The work is a study of the scattering of laser light by free electrons both theoretically and experimentally. In the experiment, electron wave packets will be created through ionization in a strong laser field and radiation from the focus at right angles to the laser beam will be observed. The radiated light from one or a few electrons is extremely weak and the experiment requires the unusual combination of quantum-optics measurement techniques and high-intensity laser technology. To separate this low-level signal from the significant background, the investigators filter in time (looking only at the signal in a nanosecond wide window), space (using baffling and a fiber coupling system to collect only photons originating from the spatial location of the focus), and wavelength (using bandpass filters to view only the relativistic red-shifted signal while explicitly masking these frequencies in the compression system). The investigators will also study the theoretical underpinnings of free-electron photoemission and how the quantum-field description might be appropriately related to a semiclassical framework. Initial work has already been accomplished in the simplified case where the driving laser and the emitted radiation are treated as plane wave fields. Extending this analysis to describe localized interactions is non-trivial, but it is necessary to create a theoretical framework for understanding radiation in this system.
The broader impacts include the study of the foundations of quantum mechanics in the context of the interface between the particle/wave nature of electrons and the particle/wave nature of light and seeks to resolve conflicting viewpoints held by different researchers in the laser-interaction community. This work will lead to a better understanding of the nature of photons, especially the connection between emitting and absorbing photons and the quantum measurement process (involving wave function collapse). The project provides opportunities for both undergraduate and graduate students to make meaningful contributions to the work while gaining valuable experience.
