Study of the effects of MeV Ag and Au implantation on the optical properties of LiNbO{sub 3}

The authors present the results of characterization of linear absorption and nonlinear refractive index of Au and Ag nanoclusters made by MeV ion implantation into LiNbO{sub 3}. Ag was implanted at 1.5 MeV to fluences of 2 to 17 {times} 10{sup 16}/cm{sup 2} at room temperature. Au was implanted to fluences of 5 to 20 {times} 10{sup 16}/c{sup 2}m at an energy of 2.0 MeV. Optical absorption spectrometry indicated an absorption peak at 560 nm for the Au implanted samples after a 30 minute heat treatment at 500 C in air. The peak shifted to {approximately} 620 nm after heat treatment at 1,000 C. The Ag implanted samples had absorption peaks at 445 to 485 nm before heat treatment. After 500 C heat treatment for 1 h the peaks decreased in height and shifted to 545--560 nm. Heat treatment at 800 C was sufficient to return the Ag implanted crystals to a clear state. The size of the clusters was determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 1 to 3 nm upon heat treatment at 1,000 C. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm)