Why are maser weapons still mostly science fiction?

[Eleventh Century Remnant]

Basically, what the title says. I'm doing some alternate- history writing at the moment, and they seem so glaringly obviously good an idea, I know I'm missing something that should be spectacularly self evident by failing to figure out how they managed not to happen.

Very recently there have emerged things like the 'pain ray' Active Denial System, 2-2.5mw in a narrow arc at a frequency absorbed by the outer layers of the skin, and an attack mode for AESA- very late model phased array radars- but these are just microwave weapons, as far as I can tell they are not actually laserlike, stimulated coherent emission.

Masers actually predate lasers, they're easier to achieve, but I don't believe any military application for them was ever sought outside science fiction. Which is strange, because an extreme but basically radio frequency, continuous, line of slight lightspeed beam weapon could have changed the world- especially if we're looking at the first prototypes being tried in the late fifties.

What, if any, are the physical reasons this wouldn't work? Should it have?

[Imperial528]

My guess is that like the laser, the maser is expensive and fragile. Conventional weapons can be expensive, but they need to be robust, and I'm sure that any military-grade maser would have much higher costs than the already expensive civilian masers.

[Bottlestein]

What, if any, are the physical reasons this wouldn't work? Should it have?

Every type of energy attenuates in atmosphere. Masers use microwaves, which attenuate a lot. (The atmosphere having a fuckton of water vapor, as well as diatomic molecules in the form of nitrogen and oxygen). Given the power consumption, lasers are (for military ranges), orders of magnitude more efficient.

The ADS does not use lasers simply because it does not fit the mission profile - you don't want to blind or kill the people, just get them to move away. Since you will be close to the target anyway, masers are suitable. Even then, note you have to mount the power supply on a humvee, and recharge it after a mission.

[Simon_Jester]

First problem is the same one underlying compact lasers and so many other SF technologies we don't have: the lack of suitably compact power supplies. A kilowatt-range microwave beam could be used as a weapon if it were tight enough, but you'd need a kilowatt-range power supply: not conveniently man-portable. It's not competitive with a kilowatt-range kinetic energy weapon (such as an automatic rifle) A megawatt-range one would work as a heavy weapon (for some purposes)... but again, the scale of power supply required is prohibitive compared to a comparably energetic kinetic weapon (a chaingun or artillery piece).

Second problem is antenna size: microwaves cannot be easily focused without fairly large components: EM waveguides come to mind. Phased array radar antennae are similarly quite large, too large to be man-portable, and a vehicle that can carry a maser can carry other, more potent weapons as well (such as a missile launcher).

Third is, yes, atmospherics: many bands of microwaves do not carry well, and carry especially poorly under certain conditions. On top of that, they are relatively easy to shield against: any armored vehicle will act as a Faraday cage, for instance. Until you get up into energy ranges and antenna sizes that allow (theoretically) the ability to physically melt through obstacles, microwave weapons are not very versatile. And at that point, they are so large that they are not competitive with kinetics.

So I guess it all really boils down to the same problem: the lack of compact power supplies and the physical constraints of building small microwave sources making masers and other microwave weapons noncompetitive with kinetic weapons.

[Eleventh Century Remnant]

Parts of the microwave band are very readily absorbed, but there are windows- in the high centimetre range for a start, which is still considered microwave, less so in the one to twenty micrometre range- that are acceptable for sensors, comms and (theoretically) orbit-to-surface beamed power.

With any kind of sense behind the project at all (of which there are, I admit, no guarantees), the weapon would have been designed around a frequency that the atmosphere passes relatively easily; spot size would be larger than for a comparable laser, but compared to not being able to do it at all, a massive improvement.

Chemical masers are fairly straightforward, I thought; the chemistry needed to get a population inversion isn't that violent or toxic; am I being too optimistic in regarding it as a straightforward outgrowth of radio technology?

Oh, Simon; the application I'm thinking about is naval air defence, essentially replacing a gun turret and mounted on a turboelectric drive warship; a natural choice for the project precisely because it would have huge amounts of electrical power available, tens of thousands of shp- well into the megawatt range, and given the nature of the mounting a twenty or thirty foot dish is not out of the question.

Fire control may be the primary problem, and also the main driver behind this; early guided missiles, around the time when the maser first appeared, were a far from sure solution- an improvement over AA guns, certainly, but nothing like as effective as they later became. The theoretical accuracy of a maser, using the brute force solution against relatively fragile targets, could make up for a multitude of difficulties.

[Bottlestein]

Parts of the microwave band are very readily absorbed, but there are windows- in the high centimetre range for a start, which is still considered microwave, less so in the one to twenty micrometre range- that are acceptable for sensors, comms and (theoretically) orbit-to-surface beamed power.

With any kind of sense behind the project at all (of which there are, I admit, no guarantees), the weapon would have been designed around a frequency that the atmosphere passes relatively easily; spot size would be larger than for a comparable laser, but compared to not being able to do it at all, a massive improvement.

Chemical masers are fairly straightforward, I thought; the chemistry needed to get a population inversion isn't that violent or toxic; am I being too optimistic in regarding it as a straightforward outgrowth of radio technology?

Oh, Simon; the application I'm thinking about is naval air defence, essentially replacing a gun turret and mounted on a turboelectric drive warship; a natural choice for the project precisely because it would have huge amounts of electrical power available, tens of thousands of shp- well into the megawatt range, and given the nature of the mounting a twenty or thirty foot dish is not out of the question.

Fire control may be the primary problem, and also the main driver behind this; early guided missiles, around the time when the maser first appeared, were a far from sure solution- an improvement over AA guns, certainly, but nothing like as effective as they later became. The theoretical accuracy of a maser, using the brute force solution against relatively fragile targets, could make up for a multitude of difficulties.

At that range of wavelengths, they are trivial to defend against (Frequency is inversely proportional to wavelength, remember.). Guided missiles are straightforward to "Faraday Cage", see Simon's reply, - they already are hardened against cosmic ray scatters which include lots of microwave range frequencies as you get higher in the atmosphere.

Simon's point about antennae size is also important - the phased array radar is a good ersatz model. That has the amount of scanning azimuth you want - air defense is pointless if it's on a fixed vector and you have to turn the ship - and the size of those dishes are way more than thirty feet. For a microwave - you need on the order of 100 times greater characteristic length if you want to use a beam-forming mechanism to scan. You could mount one single frequency emitter and turn the apparatus mechanically, but for AA defense you would need extremely fast motors that handle massive weights - and if you have motors that do that reliably you're better off mounting a 50mm autocannon

As for sensors and comms - this ties in to your radio technology question: Masers are not outgrowths of radio technology - masers use higher order molecular transitions than radio. "Population Inversion" simply refers to the Stat. Mech. process by which the photons are released - it does not say anything about the initial energy requirements for the inversion process, or the ground state energy of the system. All this means masers require more than an order of magnitude input energy than radio. So yes, masers can be used for sensors and comm work, but its more energy efficient to use radio - and we do!

[Simon_Jester]

Parts of the microwave band are very readily absorbed, but there are windows- in the high centimetre range for a start, which is still considered microwave, less so in the one to twenty micrometre range- that are acceptable for sensors, comms and (theoretically) orbit-to-surface beamed power.

With any kind of sense behind the project at all (of which there are, I admit, no guarantees), the weapon would have been designed around a frequency that the atmosphere passes relatively easily; spot size would be larger than for a comparable laser, but compared to not being able to do it at all, a massive improvement.

What's problematic is finding a chemical that works in the right frequency range- like the chemical dyes used in conventional lasers, you only get specific frequencies from specific substances, and the technology isn't tuneable.

Oh, Simon; the application I'm thinking about is naval air defence, essentially replacing a gun turret and mounted on a turboelectric drive warship; a natural choice for the project precisely because it would have huge amounts of electrical power available, tens of thousands of shp- well into the megawatt range, and given the nature of the mounting a twenty or thirty foot dish is not out of the question.

I suspect you'll find that the closest analogy to this in real life

Another problem is going to be spot size: long-wavelength beams diffract quickly. With one-centimeter wave hardware on a ten-meter antenna, for instance, the diffraction limit restricts you to a conical beam with a spread angle of about 1.2 milliradians- against a target several kilometers away, you need a ridiculous amount of beam power to do any real damage. Turboelectric drive from a World War era battleship such as USS Maryland (ah, Maryland, my Maryland! ) gives you ~20 MW if all power from the drive is dedicated to the task, and that isn't going to cut it after efficiency in the maser system is factored in.

Micrometer-wave hardware gives you better figures, but there are real questions in my mind about whether that's achievable using chemical masers, as opposed to something like an Nd-YAG laser. Even then, power efficiency is a real issue: beam power is typically only a modest percentage of applied power.

Masers just aren't lasers; they're similar conceptually in terms of the underlying physics, but they're not really all that much simpler in concept, and microwaves are so different from near-optical wavelengths in behavior that there's little comparison.

Fire control is actually a much smaller problem, in my opinion. Remember that many early AA missiles were beam-riders; they were designed to be launched by a ship that would then fire a centimeter-wave microwave beam at the target to provide illumination for the missile's passive sensors to home in on. The real problem isn't fire control, it's that with centimeter-wave applications diffraction makes putting adequate power on target impractical- while with sub-millimeter waves where you can theoretically put a megawatt or more on target from a shipboard power supply, you're really in the market for a laser again.

[Bottlestein]

Micrometer-wave hardware gives you better figures, but there are real questions in my mind about whether that's achievable using chemical masers, as opposed to something like an Nd-YAG laser. Even then, power efficiency is a real issue: beam power is typically only a modest percentage of applied power.

Actually, as a point of interest, what sort of efficiencies have they got to in chemical masers?
Does it still use the Zeeman transitions as the "pumping" method to get to inversion? In that case - efficiency must be terrible since our ability to make magnetic fields precisely sucks up lots of power.

During my undergrad, "state-of-the-art" was a dual noble gas (helium isotope & argon?) Zeeman maser - for permanent electric dipole measurements !

[Void]

MASERs would have changed nothing.

Blowing stuff up with directed energy is hard, even stuff that is inherently vulnerable to being blown up. The technology to make DEW work simply didn't exist when MASERs were first discovered, and not for lack of trying (the U.S. Airforce at one point considered lasers a viable replacement for guns on future fighters, in 1975). It still isn't practical today.

The long wavelength of microwaves is a huge barrier. Getting enough energy on target is one of the biggest challenges facing DEW and making your wavelength thousands of time larger doesn't help this. Beyond the Death Ray application (which lasers have a stranglehold on) just about any possible application of MASERs is already being filled by conventional RADAR. There just isn't any need for them.

[Sea Skimmer]

What, if any, are the physical reasons this wouldn't work? Should it have?

You think Masers are easier then lasers? I don't know what would have given you that idea. Your entire premise seems to be based on this and it’s got no basis in fact. Radar predates lasers by decades sure, but early radar is more like a flashlight then a laser beam. Focusing microwave energy into a laser like beam is virtually impossible, and that’s despite radar development having been driven to reduce beam width since it was invented. AESA was a big step towards this, but we'd need ANOTHER one or two leap forward like AESA in turn to make a maser work, but no technology is even on the horizon which would do this.

Now you could make a destructive microwave weapon today, its just it would need an antenna of several hundred square feet and a transmitter that can output 35-100 GW pulses a few thousand times a minute. The result would be a weapon you need a destroyer to haul around with an a effective range of a couple miles that cost a few billion dollars. Its not worthwhile. The electronic attack modes for AESA radars today are based on disruptive waveforms screwing with the enemy reception, they don't really damage anything.

[Sea Skimmer]

Well I misspoke some what, this laser pumped radio frequency concept might be what is needed to make the massive leap in wattage we need for destructive sort of laser like HPM weapons possible though little more has been said about it
http://www.aviationweek.com/aw/generic/ ... 2207p1.xml

For the moment though HPM is still only useful against unprotected electronics at close range, and while you can have a irectional antenna you can never totall suppress the sidelobes and backlobe. As seen blow, when you transmit a radio signal you get a complicated shape, not a single tight beam
http://www.astronwireless.com/img/aa_rad2.gif

[Simon_Jester]

Actually, as a point of interest, what sort of efficiencies have they got to in chemical masers?

I truly do not know. Sorry.

[Bottlestein]

^ I don't mean the actual percentage - but more just: Do they have a new pumping mechanism other than the Zeeman transition?

[Simon_Jester]

I don't know that either, though, and from the sound of it you know at least as much about masers as I do, probably more. You're as qualified to research the subject as I am.