Relativistic Thomson Scattering Investigations with in Situ Electrons in the Focus at the Petawatt Level

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The development of lasers capable of delivering extreme intensities in a short time period has placed us at the threshold of a new era for experimental investigation. As these tools mature over the next few years, they will enable exploration of phenomena associated with matter and antimatter that could help with the interpretation of recent astrophysical observations as well as shed light on a variety of fundamental questions such as the Standard Model of Particle Physics and Dark Matter. A major roadblock inhibiting their employment, however, is a reliable way to measure intensities. This project is devoted to developing an intensity gauge that is straightforward to implement and transferable to other laboratories. Establishing suitable techniques for intensity measurement is a long-standing desire of the laser community. 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 including underrepresented minorities and in this endeavor, this project is providing a much-needed instrument while training a diverse cadre of students.The development of multi-petawatt lasers of short duration has placed us at the threshold of a new era. Critical experimental investigations of nonlinear aspects of electrodynamics -- how light interacts with matter and itself, -- which largely undergirds our current understanding of the quantum vacuum, will be possible. A major roadblock inhibiting progress towards realizing precision measurement at the petawatt level is an ability to measure the intensity directly. This project is devoted to developing an intensity gauge that is (i) straightforward to implement, not requiring a major experimental effort to employ, (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 technique meeting these desires is based on relativistic Thomson scattering. Details of Thomson scattering are being investigated by (i) monitoring the fundamental and second-harmonic radiation, (ii) measuring the angular distribution of the radiation and (iii) measuring the energy and angular distribution of the Thomson scattered electrons, born in situ and ejected by the ponderomotive potential of the laser. Correlating the ejected electron with Doppler-shifted radiation is enabling a model of the Thomson scattering to be created. The project will include direct engagement with high-power laser facilities worldwide, including the Extreme Light Infrastructure (ELI) facilities in Czech Republic and Romania.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.