Caltech device steers light with light in 74 femtoseconds

Caltech researchers redirected a light beam in about 74 femtoseconds by using a second beam as the control signal, SciTechDaily reported, summarizing work published in Nature Nanotechnology. The approach aims at photonic systems that move and process information with light rather than relying entirely on electrical currents. Many existing devices steer or modulate light by changing a material's electronic state, which requires electrons to relax and typically limits modulation to nanoseconds or picoseconds. The Caltech group instead used an intense patterned pump beam to briefly alter the material's optical behavior and a weaker probe beam whose deflection followed the pump pattern. The method relies on the optical Kerr effect, in which an intense beam produces a tiny, temporary change in refractive index by slightly shifting electron motion within orbitals without longer-lived energy states. To strengthen the weak effect, the team fashioned amorphous silicon into a meta-surface of nanoscale pillars that briefly circulated light, amplifying the index change. Using that design, researchers steered light by as much as 13 degrees in 74 femtoseconds, matching the pump pulse duration. Lead author Claudio Hail did the work as a postdoctoral scholar in Harry Atwater's Caltech lab and is now an assistant professor at UC Berkeley. The paper notes performance is currently limited by laser pulse duration rather than the device itself, and shorter pulses could push switching times lower.