Modelling of diffraction in pillar vertical cavity surface-emitting lasers with embedded Bragg layers

An analytical expression for the reflectivity between the active cavity of a circular symmetric pillar vertical cavity surface-emitting laser (VCSEL) and Bragg mirror, which takes account of diffraction at the interface, is derived. The method (mode-matching in Hankel space) is also used to determine the reflectivity with some of the Bragg layers embedded in the cavity region. The dependence of reflectivity upon various parameters, including number of Bragg pairs, cavity radius and mode number, is discussed. The validity of using the plane wave reflectivity value (which ignores diffraction effects) is seen to depend significantly upon these parameters. As an indicator of the importance of taking these effects into account for pillar diameters of 6 m and less, the variation of threshold gain with cavity radius is given for a commonly used type of VCSEL structure.     

Specific interactions in blends of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin): FTIR and thermal study

Blends of poly(ethylene oxide) (PEO) of high molecular weight with poly(bisphenol A-co-epichlorohydrin) (PBE) with high epoxy equivalent were studied spectroscopically, thermally and morphologically. As similar systems of low molecular weight, a single T_g was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherulites as the PBE is added is also observed. Quantitative analysis from FTIR spectra provided determination of specific interactions between the constituents and their variation with PEO content. Simulations were performed utilising the spectra of the pure polymers to confirm that the observed changes in the experimental spectra of the blends were due to interaction between the polymers.     

Excited-state intramolecular charge transfer in 9-aminoacridine derivative

A new fluorochromic dye was obtained from the reaction of 9-aminoacridine with ethyl-2-cyano-3-ethoxyacrylate. It displays complex fluorescence that is ascribed to normal emission from the acridine chromophore in addition to excited-state intramolecular charge transfer (ESICT) formed upon light excitation. The analysis of the fluorescence decays in different solvents reveals two short-lived components in the range of 80-450 ps and 0.7-3.2 ns, ascribed to the formation and decay of the intramolecular charge transfer (ICT) state, in addition to a third component of about 9.0 ns, which is related to the normal emission from the acridine singlet excited state, probably in an enol-imine tautomeric form. The ICT emission is readily quenched by water addition to polar solvents, and this effect is ascribed to changes in the keto-amine/enol-imine equilibrium of this fluorochromic dye.     

Cereus jamacaru: A Non Buffered LC Quantification Method to Nitrogen Compounds

This study proposes an RP 18 LC method for the analysis of some common nitrogen-containing compounds. This method has used the ionic pair concept in the mobile phase with sulfuric acid and lauril sodium sulfate in its composition. N-Methyltyramine and hordenine have been identified for the first time in this species.