Researchers at Caltech have created a groundbreaking device that can redirect a beam of light in an incredibly short time—just 74 femtoseconds, or 74 quadrillionths of a second. This achievement uses a combination of another light beam and a specially designed nanoscale silicon structure known as a metasurface. The innovation has the potential to significantly enhance technologies related to light-based communication, computing, and sensing. The system works by using a powerful light beam, called the pump, which has a specific pattern designed to temporarily change how a material interacts with light. A second, weaker beam—referred to as the probe—then passes through the material. The direction of the probe beam is altered based on the pattern created by the pump. This effect is made possible by a phenomenon called the optical Kerr effect, where an intense light beam briefly changes the material's refractive index—the measure of how much the material bends light. To amplify this effect, the researchers developed a metasurface made from a thin layer of amorphous silicon covered with tiny, nanoscale pillars. These pillars are smaller than the wavelength of the pump light and are arranged in a specific way to keep the light within the metasurface longer. This extended interaction increases the refractive index change, allowing for more effective light steering. Using this method, the researchers successfully redirected light by up to 13 degrees in just 74 femtoseconds. The current speed of the system is limited by the laser pulses used, rather than the properties of the metasurface itself. This suggests that future improvements in laser technology could make the process even faster. The research, titled "Ultrafast, reconfigurable all-optical beam steering and spatial light modulation," was supported by multiple funding sources, including the Air Force Office of Scientific Research, the Swiss National Science Foundation, and the Kavli Nanoscience Institute at Caltech, which provided essential infrastructure and support for the work.