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Abstract: Trefoil and quatrefoil channels between air holes of two microstructure fibers can strongly confine light field and act as highly nonlinear waveguides. Polarization-dependent blue-shifted emissions of femtosecond Ti:sapphire laser pulses were carried out in these channels. The spectra bandwidth of blue-shifted emissions in a trefoil channel is narrower than 10nm and can be tuned slightly by altering the polarization state of pump light. Polarization-dependent blue-shifted emissions from a quatrefoil channel lie in a hollow beam having potential use in optical tweezers. [Copyright &y& Elsevier]

Abstract: Single-phase β-FeSi2 thin films have been grown on quartz substrates using femtosecond laser deposition (800nm, 50fs, 1KHz) under gas pressure of 3.0×10−4 Pa. X-ray diffraction (XRD) and field-emission scanning electron microscopy (SEM) were used to determine the structural properties and surface images of the films. Typical XRD patterns of the film showed that no other diffraction peak except β-FeSi2 was found. The SEM results indicated that the films were composed of well-distributed grains, in the range 50–150nm in diameter. In addition, normal incidence spectral transmittance and reflectance data suggested that the β-FeSi2 film has a direct energy gap of about 0.85eV. The thickness of the layer and the refractive index of the film were determined by performed calculation in the wavelength range 1.9–2.7μm. Furthermore, the Raman spectra of the films were also discussed. [Copyright &y& Elsevier]

Abstract: Single-phase β-FeSi2 thin films were prepared on Si(100) and Si(111) wafers by using femtosecond laser deposition with a FeSi2 alloy target for the first time. X-ray diffraction (XRD), field scanning electron microscopy (FSEM), scanning probe microscopy (SPM), electron backscattered diffraction pattern (EBSD), and Fourier-transform Raman infrared spectroscopy (FTRIS) were used to characterize the structure, composition, and properties of the β-FeSi2/Si films. The orientation of β-FeSi2 grains was found to depend on the orientation of the Si substrates, and photoluminescence at wavelength of 1.53 μm was observed from the single-phase β-FeSi2/Si thin film at room temperature (20 °C). [Copyright &y& Elsevier]

Abstract: SrAl4O7 was synthesized by Pechini method using citric acid as a chelating agent and ethylene glycol as an esterification agent. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of SrAl4O7 were investigated. Increasing the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration promoted the formation of SrAl4O7. When the molar ratio of citric acid to total metal cations concentration was 2, well crystallized, single-phase SrAl4O7 was synthesized at 900°C for 2h for the precursor with pH 7, but it could not be obtained for the precursor with pH 1. Increasing the molar ratio of citric acid to total metal cations concentration up to 4, single-phase SrAl4O7 was also synthesized at 900°C for 2h for the precursors with pH 7, but it was obtained at 1100°C for 2h for the precursors with pH 1. The stability of SrAl4O7 as a function of time and temperature was determined. We found that SrAl4O7 can be stable up to 1400°C for 2h and it shows decomposition at 1500°C for 2h. Heating single-phase SrAl4O7 powder at 1600°C for 2h, most of SrAl4O7 decomposes to SrAl12O19 as the major phase and an unidentified phase (main reflection at d =3.0149). DSC, TG, FT-IR and XRD were used to characterize the precursors and the derived oxide powders. [Copyright &y& Elsevier]

Abstract: La(Mg1/2Ti1/2)O3 was synthesized via citric acid precursor. The effect of the pH of the starting solution and the molar ratio of citric acid to total metal cations concentration CA/M on the formation of La(Mg1/2Ti1/2)O3 was studied. It is found that increasing the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration enhances the formation of La(Mg1/2Ti1/2)O3. Single-phase La(Mg1/2Ti1/2)O3 was obtained from the precursor with CA/M=1 and pH=7 at 800°C for 2h, without formation of any intermediate phase. The precursors and derived powders were characterized by DTA, TG, X-ray diffraction and Fourier transform infrared spectroscopy. [Copyright &y& Elsevier]

• We firstly propose a cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve multimode beam quality. • Radial offset between fiber 1 and fiber 2 of the cascaded multimode fiber system should be as small as possible for cascaded beam self-cleaning. • Our results also suggest that an increased number of HOMs with negligible energy along with a higher number of cascaded fibers contribute to superior multimode beam quality. Spatial beam self-cleaning has shown a nonlinear improvement in beam quality in multimode fibers (MMFs), proving its value in high-power fiber lasers and nonlinear biomedical imaging. In this Letter, we propose a novel cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve beam quality. Through this scheme, the initially speckled beam gradually evolves into a well-defined bell-shaped, primarily dominated by the fundamental mode, after undergoing two or three cascaded self-cleaning processes. Simulation results also suggest that an increased number of high-order modes (HOMs) with negligible energy along with a higher number of cascaded fibers contribute to superior beam quality. This phenomenon is attributed to the new excited HOMs acting as attractor and facilitating an energy cascade towards the fundamental mode. [ABSTRACT FROM AUTHOR]

Ultrafast electron pulses generated using femtosecond lasers offer a direct means for investigating ultrafast processes, but the yield of electron emission remains a significant practical limitation. This study demonstrates a substantial enhancement in yield of electron emission from carbon nanotubes induced by two-color (ω + 2 ω) pulses with an 80 MHz repetition rate and this enhancement is non-delay-dependent. Compared to the sum of photocurrents induced by each color pulse individually, the combined two-color pulses result in a remarkable enhancement in yield of electron emission by more than 25 times. We attribute this enhanced yield to carrier-assisted optical field emission: carbon nanotubes sustain high carrier concentration state under laser radiation thereby enhancing yield of electron emission. We propose the carrier migration emission model to provide a semi-quantitative description for the carrier-assisted optical field emission. This phenomenon introduces a new method to increase the yield of ultrafast electron pulses from CNTs and paves the way for next-generation ultrafast electron emitters and on chip ultrafast optoelectronic device. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Linear Thomson scattering by a relativistic electron of a short pulse laser has been investigated by computer simulation. Under a laser field with a pulse of 33.3-fs full-width at half-maximum, and the initial energy of an electron of , the motion of the electron is relativistic and generates an ultrashort radiation of 76-as with a photon wave length of 2.5-nm in the backward scattering. The radiation under a high relativistic energy electron has better characteristic than under a low relativistic energy electron in terms of the pulse width and the angular distribution. [Copyright &y& Elsevier]

Abstract: The characteristics of harmonic radiation due to electron oscillation driven by an intense femtosecond laser pulse are analyzed considering a single electron model. An interesting modulated structure of the spectrum is observed and analyzed for different polarization. Higher order harmonic radiations are possible for a sufficiently intense driving laser pulse. We have shown that for a realistic pulsed photon beam, the spectrum of the radiation is red shifted as well as broadened because of changes in the longitudinal velocity of the electrons during the laser pulse. These effects are more pronounced at higher laser intensities giving rise to higher order harmonics that eventually leads to a continuous spectrum. Numerical simulations have further shown that by increasing the laser pulse width broadening of the high harmonic radiations can be limited. [Copyright &y& Elsevier]

Abstract: BaTi4O9 was synthesized via polymeric precursor made of citric acid and ethylene glycol. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of BaTi4O9 were investigated. Increasing the pH of the starting solutions retarded the formation of BaTi4O9, but the increase of the molar ratio of citric acid to total metal cations concentration enhanced the formation of BaTi4O9. Single-phase BaTi4O9 was obtained at 1100°C for 2h when the molar ratio of citric acid to total metal cations concentration was unity, independent of the pH of the starting solutions. Increasing the molar ratio of citric acid to total metal cations concentration up to 2, single-phase BaTi4O9 was synthesized at 1000°C for 2h for the pH unadjusted precursors, but for the precursors with pH 6.0, the formation temperature of single-phase BaTi4O9 was increased to 1100°C. When the molar ratio of citric acid to total metal cations concentration was increased further up to 4, single-phase BaTi4O9 formed at 1000°C for 2h for the precursors with or without pH adjustment. DSC, TG, XRD and FESEM were used to characterize the precursors and the derived oxide powders. Details of the synthesis and characterizations of the resultant products were given. [Copyright &y& Elsevier]

Abstract: Single-phase La(Mg1/2Ti1/2)O3 has been prepared by ethylenediaminetetraacetic acid (EDTA) gel combustion synthesis process. The process starts with a pH adjusted aqueous solutions of La(NO3)3, Mg(NO3)2·6H2O, Ti(OC4H9)4, and EDTA. Combustion reactions occur when heating the gel to 250°C, which convert them to La(Mg1/2Ti1/2)O3 with traces of carbonaceous material directly. The derived powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, SEM and laser particle size distribution analysis. [Copyright &y& Elsevier]

Abstract: The spectral properties in different concentration of Yb ions (0.5–5mol%)-doped silica glasses are explored in this paper. The glasses are prepared by traditional melting method. The absorption spectra and the fluorescent lifetime (τ f) are measured at room temperature and low temperature (18K). The stimulated cross-section (σ emi) and potential laser properties (β min, I sat, I min) are calculated based on the absorption spectra. The absorption cross-section (σ abs) are in the range 1.08×10−20– 1.18×10−20 cm2 in different glasses, the fluorescence lifetime (τ f) change from 1.9 to 1.2ms with the increase of Yb3+ concentration. The potential laser properties indicate that lead silica glass is a good host for highly Yb ion doping glass. [Copyright &y& Elsevier]

Highlights • Our fiber curvature sensor has merits of inline compact, low cost and sensitive. • Highly sensitivity −15.33 dB/m−1 in the range 3.63–4.69 m−1 is experimentally demonstrated. • Low cross sensitivity 0.018 m−1/°C implies it is insensitive to environmental temperature change. Abstract An inline fiber structure formed by a silica tube spliced between single-mode fibers has been developed and tested for curvature measurement based on anti-resonant reflecting waveguide. A Fabry-Perot resonator with leaky modes of guided light in the silica tube is formed based on anti-resonant effect in the resonant wavelengths, which results in lossy dips in the transmission spectrum. Since the transmission power of the resonant dips is sensitive to structure bending, an inline curvature sensor can be realized. Experimental results reveal a high sensitivity up to −15.33 dB/m−1 in the wide curvature range of 3.63–4.69 m−1. The proposed sensor also demonstrates a low temperature sensitivity 0.27 dB/°C implying a small temperature cross sensitivity 0.018 m−1/°C. Our sensor has its merits of compact, low cost and high sensitivity. [ABSTRACT FROM AUTHOR]