  We have demonstrated a new mechanism for modulating light with light by
controlling the efficiency with which light is coupled into a plasmon polariton
wave. An optical fluence of 15 mJ/cm^2 in the control channel is sufficient to
achieve nearly a 10-fold intensity modulation of the signal beam reflected from
a Glass/MgF_2/Ga structure. The mechanism depends on a nanoscale light-induced
structural transformation in the gallium layer and has transient switching
times of the order of a few tens of nanoseconds. It offers high modulation
contrast for signals in the visible and near infrared spectral ranges.

Materials Science