Metamaterial for efficient second harmonic generation

A theoretical study is carried out of the possibility of effective second-harmonic generation in a metamaterial representing a structure of alternating layers of semiconductor material with intrinsic and metallic conductivity that can be grown by epitaxial methods.     

Slab waveguide with conducting interfaces as an efficient optical sensor: TE case

In this paper, three-layer slab waveguide structure is treated for optical sensing applications. Four waveguide configurations including different guiding films and analytes are assumed. A conducting two-dimensional free charge layers with a surface conductivity is assumed to exist at the substrate/film and film/cladding interfaces. The sensing sensitivity of the proposed structure to any changes in an analyte refractive index uniformly distributed in the cladding layer is investigated. Positive as well as negative surface conductivities are considered. It is found that utilizing positive surface conductivity can enhance the sensitivity, whereas using negative values of the surface conductivity reduces the sensitivity.     

Third-harmonic generation in positively dispersive gases with a novel cell

The generation of UV third-harmonic radiation by a focused laser beam in a positively dispersive gaseous medium is investigated. The nonlinear gas is confined to a focal half-space by using a differentially pumped gas cell. The resulting density gradient along the beam axis is shown to provide an efficient frequency conversion in spectral regions of positive dispersion. Experimental results obtained in argon at λ ~ 197 nm, which compare favorably with theory, are presented.     

First-order quasi-phase-matched second-harmonic generation in a LiTaO(3) waveguide

We achieved improvement in conversion efficiency in a first-order quasi-phase-matched second-harmonic generation device that uses a LiTaO(3) waveguide by experimentally characterizing the device process and the performances. Efficient overlaps among propagation light modes and the first-order periodically domain-inverted region are gained in a strongly confined waveguide fabricated by use of proton exchange annealed by a quick heat treatment. A blue-light power of 22 mW is obtained for a conversion efficiency of 18% by using a Ti:Al(2)O(3) laser. The observed FWHM temperature and wavelength acceptance bandwidths for second-harmonic generation power are 2.5 °C and 0.13 nm, respectively. Using this device with antireflection coating on the input and output facets of the waveguide, we generate 1.3 mW of blue light for a conversion efficiency of 4% by direct diode-laser doubling.     

Reduced graphene oxide-based calcium alginate hydrogel as highly efficient solar steam generation membrane for desalination

Solar-driven evaporation has been considered as one of the potentialmethods for desalination and sewage treatment.However,optical concentrators andcomplex multi-component systems are essential in advanced technologies,resulting inlow efficiency and high cost.Here,we synthesize a reduced graphene oxide-basedporous calcium alginate(CA-rGO)hydrogel which exhibits good performance in lightabsorption.More than 90%of the light in the whole spectrum can be absorbed.Meanwhile,the water vapor escapes from the CA-rGO film extremely fast.The waterevaporation rate is 1.47 kg·m^-2·h^-1,corresponding to the efficiency 77%under only 1 kW'm 2 irradiation.The high evaporation efficiency is attributed to the distinctive structureof the film,which contains inherent porous structure of hydrogel enabling rapid watertransport throughout the film,and the concave water surfaces formed in the hydrophilicpores provide a large surface area for evaporation.Hydrophobic rGO divides theevaporation surface and provides a longer three-phase evaporation line.The test onmultiple cyclic radiation shows that the material has good stability.The CA-rGO hydrogelmay have promising application as a membrane for solar steam generation indesalination and sewage treatment.     

Fock states generation in a kicked cavity with a nonlinear medium

Abstract

We discuss a model of a cavity filled with a passive nonlinear ?Kerr‘ medium and periodically kicked by a series of ultra-short laser pulses. The nonlinear medium is described by the (2q ? 1)th nonlinearity X ^(2q?1). We find analytical formulas describing the field states inside the cavity. We show that such a system can produce, depending on the order of the nonlinearity, superpositions of several Fock states with the small photon numbers (0,1; 0,1,2; etc). In particular, the one-photon state can be approached during the evolution of the system with X ⁽³⁾ nonlinearity provided the cavity losses are negligible. The purity of states generated in this process, however, can be seriously degraded by the cavity damping. We perform numerical calculations to validate our analytical results.     

Anomalous refractive indices of the amplifying medium in a waveguide CO2 laser

The relative changes in refractive index of the amplifying medium in a waveguide CO2 laser have been measured as a function of the inlet and outlet pressures, discharge current, gas flow rate, and intracavity power using an interferometric technique. The experiments have been made for two gas mixing ratios over a wide range of the inlet pressure. Saturated phenomena of the refractive index have been observed for increasing inlet pressure. The output power and the variation in impedance of the amplifying medium have been simultaneously measured. The dependence of the refractive index on the inlet pressure in the absence of the discharge, the electron density, and the estimation of errors in measurements are discussed.     

Water as a reaction medium for clean chemical processes

Solvent usage is often an integral part of manufacturing process, whether it is chemical or another industrial sector. Thus, this unavoidable choice of a specific solvent for a desired manufacturing process can have profound economical, environmental, and societal implications. Some of the impacts are long lasting especially from an environmental perspective, which has been well documented in the scientific literature. The pressing need to develop alternative solvents for manufacturing processes originates, in part, from these implications and constitutes an essential strategy under an emerging field of green chemistry. Whereas there have been excellent advances in developing several alternative clean solvents, it is unlikely that the one solvent will be a panacea for various chemical protocols. This article provides some examples of using water as an alternative solvent for chemical reactions with wide-ranging possibilities that include direct use of water soluble renewable materials, C–C bond forming reactions using organometallic reagents, and exploiting the use of alternate energy sources such as solar, microwave and ultrasound in accelerating chemical syntheses.The online version of the original article can be found at     

Water as a reaction medium for clean chemical processes

Solvent usage is often an integral part of manufacturing process, whether it is chemical or another industrial sector. Thus, this unavoidable choice of a specific solvent for a desired manufacturing process can have profound economical, environmental, and societal implications. Some of the impacts are long lasting especially from an environmental perspective, which has been well documented in the scientific literature. The pressing need to develop alternative solvents for manufacturing processes originates, in part, from these implications and constitutes an essential strategy under an emerging field of green chemistry. Whereas there have been excellent advances in developing several alternative clean solvents, it is unlikely that the one solvent will be a panacea for various chemical protocols. This article provides some examples of using water as an alternative solvent for chemical reactions with wide-ranging possibilities that include direct use of water soluble renewable materials, C–C bond forming reactions using organometallic reagents, and exploiting the use of alternate energy sources such as solar, microwave and ultrasound in accelerating chemical syntheses.An erratum to this article can be found at     

Radiation of a charge moving in a waveguide filled with a dielectric medium possessing resonance dispersion

The radiation of a point charged particle moving along the axis of a round waveguide filled with a dielectric medium possessing resonance dispersion is theoretically studied. It is shown that the dispersion significantly influences the frequencies of excited harmonic modes and the energy of radiation. Allowance for dispersion leads to suppression of all excited harmonics to an extent increasing with the order of harmonics.     

Review of techniques for efficient network generation for finite element analysis

Triangle and tetrahedron elements possess special characteristics for automatic network generation in comparison with other element types. They always admit the application of only one element type within a whole arbitrary network structure, which leads to a simplification of the generation process and therefore to a reduction of the work involved. Different techniques for automatic two- and three-dimensional network generation with the application of these two element types will be analysed in this paper. It will be seen that the techniques differ considerably not only in the generation strategy, but also in the quality of the generated network structures for the finite element computations.     

Design rules for phase-matched terahertz surface electromagnetic wave generation by optical rectification in a nonlinear planar waveguide

The theory of guided waves in metal-dielectric planar multilayer structures is applied to reduce the loss and maximize optical nonlinearity for efficient terahertz-field generation in a surface electromagnetic wave by femtosecond laser pulses confined in a (chi)((2)) nonlinear planar waveguide. For typical parameters of thin-film polymer waveguides and metal-dielectric interfaces, the optimal size of the (chi)((2)) waveguide core providing the maximum efficiency of terahertz plasmon-field generation is shown to be less than the wavelength of the optical pump field.     

Design and modelling of dispersion-engineered rib waveguide for ultra broadband mid-infrared supercontinuum generation

We report a dispersion-engineered As₂Se₃ chalcogenide glass rib waveguide structure for ultra broadband mid-infrared supercontinuum generation across molecular ‘fingerprint region’. The proposed rib waveguide structure offers non-linear coefficient as high as 18,250 W^?1 km^?1 at 2.5 μm. Supercontinuum spectrum spanning 2–15 μm, which not only covers the both atmospheric transparent windows (3–5 μm and 8–13 μm) in the mid-infrared domain but also covers the important molecular ‘fingerprint domain’, is obtained using only 4 mm-long rib waveguide structure. To the best of our knowledge, such broadband mid-infrared supercontinuum spectrum in As₂Se₃-based chalcogenide waveguide geometry is reported for the first time. The proposed design of rib waveguide has potential for robust, integrated and low-cost supercontinuum sources in various applications including frequency comb generation, chemical sensing, food quality control and early cancer diagnostics.     

Chaotic millimeter-wave generation on the basis of wideband gyro-amplifiers with a helical corrugated waveguide

The possibility of generating random noiselike radiation in gyro-amplifiers with a helical corrugated waveguide when introducing delayed feedback has been shown. The cyclotron resonance detuning corresponding to the maximum slope of the amplitude characteristic of an amplifier after saturation is optimal for implementing the mode of developed dynamic chaos. Assessments are carried out for the parameters of a noise generator based on an experimentally implemented gyro-travelling-wave tube of 35-GHz band, according to which the generation of multifrequency radiation is possible with a spectrum width of 3—4 GHz, an average power up to 70 kW, and an efficiency of order of 10%.     

RF number as a new index for assessing combustion hazard of flammable gases

A new index called RF number has been proposed for assessing the combustion hazard of all sorts of flammable gases and their mixtures. RF number represents the total expectancy of combustion hazard in terms of flammability limits and heat of combustion for each known and unknown compounds. The advantage of RF number over others such as R-index and F-number for classification of combustion hazard has been highlighted.     

An efficient algorithm for sequential generation of failure states in a network with multi-mode components

In this work a new algorithm for the sequential generation of failure states in a network with multi-mode components is proposed. The algorithm presented in the paper transforms the state enumeration problem into a K-shortest paths problem.Taking advantage of the inherent efficiency of an algorithm for shortest paths enumeration and also of the characteristics of the reliability problem in which it will be used, an algorithm with lower complexity than the best algorithm in the literature for solving this problem, was obtained.Computational results will be presented for comparing the efficiency of both algorithms in terms of CPU time and for problems of different size.     

Clustered DNA damages as dosemeters for ionising radiation exposure and biological responses.

Clustered DNA damages--two or more lesions (oxidised bases. abasic sites, or strand breaks) within a few DNA helical turns on opposing strands--are induced in DNA in solution and in vivo in human cells by ionising radiation. They have been postulated to be difficult to repair, and thus of potentially high biological significance. Since the total of clustered damages produced by ionising radiation is at about 3 to 4 times higher levels than double-strand breaks and are apparently absent in unirradiated cells, levels of clustered damages present immediately alter radiation exposure could serve as sensitive dosemeters of radiation exposure. Since some clusters may not be repairable and may accumulate in cells, they might also be useful as integrating dosemeters of biological effects of radiation damage.     

Optimized inductively coupled plasma etching for poly(methyl-methacrylate-glycidly-methacrylate) optical waveguide

Optical loss is a crucial quality for the application of polymer waveguide devices. The optimized oxygen inductively coupled plasma etching conditions, including antenna power, bias power, chamber pressure, O₂ flow rate and etching time for the fabrication of smooth vertical poly(methyl-methacrylate-glycidly-methacrylate) channel waveguide were systematically investigated. Atomic force microscopy and scanning electron microscopy were used to characterize the etch rate, surface roughness and vertical profiles. The increment of etch rate with the antenna power, bias power and O₂ flow rate was observed. Bias power and chamber pressure were found to be the main factor affecting the interface roughness. The vertical profiles were proved to be closely related to antenna power, bias power and O₂ flow rate. Surface roughness increment was observed when the etching time increased.     

Determining conditions for 13.5-nm radiation generation by a supersonic-xenon-jet laser plasma source

We propose and justify a simple calculation method for (i) evaluating the optimum conditions for the generation of extreme ultraviolet (EUV) emission by a laser plasma source employing a supersonic xenon jet and (ii) finding ways to increase in the efficiency of such sources. The main processes involved in the interaction of laser radiation with a xenon jet target, which account for the EUV emission with a wavelength of 13.5 nm, are taken into account. It is shown that one of the main factors that decreases the output efficiency of such EUV sources is the absorption of generated radiation by the gas target. Qualitative calculations of the optimum conditions for the generation at 13.5 nm have been performed for three lasers with various wavelengths. The most promising results can be expected for a CO₂ laser, for which the radiation conversion efficiency on the order of 3% at a xenon pressure of 10–15 Torr can be achieved.