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Sometimes they were called “blasters, ray guns, or even zap guns,” although that last one was sometimes also used for the “stun gun” the puny sibling to the much mightier Death Ray. Asimov had one called a “Disinto.” Hugo Gernsback was sure they’d be either radio waves or powered by radium. Fritz Leiber imagined the “fission pistol,” that had all the nuclear reactions in the gun going in the same direction. A. E. van Vogt used light to “conduct” nuclear reactions to the target, at least on the Space Beagle. In Slan, it was just raw atomic power. Once in a while the death rays were “sonic.” More frequently they were “electron guns” which actually exist in television sets, but for something else entirely (though one may argue that TV is something of a stun device). H. G. Wells began the whole thing with the “heat ray.”
And we wanted them, maybe as much as we wanted to go into space (which is maybe why I wasn’t as interested in the things as my fan boy brethren). And it wasn’t just us. During WWII, the U.S. Army’s Aberdeen Proving Ground offered a standing reward to anyone who could demonstrate a death ray capable of killing a tethered goat. Britain’s Air Ministry put up a similar prize to the inventor whose ray could kill a sheep at a range of a hundred yards. There’s a story that radar was invented partly because of a 1934 rumor that Germany had invented a microwave-based death ray.
Because hell, nobody messes with you if you’re packing a Death Ray.
A Little Knurdly Background on the Laser
A lot of people link Einstein to the Atom Bomb because of the E=MC2 thing. This is a pretty fundamental misunderstanding, because mass/energy equivalence is a general property of nature. Every chemical reaction also has E=MC2 going on; it’s just that the change in mass from a chemical reaction is too small to measure, while for nuclear reactions the change is measurable.
No, the go-to guy for the Atom Bomb was Enrico Fermi; Einstein’s primary contribution to the deal was that he wrote that famous letter to Roosevelt, ironically, a political contribution that drew on Einstein’s celebrity status, but had little to do with Einstein’s contributions to science.
Lasers, however, are a different thing entirely.
In 1916, Einstein wrote a letter to Michael Angelo Besso that included the poetic line, “A splendid light has dawned on me about the absorption and emission of radiation.” He documented his insight in a paper that was published the following year, describing the absorption and emission of photons by atoms in a gas, but which went further and described a third process, stimulated emission.
This insight of his was an “Einstein Special.” From the large-scale macroscopic properties of gases, Einstein deduced a phenomenon that occurs at very small, quantum mechanical scales. This is not something that just leaps out at you from staring at some equations for a bit. It’s one of those things that makes some people think that Einstein had God’s phone number (although, realistically, God sometimes made prank calls, like that “God does not play dice with the universe” thing. It turns out that, not only does God play dice, He uses dice with so many sides to them that they might as well be ball-bearings. Also, He uses a lot of dice).
The stimulated emission phenomenon says that, if you have an atom or molecule in an excited state of a particular energy, and you hit it with a photon of exactly that same energy, you will stimulate the emission of energy by the atom or molecule. So now you have two photons, of exactly the same energy. Moreover, they are identical in all other respects, same phase, polarization, everything. They are coherent.
The closest thing I can come up with by way of a large, mechanical analogy is, suppose you have a ledge on a pool with some ball on it, and a wave that is exactly the same height as one of the balls slaps it off the ledge and it falls into the water. And only a wave of the correct height will do that, and when it does, the ball makes another wave, exactly the same as the first one.
Yeah, I know. Crummy analogy. But it was the best I could do.
So anyway, suppose you had a huge number of these excited atoms, and you sent a single photon into the mass of them. Bingo! Now you’ve got a chain reaction, with each photon setting off two more, and so on and on. That’s the “Amplification” part of “Light Amplification by Stimulated Emission of Radiation (LASER).” All very cool. The only problem is, “how do you get all those excited atoms in a mass?”
Suppose you try to do it by shining a light on them. At first, you’re creating excited atoms, but as time goes on, more and more the atoms you are hitting are already excited, and whoops, you’ve just stimulated them into giving photons. In fact, you can never get to the point where you have more atoms amplifying the photons than absorbing them. I think that’s actually part of the thermodynamic argument that Einstein was using in the first place.
Well, it nevertheless turns out that there are ways to do it. But it took almost 40 years after Einstein’s “splendid light” for someone to do it. And man, what a Rube Goldberg device it was.
The trick of getting “amplification through stimulated emission” is the “inverted population,” (it’s a Boltzmann thing) having enough excited atoms or molecules in your mix that they predominate, rather than having the “ground state” atoms or molecules absorb your photons and shut it all down.
The first gizmo that worked, the maser, got its inverted population by separating out the excited molecules. Then this guy, Townes, obviously obsessive about the matter, got even more clever. He had the idea of using a “metastable state.”
I’ve been talking as if there were only two states, a ground state and a single excited state. But atoms and molecules actually have a lot more quantum states than that. And some of them are what’s called “metastable,” which just means that they take a long time to decay, relatively speaking.
If you hit an atom with enough energy to put it into a state higher than the metastable state, say state 2, or 3, or whatever, with the metastable state being state 1 and ground state being 0, then it will quickly decay from the higher states, but will linger in the metastable state. Presto, an inverted population.
Then Townes’ brother-in-law (okay, it was the respected Bell Labs’ physicist Arthur Schawlow, but he’d married Townes’ sister) had the idea of putting mirrors at the two ends of a lasing cylinder. This increased the path length of the photons going through the laser medium, but only in the direction at right angles to the mirrors. Moreover, if properly adjusted, the mirrors could be used to “tune” the laser to a single frequency, just like a microwave cavity. Finally, because Bell Labs was very big on solid state physics in those days, Schawlow suggested using solid state materials for the lasing medium.
By this time, Townes’ work had attracted attention and a lot of other bright guys had been added to the mix, guys like Gordon Gould, Nikolay Basov, Aleksandr Prokhorov and Theodore H. Maiman. Some of them had overlapping ideas, some had novel ideas, and pretty much all of them got involved in priority, patent, and other kind of squabbles over the next years and decades. They also won a lot of prizes, made a lot of money, got famous, the usual, and there were plenty of it all to go around.
The result was the first laser, made by Ted Maiman at Hughs Research Labs, which used a synthetic ruby as the lasing medium and was “optically pumped” via a flash tube wrapped around it. Within months, the Iranian physicist Ali Javan, working with William Bennet and Donald Herriot, made the first gas laser using helium and neon. Laser diodes were developed within two years, though we had to wait into 1970 for some that worked at room temperature.
When the laser was first announced, practically every news story referred to it as “a solution looking for a problem.” That was about as ignorant a statement as has ever been made. A strong, monochromatic, coherent light source? Man, there were scientists and engineers who had been making do with crappy things like sodium light through a pinhole for decades. Holography had been invented in 1947, but it needed lasers to make it work. There’s a patent that was filed in 1961 using a technique called a “two-dimensional fourier transform” (ask me how I knew to do a search on that phrase sometime) to interpolate between images in an animated film, that calls for a “small, coherent, monochromatic light source.” God only knows how long the inventors had been sitting on that one, waiting for the laser to be invented.
But that wasn’t the really big deal. No, the first thing we all heard about lasers doing was punching holes in a diamond. And fan boys everywhere went, “Hurrah! We have a Disintegrator! Or a Death Ray!” Frankly, we didn’t much care which. ‘Cause the ghosts of Hugo Gernsback and Amazing Stories were yelling, “Hot damn!”
(And yes, Gernsback didn’t technically die until 1967, and Amazing Stories has died and been resurrected so many times I’ve lost count. But their ghosts still walked the land in 1961, because you don’t have to die to be a ghost.)
The New Ray Gun in Town
So when lasers were announced in 1960, and we all heard that one could punch a hole in a diamond, or a metal plate, well, in a lot of manuscripts the word “blaster” got crossed out and “laser” got inserted.
Trouble was, they didn’t work like that. They were made of light.
Remember all those tales about the magic spell that is deflected by the mirror? Well, dang, you could do that to a laser, it turned out. Also, fog, smoke, not so good.
Moreover, they were damned inefficient. You had to put in kilojoules to get out joules. Later, some of them got more efficient, and some, like the CO2 laser, could be pumped by chemical reaction. I read about a 4000 watt laser in the late 1960s, from Raytheon, as I recall. It was powered by a gas turbine, basically a jet aircraft engine, and it was chemically pumped. But notice, a jet engine to pump a laser that has the output of—a couple of hair driers. (I’m talking continuous power here, the pulsed ones can put out more power than the whole U.S. power grid—for a picosecond).
CO2 lasers can get up to pretty high efficiencies these days, about 20% and some of them are upwards of a hundred kilowatts. But consider, to get water from room temperature (about 20 degrees C) to boiling, you need to put in about 330 kilojoules into it for every kilogram (about a half gallon). The heat of vaporization of water is about 2260 kilojoules per kilogram. So to boil a half gallon of water, you need around 2600 kilojoules. It takes even a 500 kilowatt laser 5 seconds to boil a half gallon of water.
You’re also boiling four times that much water in your cooling system, incidentally.
Yeah, it’ll hurt you plenty quick if you stick your hand in a laser beam that powerful, but we’re sure not in disintegrator ray territory. Not by a long shot. Was James Bond about to get his testicles cut off and be severed in two? Probably not; the thing would have set his clothing on fire, though.
So the “laser death ray” future turns out to be one that dated faster than just about any other sci-fi gimmick ever. Still, the “phaser” was a brilliant neologism. It took the “-aser” suffix, which still has some mysterioso power, even now, and added, well, what? More mysterioso. Something to do with “phase” probably. So soon it was “phaser” and “plasma rifle” and “hypervelocity rail gun,” as everyone took a quick swing back into fantasy land, which is what Space Opera is all about anyway. Nobody took the Laser Death Ray seriously after that.
Except, it turns out, for the Department of Defense. I think they’re still pushing space-based laser missile defense systems. These have the positive aspect of being largely harmless hogwash, good for tech pork and not much else. Physicists still love them some laser macho, and between the space lasers and attempts to use lasers to light fusion reactions, they get to keep playing, I’ve Got the Big One.
Dr. Evil: You know, I have one simple request. And that is to have sharks with frickin’ laser beams attached to their heads! Now evidently my cycloptic colleague informs me that that cannot be done. Ah, would you remind me what I pay you people for, honestly? Throw me a bone here! What do we have?
You can also use an ultraviolet laser to conduct a taser current (there’s that –aser mojo again). Look ma! We have a stun gun!
Too bad all you have to do is wear a wetsuit or a rubber raincoat to be immune. There’s a reason why real tasers have little sharp barbs at the end.
Then there was the gamma laser.
The Gamma Laser
In July, 2006, I saw Sharon Weinberger on the Daily Show, touting her book, Imaginary Weapons. The book is her expose of weird DOD projects involving fringe science, etc. Amid the talk about psychic espionage and mind control rays, she mentioned the “atomic hand grenade” and hafnium. Woo, talk about a stab from the past.
In the early 60s, when I was barely a teenager, there was an article in Scientific American about the gamma ray laser, graser, gaser, call it what you will. I read the article, talked about it with my science buddies, then put it in the back of my mind for a while. Then I went to RPI and joined the Rensselaer Engineer, the school’s student engineering magazine, and wrote a lot of articles, so many that some had to be under pseudonyms. One of them was on the gamma laser.
RPI’s library at the time was under fire for being inadequate, but it was good enough to get me a copy of the paper by Lev Rivlin describing the gamma laser, and I was young and cocky and indulged in a bit of speculation of my own in the article.
The gamma ray laser does all usual laser stuff with energy shells in the atomic nucleus rather than electrons in the outer atomic shell. Also, because gamma rays are more energetic than regular light, you get a problem called “dynamic line broadening.” What happens there is that, because gamma rays pack a lot of energy, they have a “kick” that causes the emitting nucleus to recoil. But that recoil lowers the energy of the emitted photon, so it’s no longer at the right energy to stimulate the emission of the next atom. Lasing action then becomes very inefficient.
What Rivlin proposed was to make use of the Mossbauer effect. In the ME, the atom is embedded in a crystal matrix, and said crystal matrix allows the atom to vibrate only at certain fixed energies, so-called “phonon resonances.” That’s another quantum effect. If the “kick” from the gamma emission doesn’t match one of these resonances, then the entire crystal matrix is what rebounds. The difference in masses between a macrocystal and a single atom is so great that all the energy goes into the photon and essentially none is lost to the matrix.
That left two problems for the gamma laser. The first is how to get the inverted population. The second is how to make an “infinite medium” i.e. get a long enough path in the lasing medium to obtain a lot of amplification. In most lasers, you put mirrors at both ends to create a “long path,” for the photons and lasing medium to do their thing.
Rivlin suggested that with a properly metastable isotope of high purity, only a few centimeters would constitute an effectively long path and no mirrors would be necessary. Others have suggested specially created crystal diffraction mirrors (which can reflect even low energy gamma rays if they are properly tuned to the correct frequency). In my little article, I suggested that low angle reflection might be sufficient, so you’d have maybe dozens of rods arranged in a polygon, each only a couple of degrees off the next, with a low angle metal surface in between. A similar trick is used for x-ray astronomy.
Pumping was something else again. I don’t think that either Rivlin or the Scientific American article suggested nuclear transmutation via neutrons, but that was something that I also speculated about.
Nothing much happened on the nuclear laser for another decade or more, but it became a hot topic for a little while during the SDI (“Star Wars”) period. There was even an underground bomb test that was briefly touted as having achieved amplification. Later that result was said to be a measurement error by some, while others hinted darkly at fraud. It appeared like the design was an attempt to “brute force” the matter (and there’s no brute like a thermonuclear bomb), but I could never figure out how they were going to solve the line broadening problem, and, by all reports, they didn’t.
In 1987 there was an experiment reported involving a metastable isotope of tantalum (Ta180m) exposed to high energy x-rays, with the result being a fluorescence that seemed to indicate some quantum stimulation was occurring. For a variety of practical and theoretical reasons, a lot of attention was then given to hafnium-178m2, the second metastable isotope of hafnium, having a half-life of about 30 years.
In 1999, a University of Texas group announced a stimulated emission result from hf178m2, triggered by a dental x-ray machine. It seemed like the Holy Grail was coming into view.
But then the criticisms began, the worst of which being that no researcher has ever replicated the original result, not even one of the UT group. Also, the original experiment did not have a control, so WTF?
Then came theoretical calculations that said that the process shouldn’t have actually reached breakeven, but a practical consideration was more important. The isotope does not occur in nature and is the product of an accelerator, which makes it hugely expensive. The idea of making a weapon out of it is ludicrous.
Well, so much for that.
But, as I say, I follow the field generally, and there is another story out in the hinterlands:
United States Patent 4,939,742 Bowman July 3, 1990 Neutron-driven gamma-ray laser
A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 .ANG. when subjected to an intense neutron flux of about 400 eV neutrons. A 250 .ANG. thick layer of Be is provided between two layers of 100 .ANG. thick layer of .sup.57 Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux .sup.57 Co becomes .sup.58 Co by neutron absorption. The .sup.58 Co then decays to .sup.57 Fe by 1.6 MeV proton emission. .sup.57 Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the .sup.57 Fe from the .sup.57 Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.
This is very similar to some of the speculations I had back in 1969, but it gets around a big problem I noticed. I thought that the target nucleus would have to be of low atomic weight (low z) because otherwise the Compton effect would be too parasitic to allow amplification. This patent suggests that the production of the excited nucleus can be made to eject the atom from its normal substrate into a medium (in this case, beryllium foil) that is very low z, where the actual lasing would occur. I was thinking thermal neutrons, but the patent uses higher energy neutrons, so that’s how the recoil would occur. I also suspect that there may be some small angle gamma/x-ray reflection occurring in the device as well.
The patent holder, Charles Bowman, is someone I’ve noticed before; he was one of the scientists analyzing the Yucca Mountain nuclear waste site and who described a scenario where there might be a (low yield) nuclear explosion from the nuclear waste. That particular bit of work fit in with some other speculations that I’ve had, about highly moderated nuclear supercritical reactions, something that’s about half-way between a so-called “dirty bomb” and a real nuke. But you already know that.
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