Catálogo de publicaciones - revistas

<jats:p>We demonstrate an all-fiberized narrow-linewidth nanosecond amplifier with high peak power, tunable pulse width, and repetition rate. A fiber-coupled narrow-linewidth laser diode operating at 1064.1 nm is employed as the seed source, which is gain-switched to generate nanosecond pulses with tunable pulse widths of 1–200 ns and tunable repetition rates of 10 Hz–100 kHz. By utilizing a very-large-mode-area Yb-doped fiber with a core diameter of 50 μm in the power amplifier, thresholds of the stimulated Brillouin scattering at different pulse widths and repetition rates are increased. The maximum average power reaches 30.8 W at the pulse width of 4 ns and a repetition rate of 100 kHz, corresponding to an optical-to-optical conversion efficiency of ∼55.2%. Pulse energy and peak power are calculated to be 0.2 mJ and 50 kW, respectively, which are limited by stimulated Brillouin scattering. The 3-dB spectral linewidth remains around 0.05 nm during the power scaling process. The stimulated Brillouin scattering limited output powers at different pulse widths and repetition rates are investigated. Peak power of 47.5 kW (0.19 mJ) is obtained for the 4 ns pulses at a repetition rate of 50 kHz, which is nearly the same as that of 4 ns pulses at 100 kHz. When the pulse width of the seed source is increased to 8 ns, peak powers/pulse energies are decreased to 19.6 kW/0.11 mJ and 13.3 kW/0.08 mJ at repetition rates of 50 kHz and 100 kHz, respectively.</jats:p>

<jats:p>The manipulating of optical waves in a microcavity is essential to developing the integrated optical devices. Generally, the two eigenmodes in a whispering-gallery-mode (WGM) microcavity possess chiral symmetry. Here we show the chiral symmetry breaking is induced by the asymmetric backscattering of counter-propagating optical waves in a whispering-gallery-mode (WGM) microcavity with a cavity-made slot filled with atomic vapor. Through tuning the dispersion relation of the atomic vapor in the cavity-made slot, the chiral modes are continuously steered. The mode frequency splitting in the transmission and reflection spectra stem from the chiral symmetry breaking of the two eigenmodes. The displacement sensitivity of the proposed system in response to the length variation of cavity-made slot exhibits a high sensitivity value of 15.22 THz/nm.</jats:p>

<jats:p>The dynamics of produced excited carriers under the irradiation of Ge crystal is investigated theoretically by using femtosecond laser pulse. A two-temperature model combined with the Drude model is also used to study the nonequilibrium carrier density, carrier and lattice temperatures, and optical properties of the crystal. The properties of the surface plasmon wave when excited are also studied. The influences of non-radiation and radiative recombination process on the photoexcitation of the semiconductor during pulse and the relaxation after the pulse are described in detail. The results show that the effects of Auger recombination on the nonequilibrium carrier density and optical properties of the crystal and the properties of the surface plasmon polariton are great, whereas the effect of radiative recombination is extremely small.</jats:p>

<jats:p>Terahertz polarization devices are an important part of terahertz optical systems. Traditional terahertz polarization devices rely on birefringent crystals, and their performances are limited by the material structures. In this work, we theoretically demonstrate that the metamaterial consisting of the medium and the periodic metal band embedded in the medium can control broadband polarization effectively. The transmission length of the subwavelength waveguide mode gives rise to a broadband transmission peak. The resonant cavity structure formed by the dielectric layer and the waveguide layer possesses a high transmission efficiency. By optimizing the metamaterial structure parameters, we design a high-efficient (&gt;90%) quarter-wave plate over a frequency range of 0.90 THz–1.10 THz and a high-efficient (&gt;90%) half-wave plate over a frequency range of 0.92 THz–1.02 THz. Besides, due to the anisotropy of the structure, the metamaterials with the same structural parameters can achieve the function of the polarized beam splitting with an efficiency of up to 99% over a frequency range of 0.10 THz–0.55 THz. Therefore, the designed metamaterial has a multifunctional polarization control effect, which has potential applications in the terahertz integrated polarization optical system.</jats:p>

<jats:p>Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian (M.G) laser beams has been presented. To investigate the linear characteristics, propagation of the laser beam in vacuum has been considered. Whereas, the nonlinear characteristics have been investigated in plasmas. Optical nonlinearity of the plasma has been modeled by relativistic mass nonlinearity of the plasma electrons in the field of laser beam. Formulation is based on finding the semi analytical solution of the wave equation for the slowly varying envelope of the laser beam. Particularly, the dynamical evolutions of the beam width and longitudinal phase of the laser beam have been investigated in detail.</jats:p>

<jats:p>A general solution is obtained to a canonical problem of the reflection and refraction of an arbitrary shaped beam by using a uniaxially anisotropic chiral slab. The reflected, internal as well as refracted shaped beams are expanded in terms of cylindrical vector wave functions, and the expansion coefficients are determined by using the boundary conditions and method of moments procedure. As two typical examples, the normalized field intensity distributions are evaluated for a fundamental Gaussian beam and Hermite–Gaussian beam, and some propagation properties, especially the negative refraction phenomenon, are discussed briefly.</jats:p>

<jats:p>Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range, the mode coupling and dispersion characteristics of two helically corrugated waveguides (HCW) in the frequency ranges of 90 GHz–100 GHz and 260 GHz–265 GHz are studied. Through analytic calculations and numerical simulations, dispersion curves and structural parameters of the two frequency ranges waveguides are obtained. A novel method was proposed to obtain the dispersion of the HCW from the eigenwave solution using a periodic boundary condition. The HCW in a frequency range of 90 GHz–100 GHz was fabricated and its dispersion performance was measured. By comparing the measured results with the theoretical and the simulated results, the validity of the analytical and simulation method is verified. Limited to our machining capability, the dispersion of the 260 GHz–265 GHz HCW was only simulated and calculated and it was found that the results agree well with each other.</jats:p>

<jats:p>The formation of nanoscale water capillary bridges (WCBs) between chemically heterogeneous (patchy) surfaces plays an important role in different scientific and engineering applications, including nanolithography, colloidal aggregation, and bioinspired adhesion. However, the properties of WCB of nanoscale dimensions remain unclear. Using molecular dynamics simulations, we investigate the geometrical and thermodynamic properties of WCB confined between chemically heterogeneous surfaces composed of circular hydrophilic patches on a hydrophobic background. We find that macroscopic capillary theory provides a good description of the WCB geometry and forces induced by the WCB on the confining surfaces even in the case of surface patches with diameters of only 4 nm. Upon stretching, the WCB contact angle changes from hydrophobic-like values (<jats:italic>θ</jats:italic> &gt; 90°) to hydrophilic-like values (<jats:italic>θ</jats:italic> &lt; 90°) until it finally breaks down into two droplets at wall separations of ∼ 9–10 nm. We also show that the studied nanoscale WCB can be used to store relevant amounts of energy <jats:italic>E</jats:italic> <jats:sub>P</jats:sub> and explore how the walls patch geometry can be improved in order to maximize <jats:italic>E</jats:italic> <jats:sub>P</jats:sub>. Our findings show that nanoscale WCB can, in principle, be exploited for the design of clean energy storage devices as well as actuators that respond to changes in relative humidity. The present results can also be of crucial importance for the understanding of water transport in nanoporous media and nanoscale engineering systems.</jats:p>

<jats:p>The physical process of a single-stage planar-pulsed-inductive accelerator is investigated. Measurements include the waveforms of circuit current, capacitor voltage, plasma radiation intensity, and temporal plasma structure photos captured by a high-speed camera. Experiments are conducted under static ambient fill condition using argon as propellant. Varied values of capacitor voltage and gas pressure are compared. Further discussions quantify the EM interaction between circuit and plasma, as well as their energy deposition and current sheet acceleration. Based on the results of experiments, physical mechanisms of the initial ionization phase and the following acceleration phase are analyzed theoretically.</jats:p>

<jats:p>Si/a-C:H(Ag) multilayer films with different modulation periods are prepared to test their potential applications in human body. The composition, microstructure, mechanical and tribological properties in the simulated body fluid are investigated. The results show the concentration of Ag first decreases and then increases with the modulation period decreasing from 984 nm to 250 nm. Whereas the C content has an opposite variation trend. Notably, the concentration of Ag plays a more important role than the modulation period in the properties of the multilayer film. The a-C:H sublayer of the film with an appropriate Ag concentration (8.97 at.%) (modulation period of 512 nm) maintains the highest sp<jats:sup>3</jats:sup>/sp<jats:sup>2</jats:sup> ratio, surface roughness and hardness, and excellent tribological property in the stimulated body fluid. An appropriate number of Ag atoms and size of Ag atom allow the Ag atoms to easily enter into the contact interface for load bearing and lubricating. This work proves that the Ag nanoparticles in the a-C:H sublayer plays a more important role in the tribological properties of the composite-multilayer film in stimulated body fluid condition.</jats:p>