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

激光产生非常短的闪光(持续时间为百万亿分之一秒)，可以用来观察自然界中非常快的过程，如分子或电子的运动。它们这样做的方式与频闪灯可以在更长的时间尺度上冻结运动的方式大致相同。此外，这种闪光可以用于切割工业材料和精密手术等应用。这种激光器可以由光纤制成，这是很有吸引力的，因为光包含在光纤中。到目前为止，在用于此目的的光纤中，光纤的纤芯非常小(百万分之几米)，并且只有一种光模式在光纤中传播。大多数人将这种图案与激光联系在一起：在其中心最亮的一个小光点。如果光纤的纤芯变得更大，其他图案就可以传播。所有允许的图案都是重叠的，所以出来的光束是它们的复杂组合。基于多种图案的激光理论上可以达到更高的功率，这是应用所需的，但必须控制图案。在过去的两年里，研究人员已经学会了如何在光纤激光器中将多个光束图案锁定在一起。来自康奈尔大学和中佛罗里达大学的研究小组将致力于制造激光和其他基于支持许多重叠光束模式的光纤的短光脉冲来源。将开发具有新能力的仪器，例如更高功率的仪器。从事该项目的研究生将接受理论和实践培训，并将为在科学和技术领域的不同职业做准备。为了增加对科学的接触并增强参与者的多样性，康奈尔大学小组将与4H组织合作，提供旨在让初中生接触科学职业的研讨会。技术描述产生超短光脉冲的激光在科学和应用方面产生了巨大的影响。超快科学领域建立在基于腔的单一横模的短脉冲激光的基础上，或支持单一横模的光纤。在支持多横模的光纤中，波的传播本质上是时空的。最近首次演示了在具有多个横模的光纤激光器中产生超短光脉冲。康奈尔大学的一个研究小组将致力于开发基于多模光纤的具有新功能的激光和光放大器。在这种激光器中，可以同时控制电磁场的空间和时间自由度。一个特别有希望的方向是将短脉冲光纤激光器扩展到更高的功率，这一直是应用所希望的。将对候选激光器设计进行数值模拟。将建立激光器并将其与模拟结果进行比较。中佛罗里达大学的合作者将为这一努力提供理论和计算支持。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.