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Lasers are great. These little gadgets are responsible for business presentations, pinpoint targeting of bombs, reading the CDs in your CD drive, LASIK surgery, welding, and even the destruction of ICBMs. Well, the latter-most ability isn’t true, and “anti-missile” lasers aren’t in the clear yet, however, the advent of plasma mirrors has brought new life to the laser complex. Yes, that’s right Virginia, plasma mirrors. The problem with current mirrors is that, when high-powered laser beams hit the reflective mirrors, the high-intensity beam melts your mirror. To save the day, a few researchers (with a paper written on the science side of Ars Technica - NOTE: Please see for the technical details) have come up with an idea to use a new kind of mirror that won’t go to pieces on you.
Well, it won’t exactly go to pieces because plasma (free electrons) is already a huge hunk of electrons. Some of you (who are smarter than me about such things) have already said, “There’s no way to reflect that laser. The plasma will move, completely wrecking your ‘mirror’.” Aha! Here’s the ticket: You really can’t nail down the plasma to any specific shape, but when any old material is ionized into plasma, the plasma keeps the shape of its prior phase for a small amount of time. However, that’s OK, as the laser pulses in question don’t last more than a hundred femtoseconds long (10^-15 seconds). Hey, I wouldn’t want to be hit by a laser packing 10^18 W/cm^2 for ANY amount of time. 10 to the 18th. Holy crap. But I digress. The other piece of that is that the material about to be converted to reflective plasma has to have an incredibly smooth surface to take any stray shots out of the question.
Another potential wrinkle is that it will take too much off of the beam to ionize the mirror. This wrinkle is a minor one, not even worthy of laser surgery to get rid of it (pardon the pun). Ionization of matter begins at 10^14 W/cm^2, and since the laser in question is 10^18 W/cm^2, following the math, that’s only around 1/1000th of the total energy in the beam. Not a problem.
Apparently, there’s also a weird phenomenon that actually compresses the emission of light wavelengths from said plasma, making the color shift (like a Doppler effect or red-shift) in the bluish direction. Sounds like it would be cool to see.
So, in closing, flat surface, check.
Incredibly-powerful laser, check.
Plasma mirrors with some funky light properties!
I love Science…
Pictures courtesy of: Westwood Studios, Wikipedia, US Federal Government;
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star wars here we come