Quantitative Measurements of Relativistic Electron Ejection from the Focus of Petawatt Lasers

This award supports development of techniques to measure the intensity of very high power laser light. The development of high-powered lasers capable of delivering extreme intensities into a small volume has placed the scientific community at the threshold of a new era for experimental investigation. Exploiting lasers to create matter out of vacuum or to shed light on dark matter are just two examples of what may become possible over the next decade. A major impediment inhibiting progress in such investigations, and constraining advancement of laser technology, is a reliable way to measure the intensity of a focused high-powered laser in real time at full power. This project is devoted to developing methodologies to enable such measurements that are straightforward to deploy and broadly applicable in laboratories across the country and around the world. A host of studies ranging from generating novel light sources to probing warm dense matter to developing laser-based medical applications will also benefit greatly from this project. Together with the emphasis on international engagement and a commitment to inclusion of underrepresented individuals in science, technology, engineering, and mathematics, this project provides a much-needed capability while training a diverse cadre of students. A major roadblock inhibiting progress towards realizing precision measurement at the petawatt and multi-petawatt level is the seemingly simple, but extremely difficult, task of assessing laser's focal volume directly at full power – such as measuring the intensity and visualizing distortions in the laser beam. This project is devoted to developing an assessment procedure that is (i) straightforward to implement without requiring a major experimental effort to deploy, (ii) minimally intrusive, allowing the primary experiment to be performed uninhibited, (iii) sensitive to beam characteristic changes that can degrade the energy in the focus from shot to shot, and (iv) single-shot capable. A promising mechanism for enabling such measurements is the well-known process of ponderomotive scattering. Electrons born in the focus of a petawatt-class laser are accelerated and ejected. Because the energy and angular distribution depend intimately on the intensity distribution in the focus, this project aims to measure the ejected energies and image the angular distributions of the electron trajectories. Such measurements coupled with numerical simulations will enable determination of the peak intensity and the non-ideality of the focal spot. The project includes direct engagement with high-power laser facilities worldwide, including the Laboratory for Laser Energetics (LLE) at the University of Rochester and the Central Laser Facility (CLF) in the United Kingdom. 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.