Gap-Induced Giant Third-Order Optical Nonlinearity and Long Electron Relaxation Time in Random-Distributed Gold Nanorod Arrays

The third-order optical nonlinearities and the hot electron relaxation time (tau) of random-distributed gold nanorods arrays on glass (R-GNRA) have been investigated by using Z-scan and optical Kerr effect (OKE) techniques. Large third-order optical susceptibility (chi((3))) with the value of 2.5 x 10(-6) esu has been obtained around the plamsonic resonance peak under the excitation power intensity of 0.1 GW/cm(2). Further decrease of the excitation power intensity down to 0.3 MW/cm(2) will lead to the significant increase of chi((3)) up to 6.4 X 10(-4) esu. The OKE results show that the relaxation time of R-GNRA around the plasmonic peak is 13.9 +/- 0.4 ps, which is more than 4 times longer than those of the individual gold nanostructures distributed in water solutions. The Finite-difference time domain simulations demonstrate that this large enhancement of chi((3)) and slow down of tau are caused by the gap-induced large local field enhancement of GNRs dimers in R-GNRA. These significant results offer great opportunities for plasmonic nanostructures in applications of photonic and photocatalytic devices.