Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Frequency up-conversion is an effective method of mid-infrared (MIR) detection by converting the long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate the MIR light carrying orbital angular momentum (OAM) from a difference frequency generation process and perform the up-conversion of it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, which is achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Researchers have long studied circular dichroism (CD) for its enormous prospects in life sciences. Many biomolecular have vibration modes in the terahertz region, and terahertz CD spectra are robust to detect biomolecular structures. However, few studies explore the terahertz CD spectra on even natural materials due to technical challenges in both fields. Here, we report a setup of home-built terahertz time-domain spectroscopy to measure the polarization states of terahertz waves. By carefully measuring the transmission Jones matrix, we obtained terahertz CD spectra of α-lactose tablets and D-glucose tablets. Our results show that the terahertz CD spectra are sensitive to vibrational motions in biochemical compounds, which will find wide applications in biosensing and biomedical diagnostics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper, the field-free alignment of molecule ClCN is investigated with a terahertz few-cycle pulse (THz FCP) based on the time-dependent density matrix theory. It is shown that a high degree of molecular alignment can be obtained by changing the matching number of the THz FCP in both adiabatic and non-adiabatic regimes. The matching number can affect both the maximum value of the alignment and the time at which it is achieved. It is also found that a higher degree of alignment by the THz FCP can be achieved at lower intensity and there exists the optimization threshold of molecular alignment with the increasing of the field amplitude. Also found is the frequency sensitive region in which the degree of maximum alignment can greatly be enhanced through the modulation of the center frequencies of different THz FCPs. The investigation demonstrates that comparing with a THz single-cycle pulse, a better result of the field-free alignment can be created by a THz FCP at the constant rotational temperature of molecule.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In order to investigate the relationship between the flow field parameters outside the vehicle and the altitude, this paper takes an atmospheric reentry demonstrator (ARD) with an angle of attack of -20° as the research object and adopts a two-temperature model coupled with the SST <jats:italic>k</jats:italic>-<jats:italic>ω</jats:italic> turbulence model to focus on the variation of flow field parameters including flow field pressure, Mach number, and temperature with the reentry altitude. It is found that the flow field high-pressure region and low Mach region both appear in the shock layer near the ARD’s head, while the maximum pressure of the surface appears on the windward side of the ARD’s head with a torus distribution, and the numerical magnitude is inversely proportional to the radius of the torus. Fluid through the shoulder of the ARD, the flow expansion plays a dominant role, the airflow velocity increases, the Mach number of the windward side of the rear cone increases, the flow field pressure and surface pressure are rapidly decreasing. When the fluid passes through the shock layer, the translational-rotation temperature will increase before the vibration-electron temperature, there is a thermal non-equilibrium effect, the two temperatures will rapidly decrease again when approaching the surface of the ARD, due to the existence of temperature gradient. At the same time, both the windward side of the shoulder and the back cover of the ARD suffer from a large thermal load and require thermal protection measures.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To study the damage of an elastic cylinder immersed in fluid, a model of an elastic cylinder wrapped with a porous medium immersed in fluid is designed. This structure can both identify the properties of guided waves in a more practical model and address the relationship between the cylinder damage degree and the surface and surrounding medium. The principal motivation is to perform a detailed quantitative analysis of the longitudinal and flexural modes in an elastic cylinder wrapped with a porous medium immersed in fluid. The frequency equations for the propagation of waves are derived, each for a pervious and an impervious surface employing Biot theory. The influences of the various parameters of the porous medium wrapping layer on the phase velocity and attenuation are discussed. The results show that the influence of porosity on the dispersion curves of guided waves is much more significant than that of thickness, whereas the phase velocity is independent of the static permeability. There is an apparent “mode switching” between the two low-order modes. The characteristics of attenuation are in good agreement with the dispersion curves results. This work can support future studies for optimizing the theory of cylinder or pipeline damage detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Highly anisotropic thermal conductive materials are of great values in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task, due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with thickness range of 0.2 to 2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach for ultrathin composite thermal conductivity determination, which may promote the evolution of ultrathin composites for potential thermal-related applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Spin orbit torque (SOT) has been considered as one of the promising technologies for the next-generation magnetic random access memory (MRAM). So far, SOT has been widely utilized for inducing various modes of magnetization switching. However, it is challenging to integrate multiple modes of magnetization switching together. Here we propose a method for implementing both unipolar and bipolar switching of the perpendicular magnetization within a single SOT device. The mode of switching could be easily altered by tuning the amplitude of the applied current. We show that the field-like torque plays an important role in the switching process. The field-like torque induces the precession of the magnetization in the case of unipolar switching, whereas it helps to generate an effective z-component torque in the case of bipolar switching. In addition, the influence of key parameters on the mode of switching is discussed, including the field-like torque strength, the bias field and the current density. Our proposal could be used to design novel reconfigurable logic circuits in the near future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The GaN-based heterostructures are widely used in optoelectronic devices, but the complex surface reconstructions and lattice mismatch greatly limit the applications. The stacking of two-dimensional transition metal dichalcogenide (TMD = MoS<jats:sub>2</jats:sub>, MoSSe and MoSe<jats:sub>2</jats:sub>) monolayers on reconstructed GaN surface not only effectively overcomes the larger mismatch, but also brings about novel electronic and optical properties. Adopting the reconstructed GaN (0001) surface with adatoms (N-ter GaN and Ga-ter GaN), the influences of complicated surface conditions on the electronic properties of heterostructures have been investigated. The passivated N-ter and Ga-ter GaN surfaces push the mid-gap states to the valence bands, giving rise to small bandgaps in heterostructures. The charge transfer between Ga-terded surface and TMD monolayers occurs much easier than that across the TMD/N-ter GaN interfaces, which induces stronger interfacial interaction and larger valence band offset (VBO). The band alignment can be switched between type-I and type-II by assembling different TMD monolayers, that is, MoS<jats:sub>2</jats:sub>/N-ter GaN and MoS<jats:sub>2</jats:sub>/Ga-ter GaN are type-II, and the others are type-I. The absorption of visible light is enhanced in all considered TMD/reconstructed GaN heterostructures. Additionally, MoSe<jats:sub>2</jats:sub>/Ga-ter GaN and MoSSe/N-ter GaN have larger conductor band offset CBO of 1.32 and 1.29 eV, respectively, extending the range from deep ultraviolet to infrared regime. Our results revel that the TMD/reconstructed GaN heterostructures may be used for high-performance broadband photoelectronic devices.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work, we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance (MKR) via dissipative four-wave-mixing (DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect (NL-KBC). The experimental results are valuable for further comprehend the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the context of Rastall gravity, the shadow and observation intensity casted by the new Kiselev-like black hole with dust field have been numerically investigated. In this system, the Rastall parameter and surrounding dust field structure parameter have considerable consequences on the geometric structure of spacetime. By considering the photon trajectories near the black hole, we investigate the variation of the radii of photon sphere, event horizon and black hole shadow under the different related parameters. Furthermore, by taking into account two different spherically symmetric accretion models as the only background light source, we also studied the observed luminosity and intensity of black holes. For the both spherical accretions background, the results show that the decrease or increase of the observed luminosity depends on the value range of relevant parameters, and the promotion effect is far less obvious than the attenuation effect on the observed intensity. One can find that the inner shadow region and outer bright region of the black hole wrapped by infalling accretion are significantly darker than those of the static model, which is closely related to the Doppler effect. In addition, the size of the shadow and the position of the photon sphere are always the same in the two accretion models, which means that the black hole shadow depend only on the geometry of spacetime, while the observation luminosity is affected by the form of accretion material and the related spacetime structure.</jats:p>