Three-Dimensional Phase-Space Design and Simulation of a Broadband THz Transmission Line Using Wigner Optics and Ray Tracing

Designing a transmission line (TL) for a widely tunable, broadband terahertz radiation source presents substantial challenges due to the complexity of beam dynamics and spectral characteristics. Here, we investigate the propagation of the most significant radiation modes expected to traverse the TL, intended for integration with an advanced particle accelerator currently under construction at the Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications. The total electromagnetic field at the source output is expressed in the frequency domain via cavity eigenmodes and transformed into an optical field representation using the Wigner distribution function (WDF). This formulation enables physically consistent modeling within the constraints of geometric optics and Wigner formalism of the spatiotemporal evolution of the radiation during propagation. The initial TL design is developed and optimized based on this representation. A 3D space–frequency analysis tool for pulsed radiation, based on the WDF, was implemented to characterize field behavior and guide system development. Complementary ray tracing simulations were conducted using the Zemax Optic Studio platform, supporting the assessment of optical feasibility through simulation and system feasibility.