Saturday, July 4, 2009
Laser Power
Friday, June 15, 2007
 Dr. Ditmire stands with part of the Petawatt Laser |
Ditmire’s instrument will create super-small amounts of super-hot, super-dense plasma to help scientists come to a better understanding of large exotic phenomena in outer space. The laser will be used to probe the fundamental properties of materials, and to explore how to generate electricity for the world.
The UT Petawatt Laser, buried in the basement under Robert Lee Moore Hall, will pack two petawatts (two billion million watts) of power, twice the amount generated by the previous record holder at the Lawrence Livermore Laboratory in California. But how will so much power be generated without dimming the rest of the lights on campus, running up the university’s electric bill, or just plain blowing stuff up?
The answer is a process called chirped-pulse amplification, where light is stretched out and squished like a Slinky through a set of sophisticated prisms.
First, the light becomes lengthier, and the lengthier the light pulse, the more energy it can hold safely. Then, this elongated light pulse is charged gradually through a series of amplifiers. The stretched-out light is then shortened, which increases its power exponentially.
The shortened beam of light exits the laser as the brightest light in the universe, 18 orders of magnitude greater than the sunlight on the surface of the sun, comparable in brightness only to black hole phenomena called gamma ray bursts.
The light pulse is so energetic, in fact, that it can’t even go through air. It would rip the electrons from atmospheric nitrogen and cause a spectacular explosion, destroying the laser. So for safety’s sake, the business end of the laser will be contained within a large vacuum chamber. No air, no explosion.
Ditmire, who came to the university in 2000 from Lawrence Livermore, already has three experiments he hopes to conduct once the leaves start changing outside and the UT Petawatt Laser is bursting with energy below the surface.
His first experiment will create a supernova in miniature, by hitting a gas with the laser and driving an energetic explosion.
The second experiment calls for shooting the laser at a cluster of deuterium atoms (one proton, one electron and one neutron), exploding the cluster, fusing the atoms and creating a “tabletop star” that emits short pulses of neutrons, which can then be used in other experiments.
In the third experiment, the laser beam will strike a small chunk of metal such as aluminum. The laser will heat the metal faster than it can expand, creating a very high-density plasma comparable to the composition of weird substellar objects called brown dwarfs.
According to Ditmire, we can learn about these large astronomical objects from tiny reactions in the laboratory because of the similarity of the mathematical equations that describe the events.
“The astrophysical objects are big, and they exist over a very big timescale. My laboratory reactions are small, and they exist over a very short timescale,” Ditmire says. “We can learn about one system by studying the other.”
Once the short-pulse Petawatt is completed, Ditmire will concentrate on constructing a long-pulse laser in the same basement laboratory. Incidentally, the short-pulse laser beam will be invisible, while the long-pulse laser beam will be green. The two lasers together can be used to study fusion energy.
While a short-pulse laser is good at heating matter, a long-pulse laser is good at compressing matter. In tandem, the two lasers can create a stable, super high-density plasma that will emit a steady stream of energy that, theoretically, can be harnessed as electricity. Laser-driven fusion energy reactors could someday offer a pollution-free way to meet the power demands of the world’s population.
And for something like the UT Petawatt Laser, which is designed to get things very, very hot very, very quickly, that’s a pretty cool thing.
