Building a Better Phaser

For you geeks out there, thanks to Defense Tech for the link.

...The main hitch early on was that ordinary lasers do too good a job at inducing ionization, which then makes the air opaque to the light beam. But more promising results have been achieved using lasers that emit extremely short pulses...

Just as Ackermann's paper was being published, an Arizona company named Ionatron demonstrated the use of laser-guided electric discharges in something it calls a "portal denial system," which can be set up in a corridor and switched on to prevent intruders from passing through. Three beams in this system create a virtual electric fence that spans the width of a hallway. Steve McCahon, Ionatron's executive vice president for technology and engineering, explains that the company's system demonstrated nonlethal levels of deterrence but "that doesn't mean you couldn't turn it up."

Are guns next? According to the boldly written claim on its Web site, "Ionatron intends to use our compact, non-lethal LIPC [laser-induced plasma-channel] technology to replace guns as the weapon of choice in close-range defense." McCahon confirms that "the thrust is extending range." Exactly how much range Ionatron has been able to achieve with such a weapon is being kept secret. And it's unclear whether the sophisticated lasers needed could ever be made very small. Still, it seems reasonable to anticipate that in the not-so-distant future, military or law-enforcement officers might be caught uttering the phrase "phasers on stun" in all seriousness.

Similar physical principles are behind a second Star Trek-like technology now coming into use, something called the "plasma window," which is the brainchild of Ady Hershcovitch, a physicist at Brookhaven National Laboratory. Hershcovitch conceived of the plasma window to serve in electron-beam welding, a technique used to fashion metal welds that are narrower and deeper than what can be accomplished with conventional tools.

The chief drawback of this technique is that the electrons used for welding must be accelerated in a vacuum (just like, for example, the electrons that light up the front of a television picture tube). Hence the objects being welded together must normally be placed within a sealed chamber from which the air has been extracted. With that constraint, one cannot make welds to, say, the deck of a battleship. Even for small work pieces, pumping down the vacuum chamber each time an object is inserted is time-consuming, making this form of welding rather costly.

To get around this difficulty, some have tried a variation of electron-beam welding that has the electrons accelerated in vacuum but the welding done at atmospheric pressure. Such systems rely on bulky, energy-hungry vacuum pumps to maintain the pressure differential between the source of electrons and the work piece. So they are awkward and costly to operate. What is more, the electron beam has a troubling tendency to spread out once it passes into the air, negating the fundamental advantage of electron-beam welding in the first place. Last May, Hershcovitch and colleagues at Acceleron, a company in Connecticut licensing his invention, described in the journal Physics of Plasmas how to sidestep these problems, making electron-beam welding that much more practical.

The trick is to send the electrons out of the welder through a window that is made up of nothing more than an electric discharge channeled through a length of ionized gas—that is, a plasma. The temperature of the plasma is searing (about 15,000 kelvins), so it can counterbalance atmospheric pressure even though its density is only two percent of normal air. The low-density plasma offers little resistance to speeding electrons passing through it, making it the perfect window for an electron-beam welder...

Perfect sense to me: if a sustained pulse increases the opacity of the air to the synchronized photons, simply use a train of millisecond pulse/ recovery cycles. There's probably an optimal number of cycles depending on the atmospheric conditions, too.

Of course if this was a .mil site it'd be classified. Academics talk about things, though. But even if they didn't, anybody going to the private contractor's site could figure out what was going on- or buy into it.