Driving Electrons and Plasmas Using Geometric Group Velocity Control of Intense Ultrafast Laser Pulses

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This award supports a research team at Colorado School of Mines to develop new methods to use ultrashort laser pulses to accelerate electrons. There is a worldwide effort to find ways for lasers to accelerate electrons, in part to bring the scale of particle accelerators down from a large multi-building facility to a tabletop. This development would address a number of national needs: secondary sources of radiation for security inspections, ultrahigh resolution electron microscopes to analyze the properties of new quantum materials, and production of electrons that can be efficiently injected into other laser-plasma based accelerators. This project will be developing methods to use shaped, intense ultrashort pulses to directly push on electrons. This approach not only pushes scientific boundaries for optical control of electrons, but it also addresses the important challenge of accelerating electrons from rest to relativistic speeds with well-defined energy and direction. The project will train undergraduate and graduate students and a postdoctoral researcher by combining theory, computational modeling and experimental work. This cutting edge research will give them experience that can lead them to careers in industry or research and academia.At the Colorado School of Mines (CSM), technology has been developed to produce shaped, ultrashort laser pulses that have an intensity profile that is tilted relative to the overall direction of the beam. For focused beams that are wide enough, this pulse front tilt has the effect of slowing down the interaction speed of the pulse with surfaces or objects, such as electrons. By slowing down the pulse, CSM calculations and simulations show that the electrons can be fully captured and accelerated in a direction perpendicular to the pulse front. Several experiments to take advantage of this method of all-optical electron acceleration will be designed and conducted. First, a short ultraviolet laser pulse will produce electrons from a nano-scale tip, then they will be injected into the focus of the laser beam. The goals of this experiment are to explore and characterize the acceleration process, and also to test whether the spatial coherence of the electrons can be preserved. If so, the result would be a new source that can be used for time-resolved coherent electron imaging. Second, tilted pulses will be used to impulsively drive strong oscillations in a plasma wave. These oscillating electrons should emit light in the terahertz part of the spectrum that can be used for measurements on novel semiconductor systems among other applications. Finally, CSM researchers will perform experiments using tilted pulse acceleration at a high-power laser facility at Colorado State University that will be the first of their kind, with the aim to accelerate electrons to relativistic energies in the MeV range.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.