Lasers: solid-state vs. free-electron?

[rhoenix]

In this article in Popular Science, works by scientists working on both solid-state lasers and free-electron lasers were cited. However, in the article, it was suggested that free electron lasers are actually better than solid-state lasers, simply because free-electron lasers can be adjusted more easily to match the atmosphere being fired within, whereas solid-state lasers, by their very design, are much more difficult to adjust.

I'm fuzzy on the science behind this, can someone confirm if this is true or not, and if possible more information as to why?

Thank you in advance.

[aerius]

A solidstate laser works on more or less the same basic concept as an LED, except on a much larger scale. Now, if you have a keychain LED, well, you can't make it go from red to green by turning a screw, you need a new LED and it's the same thing with a solidstate laser. To change the wavelength you need to swap out a crapload of parts & recalibrate it, a serious pain in the butt to say the least.

With a free electron laser, you simply change the settings on the electron beam and the wiggler device, no parts swaps required.

[rhoenix]

A solidstate laser works on more or less the same basic concept as an LED, except on a much larger scale. Now, if you have a keychain LED, well, you can't make it go from red to green by turning a screw, you need a new LED and it's the same thing with a solidstate laser. To change the wavelength you need to swap out a crapload of parts & recalibrate it, a serious pain in the butt to say the least.

That makes perfect sense, actually. Thank you for that explanation.

With a free electron laser, you simply change the settings on the electron beam and the wiggler device, no parts swaps required.

That also explains the free-electron laser's versatility, thank you also for that explanation.

So, would it make sense to suppose that a solid-state laser would be better for firing in space, where the atmopsheric resistance is, well, not there, whereas a free-electron laser would be better used in either space or an atmopshere, due to it's versatility?

[Sea Skimmer]

The solid state laser is superior as an overall weapon, because those chemicals the free electronic laser uses for fuel are horrendously toxic, difficult store, and are required in huge quantities. The mobile version of (designated M-THEL) required two semi trailers full of deuterium fluoride and atomic fluoride and this is only enough for a handful of engagements (5-10), a third trailer would hold the laser its self. This vulnerability has prevented THEL from being deployed, despite persistent rumors, and the US Army has no intention of fielding an offensive laser until solid state technology is powerful enough. ABL meanwhile, has been endlessly delayed and its now only a technology demonstrator that still doesn't even work in the lab. It was suppost to be flying in a plane years ago.

Chemical lasers also produce vast quantities of waste heat; solid state lasers are still pretty bad in this respect but they are much more compact to begin with. So the volume/weight penalty of needing a large cooling system is reduced. All you need to put into them is electrical power. Those simple practical issues are what really matter for a weapon.

[rhoenix]

The solid state laser is superior as an overall weapon, because those chemicals the free electronic laser uses for fuel are horrendously toxic, difficult store, and are required in huge quantities. The mobile version of (designated M-THEL) required two semi trailers full of deuterium fluoride and atomic fluoride and this is only enough for a handful of engagements (5-10), a third trailer would hold the laser its self. This vulnerability has prevented THEL from being deployed, despite persistent rumors, and the US Army has no intention of fielding an offensive laser until solid state technology is powerful enough. ABL meanwhile, has been endlessly delayed and its now only a technology demonstrator that still doesn't even work in the lab. It was suppost to be flying in a plane years ago.

I see, I remember reading about the modified plane being used to shoot down mortars as a test. That does make sense, thank you for that. That a solid-state is stronger, but a free-electron is more versatile.

Chemical lasers also produce vast quantities of waste heat; solid state lasers are still pretty bad in this respect but they are much more compact to begin with. So the volume/weight penalty of needing a large cooling system is reduced. All you need to put into them is electrical power. Those simple practical issues are what really matter for a weapon.

That makes this debate very interesting, then. If I'm reading what you wrote correctly, solid-state lasers are more compact than free-electron lasers, but lack their versatility.

This is going to be very interesting to learn more about as the technology progresses. Thank you again for your reply!

[Dennis Toy]

A solidstate laser works on more or less the same basic concept as an LED, except on a much larger scale. Now, if you have a keychain LED, well, you can't make it go from red to green by turning a screw, you need a new LED and it's the same thing with a solidstate laser. To change the wavelength you need to swap out a crapload of parts & recalibrate it, a serious pain in the butt to say the least.

With a free electron laser, you simply change the settings on the electron beam and the wiggler device, no parts swaps required.

that is the basis of a laser pointer. Inside there is a diode that uses solid state components to generate a laser beam.

[Crossroads Inc.]

I am reminded of an infamous quote in regards to all of this:

For the foreseable future, the most effective way of hurting or eliminating someone with a Chemical laser is to Drop it on them"

[Winston Blake]

The solid state laser is superior as an overall weapon, because those chemicals the free electronic laser uses for fuel are horrendously toxic, difficult store, and are required in huge quantities.

Correct me if i'm wrong, but you seem to be confusing free-electron lasers with chemical lasers. ABL and the THELs weren't FELs. It's funny, i haven't seen anything, besides this article, about how FELs compare to solid-state or chemical lasers. Given that it's basically a particle accelerator that happens to produce laser light i'd expect them to be pretty massive and unwieldy, probably only useful for fixed bases and the future electric ships.

[Admiral Valdemar]

FELs don't use chemicals and are run entirely electrically if need be. The only reason chemical lasers exist is because the hazardous chemicals used produce a fair amount of juice per volume, but are otherwise too much hassle. The advantage of the solid-state, diode laser is ruggedness and simplicity with high-efficiency. The FEL has the advantage of being tunable to any frequency and dealing with quite high power levels.

[rhoenix]

FELs don't use chemicals and are run entirely electrically if need be. The only reason chemical lasers exist is because the hazardous chemicals used produce a fair amount of juice per volume, but are otherwise too much hassle. The advantage of the solid-state, diode laser is ruggedness and simplicity with high-efficiency. The FEL has the advantage of being tunable to any frequency and dealing with quite high power levels.

That's a quite concise and thorough explanation. Thank you very much for that.

Now, if I get told to look this up, I'll understand, but would an X-Ray laser be more feasable as a free-electron laser, or as a solid-state laser? From what little I know, I would theorize that the template for a free-electron laser would be used, altered for the different type of radiation.

[Sea Skimmer]

Yeah I confused myself into thinking there where only two kinds of lasers

[Neko_Oni]

That's a quite concise and thorough explanation. Thank you very much for that.

Now, if I get told to look this up, I'll understand, but would an X-Ray laser be more feasable as a free-electron laser, or as a solid-state laser? From what little I know, I would theorize that the template for a free-electron laser would be used, altered for the different type of radiation.

Isn't the difficulty with x-ray lasers the fact that there's no such thing as an x-ray mirror? Or do FELs get around the mirror requirement? (Can't see how but I not too good on laser optics).

[WyrdNyrd]

The only way of creating an X-ray laser I've ever heard about, involves detonating an nuclear bomb.

The problems of practicality inherent in this solution are left to the imagination of the reader...

[rhoenix]

The only way of creating an X-ray laser I've ever heard about, involves detonating an nuclear bomb.

Right, this wouldn't be a weapon one would want for home defense.

However, I am still curious as to the beam itself - solid-state, or free-electron, or would this be a different mechanism entirely?

[Admiral Valdemar]

Theoretically, you could produce a concentrated X-ray laser using the FEL technology (there's no diode that emits in X-ray as far as I know, and X-ray machines work via high-voltage being applied to metal), but this is still beyond us right now. Gamma rays may even be possible too, though for a weapon, they'd be mainly for anti-organic work due to the penetration of the beam doing little to armour (think directed neutron bomb).

[rhoenix]

Theoretically, you could produce a concentrated X-ray laser using the FEL technology (there's no diode that emits in X-ray as far as I know, and X-ray machines work via high-voltage being applied to metal), but this is still beyond us right now.

Well, apart from the aforementioned nuclear bomb triggering the beam, as WyrdNyrd mentioned. True, this is entirely hypothetical (and in some cases suppositional) thinking, but I figured I'd ask out of curiosity.

Gamma rays may even be possible too, though for a weapon, they'd be mainly for anti-organic work due to the penetration of the beam doing little to armour (think directed neutron bomb).

Heh, I was just reading on other possibilities for lasers, and gamma-ray frequency lasers were next on the list. However, I didn't know that it would be like a directed neutron bomb - I'll have to do a bit more reading now.

Microwave-frequency lasers are another possibility, though they would have the same restrictions you mentioned about armor.

[kheegster]

Theoretically, you could produce a concentrated X-ray laser using the FEL technology (there's no diode that emits in X-ray as far as I know, and X-ray machines work via high-voltage being applied to metal), but this is still beyond us right now. Gamma rays may even be possible too, though for a weapon, they'd be mainly for anti-organic work due to the penetration of the beam doing little to armour (think directed neutron bomb).

Current FELs have hit UV ranges, and work on the next generation of X-ray FELs are in progress:

Taking free-electron lasers into the X-ray regime

Feature: July 2003

Imagine making movies of chemical reactions, watching surfaces melt in real time or taking photographs of individual molecules. These are just some of the ambitious goals that researchers have set for powerful new X-ray "free-electron lasers" that are currently being developed at the Deutsches Elektronen Synchrotron (DESY) laboratory in Hamburg and the Stanford Linear Accelerator Center (SLAC) in California. These facilities will generate intense X-ray laser light ranging from wavelengths of 10 nm down to as little as 0.1 nm. With pulses lasting just 50-500 femtoseconds, the lasers will let researchers directly study how atoms change position and how chemical bonds form.

Scientists and engineers at DESY have so far made remarkable progress. In autumn 2000 they finished building a free-electron laser that produces vacuum-ultraviolet light down to wavelengths of 80 nm. The laser has already produced its first scientific results in a study of how clusters of xenon atoms interact with intense femtosecond pulses of ultraviolet light. It is now being upgraded into a full user facility that will, by late 2004, produce light with a wavelength of just 6 nm.

By the start of the next decade, the lab hopes to have completed a fully functioning X-ray free-electron laser that can produce light with a wavelength of 0.1 nm. The laser will form part of the ambitious -3.5 bn TeV Energy Superconducting Linear Accelerator (TESLA) facility that will also be used as an electron-positron collider. Although the original plan was for the laser and collider to share the same accelerator, they will now be run as separate projects.

Designing X-ray free-electron lasers requires three groups of scientists to join forces and focus on a common goal. Specializing in accelerators, synchrotron radiation and lasers, each group views these new facilities as a natural development in its respective field.

Synchrotron scientists, for instance, see X-ray free-electron lasers as a way of continuing the almost exponential growth in the intensity of radiation obtained from synchrotron sources over the past 50 years. The new lasers will deliver a peak "brilliance" that will be some eight orders of magnitude higher than the current synchrotron sources.

Laser physicists, meanwhile, have long sought to extend optical laser technology from the visible into the X-ray region. Although the radiation from a free-electron laser is similar to that obtained from conventional optical lasers - featuring high power, narrow bandwidth, femtosecond pulses and diffraction-limited beam propagation - there is one big difference. Free-electron lasers can be continuously tuned over a wide range of wavelengths, rather than having to operate at a fixed frequency or over a very narrow range.

Finally, X-ray free-electron lasers present a new challenge for accelerator scientists, who have to create electron beams of exceptionally high quality. The systems are also more difficult to design than existing free-electron lasers operating in the infrared, visible and ultraviolet regime, as these are based on short linear accelerators or synchrotron-radiation storage rings.

In the July issue of Physics World Elke Plönjes, Josef Feldhaus and Thomas Möller from the Hamburger Synchrotronstrahlungslabor (HASYLAB) in Germany describe the huge scientific potential of free-electron lasers that operate at X-ray wavelengths.

Microwave-frequency lasers are another possibility, though they would have the same restrictions you mentioned about armor.

You want an energy weapon to deliver a maximum amount of energy per photon, hence a maser would be utterly pointless as it would deliver orders of magnitude less energy. In any case, maser technology pre-dates laser technology, so it's not exactly cutting edge sci-fi technology.