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$Ab\ Initio$ Calculation of Dielectric Function in Wurtzite GaN Based on Walter's Model
Zi-Wei Zhu, Ji-Yuan Zheng, Lai Wang, Bing Xiong, Chang-Zheng Sun, Zhi-Biao Hao, Yi Luo, Yan-Jun Han, Jian Wang, Hong-Tao Li
Chin. Phys. Lett. 2017, 34 (3):
030303
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DOI: 10.1088/0256-307X/34/3/030303
The wavelength-dependent and frequency-dependent dielectric function of wurtzite-GaN is calculated totally from fundamental parameters such as the lattice constant using Walter's ab initio model. The errors occurring in the calculation are carefully reduced by linear interpolation of energy data. The Kramers–Krönig transform of the real part of greater range is obtained by extrapolation of the real part. The calculation is time-consuming but meaningful. The long-wave results are similar to the experimental data of the photon and are useful for related investigation of properties of wide-gap semiconductors such as electron scattering like the Auger recombination and impact ionization.
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Q-Switching Pulse Operation in 1.5-μm Region Using Copper Nanoparticles as Saturable Absorber
A. R. Muhammad, M. T. Ahmad, R. Zakaria, H. R. A. Rahim, S. F. A. Z. Yusoff, K. S. Hamdan, H. H. M. Yusof, H. Arof, S. W. Harun.
Chin. Phys. Lett. 2017, 34 (3):
034205
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DOI: 10.1088/0256-307X/34/3/034205
We demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) using a copper nanoparticle (CuNP) thin film as the saturable absorber in a ring cavity. A stable Q-switched pulse operation is observed as the CuNP saturable absorber (SA) is introduced in the cavity. The pulse repetition rate of the EDFL is observed to be proportional to the pump power, and is limited to 101.2 kHz by the maximum pump power of 113.7 mW. On the other hand, the pulse width reduces from 10.19 μs to 4.28 μs as the pump power is varied from 26.1 mW to 113.7 mW. The findings suggest that CuNP SA could be useful as a potential saturable absorber for the development of the robust, compact, efficient and low cost Q-switched fiber laser operating at 1.5-μm region.
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A High-Pulse-Energy High-Beam-Quality Tunable Ti:Sapphire Laser Using a Prism-Dispersion Cavity
Chang Xu, Shi-Bo Dai, Chuan Guo, Qi Bian, Jun-Wei Zuo, Yuan-Qin Xia, Hong-Wei Gao, Zhi-Min Wang, Yong Bo, Nan Zong, Sheng Zhang, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2017, 34 (3):
034206
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DOI: 10.1088/0256-307X/34/3/034206
A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740–855 nm is obtained. At an incident pump energy of 774 mJ, the maximum output energy of 104 mJ at 790 nm with a pulse width of 100 μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor $M^{2}$ is 1.16. The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740–855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe$_{2}$BO$_{3}$F$_{2}$ measured in a wider wavelength range and to assess Miller's rule quantitatively.
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Interference from Two-Photon Sources in Silica-on-Silicon Circuits at Telecom Wavelength
Xing-Yun Li, Lu Qin, Jia-Shun Zhang, Mei-Zhen Ren, Jun-Ming An, Xiao-Hong Yang, Xing-Sheng Xu
Chin. Phys. Lett. 2017, 34 (3):
034211
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DOI: 10.1088/0256-307X/34/3/034211
The integrated photonic chip is a promising way to realize future quantum technology. Here we demonstrate a two-photon interference in the standard telecommunication band on a silica-on-silicon integrated photonic chip. Two identical photons in the 1.55 μm band, which are indistinguishable in spatial, frequency and polarization, are generated by type-I collinear spontaneous parametric down-conversion via bismuth borate. The silica-on-silicon integrated chip, which has an insertion loss less than 1 dB, is a Mach–Zehnder interferometer with a thermo-optic phase shifter. A high visibility of 100% in the classical interference and 99.2% in the two-photon interference is achieved, indicating that the two-photon interference with high interference visibility on the chip is attained successfully.
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Geoacoustic Inversion for Bottom Parameters via Bayesian Theory in Deep Ocean
Xiao-Le Guo, Kun-De Yang, Yuan-Liang Ma
Chin. Phys. Lett. 2017, 34 (3):
034301
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DOI: 10.1088/0256-307X/34/3/034301
We develop a new approach to estimating bottom parameters based on the Bayesian theory in deep ocean. The solution in a Bayesian inversion is characterized by its posterior probability density (PPD), which combines prior information about the model with information from an observed data set. Bottom parameters are sensitive to the transmission loss (TL) data in shadow zones of deep ocean. In this study, TLs of different frequencies from the South China Sea in the summer of 2014 are used as the observed data sets. The interpretation of the multidimensional PPD requires the calculation of its moments, such as the mean, covariance, and marginal distributions, which provide parameter estimates and uncertainties. Considering that the sensitivities of shallow-zone TLs vary for different frequencies of the bottom parameters in the deep ocean, this research obtains bottom parameters at varying frequencies. Then, the inversion results are compared with the sampling data and the correlations between bottom parameters are determined. Furthermore, we show the inversion results for multi-frequency combined inversion. The inversion results are verified by the experimental TLs and the numerical results, which are calculated using the inverted bottom parameters for different source depths and receiver depths at the corresponding frequency.
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Ramp-Wave Compression Experiment with Direct Laser Illumination on ShenGuang-III Prototype Laser Facility
Feng Wang, Quan-Xi Xue, Teng Ji, Yu-Long Li, Tao Xu, Xiao-Shi Peng
Chin. Phys. Lett. 2017, 34 (3):
035201
.
DOI: 10.1088/0256-307X/34/3/035201
Ramp-wave compression experiment to balance the high compression pressure generation in aluminum and x-ray blanking effect in transparent window is demonstrated with an imaging velocity interferometer system for any reflector (VISAR) on ShenGuang-III prototype laser facility. The highest pressure is about 500 GPa after using the multilayer target design Al/Au/Al/LiF and $\sim$10$^{13}$ W/cm$^{2}$ laser pulse illuminated on the planar Al target, which generates the spatial uniformity to $ < $1% over 500 μm on the ablation layer. A 2-μm-thick Au layer is used to prevent the x-ray from preheating the planar ablation Al layer and window material LiF. The imaging VISAR system can be used to record the abrupt loss of the probe beam ($\lambda=532$ nm) caused by absorption and reflection of 20-μm, 30-μm and 40-μm-thick Al, i.e., the blanking effect. Although there are slight shocks in the target, the peak pressure 500 GPa, which is the highest data up to now, is obtained with ramp-wave compression.
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Microstructural Changes of Graphene/PLA/PBC Nanofibers by Electrospinning during Tensile Tests
Wei-Dong Cheng, Chuan-Hui Ren, Xiao-Hua Gu, Zhao-Jun Wu, Xue-Qing Xing, Guang Mo, Zhong-Jun Chen, Zhong-Hua Wu
Chin. Phys. Lett. 2017, 34 (3):
036101
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DOI: 10.1088/0256-307X/34/3/036101
This study focuses on the nanostructure and nanostructural changes of novel graphene/poly(lactic acid) (PLA)/ poly(butylene carbonate) (PBC) nanofibers via electrospinning, which are characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile test and in situ small angle x-ray scattering. DSC indicates that the endothermic peak at 295$^\circ\!$C of pure PLA/PBC nanofibers shifted from 317$^{\circ}\!$C to lower 290$^{\circ}\!$C with the increasing graphene content. SEM observations reveal a fine dispersion of graphene in the nanofiber matrices. The graphene/PLA/PBC nanofibers exhibit good improvements in mechanical property. The tensile strength of nanofibers increases with the addition of 0.01 g graphene but reduces with further addition of 0.04 g graphene. The scattering intensities increase dramatically when the strain levels are higher than the yield point due to the nucleation and growth of nanovoids or crystals. However, the increasing content of graphene in the PLA/PBC matrix provokes a strong restriction to the deformation-induced crystals.
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Anomalous Magneto-Transport Behavior in Transition Metal Pentatelluride HfTe$_{5}$
Ling-Xiao Zhao, Xiao-Chun Huang, Yu-Jia Long, Dong Chen, Hui Liang, Zhan-Hai Yang, Mian-Qi Xue, Zhi-An Ren, Hong-Ming Weng, Zhong Fang, Xi Dai, Gen-Fu Chen
Chin. Phys. Lett. 2017, 34 (3):
037102
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DOI: 10.1088/0256-307X/34/3/037102
There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe$_{5}$. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe$_{5}$. It is found that a three-dimensional topological Dirac semimetal state emerges only at around $T_{\rm p}$ (at which the resistivity shows a pronounced peak), as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe$_{5}$. Our work not only provides the first evidence of a temperature-induced critical topological phase transition in HfTe$_{5}$ but also gives a reasonable explanation on the long-lasting question.
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Observation of an Even–Odd Asymmetric Transport in High Landau Levels
Guang-Tong Liu, Yu-Ying Zhu, Qin Wang, Yuan Pang, Jie Fan, Xiu-Nian Jing, Zhong-Qing Ji, Chang-Li Yang, Li Lu, Rui-Rui Du, L. N. Pfeiffer, K. W. West
Chin. Phys. Lett. 2017, 34 (3):
037301
.
DOI: 10.1088/0256-307X/34/3/037301
Magnetotransport experiments including tilt fields are performed on ultrahigh mobility L-shaped Hall-bar samples of GaAs/AlGaAs quantum wells. The low-temperature longitudinal resistivity ($\rho_{xx}$) data demonstrate that a striking even–odd asymmetric transport exists along the [1$\overline{1}$0] direction at half filling in $N\geq 2$ high Landau levels. Although the origin for the peculiar even–odd asymmetry remains unclear, we propose that the coupling strength between electrons within the same Landau level and between the neighboring two Landau levels should be considered in future studies. The tilt field data show that the in-plane field can suppress the formation of both bubble and stripe phases.
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Significant Improvement of Passivation Performance by Two-Step Preparation of Amorphous Silicon Passivation Layers in Silicon Heterojunction Solar Cells
Yue Zhang, Cao Yu, Miao Yang, Lin-Rui Zhang, Yong-Cai He, Jin-Yan Zhang, Xi-Xiang Xu, Yong-Zhe Zhang, Xue-Mei Song, Hui Yan
Chin. Phys. Lett. 2017, 34 (3):
038101
.
DOI: 10.1088/0256-307X/34/3/038101
The key feature of amorphous/crystalline silicon heterojunction solar cells is extremely low surface recombination, which is related to superior passivation on the crystalline silicon wafer surface using thin hydrogenated amorphous silicon (a-Si:H) layers, leading to a high open-circuit voltage. In this work, a two-step method of a-Si:H passivation is introduced, showing excellent interface passivation quality, and the highest effective minority carrier lifetime exceeds 4500 μs. By applying a buffer layer deposited through pure silane plasma, the risk of film epitaxial growth and plasma damage caused by hydrogen diluted silane plasma is effectively reduced. Based on this, excellent passivation is realized through the following hydrogen diluted silane plasma process with the application of high density hydrogen. In this process, hydrogen diffuses to a-Si/c-Si interface, saturating residual dangling bonds which are not passivated by the buffer layer. Employing this two-step method, a heterojunction solar cell with an area of 239 cm$^{2}$ is prepared, yielding to open-circuit voltage up to 735 mV and total-area efficiency up to 22.4%.
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31 articles
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