We obtain a well-defined topological charge signature from the intensity correlation of two spatially incoherent Laguerre-Gauss beams of differing orders when each beam is diffracted by a triangle. We show that the value of the obtained topological charge follows a correlation rule such that its value is related to the topological charges associated to both incoherent beams. This paper suggests a way to measure an effective topological charge of the coherence function, and opens a new window for studies of correlation between different orders of optical vortex beams.
We report on the first experimental observation of a large spatial lateral shift in the interaction of obliquely oriented spatial-dark soliton stripes. We demonstrate by numerical simulations that this new effect can be attributed to the specific features of optical media with nonlocal nonlinear response.
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.
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.
One of the most surprising things about photonic crystals is not the existence of the band gap, but the fact that a large, ordered array of scatters can be transparent to light within certain spectral regions. We have identified a new, general effect in which the band gap of a photonic lattice can be suppressed by unexpected mode degeneracy, rendering a photonic crystal completely transparent to all frequencies across two or more distinct 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.
We report on the theoretical and experimental demonstration of a geometrical representation for nondiffracting beams with orbital angular momentum. This representation is a SU(2) structure equivalent to the Poincare sphere for the polarization states of light, which describes the different states of light beams possessing orbital angular momentum in terms of nondiffracting beams. We have also investigated unitary transformations within our geometrical representation using linear optical elements, equivalent to a polarization state rotation on the Poincare sphere. A new class of nondiffracting beams is also suggested.
Recent manifestations of apparently faster-than-light effects confirmed our predictions that the group velocity in transparent optical media can exceed c. Special relativity is not violated by these phenomena. Moreover, in the electronic domain, the causality principle does not forbid negative group delays of analytic signals in electronic circuits, in which the peak of an output pulse leaves the exit port of a circuit before the peak of the input pulse enters the input port. Furthermore, pulse distortion for these 'superluminal' analytic signal scan be negligible in both the optical and electronic domains. Here we suggest an extension of these ideas to the microelectronic domain. The underlying principle is that negative feedback can be used to produce negative group delays. Such negative group delay scan be used to cancel out the positive group delays due to 'transistor latency' as well as the 'propagation delays' due to the interconnects between transistors. Using this principle, it is possible to speed up computer systems.
We discuss the theory, the experiment and applications to the interference resulting of the superposition of two or more Bessel beams propagating in free space and showed for first time a self imaging effect using nondiffracting beams.