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Measurements of refractive indices, electro-optic coefficients and photorefractivity are performed for a set of Zirconium-doped congruent lithium niobate (Zr:LN) crystals as functions of the dopant concentration in the range 0.0-3.0 mol%. The photorefractive properties are studied by measuring the green-light induced birefringence change and by direct observation of the transmitted-beam distortion. The index of refraction data show that the threshold concentration, above which there is a change in the Zr incorporation mechanism, is about 2.0 mol%, but photorefractivity results suggest that the concentration of ZrO 2 required to strongly reduce the photorefractive effect is somewhat larger than the 2.0 mol% "threshold" concentration derived from index-of-refraction data. The electro-optic coefficients are little influenced by Zr-doping. All the reported results confirm that Zr:LN is a very promising candidate for the realization of efficient electro-optic and all-optical nonlinear devices working at room temperature

This Letter reports on the first observation of elastic and magnetic dynamics of ordered arrays of permalloy nanodots excited by low-intensity 120 fs light pulses. The first order of the diffraction pattern, generated by the probe beam in a pump-probe configuration, is used for time-resolved reflectivity and time-resolved magneto-optical Kerr effect measurements. The nonadiabatical absorption of the pump triggers an acoustic standing wave, detected by the reflected probe signal, with a frequency related to the array wave vector. Instead, the magneto-optical signal exhibits, on the nanosecond time scale, the signature of the heat-exchange diffusion processes. In addition, a clear oscillation of the magnetic signal, at a frequency close to the frequency of the acoustic wave, is unambiguously detected. Finally, the interplay between the elastic and magnetic dynamics is analyzed and interpreted.

make the hydrophobic inner micronetwork water soluble. Experiments directed at the synthesis of hollow micronetworks, which exhibit two shells of different polarity, are currently in progress. ExperimentalThe micronetworks were prepared, by the base catalyzed procedure, as described previously [17±19]. For the preparation of the hollow spheres (sample HK70) the surfactant benzethonium chloride (3.0 g, Aldrich, M = 448 g mol ±1 ) was dissolved in water (125.0 g) containing NaOH (300 mg, 10 wt.-%). Dimethoxydimethylsilane (11.0 g) was added, with vigorous stirring, at room temperature over 1 h. After stirring for a further 12 h the silanol end groups of the PDMS chains were endcapped using methoxytrimethylsilane (100 mg).A mixture of methytrimethoxysilane (10.0 g) and dimethoxydimethylsilane (4.0 g) was added over 1 h and the resultant mixture stirred for a further 5 h. In order to prevent the remaining reactive silanol groups from undergoing interparticle condensation, the endcapping procedure was repeated twice more, with methoxytrimethylsilane (2.5 g), before the removal of the surfactant. The dispersion was destabilized by the addition of methanol and centrifuged. The precipitate was washed three times with methanol, to remove the surfactant, and then dissolved in toluene.At this stage the endcapping of the silanol groups is not yet quantitative. Therefore, hexamethyldisilazane (5.0 g, Wacker-Chemie GmbH, M = 164 g mol ±1 ) was added to the toluene solution and the reaction mixture was stirred, at room temperature, for 12 h. The micronetworks were again precipitated with methanol, centrifuged and dried. A colorless, sticky residue was obtained.In order to remove the linear PDMS chains from the core of the micronetworks the residue was dissolved in THF and ultrafiltered (Millipore cellulose 30 000) 4±5 times. The solvent was evaporated, the solid residue dissolved in benzene, and freeze-dried overnight. Yield: 3.5 g of a colorless powder. Sample VK70 was prepared as described previously [19].Static and dynamic light scattering measurements were performed with standard equipment utilizing an ALV SP-86 goniometer, an ALV 3000 correlator, and a Spectra Physics 2060-11s Krypton ion laser light source (647.1 nm wavelength, 500 mW power) or an ALV SP-125 goniometer, an ALV 5000 correlator, and a Spectra Physics 2060-04s Argon ion laser light source (514.0 nm, 250 mW). Correlation functions were analyzed by the method of cumulants.All samples described here exhibited normalized second cumulants of m 2 < 0.05, and no angular dependence of the diffusion coefficients was observed. Before conducting any measurements the toluene solution (0.2 g L ±1 < c < 1.5 g L ±1 ) was filtered through a 0.2 mm Millex FGN Teflon filter.The refractive index increments were measured with a special, homebuilt, interferometer utilizing a small laser (Polytec, wavelength 543 nm or uniphase, 632 nm) [20].Atomic force micrographs were recorded with a Nanoscope III instrument (Digital Instruments, St. Barbara, CA) operating in tapping mode at a ...

We report the two-photon absorption (TPA) spectrum of a film of poly[4,6-dacadiyne-1,10-diolbis(3-butoxycarbonyl-methyl-urethane)]—commonly known as poly(3-BCMU)—in the wavelength range λ=1.6–0.7 μm. We find that the TPA coefficient of the film, which was prepared by spin coating, increases from ≈2 cm/GW at 1.45 μm to 170 cm/GW at 0.8 μm. The main features of the spectrum can be accounted for by a three-level model with a two-photon state positioned at 2.8 eV.