Enhancement of second harmonic signal in nanofabricated cones.

Geometrical effects in optical nanostructures on nanoscale can lead to interesting phenomena such as inhibition of spontaneous emission,1,2 high-reflecting omnidirectional mirrors, structures that exhibit low-loss-waveguiding,3 and light confinement.4,5 Here, we demonstrate a similar concept of exploiting the geometrical effects on nanoscale through precisely fabricating lithium niobate (LiNbO3) nanocones arrays devices. We show a strong second harmonic generation (SHG) enhancement, shape and arrangement dependent, up to 4 times bigger than the bulk one. These devices allow below diffraction limited observation, being perfect platforms for single molecule fluorescence microscopy6 or single cell endoscopy.7 Nanocones create a confined illumination volume, devoid from blinking and bleaching, which can excite molecules in nanocones proximity. Illumination volume can be increased by combining the SH enhancement effect with plasmon resonances, excited thanks to a gold plasmonic shell deposited around the nanostructures. This results in a local further enhancement of the SH signal up to 20 times. The global SH enhancement can be rationally designed and tuned through the means of simulations.

Broadband wide-angle dispersion measurements: instrumental setup, alignment, and pitfalls.

The construction, alignment, and performance of a setup for broadband wide-angle dispersion measurements, with emphasis on surface plasmon resonance (SPR) measurements, are presented in comprehensive detail. In contrast with most SPR instruments working with a monochromatic source, this setup takes advantage of a broadband∕white light source and has full capability for automated angle vs. wavelength dispersion measurements for any arbitrary nanostructure array. A cylindrical prism is used rather than a triangular one in order to mitigate refraction induced effects and allow for such measurements. Although seemingly simple, this instrument requires use of many non-trivial methods in order to achieve proper alignment over all angles of incidence. Here we describe the alignment procedure for such a setup, the pitfalls introduced from the finite beam width incident onto the cylindrical prism, and deviations in the reflected∕transmitted beam resulting from the finite thickness of the sample substrate. We address every one of these issues and provide experimental evidences on the success of this instrument and the alignment procedure used.

[Economic changes and urban primacy]. / Cambios economicos y primacia urbana.

PIP: The recently published "Economic Change and Urban Primacy in Latin America" by the Colombian researcher L. M. Cuervo analyzed the principal focuses on the relations between the urban network and the economic situation in Latin America. Shortcomings identified by Cuervo include concentration on short-term changes and inadequacy of theory. The three theoretical traditions that have guided most research, dependent urbanization theory, logical empiricism, and historical investigation, should be integrated into one framework to exploit their complementary viewpoints. A comparison of the dominant features of Latin American urban primacy with urban patterns in six European countries indicates that urban primacy is related to the industrial stage of capitalism in both Europe and Latin America, and appears to be more determined by time factors than by economic development. A declining phase of urban primacy appears to be underway in some countries despite strong inertial forces. Cuervo argues that the proportion of the total population in the largest city is a better indictor of trends than is the relationship of the largest city's population to the total for the next three. He warns that signs of declining primacy may reflect only temporary pauses.^ieng