Abstract

The nonlinear optical properties of nano-scale semiconductor clusters have developed into a field of increased interest in recent years.¹ Many fabrication techniques have been used to prepare nanocluster films, however, the largest χ⁽³⁾ values (10⁻³-10⁻⁵ esu) have been reported on laser-ablated films.^1,2 These films are composed of micron-size droplets that are made of nano-scale clusters. The samples were grown on fused quartz substrates in vacuum via laser ablation using a KrF excimer laser (λ = 248 nm, P_avg = 3W, τ_P = 8 ns, rep. rate = 50' Hz) and a silicon wafer target (〈100〉), n-type 10¹⁶ cm⁻³). X-ray diffraction indicates that the films are made of nano-size crystallites. The information on the clusters within the droplets was gathered indirectly by μ,-Raman spectroscopy.³ Nanosecond excitation experiments¹ revealed a lifetime of the transition at λ = 532 nm of approximately 5 ns, limited by the laser pulse duration. Amorphous or polycrystalline silicon films have never exhibited such a high value of χ⁽³⁾ although lifetime values of that order have been reported in the past. The origin of the large nonlinearity is still a mystery.

© 1998 Optical Society of America