UCLA

Coherent transition radiation (CTR) provides a powerful link between the spatiotemporal structure of charged-particle beams and the emitted electromagnetic fields, underpinning a wide range of beam diagnostics and radiation sources. Despite their long-standing theoretical foundations, existing CTR frameworks have historically been restricted to simplified beam and boundary geometries. We introduce a unified, first-principles CTR framework applicable to arbitrary three-dimensional electron bunches. Beginning with the classical Ginzburg-Frank formulation, we develop a systematic and instructional description of coherent emission in terms of the bunch form factor, establishing it as the central quantity governing spectral and angular radiation characteristics. We further present a general numerical pipeline that enables the computation of CTR spectra from arbitrarily structured electron beams beyond the conventional Gaussian form factor, and provide examples of hollow Gaussian and Airy-like electron beam distributions. By extending CTR theory to arbitrarily structured charged-particle beams, this work establishes a new, generalizable foundation for interpreting experimental measurements, designing next-generation beam diagnostics, and exploring previously inaccessible regimes of structured, broadband radiation sources.In addition to this theoretical and computational work, experimental production and measurement of coherent transition radiation at the ARES accelerator at DESY were conducted. CTR was generated from strongly compressed, 120 MeV electron bunches using a silver radiator oriented at 45 degrees to the electron trajectory, and wavelength-resolved radiation was measured over approximately 200–1100 nm. Measurements performed at TWS2 phases of 32, 33, and 34 degrees were compared with Gaussian CTR spectra generated using the computational framework developed in this thesis. The resulting spectral fits correspond to characteristic RMS bunch durations of approximately 1.22–1.26 fs. The model additionally predicts the onset of coherence-dominated emission near 550 nm, consistent with the experimentally observed transition to quadratic charge scaling. Together, the numerical and experimental results demonstrate the use of CTR as both a source of broadband coherent radiation and a diagnostic of ultrashort electron-bunch structure.