Ultrafast Modulation\nof a Nonlocal Semiconductor Metasurface\nunder Spatially Selective Optical Pumping

Time-varying optical metasurfaces have attracted significant\nresearch\nattention for their ability to dynamically modulate the spectral characteristics\nof light and achieve effects not possible in static systems. Nonlocal\nmetasurfaces, with their spatially extended resonant modes, have the\npotential to further expand these capabilities by enabling spatially\nselective modulation. Here, we experimentally explore the application\nof spatially structured femtosecond laser pumping to modulate a leaky\nguided mode in a semiconductor metasurface. Using angle-resolved transient\ntransmission spectroscopy, we study the dynamic response of the system\nacross a range of wavelengths and angles of incidence, observing frequency\nand momentum conversion. When the pumping location is varied, this\ntechnique allows for reconstructing the temporal dynamics of the probe\npulse propagating in the metasurface mode. Our results not only demonstrate\na versatile toolkit for spatiotemporal light control but also provide\nfundamental insight into the excitation of spatially extended modes\nin nonlocal metasurfaces.