Visualized Geometric Phase of Caustic Geometric Beams

Abstract: Detecting Pancharatnam-Berry geometric phases of light typically requires interferometry or diffraction through a specially truncated aperture. Here, we introduce a simpler method that allows direct and fully visual detection of geometric phases in structured light without using interferometers or beam truncation. Our approach takes advantage of the geometric phase that naturally arises in SU(2) structured beams, where spatial wave packets follow caustic trajectories during propagation. By observing the evolution of these caustic-linked wave packets, we directly visualize both the geometric phase and the Gouy phase. This visual detection method provides new insight into geometric phases in complex optical fields and expands the possibilities for designing optical systems that exploit phase geometry.