Intense Laser-Plasma Interactions with Structured Ultrafast Laser Pulses

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Plasma is a gas-like state of matter with properties determined by collective interactions between free-roaming electrons and ions. In this project, ultra-intense lasers will be used to create, control and study plasmas. Pulses of laser light from modern lasers can be made so focused as to allow the laser fields to push on electrons like a snowplow. In this project, the laser pulses are shaped so that they travel with a tilt, much as a tilted snowplow blade scoops up the snow and pushes it to the side. With careful laser control, the electrons can be separated from the ions and be formed by such a tilted snowplow into a beam. If the range of electron beam angles and energies can be made as small as the calculations predict, and the beam energy as high as the calculations predict, the electron beam can be used to study materials, or be boosted to even higher energies with additional particle acceleration techniques. The project will support and train one PhD student and two undergraduate students at the Colorado School of Mines. This project exploits the structuring of the spatial and temporal shape of intense, ultrafast laser pulses to control electron dynamics in plasmas. One type of structuring that will be used is where the spectral components of the laser pulse are overlapped at the focus with an incident angle that is linearly dependent on the frequency. This results in a pulse that sweeps across the focal plane with a speed that can be much lower than the speed of light. This reduced speed allows the light pressure on the electrons to capture and accelerate them to the side. With careful shaping of the transverse intensity profile, theory predicts electrons can be accelerated with a narrow energy and angular spread, making them useful for ultrafast electron diffraction and injection into other laser-based electron accelerators. In this project, the physics of this acceleration mechanism will be experimentally and computationally explored. At higher density, the fast current pulse created by this mechanism is predicted to produce terahertz radiation that will be characterized with novel single pixel imaging techniques. Another method of structuring the laser light involves converting the polarization state of the laser beam to transverse electric. When this azimuthally polarized beam is focused tightly, the magnetic field develops a longitudinal component on axis that can be over 10 kTesla, orders of magnitude higher than the strongest magnets. A short wavelength probe beam propagating along this field will be used to probe how waves are altered by this strong magnetic field.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.