Pictured: Professor Howard Milchberg
What if you could take the combined output of all the US’s power plants and harness it with pinpoint accuracy?
What if you could do this on an apparatus that fit on your dining room table?
Both are possible with the newly-developed high-intensity tabletop lasers. These lasers may lead to the advent of compact particle accelerators, as well as a new type of x-ray micrscope.
A research team led by Professor Howard Milchberg is making findings that could lead to both of these applications. Ever since 1993, when the team patented a “method for channeling high-intensity laser pulses through a gas for surprisingly long distances,” the scientific community has been paying attention.
Until then, not only was it hard to produce power, but to confine the laser light to a channel narrow enough for accelerator and x-ray microscope applications was thought to be impossible.
A method called chirp-pulse amplification is the key to producing intense pulses. Using this strategy, researchers stretch out a laser by 1,000’s of times its original length, and amplify it. Next, they compress the laser pulse, creating incredible intensity - as much as 1018 W/cm2. This laser is released in short, femtosecond (ten thousandth of one billionth of a second) pulses.
But what Milchberg’s team figured out how to do is focus and confine this energy. They did it by first shooting a laser through an axicon lens (a device Milchberg saw Russian scientists using during a visit there) and into a gas. This created a channel of ionized gas, or plasma. Then, they shot the ultra-intense pulse through the channel, confining the laser pulse and allowing it to travel further - while still retaining its energy. Currently, Milchberg’s team has the ultra-intense beams traveling at lengths of up to 3 cm, and focused down to 10 microns.
Having this much power in such a small area has a great deal of potential applications. One of them is in the field of particle accelerators. Currently, machines designed to accelerate electrons can cost billions of dollars and take up miles of space. Newer ones, however, may fit in an area the size of the average kitchen table.
Maryland researchers are investigating methods of accelerating electrons using the wake produced by an intense laser pulse passing through a plasma. The electric fields in this wake are strong enough to accelerate electrons to a fraction of the energy of the behemoth machines, but in a distance of several centimeters instead of several miles.
What’s more, researchers have discovered that the plasma tunnel created by the initial laser emits soft x-rays. These x-rays have wavelengths of about 10-20 nanometers, which could enable scientists to resolve very small structures. Plus, the fact that the pulses are so short could make femtosecond time resolution possible. A soft x-ray microscope could be especially useful, as it would not damage things like living tissue as it samples them. This type of microscope could also be used for the design of smaller computer chips, which are already being crafted in the micrometer range.
Until now, Milchberg’s team wanted to prove channeling could be done. Now, they are working on how to use it, conducting research related to coherent x-ray generators, compact laser-driven accelerators, and soft x-ray microscopes.
Professor Thomas Antonsen, Jr. is another Department of Electrical Engineering faculty member involved with Milchberg’s research team. Funding is supplied by the Department of Energy’s Division of High Energy Physics.
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