Optical nonlinearity resulting from a light-induced structural transition in gallium nanoparticles

We report that a light-induced structural transformation between different phases of gallium provides a mechanism for a strong optical nonlinearity. The nonlinearity has been studied in transient pump-probe experiments on nanoparticle films deposited on the ends of optical fibers. The magnitude and relaxation time of the response show hysteretic dependencies on temperature in the range from 100 to 300 K, are enhanced near the phase transition points and disappear at temperatures above 220 K.