High Powered Lasers

Laser physics: Extreme light

Ed Gernster

Nature, 446, 16--18 (2007)

URL: http://www.nature.com/news/2007/070226/full/446016a.html

Every so often, I come across an article that really excites me. It makes me feel like running to the library and checking out 3 or 4 textbooks so I can learn more about the subject. These books usually sit on my shelves for a couple months, until I come across another article. I feel guilty about having 8 library books out at a time, so I trade in my first set for a different one, a little disappointed that I don't have the knowledge I was so excited about learning a couple months ago. Well, I think it's about time for a trip to the library.

This article blew me away. Ed wrote about the advances in laser technology that have taken place in the last 50 years, and about the new facilities under construction.

The first tid-bit that caught my attention was that an electric field of 8 x 10^18 V/m will make the vacuum boil. It will rip apart the pairs of virtual particles that pop into and out of existence. This is called the Schwinger limit.

Sounds exciting, but all kinds of neat things are supposed to happen when you probe the Planck length too. The exciting thing about the Schwinger limit is that experimentalists are only 3 orders of magnitude away right now. (For comparison, I think the people at CERN will still be 15 orders of magnitude away from the Planck energy.)

You hear about lasers all the time. What's so great about them? Nonlinear optics. "In the 1960s, the fact that early lasers were powerful enough to change the refractive index of the medium through which they travelled opened up fresh vistas in nonlinear optics." Todays lasers can acclerate all the electrons around them to relativistic speeds. The next generation will be able to do the same for ions.

What a neat idea! I could shine a laser on a block of metal on my desk and be able to probe relativistic interactions between charged particles.

Another really neat idea is that these lasers could produce accelerations the same order of magnitude as the gravitational accelerations in black holes. Einstein said that gravity and acceleration are the same. Hawking said gravity can make radiation. In the 1970s, Unruh connected these ideas and said that an accelerated particle will see Hawking-like radiation, even if it's not in a gravitational field.

To quote one of Gernster sources, Bob Bingham, "The vacuum really doesn't care if it's an electric field, a magnetic field, a gravitational field, ... If you can packe enough energy i, you can excite particles out ofthe vacuum. ... Nothing generates fileds even close to those produced by an ultra-high intensity laser --- except perhaps a black hole."

Another sources points out the analog of ultrarelativistic lasers with the nonlinear phenomena of the 1960s through the present: "We're going to change the index of refraction of the vacuum." What a concept!

Gernster gives a very clear description of how lasers are able to do what they do. The take a lot of energy, but not a whole lot --- on the order of a kilowatt hour. But instead of spreading the energy out over an hour, the compress it down to a few femtoseconds. The energy is the same, but the difference in power is huge.

Excellent article.