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A Longitudinal Zeeman Slower Based on Ring-Shaped Permanent Magnets for a Strontium Optical Lattice Clock
WANG Qiang, LIN Yi-Ge, GAO Fang-Lin, LI Ye, LIN Bai-Ke, MENG Fei, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2015, 32 (10):
100701
.
DOI: 10.1088/0256-307X/32/10/100701
We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter but different inner diameters. The maximum variation of the axial field from its target values is less than 2%. In most parts of the Zeeman slower, the intensity variations of the field in radial spatial distribution are less than 0.1 mT. With this Zeeman slower, the strontium atoms are slowed down to 95 m/s, and approximately 2% of the total atoms are slowed down to less than 50 m/s.
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Identification of Y(4008), Y(4140), Y(4260), and Y(4360) as Tetraquark States
ZHOU Ping, DENG Cheng-Rong, PING Jia-Lun
Chin. Phys. Lett. 2015, 32 (10):
101201
.
DOI: 10.1088/0256-307X/32/10/101201
Within the framework of a color flux-tube model with a four-body confinement potential, the tetraquark states [cq][cq] (q=u or d) with IJPC=01– are systematically investigated. The numerical results indicate that states Y(4008), Y(4140), Y(4260), and Y(4360) can be uniformly described as tetraquark states [cq][cq] with n2S+1LJ of 11P1, 15P1, 25P1 and 15F1, respectively, in the color flux-tube model. They are compact three-dimensional spatial configurations similar to a rugby ball, higher orbital angular momentum L, more prolate. The four-body confinement interaction based on a color flux-tube picture should be responsible for the formation of those compact tetraquark states.
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High-Power Dual-End-Pumped Actively Q-Switched Ho:YAG Ceramic Laser
DUAN Xiao-Ming, YUAN Jin-He, YAO Bao-Quan, DAI Tong-Yu, LI Jiang, PAN Yu-Bai
Chin. Phys. Lett. 2015, 32 (10):
104201
.
DOI: 10.1088/0256-307X/32/10/104201
We present a high-power Ho:YAG ceramic laser pumped at 1908 nm. Using a dual-end-pumped structure, the maximum continuous-wave output power of 48 W is obtained, corresponding to a slope efficiency of 70.4% with respect to the absorbed pump power. At actively Q-switched mode, the maximum average output power of 46 W and the minimum pulse width of 21 ns are achieved at a pulse repetition frequency of 20 kHz, corresponding to a peak power of approximately 109.5 kW. In addition, the beam-quality M2 factor is found to be 1.4 at the maximum output power.
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High-Power and High-Efficiency Operation of Terahertz Quantum Cascade Lasers at 3.3 THz
LI Yuan-Yuan, LIU Jun-Qi, WANG Tao, LIU Feng-Qi, ZHAI Shen-Qiang, ZHANG Jin-Chuan, ZHUO Ning, WANG Li-Jun, LIU Shu-Man, WANG Zhan-Guo
Chin. Phys. Lett. 2015, 32 (10):
104203
.
DOI: 10.1088/0256-307X/32/10/104203
A high-power and high-efficiency GaAs/AlGaAs-based terahertz (THz) quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758 mW with a threshold current density of 120 A/cm2 and a wall-plug efficiency of 0.92% at 10 K and 404 mW at 77 K are obtained in pulsed operation. The maximum operating temperature is as high as 115 K. In the cw mode, a record optical output power of 160 mW with a threshold current density of 178 A/cm2 and a wall-plug efficiency of 1.32% is achieved at 10 K.
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Attosecond-Resolution Er:Fiber-Based Optical Frequency Comb
YAN Lu-Lu, ZHANG Yan-Yan, ZHANG Long, FAN Song-Tao, ZHANG Xiao-Fei, GUO Wen-Ge, ZHANG Shou-Gang, JIANG Hai-Feng
Chin. Phys. Lett. 2015, 32 (10):
104207
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DOI: 10.1088/0256-307X/32/10/104207
Highly stable frequency-controlled optical frequency combs are key elements of many applications in time-frequency and optical-metrology domains. In this work, we demonstrate a highly stable frequency-controlled erbium-fiber-based optical frequency comb system. Its repetition rate is phase-stabilized to a continuous-wave laser with both an intra-cavity electro-optic modulator and a piezo-transducer; while the carrier-envelope-offset frequency is phase-locked to a radio-frequency signal generator by controlling the pump power. In-loop relative frequency stabilities of the comb are below 1 ×10?16 at 1 s, and integrate down to low 10?20 level at 104 s. The corresponding timing uncertainties are 100–200 as over the full measurement range.
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Cr2+:ZnS Saturable Absorber Passively Q-Switched Ho:LuVO4 Laser
CUI Zheng, YAO Bao-Quan, DUAN Xiao-Ming, BAI Shuang, LI Jiang, YUAN Jin-He, DAI Tong-Yu, LI Chao-Yu, PAN Yu-Bai
Chin. Phys. Lett. 2015, 32 (10):
104208
.
DOI: 10.1088/0256-307X/32/10/104208
We report a cw Tm:YAP laser resonantly pumped Ho:LuVO4 laser in passively Q-switched (PQS) mode with Cr2+:ZnS as a saturable absorber (SA). The influence of different transmittances of the output coupler on laser output performance is analyzed. With T=50%, the maximum PQS average output power of 2.3 W is obtained, corresponding to the slope efficiency and the optical–optical conversion efficiency are 35.1% and 19.8%, respectively. Also, the minimum pulse width of 100 ns is achieved at the maximum pulse repetition frequency of 34.2 kHz. When the maximum cw output power is 2.7 W, the beam quality factor of the horizontal direction M2x=1.04 and the vertical direction M2y=1.10 are obtained. In addition, the central wavelength of the laser output remains to be 2057.5 nm with the output coupler transmittances of 50% and 60% in both cw and PQS operations. The results show that the Cr2+:ZnS can be used as an SA in a Ho:LuVO4 laser around 2-μm wavelength.
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Growth and Characterization of InAs1?xSbx with Different Sb Compositions on GaAs Substrates
SUN Qing-Ling, WANG Lu, WANG Wen-Qi, SUN Ling, LI Mei-Cheng, WANG Wen-Xin, JIA Hai-Qiang, ZHOU Jun-Ming, CHEN Hong
Chin. Phys. Lett. 2015, 32 (10):
106801
.
DOI: 10.1088/0256-307X/32/10/106801
InAs1?xSbx with different compositions is grown by molecular beam epitaxy on (100)-oriented semi-insulating GaAs substrates. The increase of Sb content in the epilayer results in the deterioration of crystal quality and surface morphology. Hall measurements show that the carrier concentration increases with the composition of Sb. The electron mobility decreases initially, when Sb composition exceeds a certain value, and the mobility increases slightly. In this work, we emphasize the comparison of crystal quality, surface morphology and electrical properties of epilayers with different Sb compositions.
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Observation of Fermi Arcs in Non-Centrosymmetric Weyl Semi-Metal Candidate NbP
XU Di-Fei, DU Yong-Ping, WANG Zhen, LI Yu-Peng, NIU Xiao-Hai, YAO Qi, Dudin Pavel, XU Zhu-An, WAN Xian-Gang, FENG Dong-Lai
Chin. Phys. Lett. 2015, 32 (10):
107101
.
DOI: 10.1088/0256-307X/32/10/107101
We report the surface electronic structure of niobium phosphide NbP single crystal on (001) surface by vacuum ultraviolet angle-resolved photoemission spectroscopy. Combining with our first principle calculations, we identify the existence of the Fermi arcs originated from topological surface states. Furthermore, the surface states exhibit circular dichroism pattern, which may correlate with its non-trivial spin texture. Our results provide critical evidence for the existence of the Weyl Fermions in NbP, which lays the foundation for further research.
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Wet Chemical Etching of Antimonide-Based Infrared Materials
HAO Hong-Yue, XIANG Wei, WANG Guo-Wei, XU Ying-Qiang, REN Zheng-Wei, HAN Xi, HE Zhen-Hong, LIAO Yong-Ping, WEI Si-Hang, NIU Zhi-Chuan
Chin. Phys. Lett. 2015, 32 (10):
107302
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DOI: 10.1088/0256-307X/32/10/107302
The roughness and the crystallographic orientation selectivity of etched antimonide-based infrared materials are examined and are used to optimize the chemical mesa etching process of the InAs/GaSb superlattice photodiode with the goal of reducing the dark current. The etchant used is based on phosphoric acid (H3PO4), citric acid (C6H8O7) and hydrogen peroxide (H2O2). The roughness of the mesa sidewalls and etching rates are compared and used to find an optimized etchant, with which we obtain optimized mid-wavelength infrared photodiodes possessing an R0A value of 466 Ω?cm2 and a detectivity of 1.43×1011 cm?Hz1/2W?1. Crystallographic orientation selectivity is seen in InAs etching, and also is seen in the InAs/GaSb superlattice wet chemical etching process.
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Waveguide Mode Splitter Based on Multi-mode Dielectric-Loaded Surface Plasmon Polariton Waveguide
CAI Yong-Jing, LI Ming, XIONG Xiao, YU Le, REN Xi-Feng, GUO Guo-Ping, GUO Guang-Can
Chin. Phys. Lett. 2015, 32 (10):
107305
.
DOI: 10.1088/0256-307X/32/10/107305
In photonic integrated circuits, information is usually encoded in the optical path. In this work, based on the multi-mode dielectric-loaded surface plasmon polariton waveguide, we numerically design a directional coupler, which can divide the different waveguide eigenmodes into different optical paths. The results show a possibility to encode information onto different waveguide modes. We also experimentally demonstrate that the splitting ratio of this directional coupler structure can be tuned without changing its size.
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New Superconductivity Dome in LaFeAsO1−xFx Accompanied by Structural Transition
YANG Jie, ZHOU Rui, WEI Lin-Lin, YANG Huai-Xin, LI Jian-Qi, ZHAO Zhong-Xian, ZHENG Guo-Qing
Chin. Phys. Lett. 2015, 32 (10):
107401
.
DOI: 10.1088/0256-307X/32/10/107401
High-temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsO1−xFx (x≤0.2) and many other iron-based superconductors, which leads to proposals that superconductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1−xFx with 0.25≤x≤0.75, where the maximal critical temperature Tc at xopt=0.5–0.55 is even higher than that at x ≤0.2. By nuclear magnetic resonance and transmission electron microscopy, we show that a C4 rotation symmetry-breaking structural transition takes place for x>0.5 above Tc. Our results point to a new paradigm of high temperature superconductivity.
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Synthesis, Structure and Optical Properties of CdO Nanocrystals Directly Grown on Cd Foil
LI Yong, LING Hong, GAO Lei, SONG Yue-Li, TIAN Ming-Li, ZHOU Feng-Qun
Chin. Phys. Lett. 2015, 32 (10):
107802
.
DOI: 10.1088/0256-307X/32/10/107802
Semiconductor nanocrystals directly grown on the conducting metal can lower the contact resistance and can benefit the electron transfer between the semiconductor and the metal. In the present work, CdO nanocrystals are directly synthesized on the conducting Cd foil through a simple solvothermal method. Cd foil is used as the Cd2+ source and the substrate. The average size of CdO nanocrystals is ∼23.1 nm by analyzing the XRD data. Moreover the growth mechanism is discussed. A hierarchic structure characterized by the nano rods and nano particles in the top and bottom layers, respectively, can be observed. From the UV-vis absorption analyzed by Tauc's relation, the two different optical band gaps are obtained. The photoluminescence spectrum is obtained and studied.
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Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources
WANG Hai-Yan, SU Dan, YANG Shuang, DOU Xiu-Ming, ZHU Hai-Jun, JIANG De-Sheng, NI Hai-Qiao, NIU Zhi-Chuan, ZHAO Cui-Lan, SUN Bao-Quan
Chin. Phys. Lett. 2015, 32 (10):
107804
.
DOI: 10.1088/0256-307X/32/10/107804
We investigate metallic microdisk-size dependence of quantum dot (QD) spontaneous emission rate and micro-antenna directional emission effect for the hybrid metal-distributed Bragg reflector structures based on a particular single QD emission. It is found that the measured photoluminescence (PL) intensity is very sensitive to the size of metallic disk, showing an enhancement factor of 11 when the optimal disk diameter is 2 μm and the numerical aperture of microscope objective NA=0.5. It is found that for large metal disks, the Purcell effect is dominant for enhanced PL intensity, whereas for small size disks the main contribution comes from plasmon scattering at the disk edge within the light cone collected by the microscope objective.
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High-Performance Hybrid White Organic Light-Emitting Diodes Utilizing a Mixed Interlayer as the Universal Carrier Switch
DING Lei, LI Huai-Kun, ZHANG Mai-Li, CHENG Jun, ZHANG Fang-Hui
Chin. Phys. Lett. 2015, 32 (10):
107805
.
DOI: 10.1088/0256-307X/32/10/107805
A new interlayer is successfully used to be a universal carrier switch, developing high-performance hybrid white organic light-emitting diodes (WOLEDs). By dint of this interlayer, the two-color hybrid WOLED shows a maximum total current efficiency (CE) and power efficiency (PE) of 48.1 cd/A and 37.6 lm/W, respectively, while the three-color hybrid WOLED shows a maximum total CE and PE of 33.8 cd/A and 25.7 lm/W, respectively. The color rendering index of the three-color hybrid WOLEDs are ≥75, which is already a sufficient level for many commercial lighting applications. In addition, both the two-color and three-color hybrid WOLEDs show low efficiency roll-off and stable color. Furthermore, devices with the new interlayer show much higher performance than devices with the most commonly used 4,4-N,N-dicarbazolebiphenyl and N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine interlayers.
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Fabrication and Piezoelectric Characterization of Single Crystalline GaN Nanobelts
WU Dong-Xu, CHENG Hong-Bin, ZHENG Xue-Jun, WANG Xian-Ying, WANG Ding, LI Jia
Chin. Phys. Lett. 2015, 32 (10):
108102
.
DOI: 10.1088/0256-307X/32/10/108102
GaN nanobelts are synthesized using the chemical vapor deposition method with the catalyst of Ni. The microstructure, composition and photoluminescence property are characterized by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectra. The results demonstrate that the single crystalline GaN nanobelts are grown with a hexagonal wurtzite structure, in width ranging from 500 nm to 2 μm and length up to 10–20 μm. Moreover, a large piezoelectric coefficient d33 of 20 pm/V is obtained from GaN nanobelts by an atomic force microscopy and the high piezoelectric property implies that the perfect single crystallinity and the freedom of dislocation for the GaN nanobelt have significant impact on the electromechanical response.
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44 articles
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