Spatiotemporal Dynamics of Multimode Optical Pulse Propagation: Route to High-Performance Ultrafast Lasers

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Lasers that produce very short flashes of light (billionths of millionths of seconds in duration) can be used to observe very fast processes in nature, such as the motion of molecules or electrons. They do this in much the same way a strobe light can freeze motion on much longer time scales. In addition, such flashes of light can be used in applications such as cutting industrial materials and precise surgery.Such a laser can be made of optical fiber, which is attractive because the light is contained inside the fiber. In fibers used for this purpose to date, the core of the fiber is very small (a few millionths of a meter) and only a single pattern of the light propagates in the fiber. This pattern is what most people associate with a laser beam: a small spot that is brightest in its center. If the core of the fiber is made larger, other patterns can propagate. All of the allowed patterns overlap, so the beam that comes out is a complicated mix of them. Lasers based on multiple patterns can theoretically reach much higher powers, which are needed for applications, but the patterns must be controlled. In the last two years researchers have learned how to lock together multiple beam patterns in fiber lasers. Groups from Cornell University and the University of Central Florida will work to make lasers and other sources of short light pulses based on fibers that support many overlapping beam patterns. Instruments with new capabilities, such as much higher powers, will be developed. Graduate students who work on this project will receive theoretical and practical training, and will be prepared for diverse careers in science and technology. In an effort to increase exposure of science and enhance diversity of participants, the Cornell group will work with the 4H organization to offer workshops aimed at exposing junior-high-school students to science careers. Technical DescriptionLasers that generate ultrashort light pulses have had enormous impact in science and applications. The field of ultrafast science has been built on a foundation of short-pulse lasers based on a single transverse mode of a cavity, or optical fibers that support a single transverse mode. In fibers that support multiple transverse modes, wave propagation is inherently spatiotemporal. The generation of ultrashort light pulses in a fiber laser with many transverse modes was recently demonstrated for the first time.A group from Cornell University will work to develop lasers and optical amplifiers with new capabilities, based on multimode optical fibers. In such a laser it is possible to control both the spatial and temporal degrees of freedom of the electromagnetic field. A particularly promising direction is scaling short-pulse fiber lasers to higher powers, which are always desired for applications. Numerical simulations of candidate laser designs will be performed. Lasers will be built and compared to the simulation results. Collaborators from the University of Central Florida will provide theoretical and computational support for this effort. The limits of performance will be investigated, and lasers will be designed for optimum performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.