Diode both ends pumped two crystals Tm:YLF laser

In this paper, we report two crystals Tm:YLF laser pumped by a fiber coupled diode laser with total power of 180 W at 792 nm. When the incident power reached up to 117.0 and 37.3 W of the emission wave-length at 1.91 μm was achieved. Through linear fit, the corresponding slope efficiency of 38.5%, optical-to-optical conversion efficiency of 31.9% and the beam quality factor of M ² ∼ 1.1 were obtained, indicating nearly diffraction limited beam propagation. To our best knowledge, this is the best beam quality among the reported paper results under the similar experiments.     

Concentration scheme for partially entangled photon states via entanglement reflector and no Bell-state analysis

We propose a protocol to concentrate partially entangled states of photons using entanglement reflector, which consists of a single electron spin confined in a charged quantum dot inside a single-sided microcavity. The outstanding advantage of the proposed scheme is its experimental simplicity and feasibility since it only needs to perform a single local measurement on electronic spins rather than a joint Bell-state measurement on photons. We then extend this scheme to concentrate N-photon Greenberger-Horne-Zeilinger state. Finally, we analyze the influence of various imperfections on the scheme.     

光学多普勒层析三维矢量测速方法研究

光学多普勒层析术(ODT)是一种高分辨、非侵入的生物医学成像手段,能同时得到组织的结构信息和组织内血管的流速信息.提出了一种新型的基于相位分辨技术的ODT三维矢量测速方法.在ODT系统样品臂的准直镜和聚焦透镜之间加入窄带相位片,形成三个不同的相位延迟,通过计算多普勒频移和不同相位延迟下的多普勒展宽,可得到毛细管内的三维矢量流场分布.对已知浓度的聚苯乙烯溶液进行了一系列不同角度和不同流速的实验,结果证明这种新型的ODT矢量测速方法可以较精确的实现三维矢量流速的测量.     

A facile method to synthesize nitrogen and fluorine co-doped TiO2 nanoparticles by pyrolysis of (NH4)2TiF6

The nitrogen and fluorine co-doped TiO₂ (N-F-TiO₂) nanoparticles of anatase crystalline structure were prepared by a facile method of (NH₄)₂TiF₆ pyrolysis, and characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet visible (UV-Vis) spectroscopy etc. With the increase of calcination temperature, (NH₄)₂TiF₆ decomposed into TiOF₂ and NH₄TiOF₃ at first, and then formed anatase-type TiO₂ with thin sheet morphology. H₃BO₃ as oxygen source can promote the formation of anatase TiO₂, but decrease the F content in the N-F-TiO₂ materials due to the formation of volatile BF₃ during the precursor decomposition. The photocatalytic activity of the obtained N-F-TiO₂ samples was evaluated by the methylene blue degradation under visible light, and all the samples exhibited much higher photocatalytic activity than P25. Moreover, the merits and disadvantages of this proposed method to prepare doped TiO₂ are discussed.     

Observation of an excited charm baryon Omega c* decaying to Omega c0gamma

We report the first observation of an excited singly charmed baryon Omega c* (css) in the radiative decay Omega c0gamma, where the Omega c0 baryon is reconstructed in the decays to the final states Omega(-)pi+, Omega(-)pi+pi0, Omega(-)pi+pi(-)pi+, and Xi(-)K(-)pi+pi+. This analysis is performed using a data set of 230.7 fb(-1) collected by the BABAR detector at the PEP-II asymmetric-energy B factory at the Stanford Linear Accelerator Center. The mass difference between the Omega c* and the Omega c0 baryons is measured to be 70.8+/-1.0(stat)+/-1.1(syst) MeV/c2. We also measure the ratio of inclusive production cross sections of Omega c* and Omega c0 in e+e(-) annihilation.     

Microwave photonics reconfigurable mixer based on polarization modulator

A reconfigurable and stable mixer is proposed and demonstrated in this paper. It mainly consists of a dual-driven Mach–Zehnder modulator and a polarization modulator with several polarization controllers (PC) and polarizers (Pol). According to the theoretical analysis, different functions (such as single ended mixer, balanced mixer, I/Q mixer and image rejection mixer) can be realized by adjusting the PCs and Pols. The simulation results verify the possibility of multi-functions that realized by the reconfigurable mixer. In addition, another research on how the non-ideal parameters affect the image rejection ratio (ISR) and conversion efficiency of the mixer is also carried. The results show that both of them perform better as the extinction ratio gets higher. However, they are incurring a sharp decrease if the DC bias points deviate from the settled values. In the meantime, the results also indicate that the higher modulation indices lead to a better ISR. A 57.12 dB ISR can be achieved with conversion efficiency of ? 9.53 dB.     

Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system

A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.     

Enhanced electrochemical properties and thermal stability of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by surface modification with Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>

Layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode material is synthesized via a sol-gel method and subsequently surface-modified with Eu₂O₃ layer by a wet chemical process. The effect of Eu₂O₃ coating on the electrochemical performances and thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂@Eu₂O₃ cells is investigated systematically by the charge/discharge testing, cyclic voltammograms, AC impedance spectroscopy, and DSC measurements, respectively. In comparison, the Eu₂O₃-coated sample demonstrates better electrochemical performances and thermal stability than that of the pristine one. After 100 cycles at 1C, the Eu₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode demonstrates stable cyclability with capacity retention of 92.9 %, which is higher than that (75.5 %) of the pristine one in voltage range 3.0–4.6 V. Analysis from the electrochemical measurements reveals that the remarkably improved performances of the surface-modified composites are mainly ascribed to the presence of Eu₂O₃-coating layer, which could efficiently suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of active material.