ULTRAFAST OPTICAL SWITCHING OF 2ND-HARMONIC GENERATION AT THE C-60 SINGLE-CRYSTAL SURFACE

The switching of second-harmonic generation (SHG) at a C-60 single-cry stal surface has been observed in a pump-and-probe experiment. The SHG signal from. a picosecond 1.17 eV laser pulse is suppressed by one or der of magnitude upon illuminating the crystal. surface with a 3.49 eV pump pulse. The nonlinear optical response is faster than 45 ps and p ersists for longer than 20 ns. SHG suppression to 1/e occurs at pump d ensities as low as 2.8 mu J/cm(2). We suggest that nonlocalized excite d electronic states determine the change in the nonlinear optical beha vior. (C) 1996 American Institute of Physics.