Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Ionization of molecules in femtosecond laser fields is the most fundamental and important step of various strong-field physical processes. In this study, we experimentally investigate strong field ionization of linear N<jats:sub>2</jats:sub>O molecules using a time-of-flight mass spectrometer in 800-nm laser fields. Yields of the parent ion and different fragment ions are measured as a function of laser intensity in the range of 2.0×10<jats:sup>13</jats:sup> W/cm<jats:sup>2</jats:sup> to 3.6×10<jats:sup>14</jats:sup> W/cm<jats:sup>2</jats:sup>. We also investigate the dependence of strong field ionization and dissociation of N<jats:sub>2</jats:sub>O on laser ellipticity and polarization direction. The significant role of laser induced electron re-collision in the formation of highly charged fragment ions is proved. The physical mechanism of strong field ionization and fragmentation is discussed, based on our experimental results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A time-dependent quantum wave packet method is used to investigate the dynamics of the Li+ H(D)Cl reaction based on a new potential energy surface (<jats:italic>J. Chem. Phys.</jats:italic> <jats:bold>146</jats:bold> 164305 (2017)). The reaction probabilities of the Coriolis coupled (CC) and centrifugal sudden (CS) calculations, the integral cross sections, the reaction rate constants are obtained. The rate constants of the Li+ HCl reaction are within the error bounds at low temperature. A comparison of the CC and CS results reveals that the Coriolis coupling plays an important role in the Li+ H(D)Cl reaction. The CC cross sections are larger than the CS results within the entire energy range, demonstrating that the Coriolis coupling effect can more effectively promote the Li+ DCl reaction than the Li+ HCl reaction. It is found that the isotope effect has a great influence on the title reaction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We demonstrate the production of cold, slow NH<jats:sub>3</jats:sub> molecules from a supersonic NH<jats:sub>3</jats:sub> molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH<jats:sub>3</jats:sub> molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH<jats:sub>3</jats:sub> molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH<jats:sub>3</jats:sub> molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK. The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH<jats:sub>3</jats:sub> beam from 333 m/s to 24 m/s, with a final temperature of 2.9 mK. It is clear that the second mode promises to produce colder (high-energy-resolution) molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is well-established that waves are inhomogeneous in a lossy isotropic medium, and the validation of the classical Snell's law is still questionable for light refraction at the dissipative and dispersive interface. With high absorption, direct experimental investigation is rather difficult due to the extremely short penetration depth; i.e., the skin depth. In this paper, a simple and unified description of this issue is proposed, which can be applied to both materials with anomalous dispersion and in the Drude region. The gradient <jats:inline-formula> <jats:tex-math> <?CDATA ${{\boldsymbol{\nabla }}}_{k}\omega $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="bold">∇</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> </mml:msub> <mml:mi>ω</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_5_054201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is found to be incident angle <jats:italic>θ</jats:italic> <jats:sub>i</jats:sub>-dependent, and the direction of the group velocity may deviate significantly from the phase velocity due to the loss induced permittivity structure. The physics behind the negative refraction effect is explained, and a novel loss induced super-prism effect is also predicted.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the dynamics of airy beams propagating in the parity–time (<jats:italic>PT</jats:italic>) symmetric optical lattices in linear and nonlinear regimes, respectively. For the linear propagation, the position of the channel guided by the <jats:italic>PT</jats:italic> lattice can be shifted by tuning the lattice frequency. The underlying physical mechanism of this phenomenon is also discussed. An interesting phenomenon is found in the nonlinear regime in that the airy beam becomes a tilt channel with several Rayleigh lengths. These findings create new opportunities for optical steering and manipulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We experimentally demonstrate an electrically triggered terahertz (THz) dual-band tunable band-pass filter based on Si<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub>–VO<jats:sub>2</jats:sub>–Si<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub> sandwich-structured hybrid metamaterials. The insulator–metal phase transition of VO<jats:sub>2</jats:sub> film is induced by the Joule thermal effect of the top metal layer. The finite-integration-time-domain (FITD) method and finite element method (FEM) are used for numerical simulations. The sample is fabricated using a surface micromachining process, and characterized by a THz time-domain-spectrometer (TDS). When the bias current is 0.225 A, the intensity modulation depths at two central frequencies of 0.56 THz and 0.91 THz are about 81.7% and 81.3%, respectively. This novel design can achieve dynamically electric–thermo–optic modulation in the THz region, and has potential applications in the fields of THz communications, imaging, sensing, and astronomy exploration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Opto–electromechanical coupling at the nanoscale is an important topic in new scientific studies and technical applications. In this work, the optically manipulated electromechanical behaviors of individual cadmium sulfide (CdS) nanowires are investigated by a customer-built optical holder inside transmission electron microscope, wherein <jats:italic>in situ</jats:italic> electromechanical resonance took place in conjunction with photo excitation. It is found that the natural resonance frequency of the nanowire under illumination becomes considerably lower than that under darkness. This redshift effect is closely related to the wavelength of the applied light and the diameter of the nanowires. Density functional theory (DFT) calculation shows that the photoexcitation leads to the softening of CdS nanowires and thus the redshift of natural frequency, which is in agreement with the experimental results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A compact high power diode-pumped passively mode-locked Nd:YVO<jats:sub>4</jats:sub> laser with high repetition rate is realized. Using an Nd:YVO<jats:sub>4</jats:sub> crystal and a semiconductor saturable absorber mirror (SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square (RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours, showing a superior stability with the compact configuration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Supercontinuum generation (SCG) and its application on all-optical quantization of all-optical analog-to-digital conversions (AOADCs) at the mid-infrared region in an AlGaAs strip waveguide are investigated numerically. The simulation results show that when the parabolic pulse is input, not only broader and higher-coherence SCG is obtained and a higher effective number of bits (ENOB) can be achieved, compared with the input pulse with hyperbolic-secant and Gaussian shaping. A four-bit quantization resolution is achieved along with a signal-to-noise ratio of 24.02 dB and an ENOB of 3.99 bit, and the required input peak power is 760 mW.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An automatic detection method is employed to identify and track eddies in the Gulf of Mexico. The physical parameters of the eddies, such as lifespan, radius, and distribution position are first examined and used to determine the spatio–temporal evolution of a strong warm eddy separated from the Mexico current. Then, the influence of this strong warm eddy on sound propagation during its lifespan are comprehensively analyzed with the parabolic equation and explained by using the normal mode and ray theories. Additionally, the influence of mesoscale eddies on the redistribution of total depth-integrated energy among the normal modes in the deep water is also discussed. The variation of arrival angle is investigated to explain the spreading acoustic energy caused by eddies. Overall, the results show that warm eddies can change the propagation paths and cause the convergence zone to broaden and approach the sound source. Moreover, the warm eddy can disperse sound energy and cause the total depth-integrated energy to incline to a lower normal mode. Throughout the whole of these three periods (eddy generating, eddy maturing, and eddy terminating), the fluctuation in the transmission loss is up to 30 dB (depending on the relative location of eddy center to the source).</jats:p>