Probing Beam Coherence via Terahertz Metasurface

Motivated by the recent advancements in terahertz metaoptics, this study demonstrates a metasurface exhibiting distinct optical characteristics with coherent and incoherent illuminations at terahertz (THz) frequencies. Traditionally, periodic boundary conditions are exercised to simulate metasurface responses under coherent illumination, while under incoherent illumination, both the simulation as well as the experiment become more complex and challenging. In the present study, we discuss two different approaches to determine the response of a metasurface under incoherent illuminationone with multiple finite-sized source patches and the second is based on the Van Cittert-Zernike theorem that relates wavevector content to the spatial coherence width. The experimental measurements show good agreement with the simulation results. Further, on the application end, the metasurface as a spatial low-pass filter is discussed briefly. The designed THz metasurface has potential applications in optical imaging, spatial filtering, improving signal-to-noise ratio in optical communication, etc.