Threshold Optical Nonlinearity of Dielectric Nanocomposite

Abstract

Optical properties of small particles are being investigated more than 100 years if dating from the Mie’s works. However, the intense investigations of these properties have been started in the last decades with intense studies of optical properties of nanocomposites, including heterogeneous liquid-phase nanocomposites (HLPN) based upon semiconductor, metal or structured nanoparticles with both a core and electron shell of different electrical properties (Mixeeva & Sidorov, 2004, Fedorov & Baranov, 2005, Kul'chin(a) et.al.,2008, Kul'chin(b) et.al.,2009, Kul'chin(c) et.al.,2009, Irimpan et.al.,2008, Krishnana et.al.,2008, Ryasnyanskiy et.al.,2009, Kreibig & Vollmer, 1995). It is concerned with the fact that nanocomposites based upon semiconductor and dielectric nanoparticles are of special interest for those who develop illumination control means for optical information systems, because of such nanoparticles’ great nonlinear-optical response in the near infrared and visible ranges of light. Nonlinear optical properties of nanocomposites are directly connected with physical processes which occur inside nanoobjects under an influence of a laser radiation, and they depend on electronic structure of nanoparticles. In particular, in metal nanoparticles as well as in dielectric ones with a metal shell, on condition of plasmonic resonance, an increase of effective nonlinearity of the nanocomposite’s medium and a decrease in energetic threshold of nonlinear response can occur. Low nonlinear optical threshold in the ranges of near infrared and visible light can be observed in wide-gap semiconductor nanoparticles as well. For example, the investigation of dependence of the density of energy, passed through a nanoparticle array in transparent dielectric liquid matrix, on the density of incident energy have shown that threshold of nonlinear optical response for the sample based upon TiO2 illuminated with impulses of τ = 10 ns on the wavelength of λ = 1.06 μm is no greater than 0.15 nJ/sm2, impulses with the wavelength of 0.53 μm provided the response less than 0.1 nJ/sm2. Nonlinear optical properties of nanocomposites based upon dielectric nanoparticles with higher energy-gap width Er were investigated to a less extent. It was concerned, presumably, with the considerations that such energy-gap width could cause the nonlinear optical response of the medium in the ultraviolet range of light. However, recent studies (Kul'chin et.al., 2008, Kul'chin et.al.,2009 ) have shown that HLPN based upon dielectric nanoparticles can feature low-threshold nonlinear optical response to an external illumination, impulse and continuous alike, in the near infrared or visible ranges of light.