proaches based on averaging the optical properties of bulk materials are not applicable to these systems.During the preparation of this paper, a work by Kooij et al. [17] was brought to our attention. In that work, the properties of gold nanoparticle films were studied by spectroscopic ellipsometry, extremely small k values (< 0.15) were found for their nanoparticle films. It is believed that the main reason for the difference between the optical constant reported in that work and those in this paper is that Kooij and co-workers used colloidal gold, and the films studied were of lower coverage compared with those studied here.In summary, thin films of gold nanoparticles were fabricated on a gold substrate by a LBL self-assembly approach using a dithiol as the linking agent. The optical properties of these nanoparticle thin films have been investigated using a variable angle spectroscopic ellipsometer. The refractive indices were obtained from the ellipsometric data by fitting to a Lorentz oscillator dispersion model. The modeled data show good agreement with the experimental results. The refractive indices of nanoparticle films undergo dramatic variation in the range close to the plasmon band. It is suggested that this dramatic variation of refractive index could cause difficulties for studies using conventional ellipsometers at a fixed wavelength and is possibly responsible for the significant discrepancies in refractive indices reported in the literature. Furthermore, it is found that nanoparticle films show unique optical constants different from those of typical metals or insulators. ExperimentalSolutions of gold nanoparticles in toluene were prepared as described previously [4]. Particle sizes measured by TEM were in the range 5 ± 0.6 nm. Gold substrates were prepared by thermal deposition of 150 nm gold layers on to glass microscope slides covered with a 10 nm Cr adhesion layer. The substrates were then cleaned thoroughly with hot piranha solution (30:70 H 2 SO 4 /H 2 O 2 ) for 5 min, then rinsed with water and methanol and dried in a nitrogen stream. The cleaned substrates were then left in a 1 mM 1,9-nonanedithiol toluene solution overnight. The dithiol-functionalized gold substrates were first rinsed with copious amounts of toluene and subsequently ultrasonicated in toluene for 1 min, prior to being immersed in the gold nanoparticle solution for 1 h to form the first nanoparticles layer. Subsequent layers were deposited by repeated alternate immersion in solutions of dithiol and gold nanoparticles, respectively. Rinsing and ultrasonication with toluene were performed between each immersion to remove any nonchemical adsorption.A spectroscopic Beaglehole Picometer ellipsometer was used to study the optical properties of the nanoparticle film and to follow the thickness changes as a function of the number of assembled layers. Refractive indices of the gold substrate were evaluated from a clean gold sample, and were found to be in good agreement with previous reports [14]. For each nanoparticle film, spectr...

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An organic film formed of newly synthesized dye aggregates with an absorption peak in telecommunication wavelength range exhibited large third-order nonlinear optical susceptibility χ(3) and fast recovery of bleached absorption. A derivative with a di(benzofuranonyl)methanolate structure forms stable aggregates in a spin-coated film and shows an absorption maximum at 1.24 μm. An imaginary part χI(3) of the film assumes a maximum at 1.30 μm, which is −0.83×10−7 esu. The time evolution of differential transmission spectra indicates that the time constant of the recovery of bleached absorption is 80–240 fs for a fast component and 2.2–6.5 ps for a slow one. This organic film has considerable advantages for future planar optical devices.

We report ultrafast all-optical switching at optical communication wavelength using a device with a layered structure containing organic films. Spin-coated layers of di(benzofuranonyl)methanolate (BM) derivative are formed alternately with vacuum evaporated layers of germanium (II) oxide. An optical Kerr shutter is constructed using this BM multilayer with 1.55μm signal and 1.63μm gate pulses of 100fs time durations. As a result, optical switching with signal-to-noise ratio over 20dB is attained at gate-pulse intensity above 30pJ∕μm2 and a response time comparable to pulse width is observed. The BM multilayer could be an efficient optical communication device for parallel data processing.

A semiconductor bulk crystal has several advantages as a nonlinear optical material, such as low processing cost, long interaction length, and alleviation of the free-carrier absorption caused by two-photon absorption (TPA). We examine optical properties of semiconductor bulk crystals with different orientations at 1.55μm and find that CdTe[111] has favorable capabilities, such as nonlinear refractive index of 5.23×10−17(m2W), TPA coefficient of 18.3(mmGW), and consequent figure of merit of 0.54. Optical three-dimensional measurements of reflective material are carried out using CdTe[111] as ultrafast optical Kerr shutter and clear images corresponding to surface steps are obtained.