Chirped-cavity dispersion-compensation filter design

A new basic structure of a dispersive-compensation filter, called a chirped-cavity dispersion-compensator (CCDC) filter, was designed to offer the advantages of small ripples in both reflectance and group-delay dispersion (GDD). This filter provides a high dispersion compensation, like the Gires-Tournois interferometer (GTI) filter, and a wide working bandwidth, like the chirped mirror (CM). The structure of the CCDC is a cavity-type Fabry-Perot filter with a spacer layer (2 mH or 2 mL) and a chirped high reflector. The CCDC filter can provide a negative GDD of -50 fs2 over a bandwidth of 56 THz with half the optical thickness of the CM or the GTI.     

Design, fabrication, and analysis of chirped multilayer mirrors for reflection of extreme-ultraviolet attosecond pulses

Chirped Mo/Si multilayer coatings have been designed, fabricated, and characterized for use in extreme-ultraviolet attosecond experiments. By numerically simulating the reflection of the attosecond pulse from a multilayer mirror during the optimization procedure based on a genetic algorithm, we obtain optimized layer designs. We show that normal incidence chirped multilayer mirrors capable of reflecting pulses of approximately 100 attoseconds (as) duration can be designed by enhancing the reflectivity bandwidth and optimizing the phase-shift behavior. The chirped multilayer coatings have been fabricated by electron-beam evaporation in an ultrahigh vacuum in combination with ion-beam polishing of the interfaces and in situ reflectivity measurement for layer thickness control. To analyze the aperiodic layer structure by hard-x-ray reflectometry, we have developed an automatic fitting procedure that allows us to determine the individual layer thicknesses with an error of less than 0.05 nm. The fabricated chirped mirror may be used for production of 150-160 as pulses.     

Femtosecond laser-induced damage of HfO₂/SiO₂ mirror with different stack structure

Laser-induced damage of the "standard" (λ/4 stack structure) and "modified" (reduced standing-wave field) HfO₂/SiO₂ mirrors were investigated by a commercial 800?nm Ti:sapphire laser system. Three kinds of pulse duration of 50?fs, 105?fs, and 135?fs were chosen. The results show that the single-shot damage threshold of the "modified" mirror was about 14%-23% higher compared to that of the "standard" mirror. A model based on the rate equation for free electron generation was adopted to explain the threshold results. It took in account the transient changes in the dielectric function of material during the laser pulse. The simulated threshold agreed with the experimental very well. Besides, for two kinds of mirror, typical breakdown craters for both the single-shots and multi-shots damage tests reveal striking distinct characteristics. Interestingly, the multi-shots damage crater with zigzag-like edge was observed only on the "standard" mirror. These phenomena were illustrated reasonably by the distribution features of the electric field intensity within the mirrors.     

Hybrid integrated photodetector with flat-top steep-edge spectral response

Hybrid integrated photodetectors with flat-top steep-edge spectral responses that consist of an Si-based multicavity Fabry-Perot (F-P) filter and an InP-based p-i-n absorption structure (with a 0.2?μm In_0.53Ga_0.47As absorption layer), have been designed and fabricated. The performance of the hybrid integrated photodetectors is theoretically investigated by including key factors such as the thickness of each cavity, the pairs of each reflecting mirror, and the thickness of the benzocyclobutene bonding layer. The device is fabricated by bonding an Si-based multicavity F-P filter with an InP-based p-i-n absorption structure. A hybrid integrated photodetector with a peak quantum efficiency of 55% around 1549.2?nm, the -0.5 dB band of 0.43?nm, the 25?dB band of 1.06?nm, and 3?dB bandwidth more than 16?GHz, is simultaneously obtained. Based on multicavity F-P structure, this device has good flat-top steep-edge spectral response.     

Carbon nanotube-TiO(2) hybrid films for detecting traces of O(2)

Hybrid titania films have been prepared using an adapted sol-gel method for obtaining well-dispersed hydrogen plasma-treated multiwall carbon nanotubes in either pure titania or Nb-doped titania. The drop-coating method has been used to fabricate resistive oxygen sensors based on titania or on titania and carbon nanotube hybrids. Morphology and composition studies have revealed that the dispersion of low amounts of carbon nanotubes within the titania matrix does not significantly alter its crystallization behaviour. The gas sensitivity studies performed on the different samples have shown that the hybrid layers based on titania and carbon nanotubes possess an unprecedented responsiveness towards oxygen (i.e.?more than four times higher than that shown by optimized Nb-doped TiO(2) films). Furthermore, hybrid sensors containing carbon nanotubes respond at significantly lower operating temperatures than their non-hybrid counterparts. These new hybrid sensors show a strong potential for monitoring traces of oxygen (i.e.?≤10?ppm) in a flow of CO(2), which is of interest for the beverage industry.     

Group delay dispersion measurement of a dispersive mirror by spectral interferometry: comparison of different signal processing algorithms

We built a dispersive white-light spectral interferometer for precisely measuring the dispersion properties of a multilayer thin-film structure. A novel algorithm with improved robustness to measurement errors is presented by combining a windowed Fourier transformation with wavelet-based differentiation. Compared with previously published algorithms, this method shows substantial resistance to measurement errors. The group delay dispersion properties of bulk materials and a homemade chirped mirror are measured by our apparatus, and the measurement result manifests considerable accuracy and robustness. The technique shows reasonable potential for the characterization of ultrabroadband chirped mirrors.     

Synthesis of fluorescent and photovoltaic Cu(2)O nanocubes

Hollow and filled Cu(2)O nanocubes of about 28 ± 5?nm in edge length with a band gap ～2.42?eV have been prepared from cupric nitrate in alkaline aqueous solutions containing fructose and ascorbic acid at room temperature. To the best of our knowledge, this simple strategy demonstrates the first example of preparing high-quality Cu(2)O nanocubes (yield>95%) with sizes smaller than 30?nm. By controlling several important experimental parameters such as pH, concentrations of fructose, and molar ratios of fructose/copper (II), different Cu(2)O nanostructures were prepared. The cubic nanostructures were evidenced by the metal shadowing and transmission electron microscope (TEM) images. We confirmed that the Cu(2)O nanocubes were formed from hollow to filled structures by conducting time-evolution TEM measurements. The thus-prepared Cu(2)O nanocubes possess size-dependence absorption and luminescence characteristics; they absorb light at wavelengths 360 and 454?nm and fluoresce at 493?nm (quantum yield 6.6 × 10(-2)%) when excited at 360?nm. A film of Cu(2)O nanocubes provided a photocurrent density of ～80?mA?m(-2) at a biased voltage 3?V under sunlight illumination (100?mW?cm(-2)).     

Synthesis and characterization of insulin/zirconium phosphate@TiO2 hybrid composites for enhanced oral insulin delivery applications

Abstract

In this work, a series of composites of insulin (Ins)/zirconium phosphate (ZrP) were synthesized by intercalation method, then, these composites were coated with TiO₂ by sol-gel method to prepare Ins/ZrP@TiO₂ hybrid composites and the drug release of the composites was investigated by using UV-Vis spectroscopy. Ins/ZrP (10, 30, 60?wt%) composites were prepared by intercalation of insulin into the ZrP layers in water. Then Ins/ZrP composites were coated with different amounts of TiO₂ (30, 50, 100?wt %) by using titanium tetra n-butoxide, as precursor. Formation of intercalated Ins/ZrP and Ins/ZrP@TiO₂ hybrid composites was characterized by FT-IR, FE-SEM, BET and XRD analysis. Zeta potential of the optimized Ins/ZrP@TiO₂ hybrid composite was determined ?27.2?mV. Cytotoxic effects of the optimized Ins/ZrP@TiO₂ hybrid composite against HeLa and Hek293T cell lines were evaluated using MTT assay and the results showed that designed drug delivery system was not toxic in biological environment. Compared to the Ins/ZrP composites, incorporation of TiO₂ coating enhanced the drug entrapment considerably, and reduced the drug release. The Ins/ZrP composites without TiO₂ coating released the whole drug after 30?min in pH 7.4 (phosphate buffer solution) while the TiO₂-coated composites released the entrapped drug after 20?h. In addition to increasing the shelf life of hormone, this nanoencapsulation and nanocoating method can convert the insulin utilization from injection to oral and present a painless and more comfortable treatment for diabetics.     

Low-Loss Dielectric Mirror with Ion-Beam-Sputtered TiO 2-SiO 2 Mixed Films

Ion-beam-sputtered TiO(2)-SiO(2) mixed films with 17% SiO(2) concentration were used as high-refractive-index layers in a multilayered-stack dielectric mirror. Experimental results indicated that total loss of the as-deposited mirror was 34% lower than that of the as-deposited conventional mirrors with pure TiO(2) films used as high-refractive-index layers. In addition, annealing reduced total loss of the mirrors. Although decreasing with an increasing annealing temperature, total loss of the conventional mirrors dramatically increased above ~200 degrees C annealing temperature, owing to increased scattering from an amorphous-to-crystalline phase transition in the TiO(2) films. In addition, total loss of the mirrors with the mixed films continuously decreased with an increasing annealing temperature up to 400 degrees C without the phase transition. Total loss was reduced 88% by means of decreasing absorption in the mixed films. Moreover, the annealed mirror with mixed films was better than both the as-deposited mirror and the conventional mirror with pure films in terms of laser-damage resistance.     

Development of Ni-based and CeO2-modified coatings by microwave heating

In the present investigation the microwave hybrid heating process was used to develop coatings on P20 tool steel substrates. The experiments were carried out in a domestic microwave oven of 900?W and 2.45?GHz frequency for a duration of 360?s. Ni-based clads/coatings without cerium oxide (CeO₂;unmodified coating) and with the addition of CeO₂ (modified coating) with varying wt.% of 1–3 were developed by the microwave hybrid heating process. The effect of CeO₂ addition on the microstructure, X-ray diffraction, and Vickers hardness, and the abrasive wear behavior of the developed clads was studied under varying sliding speeds and grit sizes. Investigation showed that the optimal addition of CeO₂ (1?wt.%) can effectively improve the microstructure, hardness, and abrasive wear behavior of the coatings. The Vicker’s microhardness of the modified coating with 1?wt.% of CeO₂ was 30% higher than the unmodified coating. Abrasive wear resistance of the modified coatings was found higher with an optimal addition of 1?wt.% CeO₂ at varying sliding speeds and grit sizes.     

Visualization of the electrocatalytic activity of three-dimensional MoSe<Subscript>2</Subscript>@reduced graphene oxide hybrid nanostructures for oxygen reduction reaction

Developments of nanostructured transition metal dichalcogenides (TMDs) materials as novel electrocatalyst candidates for oxygen reduction reaction (ORR) is a new strategy to promote the developments of non-precious metal ORR catalysts. In this work, a three-dimensional (3D) hybrid of rosebud-like MoSe₂ nanostructures supported on reduced graphene oxide (rGO) nanosheets was successfully synthesized through a facile hydrothermal strategy. The prepared MoSe₂@rGO hybrid nanostructure showed enhanced electrocatalytic activity for the ORR in alkaline medium compared to that of the pure MoSe₂, rGO, and their simple physical mixture, which could benefit from the excellent oxygen adsorption ability of the abundantly exposed active edge sites of the ultrathin MoSe₂ layers, the conductivity and aggregation-limiting effect of the rGO platform, as well as the unique 3D rosebud-like architecture of the hybrid material. The electrocatalytic activity of the MoSe₂@rGO hybrid towards ORR was comparable to that of commercial Pt/C catalysts. And the promoted reaction was revealed to involve a nearly four-electron-dominated ORR process by analysis of the obtained Koutecky–Levich plots. The scanning electrochemical microscopy (SECM) technique, with the advantages of investigating of the local catalytic activity of samples with high spatial resolution and simultaneously evaluating activities of different catalysts in a single experiment, was further applied to investigate the local ORR electrocatalytic activity of MoSe₂@rGO and compare it with those of other catalyst samples through applying different sample potentials. The excellent stability and methanol tolerance of the 3D nanostructured MoSe₂@rGO hybrid against methanol further prove the 3D nanostructured MoSe₂@rGO hybrid as a promising ORR electrocatalyst in alkaline solution for potential applications in fuel cells and metal–air batteries.

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Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSe(x)Te(1-x) nanocrystals

A series of ternary tetrapodal nanocrystals of CdSe(x)Te(1-x) with x = 0?(CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V(oc)), short-circuit current (J(sc)) and power conversion efficiency (η) of the devices all increased with increasing Se content in the CdSe(x)Te(1-x) nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1?w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80?mW?cm(-2), and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510?nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals.     

Application of liquid chromatography/quadrupole-linear Ion trap mass spectrometry and time-of-flight mass spectrometry to the determination of pharmaceuticals and related contaminants in wastewater

This paper describes an enhanced liquid chromatography-mass spectrometry (LC-MS) strategy for the analysis of a selected group of 56 organic pollutants in wastewater. This group comprises 38 pharmaceuticals and 10 of their most frequent metabolites, 6 pesticides, and 2 disinfectants. The LC-MS methodology applied is based in the use of a hybrid triple-quadrupole linear ion trap mass spectrometer (QTRAP) in combination with time-of-flight mass spectrometry (TOF-MS). The join application of both techniques provided very good results in terms of accurate quantification and unequivocal confirmation. Quantification was performed by LC-QTRAP-MS operating under selected reaction monitoring (SRM) mode in both positive and negative electrospray ionization. Unequivocal identification was provided by the acquisition of three SRM transitions per compound in most of the cases and by LC-TOF-MS analysis, which allows obtaining accurate mass measurements of the identified compounds with errors lower than 2 ppm. Additionally, the use of TOF-MS permits retrospective analysis, since the full spectrum is recorded at all times with a high sensitivity. Thus, review of recorded chromatograms looking for new compounds or transformation products suspected to be present in the samples is feasible allowing one to increase the scope of the method along the monitoring program. The analytical performance of the quantitative LC-QTRAP-MS method was evaluated in effluent wastewater samples. Linearity of response over 3 orders of magnitude was demonstrated for most compounds (R(2) > 0.99). Method limits of detection were between 0.04 and 50 ng L(-1). Finally, the methodology was successfully applied to a monitoring study intended to characterize wastewater effluents of six sewage treatment plants in Spain. The presence of most of compounds was detected at concentrations ranging from 9 ng L(-1) (atrazine) to 15 microg L(-1) (paraxanthine).     

Theoretical and experimental studies of broadband phase-controlled attosecond mirrors

We present procedures to develop and characterise chirped multilayer mirrors for attosecond pulses. The design procedure involves a simulated annealing optimisation algorithm to obtain a multilayer structure with the desired performances. The characterisation step requires the use of well-calibrated attosecond and synchrotron beam lines, allowing one to measure the amplitude and phase response of the mirror. We illustrate these approaches with a set of mirrors designed to have zero or negative dispersion. The remarkable agreement between theoretical and experimental performances validates this overall process, and demonstrates the capability of such mirrors to control the temporal profile of attosecond pulses. These tools and techniques for developing attosecond chirped mirrors will facilitate the generalisation of such components on attosecond experiments.     

Intracavity Beam Behavior in Hybrid Resonator Planar-Waveguide CO(2) Lasers

We describe a combined computer simulation and experimental investigation of the intracavity spatial beam profile characteristics of a planar-waveguide rf-excited CO(2) laser that incorporates a hybrid waveguide confocal unstable negative-branch resonator. The study includes results for the intracavity lateral beam intensity profile and output power of the laser as a function of resonator mirror misalignment. In addition, the behavior of the unstable resonator, observed experimentally and predicted by the simulation, in generating localized high intensity hot-spots when it is subjected to relatively large misalignment angles is reported.     

Compact Integrated Optical Immunosensor using Replicated Chirped Grating Coupler Sensor Chips

A novel compact multichannel integrated optical sensor module isdescribed. Its performance is demonstrated by measurement of the mass adsorption of an analyte molecule to the transducer surface by refractometry in an immunosensor experiment. The signal transduction is achieved by means of chirped grating couplers, which allow simple yet highly functional sensor modules to be built. The experiments were performed with high-sensitivity replicated polycarbonate TiO(2) waveguide sensor chips for detecting the binding of rabbit immunoglobulin to immobilized protein A. Aresolution of ?3 pg/mm(2) surface mass coverage was obtained in a dual-channel module with size 10 cm x 10 cm x10 cm.     

PU(U)A/SiO2杂化水分散液及成膜性能研究

用异佛尔酮二异氰酸酯(IPDI)、聚酯二元醇、二羟甲基丙酸(DMPA)、乙二胺、二乙醇胺、甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)、甲基丙烯酸羟乙酯(HEMA)通过原位聚合方法合成了聚氨酯(脲)/聚丙烯酸酯水分散液,并且通过溶胶-凝胶方法合成了聚氨酯(脲)/聚丙烯酸酯/硅溶胶(PU(U)A/SiO2)杂化水分散液.杂化水分散液在pH值为7～11时的贮存稳定性大于1年;经高温、冻融试验后,无絮凝或沉淀出现,与PU(U)A水分散液相同.杂化膜的摆杆硬度、粘附力、耐吸水性、耐溶剂性比无硅溶胶的膜性能好.PU(U)A/SiO2杂化水分散稀溶液成膜后的透射电镜(TEM)结果表明,粒径为8～10nm的硅溶胶(SiO2)包覆在粒径 为50～200nm的PU(U)A粒子外围.ART-FTIR分析结果表明,杂化膜表面富含Si-O-Si官能团.AFM结果表明,与PU(U)A膜相比,杂化膜的硬区相畴尺寸变小.     

Chirped femtosecond pulse scattering by spherical particles

Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g(τ) = exp[-π(1 + ib)τ(2)], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength (λ(0) = 0.5 μm) and pulse-filling coefficient (l(0) = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the chirped-pulse scattering seems blind: it depends only on the amount of chirp (|b|), regardless of upchirp (b > 0) or downchirp (b< 0).     

Frequency switching multiwavelength Brillouin Raman fibre laser based on feedback power adjustment technique

A simple switchable multiwavelength Brillouin–Raman fibre laser (BRFL) was demonstrated. The laser was arranged in a half-open cavity configuration including a physical mirror device with an adjustable reflectivity at one side of the laser cavity. The impact of the feedback power adjustment on frequency switching was carried out by comparing the peak power difference between odd- and even-order Stokes lines. Up to 468 flat-amplitude lines with a 10?GHz frequency spacing and average optical signal to noise ratio (OSNR) of 33 dB were observed with mirror reflectivity values of ～15% up to 60% at a 1534?nm Brillouin pump power of 7?dBm and 0.9?W Raman pump power of 0.9?W. – Under the same pumping conditions, setting the mirror reflectivity at its OFF state (where reflectivity is nearly 0%) allows for up to 242 lines with 20?GHz spacing to be realized, with ONSR values of ～35?dB.     

Efficient analytic computation of dispersion from multilayer structures

We demonstrate an inductive method for computing exact derivatives of reflection phase for layered media by using the transfer-matrix formalism. The algorithm scales linearly with the number of layers. We show a physically realistic approximation that leads to an efficient procedure for accurately computing dispersion significantly faster than with standard finite-difference methods. We discuss the theory behind the approximation and show results for a dispersion-compensating chirped mirror from a Ti: sapphire laser.