Characterization of stimulated Brillouin scattering in small core microstructured chalcogenide fiber

We report a full modal characterization of the stimulated Brillouin scattering (SBS) properties in small core As₂Se₃-based chalcogenide photonic crystal fibers (PCFs). Our results include the calculation of Brillouin gain spectrum (BGS), Brillouin gain coefficient (g_B), Brillouin frequency shift (BFS) by taking into account the contribution of the higher-order acoustic modes. We show that for a highly nonlinear PCF having a 2-μm hole-to-hole pitch and a 0.5-μm hole diameter, a Brillouin gain coefficient g_B = 5.91 10^? 9 m.W^? 1 is obtained around the acoustic frequency of 8.19 GHz, which is more than 340 times larger than that of the same PCF made with silica glass. We demonstrate that the BGS of small core PCF structures show strong SBS and multipeaked behavior, with a presence of a second peak, when decreasing the core diameter which is to be attributed to the higher-order acoustic modes. We designed small core PCFs with tailored Brillouin response for a wide range of applications.     

Ionic conductivity in borate glasses with three types of mixed alkali cations

We have investigated the temperature- and frequency-dependent ionic conductivity in (Li_0.67 ? xNa_0.33 Rb_x)₂B₄O₇ (LNRBO) glasses with x = 0, 0.07, 0.2, 0.33, 0.47, and 0.6. The mixed alkali effect of the ternary mixed alkali system LNRBO is compared with that of the binary mixed alkali systems (Li_1 ? xNa_x)₂B₄O₇ (LNBO), (Li_1 ? xRb_x)₂B₄O₇ (LRBO) and the single alkali glass Rb₂B₄O₇ (RBO). From the results of the dc conductivity and dc activation energy, we observe that the LNRBO system exhibits the combined characteristic of binary mixed alkali systems LNBO and LRBO. It is found that the power-law exponent n for binary alkali glass is the same as that for ternary alkali glass but it is lower than that for single alkali glass. This indicates that the dimensionality of conducting pathway in the mixed alkali glasses of LNBO, LRBO and LNRBO is lower than that in the single alkali RBO. We discuss the concentration dependence of the dc conductivity and dc activation energy in the framework of the bond valence technique to reverse Monte Carlo produced structural model [Phys. Rev. Lett. 90, 155507 (2003)].     

Differential structure on the κ-Minkowski spacetime from twist

We study four-dimensional κ  -Minkowski spacetime constructed by the twist deformation of U(igl(4,R))$U(\mathit{igl}(4,R))$. We demonstrate that the differential structure of such twist-deformed κ-Minkowski spacetime is closed in four dimensions contrary to the construction of κ-Poincaré bicovariant calculus which needs an extra fifth dimension. Our construction holds in arbitrary dimensional spacetimes.     

Full modal analysis of the Brillouin gain spectrum of an optical fiber

We present a numerical study of stimulated Brillouin scattering in optical fibers based on a full modal analysis of the acoustic and optical properties. The computation of each acoustic mode supported by the fiber structure allows us an accurate and detailed investigation of the characteristics of the Brillouin gain spectrum. We focus our attention on the contribution of the higher-order acoustic modes which are sometimes ignored because of computational issues in particular on optical fibers that act as acoustic antiwaveguides. Our analysis clearly highlights their role and their dependence on the physical and geometrical structure of the fiber.     

Carleson Measures via BMO

We obtain new characterizations of Carleson measures via uniform boundedness of BMO norms of certain mass functions associated with the given measure in a natural way. This research was performed during M. Stessin’s visit to Korea University. He thanks the Mathematics Department of Korea University and the “Brain Pool” program for their hospitality and support. The first two authors were supported by the Korea Research Foundation Grant funded by the Korean Government (KRF-2008-314-C00012).     

High energy femtosecond supercontinuum light generation in large mode area photonic crystal fiber

A large mode area photonic crystal fiber (LMA PCF) with an effective area of 180 μm² is used to generate a high energy, micro-joule range, flat, octave spanning supercontinuum (SC) extending from ~ 600 nm to ~ 1720 nm. A train of femtosecond pulses from a widely-tunable parametric amplifier pumped by a Ti:Sapphire regenerative amplifier system are coupled into a 20 cm length of LMA PCF generating a SC of 1.4 μJ energy. We present an experimental study of the high energy SC as a function of the input power and the pumping wavelength. The spectrum obtained at a pump wavelength of 1260 nm presents spectral flatness variation less than 12 dB over more than 1.1 octave bandwidth. The physical processes behind the SC formation are described in the normal and the anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation.     

Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

Optoelectronic and conductivity of ᴫ‐conjugated polymers based on phenylenevinylene, 1,3,4‐thiadiazole and thiophene: Suitable candidates for n‐type organic semiconductors

New poly‐phenylenevinylenes PPVs containing 1,3,4‐thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time‐dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH₂–P(=O)(OCH₃)₂, and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy E_vert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n‐type semiconductors.     

Green chemistry: Analytical and chromatography

Nowadays, the environment protection and the personal health and safety are given more consideration in the field of chemistry, thus resulting in an increased number of published researches about how to work according to green instructions, to follow up the recommendations of environmental agencies and to obtain better clean handling of chemistry. In this review, green chemistry definition, importance, principles, and some recent applications in the field of green chemistry were discussed. In addition, the review summarizes the evolution of green analytical chemistry (GAC) with its specific principles and how to make the analytical process more environmentally benign with special emphasis on recent applications of GAC. Moreover, the green chromatography, its methods, and some of its applications were outlined. Finally, different techniques available up till now for the assessment of greening of the methods were also presented.