obviously, 4*10^15J = 4*10^9MJ per pulse.
1000MW means 10^3MJ per second.

So if your laser takes 4*10^6 seconds to charge up between shots, and asuming no losses, you can run it off my power plant.

That's one shot every one-and-a-half months...

[Sea Skimmer]

The US Army THEL system is a fine example of why chemical lasers aren’t everu practical. The things ammo supply fills up two large semi trailer mounted tanks, and provides enough ammo for only five to seven shots. The laser its self eats up another large semi trailer, with yet another semi trailer to house its massive water cooling system.

[Setesh]

How do would I express a laser's power in Watts, Joules etc when I currently rate the laser power in tons? For example, how powerful in watts/joules would a laser that imparts 1 Megaton of energy per one-millisecond blast to a target?

http://www.onlineconversion.com/

An aside DARPA is leaning heavily on making diode lasers into weapons since they are more efficient than chemical lasers. There are just as many problems however.