Lasers that produce very short pulses of light (millionths of millionths of seconds in duration) have begun to find applications that range from imaging of cells in tissue to surgery, to industrial material processing, as examples. Such a laser can be made of optical fiber, which is attractive because the light is automatically kept 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 mode, or pattern, of the light propagates in the fiber. This mode 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. The light field varies in space and in time as it propagates in the fiber. Lasers based on multiple patterns can theoretically reach much higher powers, which are needed for applications, but the patterns must be controlled. Control of the patterns will also allow new capabilities, such as the generation of short light pulses at new wavelengths (colors, including infrared and ultraviolet). Advances in theoretical understanding and experimental techniques in the last few years now give researchers the tools to develop lasers based on fibers with many overlapping patterns or modes. Groups from Cornell University and the University of Central Florida will work to develop lasers and other sources of short light pulses based on such fibers. 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 and possible careers.
A group from Cornell University will perform theoretical and experimental studies of the propagation of ultrashort light pulses in optical fibers that support many transverse modes of the electromagnetic field. As a result of recent advances in understanding of multimode pulse propagation, which is inherently spatiotemporal in nature, it is now feasible to begin to design sources of ultrashort light pulses based on multimode fiber. High-power lasers, and sources of broadly-tunable intense infrared pulses will be constructed and studied. Collaborators from the University of Central Florida will provide computational support. The field of ultrafast science has been built largely with short-pulse lasers based on a single transverse mode of a cavity, or optical fibers that support a single transverse mode. Exploitation of spatiotemporal wave propagation for the design of new sources of ultrashort pulses has not been considered previously. The new pulse-shaping mechanisms that will be investigated offer enhanced or completely-new capabilities for high-energy and ultrashort pulses. Optical fiber offers an ideal setting to study new nonlinear waves. Knowledge gained in the proposed effort will be pertinent to future telecommunications systems based on mode-division multiplexing. The nonlinear dynamics investigated in this project will correspond to related effects in a variety of systems, such as Bose-Einstein condensates, and multimode propagation will be relevant to optical studies of turbulence.
