The US Navy's Laser Ray of DOOM!

[Count Chocula]

Saw this on Wired:

Unexpectedly, Navy’s Superlaser Blasts Away a Record
By Spencer Ackerman February 18, 2011 | 3:36 pm | Categories: Lasers and Ray Guns

NEWPORT NEWS, Virginia — Walking into a control station at Jefferson Labs, Quentin Saulter started horsing around with his colleague, Carlos Hernandez. Saulter had spent the morning showing two reporters his baby: the laboratory version of the Navy’s death ray of the future, known as the free-electron laser, or FEL. He asked Hernandez, the head of injector- and electron-gun systems for the project, to power a mock-up electron gun — the pressure-pumping heart of this energy weapon — to 500 kilovolts. No one has ever cranked the gun that high before.

Smiling through his glasses and goatee, Hernandez motioned for Saulter to click and drag a line on his computer terminal up to the 500-kV mark. He had actually been running the electron injector at that kilovoltage for the past eight hours. It’s a goal that eluded him for six years.

Saulter, the program manager for the free-electron laser, was momentarily stunned. Then he realized what just happened. “This is very significant,” he says, still a bit shocked. Now, the Navy “can speed up the transition of FEL-weapons-system technology” from a Virginia lab to the high seas.

Translated from the Nerd: Thanks to Hernandez, the Navy will now have a more powerful death ray aboard a future ship sooner than expected, in order to burn incoming missiles out of the sky or zap through an enemy vessel’s hull.

You can read the full story at the linky. In its current form, it can cut through twenty feet of steel per second. Booyah!

[The Romulan Republic]

Holy shit. That's impressive. And scary.

[Chardok]

Okay, that looks impressive. but I'm....well, lost. Can anyone give me comparitves or examples of what to expect beyond "Yo, this will totally 'zap' (I hate that simp word) through a hull."

[That NOS Guy]

Okay, that looks impressive. but I'm....well, lost. Can anyone give me comparitves or examples of what to expect beyond "Yo, this will totally 'zap' (I hate that simp word) through a hull."

A laser CIWS would certainly be useful, since per shot it's probably cheaper than a RAM and definately moreso then a Standard.

[Count Chocula]

Well the way I read it, the free-electron laser is basically a tunable lightning gun, with 300kV of potential and (right now) 14 kilowatts. 14 kW is about the electrical usage of two houses, but the beam does not have a lot of power behind it; with about 5 hundredths of an Amp of power (assuming continuous beam and 14kW/300kV) the FEL can drill through metal!

The target is 1 megawatt, with 100kW making it a useful ship weapon. With only 3.333 Amps of power. High voltage is magic!

[Simon_Jester]

Well the way I read it, the free-electron laser is basically a tunable lightning gun, with 300kV of potential and (right now) 14 kilowatts. 14 kW is about the electrical usage of two houses, but the beam does not have a lot of power behind it; with about 5 hundredths of an Amp of power (assuming continuous beam and 14kW/300kV) the FEL can drill through metal!

The target is 1 megawatt, with 100kW making it a useful ship weapon. With only 3.333 Amps of power. High voltage is magic!

Well the way I read it, the free-electron laser is basically a tunable lightning gun...

Ah, no. This article is pretty sensationalist, though the project is genuinely running and they do sincerely expect to build a working laser cannon eventually.

I suspect if I ask around I'll find I'm two to three degrees of separation from the people mentioned here; there are people at my lab who go down to Jefferson Lab on a semi-regular basis. A free electron laser runs an intense electron beam through a series of magnets that cause the beam to wiggle back and forth; this process generates coherent light- hence "laser." The electron beam is the medium of the laser, much as a vat of chemicals or a crystal or a tank of gas might be in a dye, ruby, or CO2 laser.

It is tunable: you can adjust the frequency of the laser by fooling around with the magnets, which is very useful for getting a laser beam that functions well at sea level- this is why they can't just take the Air Force's YAL and mount it on a warship; the beam from a COIL laser doesn't propagate well at sea level.

Whoever wrote this article is sensationalizing, as I said, though if they reported the scene accurately my congratulations go out to Hernandez for getting something done faster than his boss expected. But people here seem to be confusing the voltage of the power source with the power of the beam.

The problem is that because of inefficiencies, you're likely to end up feeding quite a few watts into the electron gun to generate the electron beam, in order to get one watt of power out the laser beam. So to get that (for example) 14 kW laser beam, you would be feeding some indefinite but fairly large amount of DC power into a high voltage power supply- one that generates the fields to push an electron beam up to speed, so that it can be used as the lasing medium.

Thus, this becomes a difficult exercise in high-voltage engineering: you need to design a power supply that won't short out, and that is reasonably compact... and it needs to be DC, when high voltage applications in engineering are usually AC systems like transformers. So, not easy.

But ultimately, the "300 kV" or "500 kV" or whatever voltage they run the electron gun (the "injection" system) at is totally irrelevant to the power output of the laser itself- and for that matter, doesn't let you do any estimates of the power consumption of the laser, either. From the Navy's perspective, there is nothing all that special about a 500 kilovolt DC power supply, or about the 500 keV electron beam it generates. What is special is the laser beam generated using the electron beam as a medium; the 500 kV power supply is merely a means to that end.

And unless I'm much mistaken, the Wired article does not say thing one about any actual improvement to the laser performance above the... 14 kW or so, as I recall that they have already achieved. Yes, they're working on it, but this is in and of itself a purely incremental advance- on par with figuring out some trick to accomplish the goal in designing a jet engine. You're a long way from actually building the fighter jet, even though you've done something that'll help.

[Sarevok]

Can someone give us actual numbers ? Twenty feet of steel says nothing quantifiable. It also sounds frankly impossible given power and cooling requirements. Is this like existing terawatt lasers that only fire for a minuscule pulse duration ?

[Spectre_nz]

In crude terms, the basic components of any laser will include; Optics, a power source and a gain medium.
The 'free election' bit is in reference to the gain medium of this type of laser; a beam of free electrons held in a very high vacuum.

Something like a YAG laser or an argon laser will operate at a very specific wavelength or set of wavelengths, as it basically comes down to the quantum energy levels of the gain medium as to what wavelength the photons they emit.
Free electron, gas or solid state all need an external power source to pump them; basically you feed power into the gain medium to build up a large number of photons bouncing back and forth along a single axis - basically because you position a reflector front and back only, photons traveling in other directions are lost and you end up with just a single coherent stream. Then you allow a few to leak out one end and they're your laser beam.
You can also do some funky tricks with mode locking, sometimes called Q switching, where you can store the photons up a bit like a capacitor stores electricity, then at the flip of a switch, let them all out in a tight bunch for much higher peak power; pulse lasers. The NIF pulse laser is apparantly a 1.8 megajoule, 700TW peak power beastie. Not much use for shooting down missiles however.

But yeah. As Simon.J said; it's a variation on the gain medium. You've still got the pumping efficiency to worry about. Unlike a solid state or gas laser you've got a lot more wavelengths to pick from. Unlike an excimer laser you can pump it with electrical power. All that added flexibility is I think why the military is keen on them. But you trade carrying around chemicals for an excimer or the weight of a gas or solid state gain medium for the weight of a high vacuum chamber.

I haven't seen any good numbers on what the beam power on this thing is. I assume it's a continuous beam, rather than a pulse, but that's just an educated guess based on the fact that if you want to pulse a laser its easier to do it with a solid state.
Edit: or because you have to pulse them because of the limitation of your pump system

[Ford Prefect]

Can someone give us actual numbers ? Twenty feet of steel says nothing quantifiable.

Are you for real?

[Sarevok]

What's your problem little boy ?

[Sarevok]

Anyway I thought the main problem with defeating supersonic and sea skimming targets was detection time. Many existing shipboard weapons already have the kinematic performance to engage such weapons. It's just that the threat can often close in before it can be destroyed. Therefore it is better to shoot down a missile before it enters within the radar horizon. In shooting down anti shipping weapons a laser is facing same problem as an existing CIWS system. It is a line of sight weapon with same problem of having very little time to splash a fast moving target. If a missile is intercepted only a few hundred meters to a kilometer away it can still has enough forward momentum to crash into the ship.

[Aaron]

What's your problem little boy ?

We're on a site that gives estimates for pew-pew space weapons by assuming certain materials and you can't do that for 20 feet of steel? I know there are many different types of steel but if you chose a mild steel you might just get a lower limit. Jesus dude.

[Sarevok]

I don't think you understood my point Aaron. Simon, being related to lasers may be able to explain it better but I will try.

Suppose someone talks about a really really powerful laser. Like this petawatt laser one used for nuclear fusion and other research. A petawatt implies a lot of power, the entire world does not produce anywhere that amount of electricity. So how does a petawatt laser exist ? The answer is it does not*. The beam fires for a minuscule period of time.

Livermore's Petawatt laser operated for three years, until its last shot was fired on May 27, 1999. At full energy of about 680 joules, the shots delivered more than a quadrillion watts (or petawatt, which equals 1015 watts) of power, exceeding the entire electrical generating capacity of the U.S. by more than 1,200 times. But the Petawatt's shots lasted for just a fleeting moment-less than a trillionth of a second, or 440 femtoseconds to be precise.

So this laser fires for less than a trillionth of a second. Technically yeah it IS a petawatt laser but in terms of damage potential it is puny. It fires for such a fanatically microscopic period of time the amount of energy delivered cant probably even light a cigarette. We can't actually construct terawatt or similar fantastically higher power lasers that can fire a full second - all we can do is deliver that rate of energy for a very small fraction of a second.

Now how does this all tie into the "strong enough to cut 20 feet of steel" statement ? We have no idea if the laser can do that without knowing the pulse duration. Currently other leading edge FELs struggle to maintain 100 kw beams which against steel of any type would barely do a scratch. So when a sensationalist article suddenly claims we have invented lasers that put science fiction weapons to shame you can understand my surprise.

My only guess is the authors saw a very high power value somewhere and equated that with the laser being actually able to fire continuously as opposed to maybe a milisecond or two at most.

[Aaron]

Well it's not like journalists haven't fucked up before.

[Sarevok]

Well it IS Wired who are proclaiming the second coming of the Cylons and Terminators each time they publish a stock photo of a MQ-9 Reaper.

So no surprise there.

[Simon_Jester]

Can someone give us actual numbers ? Twenty feet of steel says nothing quantifiable. It also sounds frankly impossible given power and cooling requirements. Is this like existing terawatt lasers that only fire for a minuscule pulse duration ?

The J-Lab FEL is a continuous-beam device, as will be the weaponized lasers descended from it. Realistically it will be fired in bursts, but these bursts may well be on the order of a second based on what I know.

You will note the power figures being given: 14 kW today, 100 kW to 1 MW for a weaponized version. That would be a joke by the standards of 'very short pulse' lasers; those are sustained power figures you're looking at.

Anyway I thought the main problem with defeating supersonic and sea skimming targets was detection time. Many existing shipboard weapons already have the kinematic performance to engage such weapons.

That they do, but a laser simplifies the problem considerably- you can mount it on your radar system as a co-ax, as it were. So if you need a final close-in defense system, a point defense laser will be able to engage from farther out simply because you've removed the time of flight of the bullets from the equation.

[Ford Prefect]

What's your problem little boy ?

Everything I quoted is a known quantity.

[Simon_Jester]

Hmm. The Wired article cites 200 kW of power going into the electron gun (the source of the beam used as the lasing medium) for a 14 kW laser. That's the closest I've heard to an efficiency figure, and it's better than I'd expected... though there are other power-consuming elements in a particle accelerator, which probably pushes consumption up past that 200 kW mark.

[erik_t]

Anyway I thought the main problem with defeating supersonic and sea skimming targets was detection time. Many existing shipboard weapons already have the kinematic performance to engage such weapons.

That they do, but a laser simplifies the problem considerably- you can mount it on your radar system as a co-ax, as it were. So if you need a final close-in defense system, a point defense laser will be able to engage from farther out simply because you've removed the time of flight of the bullets from the equation.

It's also immensely attractive to have a weapon powered by such insensitive, easy to store and easy to transfer stuff as dead dinos.

[Simon_Jester]

In all probability, the system will see first deployment on nuclear-powered ships, for that matter. It's going to be fairly bulky.

[Iroscato]

Anyone else wondering if they say `commence primary ignition!` before they fire?

[someone_else]

Uhm. I think the steel-cutting figure is debatable.

Lasers aren't flashy light travelling in a straight line like the aferage SF raygun (phaser, blaster, disintegrator, what-have you), but a high tech version of a kid burning stuff with a lens.

The laser allows the lens to focalize the beam better and at more distance, but the "beam" is in fact a cone with a pointy end focalized on the target's surface. (the reason for this setup is not burning the optic system)
This, among other things, means that after you drilled a hole long enough, the cone at the entry hole is larger than the entry hole itself, resulting in crappy penetration beyond that point.
Laser cutters have to stay very close to the entry hole to achieve good penetration. I think they can reach around fifty times the entry hole diameter in depth, but most ranged lasers shouldn't drill a hole deeper than twenty times the entry hole.

Range and damage depend from the optic system employed, and also on how much time there is between the laser pulses that compose each "shot".

That said, more powerful emitters are always a good thing to hear.

I think they will run on batteries for non-nuclear crafts, or they will have to couple the main engines to a generator (most destroyers have multiple very powerful engines, like the Arleigh Burke with 4 gas turbines that produce 20 megawatts each, but aren't designed to produce electrical power)

[LaCroix]

Well, laser cutters aim for precision cutting, so the rig is set up in order to do less penetration to increase precision. The deeper you burn, the longer it takes, and thermal transfer warps the material or causes edges to melt, killing the precision.

Lasers used for "burn a hole through that MF!" aren't touchy about uneven edges. The people designing such a weapon don't really care about the rest of the material around the beam path melting away. I believe they might even be happy about that.

[Simon_Jester]

Someone_else, I suspect these lasers are meant to be installed on ships with all-electric propulsion: the main engines drive a generator that powers electric motors to move the ship. This is actually not new technology; the US Navy had a number of battleships and carriers with 'turboelectric' propulsion around the time of the First World War.

But the idea languished for a number of reasons, and is now being re-explored. The Zumwalt-class destroyers have a lot of problems that I'm not the best person to comment on, but one of the many, many novel features they're throwing into the ship is all-electric propulsion... precisely so they can power energy-intensive 'futuristic weapons.'

[Sarevok]

The Zumwalt is not alone in this. The new British carriers are also going to use full electric propulsion. IIRC several other future ship designs across the world are to use integrated electric propulsion as well. The trend seem to be towards preparing warships to support upcoming systems that are very energy hungry. Such as directed energy weapons for surface combatants or electromagnetic launch systems for carriers for instance.