We report on the observation of a large thermal nonlinearity of an organic material enhanced by the presence of gold
nanoparticles. The studied system consisted of a colloid of castor oil and gold particles with average diameter of 10 nm,
with filling factor of 4.0x10<sup>-5</sup>. Z-scan measurements were performed for an excitation wavelength tuned at 810 nm in the
CW regime. It was observed that this colloidal system presents a large thermal nonlinear refractive index, which was
equal to -7.4x10<sup>-8</sup> cm<sup>2</sup>/W. This value is about 41 times larger than the n<sub>2</sub> of the host material. The thermo-optic
coefficient of the colloid was also evaluated, and a large enhancement was observed in its value owing to the presence of
the gold nanoparticles in the organic material.
Three kinds of colloids containing gold nanoparticles (AuNP) were obtained by three different methods of synthesis,
using castor oil as dispersant agent and tetrachloroauric (III) acid as gold source. The colloidal systems were
characterized by Uv-vis spectroscopy and transmission electron microscopy (TEM). Each method gave rise to quasispherical
shape and different size distribution of AuNP. The TEM images of the nanostrutured systems show that from
each method of synthesis, nanoparticles of different average sizes, equal to 7, 15, and 55 nm, were produced. These
characteristics are reflected by the presence of different maximum wavelength absorption, indicating that each colloid
presents distinct surface Plasmon resonance bands.
Spectroscopic properties of ytterbium-doped tellurite glasses with different compositions are reported. Results of linear refractive index, absorption and emission spectra, and fluorescence lifetimes are presented. The studied samples present high refractive index (~2.0) and large transmission window (380-6000nm). Absorption and emission cross-sections are calculated as well as the minimum pump laser intensity. The results are compared with the values of other laser materials, in order to investigate applications as laser media in the infrared region.
Spatial self-phase modulation was observed when a CW laser beam propagated along a cell containing castor oil. The minimum power needed to excite this effect decreases when the sample length is increased, as well as when the laser wavelength approaches to the absorption band of the medium. The same phenomenon was also observed when a laser beam interacts with a colloidal solution of gold nanoparticles in castor oil. For this system the self-phase modulation
minimum power decreased dramatically, which indicates that the nonlinear refractive index for this system is enhanced due to the gold nanoparticles. Moreover, for laser wavelength near to the plasmon resonance of the gold nanoparticles, this enhancement factor is even higher. Although the large value of those media nonlinearity, its temporal response is slow. This fact suggests that this phenomenon is due to thermal effects mainly.
A new conical diffraction phenomenon was observed when two beams of the same or different frequencies intersect as they pass through a CS<sub>2</sub> cell. Light is emitted on the surface of a circular cone that is centered in each one of the two beams and has an angular extent equal to twice the crossing angle between the incident beams. The origin of this effect is discussed and a quantitative study of the conical emission intensity is given.
We developed a new technique which allows measurements of the relative amplitudes of the third- and fifth-order susceptibilities, as well as their relative phases. Preliminary results for a semiconductor doped glass that illustrate the theoretical predictions are presented.
We report the observation of conical emission induced by cross-phase-modulation when a strong beam copropagates with a weak beam through dimethylsulfoxide. Laser beams at 1064 nm and 597 nm, in the transparency window of the material, were used. The phenomenon is understood in terms of a nonlinear spatial modulation of the refractive index.