I thought I would write my first real blog post on the question I get asked most frequently these days, which is some version of "When are you graduating?" My answer varies, but it usually it ends up as some half-joking response that sounds a lot like never. But that's not true, I will graduate, and sooner rather than later.
So what's going on? Pardon the nerdiness that follows, but here's the thing. In 1998, these guys up at Dartmouth College published a paper on a what's called a Smith-Purcell Free Electron Laser. Smith and Purcell are these guys who back in the 50s predicted and showed that an electron scooting past a wiggly piece of metal gets encouraged to do a little wiggling of its own, which in turn makes it radiate some light.
Turns out that if you can squeeze a bunch of electrons together and scoot them really close to a wiggly piece of metal at the same time they actually start to wiggle together. Like at a baseball game, when you're down to the last out and the batter has two strikes, the crowd will start this slow clapping to freak him out. Nobody is really leading the clapping but after a while everybody is clapping together and it gets louder. It's the same with my little electrons, sort of. Once they start wiggling you can get them all to wiggle together and the the light given off (like the clapping) gets brighter (louder).
The wiggling behavior was described by Smith and Purcell. The wiggling together is what makes it a laser, and they are free electrons because they're scooting along inside a vacuum and not tied down to an atom like electrons usually are. So you've got a Smith-Purcell Free Electron Laser.
Except that we don't have one. We have all the parts but it ain't happening. And so we've been working on the math a lot, and it turns out that the speed of the clapping of our little cheering electrons is different in the theory than in the Dartmouth experiment. They measured the speed of the clapping carefully (it's the color of the light that comes out), and we're pretty sure we've got the theory part down. But they don't agree. And so far our version of the experiment doesn't work. When it does, we have lots of ideas for testing the theory in ways the Dartmouth group couldn't try to do very easily.
So that's what I am up to, getting the experiment to work so I can test our theory. I need to squeeze the electrons together very tightly and put them really close to this metal grating (it's just a little piece of aluminum that we cut long grooves into with a saw to make the surface wiggly). And we need a lot of electrons to get it going.
So simple. So not working.
The little picture shows the grating. The grooves are on top of the piece shown, but they are really small (think width of a hair) so they are hard to see.
If it really doesn't work, then I have to convince my committee that I have contributed enough to theory and to the building and planning of the experiment to graduate. I think I can sell them on that, and that's why I say I am graduating sooner rather than later. But everything would go a lot smoother if I could just get my little electrons to cooperate!