After Kerr Has Gone

Hail and Atwater — amorphous-silicon metasurface of high-Q nanopillars.

A patterned pump writes a transient grating through the optical Kerr effect; the probe steers up to plus or minus thirteen degrees; the write-and-fade is pulse-limited at seventy-four femtoseconds.

Press says steering light in a flash, less than a trillionth of a second. Computing and signal-processing sit at the elbow.

Instantaneous is a late mouth once the step is caught — same family as jump once we could catch the step. Looking is the Kerr grating that goes with the pump, pulse-limited, no waiting for carriers to relax.

The leftover is both: the grating that lasts only as long as the pump pulse, and the slower free-carrier background from two-photon absorption that stays after Kerr has gone.

One looking gone with the light; one that hangs.