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Dynamic metasurfaces have emerged as a disruptive change in the way the response of optical systems can be tailored by combining the flexibility of flat optics in spatially engineering materials at the nanoscale with the opportunity to reconfigure the metasurfaces' properties reversibly upon external stimuli over time. In this context, the far-reaching interest in pushing the tuning speed has driven the development of 'ultrafast all-optical metasurfaces' in which transient nonlinearities photoinduced by femtosecond laser pulses empower to achieve GHz modulation rates. While holding great promises to unlock forefront applications, the future frontiers of this class of spatiotemporal all-optical metasurfaces are accompanied by formidable challenges. In this Perspective, alongside a brief panorama of the state of the art, we spotlight some of the emerging frontiers for ultrafast light-driven metasurfaces, with special emphasis on the all-optical control of light, the enhancement of light–matter interactions, and the time-variant frequency conversion, in the hope our vision will prompt new ideas and horizons to explore.
Maiuri et al. (Wed,) studied this question.