University Of Arizona Awarded $7.5M Laser Research Project

The University of Arizona is among a small group of institutions nationwide to receive a highly competitive, multi-million dollar federal grant to investigate the effects of highly specialized lasers on the atmosphere.

University of Arizona researcher Jerome Moloney is leading a team that's investigating lasers with practical implications, such as generating terahertz waves for use in airport scanners or in creating detection systems that could be used over long distances.

Generated by lab-based scientific researchers, multi-terawatt femtosecond laser pulses deliver extreme power densities in incredibly short bursts, creating havoc as they pass through the atmosphere.

Moloney said applied mathematicians, physicists and experimental optical scientists have worked to expand knowledge related to the intense interactions and explosive effects the pulses cause.

"But we need a more profound, fundamental understanding," said Moloney, a UA mathematics and optical sciences professor.

Moloney is heading up a multidisciplinary, multi-institution research effort to investigate femtosecond laser pulses, focusing on their effects in the atmosphere and ways to improve their propagation over many kilometers.

Moloney is principal investigator on a new five-year, $7.5M U.S. Department of Defense grant to fund the project, "Propagation of Ultrashort Laser Pulses Through Transparent Media."

The highly competitive award is part of an initiative out of the Air Force Office of Scientific Research – the Multidisciplinary University Research Initiative, or MURI. The UA is one of fewer than 70 institutions to be granted the award.

The federal program supports projects that "intersect more than one traditional science and engineering discipline in order to accelerate both research progress and transition of research results to application," the Department of Defense reported.

All told, more than 150 funding proposals were submitted to the federal agency, which recently announced that 67 institutions would receive funding for 32 research projects at $227M over a five-year period.

The UA-led project will involve researchers Moloney handpicked from the University of Colorado, Colorado School of Mines, Cornell University, Temple University and the University of Central Florida.

"They are all very top notch groups," Moloney said, adding that he choose researchers based on their expertise in a range of disciplines.

Moloney also assembled a core group of applied mathematicians and theoretical and experimental physicists at UA to anchor the project. The external collaborators will provide input to the group.

Group members will work collaboratively to design new types of experiments to test physical models and mathematical descriptions while providing new paradigms for long distance propagation of the laser pulses, he said.

Improved understanding of the pulses would create the groundwork for a new class of robust laser beams that are more effective in overcoming scattering caused by atmospheric turbulence, water droplets in clouds, mist and rain, Moloney said.

When launched up into the atmosphere, the laser pulses with a tremendous burst of power, producing "explosive" effects, Moloney said. For example, the pulses strip electrons off oxygen and nitrogen molecules to create plasma channels.

Additionally, the extreme intensities in the pulses creates a white light "supercontinuum" spectroscopic source that covers all wavelengths, spanning the ultraviolet and visible to far infra-red.

The terawatt power levels attained in such laser pulses is comparable to the entire electrical generating capacity of the U.S., Moloney said.

But this entire process occurs on femtosecond time scales – a rate of 1 millionth of 1 billionth of a second.

"Essentially when the laser propagates in any material, it undergoes a process called critical self-focusing and suddenly, its intensity grows without bound until it strips the electrons off the oxygen and nitrogen molecular constituents of air," Moloney said, noting that this event is associated with a singularity of a famous equation, the Nonlinear Schrödinger equation.

"The extremely complex physics occurring in these extreme intensity regions leads to many effects that have to potential to be exploited in differing applications," he added.

One example is the generation of T-rays, or terahertz waves, which are currently being planned for use in airport scanners, enabling screeners to see through clothing to detect hidden weapons and identify harmful substances. An anticipated application would be to create a remote stand-off system to detect targets hundreds of meters to kilometers away.

Another occurrence is the production of plasma – a type of "electron" gas that results when molecules are ionized. Such plasma channels are comparable to conducting wires that can be placed at selected remote locations. Experiments are under way to determine if such plasmas can be used to initiate or redirect lightning strikes.

This extremely bright source could act as an artificial star, a so-called guidestar, to aid astronomers in correcting for distortion because of atmospheric turbulence, Moloney said.

"It's like an extreme light bulb that can be lit remotely at any point in the atmosphere," he noted.

"These are not weapons systems, even though they have very large intensities, they do not deposit a lot of energy," he added, though he noted they could be used as part of remote interrogation and detection systems.

At the UA, Moloney's collaborators include applied mathematicians and experimental physicists who are members of the Arizona Center for Mathematical Sciences, or ACMS. Miroslav Kolesik and Pavel Polynkin, both UA associate research professors of optical sciences, are among those involved.

The UA MURI team will also collaborate with William "Pat" Roach, senior science advisor in the Advanced Electric Laser Branch at the Air Force Research Laboratory in Albuquerque, N.M. Roach will run a large field testing ultrashort laser facility.

The UA-led team's work follows a critical experiment completed in 1997 by researchers at the Jena University. That year, researchers in Germany launched terawatt laser pulses vertically into the atmosphere and were able to detect molecular species in the stratosphere using the "white-light" source.

That effort led to the creation of the TERAMOBILE project a collaborative effort among researchers in France and Germany. Additionally, the UA-led team intends to collaborate with members of the TERAMOBILE group and other European and Canadian researchers.

The ACMS group at the UA has since laid the theoretical foundation and built sophisticated simulation models that gave the initial impetus for an initial understanding of the complex atmospheric propagation effects, Moloney said.

Other research has indicated that the laser pulses can detect chemical and bio agents and also simulate lightning and produce water condensation, among other things.

"We need to understand better and improve our physical understanding of each step as the laser beam initially strips electrons of molecules to create the plasma and the laser pulse, or other laser pulses, interact with that plasma," Moloney said.

"The project, as a whole, is to explore how we can come up with unconventional laser beam shapes that can hold together over larger distances in the atmosphere. That is one of the biggest issues and challenges."

SOURCE: University of Arizona