Catálogo de publicaciones - revistas

<jats:p>Diamond based quantum sensing is a fast-emerging field with both scientific and technological significance. The nitrogen–vacancy (NV) center, a crystal defect in diamond, has become a unique object for microwave sensing applications due to its excellent stability, long spin coherence time, and optical properties at ambient condition. In this work, we use diamond NV center as atomic receiver to demodulate on–off keying (OOK) signal transmitted in broad frequency range (2 GHz–14 GHz in a portable benchtop setup). We proposed a unique algorithm of voltage discrimination and demonstrated audio signal transceiving with fidelity above 99%. This diamond receiver is attached to the end of a tapered fiber, having all optic nature, which will find important applications in data transmission tasks under extreme conditions such as strong electromagnetic interference, high temperatures, and high corrosion.</jats:p>

<jats:p>We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays. Three radar probe signals are generated by driving lasers constructed by a three-element laser array with self-feedback. The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection, which are utilized as nonlinear nodes to realize the reservoirs. We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir, even when parameter mismatches exist between the response laser array and the driving laser array. Based on this, the three synchronous probe signals are utilized for ranging to three targets, respectively, using Hilbert transform. It is demonstrated that the relative errors for ranging can be very small and less than 0.6%. Our findings show that optical reservoir computing provides an effective way for applications of target ranging.</jats:p>

<jats:p>Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently. Therefore, any optical frequency in visible to near-infrared region can be directly traced to a microwave frequency. As a result, the length unit “meter” is directly related to the time unit “second”. This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared region. Optical frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequency-doubling scheme. The signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633, 698, 729, 780, 1064, and 1542 nm is better than 30 dB. The frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1 × 10<jats:sup>−13</jats:sup> at 1-s averaging time. The measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylene-stabilized 1542-nm laser. The results are within the uncertainty range of the international recommended values. Our results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb, which is not only important for the precise and accurate traceability and calibration of the laser frequencies, but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.</jats:p>

<jats:p>Diffractive lenses (DLs) can realize high-resolution imaging with light weight and compact size. Conventional DLs suffer large chromatic and off-axis aberrations, which significantly limits their practical applications. Although many achromatic methods have been proposed, most of them are used for designing small aperture DLs, which have low diffraction efficiencies. In the designing of diffractive achromatic lenses, increasing the aperture and improving the diffraction efficiency have become two of the most important design issues. Here, a novel phase-coded diffractive lens (PCDL) for achromatic imaging with a large aperture and high efficiency is proposed and demonstrated experimentally, and it also possesses wide field-of-view (FOV) imaging at the same time. The phase distribution of the conventional phase-type diffractive lens (DL) is coded with a cubic function to expand both the working bandwidth and the FOV of conventional DL. The proposed phase-type DL is fabricated by using the laser direct writing of grey-scale patterns for a PCDL of a diameter of 10 mm, a focal length of 100 mm, and a cubic phase coding parameter of 30<jats:italic>π</jats:italic>. Experimental results show that the working bandwidth and the FOV of the PCDL respectively reach 50 nm and 16° with over 8% focusing efficiency, which are in significant contrast to the counterparts of conventional DL and in good agreement with the theoretical predictions. This work provides a novel way for implementing the achromatic, wide FOV, and high-efficiency imaging with large aperture DL.</jats:p>

<jats:p>A radiation–temperature coupling model of optical fiber attenuation spectrum has been developed. The spectrum in Ge/P co-doped fiber ranging from 800 nm–1600 nm at different temperatures and doses was measured and decomposed according to the configurational coordinate model based on which the power-law model was employed to predict the intensity of the color center absorption band at different doses. And the fiber loss in space was predicted by the model. This work will benefit the application of fibers in a complicated radiation environment.</jats:p>

<jats:p>Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They achieve the effect of focusing through phase control under a subwavelength scale, and are called metalenses. They are poised to revolutionize optics by enabling complex low-cost systems. However, there are severe monochromatic aberrations in the metasurfaces. In this paper, the coma of the long-wave infrared optical system is eliminated through a single-layer metasurface. By changing the phase function, this metalens has a numerical aperture of 0.89, a focal length of 150 μm and a field of view of 120° (0.4@60 line pairs/mm) that enables diffraction-limited monochromatic imaging along the focal plane at a wavelength of 10.6 μm. The designed metasurface maintains a favorable value of the modulation transfer function at different angles. This equipment can be widely used in imaging and industrial processing.</jats:p>

<jats:p>The turbulent boundary layer (TBL) is actively controlled by the synthetic jet generated from a circular hole. According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry (TR-PIV) system, the average drag reduction rate of 6.2% in the downstream direction of the hole is obtained with control. The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream, while the reverse vortex decays rapidly. From the statistical average, it can be found that a low-speed streak is generated downstream. Induced by the two vortex legs, the fluid under them converges to the middle. The drag reduction effect produced by the synthetic jet is local, and it reaches a maximum value at <jats:italic>x</jats:italic> <jats:sup>+</jats:sup> = 400, where the drag reduction rate reaches about 12.2%. After the extraction of coherent structure from the spatial two-point correlation analysis, it can be seen that the synthetic jet suppresses the streamwise scale and wall–normal scale of the large scale coherent structure, and slightly weakens the spanwise motion to achieve the effect of drag reduction.</jats:p>

<jats:p>This paper uses the implicit Monte–Carlo full-orbit-following parallel program ISSDE to calculate the prompt loss and slowing down process of neutral beam injection (NBI)-generated fast ions due to Coulomb collisions in the equilibrium configuration of Experimental Advanced Superconducting Tokamak (EAST). This program is based on the weak equivalence of the Fokker–Planck equation under Rosenbluth MacDonald Judd (RMJ) potential and Stratonovich stochastic differential equation (SDE). The prompt loss with the LCFS boundary and the first wall (FW) boundary of the two co-current neutral injection beams are studied. Simulation results indicate that the loss behavior of fast ions using the FW boundary is very different from that of the LCFS boundary, especially for fast ions with a large gyration radius. According to our calculations, about 5.11% of fast ions generated by perpendicular injection drift out of the LCFS and then return inside the LCFS to be captured by the magnetic field. The prompt loss ratio of fast ions and the ratio of orbital types depend on the initial distribution of fast ions in the <jats:italic>P<jats:sub>ζ</jats:sub> </jats:italic>–<jats:italic>Λ</jats:italic> space. Under the effect of Coulomb collisions, the pitch-angle scattering and stochastic diffusion happens, which will cause more fast ion loss. For short time scales, among the particles lost due to collisions, the fraction of banana ions reaches 92.31% in the perpendicular beam and 58.65% in the tangential beam when the fraction of banana ions in the tangential beam is 3.4% of the total ions, which means that the effect of Coulomb collisions on banana fast ions is more significant. For long time scales, the additional fast ion loss caused by Coulomb collisions of tangential and perpendicular beams accounted for 16.21% and 25.05% of the total particles, respectively. We have also investigated the slowing down process of NBI fast ions.</jats:p>

<jats:p>To understand the effect of injected deuterium (D) pellets on background plasma, the ablation of D pellets and the transport of D species in both atomic and ionic states in the EAST device are simulated using a modified dynamic neutral gas shield model combined with the edge plasma code SOLPS-ITER. The simulation results show that there is a phenomenon of obvious atomic deposition in the scrape-off layer (SOL) after pellet injection, which depends strongly on the injection velocity. With increasing injection velocity, the atomic density in the SOL decreases evidently and the deposition time is relatively shortened. Possible effects for triggering of edge localized modes (ELMs) by D and Li pellets are also discussed. With the same pellet size and injection velocity, the maximum perturbation pressure caused by D pellets is obviously higher. It is found that the resulting maximum perturbed pressure is remarkably enhanced when the injection velocity is reduced from 300 m/s to 100 m/s for a pellet with a cross section of 1.6 mm, which indicates that the injection velocity is important for ELM pacing. This work can provide reasonable guidance for choosing pellet parameters for fueling and ELM triggering.</jats:p>

<jats:p>Solid H<jats:sub>2</jats:sub>S as the precursor for H<jats:sub>3</jats:sub>S with incredible superconducting properties under high pressure, has recently attracted extensive attention. Here in this work, we propose two new phases of H<jats:sub>2</jats:sub>S with <jats:italic>P</jats:italic>4<jats:sub>2</jats:sub>/<jats:italic>n</jats:italic> and <jats:italic>I</jats:italic>4<jats:sub>1</jats:sub>/<jats:italic>a</jats:italic> lattice symmetries in a pressure range of 0 GPa–30 GPa through first-principles structural searches, which complement the phase transition sequence. Further an <jats:italic>ab initio</jats:italic> molecular dynamics simulation confirms that the molecular phase <jats:italic>P</jats:italic>2/<jats:italic>c</jats:italic> of H<jats:sub>2</jats:sub>S is gradually dissociated with the pressure increasing and reconstructs into a new <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> structure at 160 GPa, exhibiting the superconductivity with <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> of 82.5 K. Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H<jats:sub>2</jats:sub>S.</jats:p>