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We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for. Instead of employing a phase discriminator and a phase locking loop in the conventional active phase control scheme, the passive phase noise cancellation is realized by feeding double-trip beat-note frequency to the driver of the acoustic optical modulator at the local site. This passive scheme exhibits fine robustness and reliability, making it suitable for long-distance and noisy fiber links. An optical regeneration station is used in the link for signal amplification and cascaded transmission. The phase noise cancellation and transfer instability of the 972-km link is investigated, and transfer instability of 1.1 × 10−19 at 104 s is achieved. This work provides a promising method for realizing optical frequency distribution over thousands of kilometers by using fiber links. [ABSTRACT FROM AUTHOR]

We investigate theoretically the spectral shift of the high-order harmonic generation (HHG) in ZnO driven by a combined laser field by solving the two-band semiconductor Bloch equations (SBEs) in the velocity gauge. The combined laser field is synthesized by a fundamental laser pulse and its seventh-frequency laser pulse. When the seventh-frequency laser pulse is added to the rising or falling parts of the fundamental laser field, we find that the spectral blueshift or redshift appears, which is due to the unequal contribution of the rising and falling parts in the fundamental laser field to the harmonics. By analyzing the time-dependent conduction band population in k space, we found that, in addition to the tunneling ionization channel, there is also the resonant electron injection channels which is induced by the seventh-frequency laser pulse. The harmonics generated by the different channels show the spectral redshift or the spectral blueshift, respectively. Through analyzing the k -integrated transient conduction band population of the electrons from different channels, we found that if there is a certain delay in the process of the electron excitation, it will lead to the delay in the harmonic emission, which results in the spectral redshift of the harmonics. [ABSTRACT FROM AUTHOR]

The mobility limited by cluster scattering in ternary alloy semiconductor quantum wire (QWR) is theoretically investigated under Born approximation. We calculate the screened mobility due to clusters (high indium composition InGaN) scattering in the InxGa1−xN QWR structure. The characteristics of the cluster scattering mechanism are discussed in terms of the indium composition of clusters, the one-dimensional electron gas (1DEG) concentration, and the radius of QWR. We find that the density, breadth of cluster, and the correlation length have a strong effect on the electron mobility due to cluster scattering. Finally, a comparison of the cluster scattering is made with the alloy-disorder scattering. It is found that the cluster scattering acts as a significant scattering event to impact the resultant electron mobility in ternary alloy QWR. [ABSTRACT FROM AUTHOR]

The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility. [ABSTRACT FROM AUTHOR]

Highly transparent Yb, Ho doped (YLa)2O3 ceramic was fabricated by conventional ceramic processing with nanopowders. The absorption and emission spectra of the ceramic was investigated. The energy transfer mechanism between Yb3+ and Ho3+ was also discussed. The strong emission band around 2 µm indicated that the Yb-Ho: (Y0.90La0.10)2O3 transparent ceramic is a promising gain medium for the generation of 2 µm laser emissions. The laser operation of Yb-Ho co-doped (YLa)2O3 ceramic at 2.1 µm is first reported. [ABSTRACT FROM AUTHOR]

This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency (RF) output window. This study is motivated by 800 kW continuous wave (CW), 650 MHz klystrons for the future plan of circular electron–positron collider (CEPC) project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology (CST) microwave studio and the return loss of the window has been established to be less than −90 dB. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling. The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper. [ABSTRACT FROM AUTHOR]

Superlattices in chaotic state can be used as a key part of a true random number generator. The chaotic characteristics of the signal generated in the superlattice are mostly affected by the parameters of the superlattice and the applied voltage, while the latter is easier to adjust. In this paper, the model of the superlattice is first established. Then, based on this model, the chaotic characteristics of the generated signal are studied under different voltages. The results demonstrate that the onset of chaos in the superlattice is typically accompanied by the mergence of multistability, and there are voltage intervals in each of which the generated signal is chaotic. [ABSTRACT FROM AUTHOR]

Recently, graphene-based photodetectors have been rapidly developed. However, their photoresponsivities are generally low due to the weak optical absorption strength of graphene. In this paper, we fabricate photoconductive multi-layer graphene (MLG) photodetectors on etched silicon-on-insulator substrates. A photoresponsivity exceeding is obtained, which enables most optoelectronic application. In addition, according to the analyses of the high photoresponsivity and long photoresponse time, we conclude that the working mechanism of the device is photoconductive effect. The process of photons conversion into conducting electrons is also described in detail. Finally, according to the distinct difference between the photoresponses at 1550 nm and 808 nm, we estimate that the position of the trapping energy is somewhere between 0.4 eV and 0.76 eV, higher than the Fermi energy of MLG. Our work paves a new way for fabricating the graphene photoconductive photodetectors. [ABSTRACT FROM AUTHOR]

Lattice, charge, orbital, and spin are the four fundamental degrees of freedom in condensed matter, of which the interactive coupling derives tremendous novel physical phenomena, such as high-temperature superconductivity (high-Tc SC) and colossal magnetoresistance (CMR) in strongly correlated electronic system. Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it, and also indispensable for designing new materials and devices. Scanning transmission electron microscopy (STEM) integrating multiple techniques of structure imaging and spectrum analysis, is a comprehensive platform for providing structural, chemical and electronic information of materials with a high spatial resolution. Benefiting from the development of aberration correctors, STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization; many improvements have been achieved in recent years, thereby giving an in-depth insight into material research. Here, we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides; atomic-scale mapping of ferroelectric polarization, octahedral distortions and rotations, valence state, coordination and spin ordering are presented. We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides. [ABSTRACT FROM AUTHOR]

H2O-based and O3-based LaxAlyO nanolaminate films were deposited on Si substrates by atomic layer deposition (ALD). Structures and performances of the films were changed by different barrier layers. The effects of different structures on the electrical characteristics and physical properties of the LaxAlyO films were studied. Chemical bonds in the LaxAlyO films grown with different structures and different oxidants were also investigated with x-ray photoelectron spectroscopy (XPS). The preliminary testing results indicate that the LaxAlyO films with different structures and different oxidants show different characteristics, including dielectric constant, equivalent oxide thickness (EOT), electrical properties, and stability. [ABSTRACT FROM AUTHOR]

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13-channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickness of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick matching layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W. [ABSTRACT FROM AUTHOR]

The corrosion of steels in liquid metal lead (Pb) and bismuth (Bi) is a critical challenge in the development of accelerator driven systems (ADS). Using a first-principles method with a slab model, we theoretically investigate the interaction between the Pb (Bi) atom and the iron (Fe) (100) surface to assess the fundamental corrosion properties. Our investigation demonstrates that both Pb and Bi atoms favorably adsorb on the (100) surface. Such an adsorption decreases the energy required for the dissociation of an Fe atom from the surface, enhancing the dissolution tendency significantly. The segregation of six common alloying elements (Cr, Al, Mn, Ni, Nb, and Si) to the surface and their impacts on the corrosion properties are also considered. The present results reveal that Si seems to have a relatively good performance to stabilize the surface and alleviate the dissolving trend caused by Pb and Bi. [ABSTRACT FROM AUTHOR]