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Optical-Electrical Characteristics and Carrier Dynamics of Semi-Insulation GaAs by Terahertz Spectroscopic Technique
Xiao-Wei Han, Lei Hou, Lei Yang, Zhi-Quan Wang, Meng-Meng Zhao, Wei Shi
Chin. Phys. Lett. 2016, 33 (12):
120701
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DOI: 10.1088/0256-307X/33/12/120701
GaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a semi-insulation (SI) GaAs wafer is investigated by the terahertz (THz) non-destructive testing technology. Using an air biased coherent generation and detection THz time domain spectroscopy system, the THz time domain waveform and spectrum of SI-GaAs are obtained by the time domain spectroscopy module, and its optical-electrical characteristics including complex refractive index, permittivity and dielectric loss angle are calculated. Its carrier lifetime is measured by the optical-pump THz-probe module, and the THz pulse induced intervalley scattering in photo-excited SI-GaAs is discussed.
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Electromagnetically Induced Transparency in a Cold Gas with Strong Atomic Interactions
Yue-Chun Jiao, Xiao-Xuan Han, Zhi-Wei Yang, Jian-Ming Zhao, Suo-Tang Jia
Chin. Phys. Lett. 2016, 33 (12):
123201
.
DOI: 10.1088/0256-307X/33/12/123201
Electromagnetically induced transparency (EIT) is investigated in a system of cold, interacting cesium Rydberg atoms. The utilized cesium levels $6S_{1/2}$, $6P_{3/2}$ and $nD_{5/2}$ constitute a cascade three-level system, in which a coupling laser drives the Rydberg transition, and a probe laser detects the EIT signal on the $6S_{1/2}$ to $6P_{3/2}$ transition. Rydberg EIT spectra are found to depend on the strong interaction between the Rydberg atoms. Diminished EIT transparency is obtained when the Rabi frequency of the probe laser is increased, whereas the corresponding linewidth remains unchanged. To model the system with a three-level Lindblad equation, we introduce a Rydberg-level dephasing rate $\gamma_{3}=\kappa \times (\rho_{33}/{\it \Omega}_{\rm p})^2$, with a value $\kappa$ that depends on the ground-state atom density and the Rydberg level. The simulation results are largely consistent with the measurements. The experiments, in which the principal quantum number is varied between 30 and 43, demonstrate that the EIT reduction observed at large ${\it \Omega}_{\rm p}$ is due to the strong interactions between the Rydberg atoms.
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Low Power Consumption Distributed-Feedback Quantum Cascade Lasers Operating in Continuous-Wave Mode above 90$^{\circ}\!$C at $\lambda \sim7.2$μm
Yue Zhao, Jin-Chuan Zhang, Zhi-Wei Jia, Ying-Hui Liu, Ning Zhuo, Shen-Qiang Zhai, Feng-Qi Liu, Zhan-Guo Wang
Chin. Phys. Lett. 2016, 33 (12):
124201
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DOI: 10.1088/0256-307X/33/12/124201
We report on the design and fabrication of $\lambda\sim 7.2$ μm distributed feedback quantum cascade lasers for very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90$^{\circ}\!$C. For a 2-mm-long and 10-μm-wide laser coated with high-reflectivity on the rear facet, more than 170 mW of output power is obtained at 20$^{\circ}\!$C with a threshold power consumption of 2.4 W, corresponding to 30 mW with a threshold power consumption of 3.9 W at 90$^{\circ}\!$C. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current.
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The Image Property in an EIT Information Transfer System
Li-Yun Zhang, Hua-Jie Hu, Xin Yang, Ming-Tao Cao, Dong Wei, Pei Zhang, Hong Gao, Fu-Li Li
Chin. Phys. Lett. 2016, 33 (12):
124203
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DOI: 10.1088/0256-307X/33/12/124203
We focus on the study of the transferred image property in an electromagnetically induced transparency (EIT) system. In our experiment, a triple-peak image is effectively transferred from a coupling beam to a signal beam based on the EIT effect. It is found that the transferred image intensity profile of the signal beam is the same as that of the coupling beam while not in phase. Furthermore, the propagation property of the transferred image is studied. Due to the narrowing effect, the transferred image keeps narrowing and maintains the shape well within a certain distance outside of the medium. Our experimental results are in excellent agreement with the theoretical analysis.
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Large Signal Modulation Characteristics in the Transition Regime for Two-State Lasing Quantum Dot Lasers
Zun-Ren Lv, Hai-Ming Ji, Xiao-Guang Yang, Shuai Luo, Feng Gao, Feng Xu, Tao Yang
Chin. Phys. Lett. 2016, 33 (12):
124204
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DOI: 10.1088/0256-307X/33/12/124204
Large-signal modulation capability, as an important performance indicator, is directly related to the high-speed optical communication technology involved. We experimentally and theoretically investigate the large-signal modulation characteristics of the simultaneous ground-state (GS) and the excited-state (ES) lasing in InAs/GaAs quantum dot laser diodes. The large-signal modulation capability of total light intensity in the transition regime from GS lasing to two-state lasing is unchanged as the bias-current increases. However, GS and ES large-signal eye diagrams show obvious variations during the transition. Relaxation oscillations and large-signal eye diagrams for GS, ES, and total light intensities are numerically simulated and analyzed in detail by using a rate-equation model. The findings show that a complementary relationship between the light intensities for GS and ES lasing exists in both the transition regime and the two-state lasing regime, leading to a much smaller overshooting power and a shorter settling time for the total light intensity. Therefore, the eye diagrams of GS or ES lasing are diffuse whereas those of total light intensity are constant as the bias-current increases in the transition regime.
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Spectral Beam Combining of Fiber Lasers by Using Reflecting Volume Bragg Gratings
Tai-Dou Zhou, Xiao-Bao Liang, Chao Li, Lei Zhao, Jian-Jun Wang, Feng Jing
Chin. Phys. Lett. 2016, 33 (12):
124205
.
DOI: 10.1088/0256-307X/33/12/124205
By employing three reflecting volume Bragg gratings, a near-infrared 4-channel spectral-beam-combining system is demonstrated to present 720 W combined power with a combining efficiency of 94.7%. The combined laser beam is near-diffraction-limited with a beam factor $M^{2}\sim1.54$. During this 4-channel beam-combining process, no special active cooling measures are used to evaluate the volume Bragg gratings as combining elements are under the higher power laser operation. Thermal expansion and period distortion are verified in a 2 kW 2-channel beam-combining process, and the heat issue in the transmission case is found to be more remarkable than that in the diffraction case. Transmitted and diffracted beams experience wave-front aberrations with different degrees, thus leading to distinct beam deterioration.
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Measurement of the Elasticity of Biological Soft Tissue of Finite Thickness
Hong-Sheng Zhou, Tong-Yu Wang, Zheng Xu, Qian Cheng, Meng-Lu Qian, Xiao-Yi Liu
Chin. Phys. Lett. 2016, 33 (12):
124601
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DOI: 10.1088/0256-307X/33/12/124601
Elasticity is of profound significance to evaluating the function of a biological soft tissue. When the elasticity of a tissue is macroscopically changed, it means that the biological function of the tissue is abnormal and some disease or injury may occur. In the present work, an elastometer is developed to measure the elasticity of biological soft tissues. The measurement is based on the indentation method and the force is measured by the bending of the cantilever. The force-indentation data of the soft tissue is experimentally measured by this elastometer and Young's modulus of the tissue is calculated using the Hertz–Sneddon model. For comparison, a numerical model for the indentation method is established using the finite element method. The difference between the actual modulus and the measured modulus is discussed. The effect of the thickness of the specimen on the measurement is investigated. Young's moduli of beef, porcine liver and porcine kidney are experimentally measured. The results indicate that our elastometer is effective in measuring Young's modulus of a soft tissue quantitatively.
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Experimental Investigation of Electronic Structure of La(O,F)BiSe$_{2}$
Jun Ma, Bin-Bin Fu, Jun-Zhang Ma, Ling-Yuan Kong, Di Chen, Ji-Feng Shao, Chang-Jin Zhang, Tian Qian, Yu-Heng Zhang, Hong Ding
Chin. Phys. Lett. 2016, 33 (12):
127401
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DOI: 10.1088/0256-307X/33/12/127401
La(O,F)BiSe$_{2}$ is a layered superconductor and has the same crystal structure with La(O,F)BiS$_{2}$. We investigate the electronic structure of La(O,F)BiSe$_{2}$ using the angle-resolved photoemission spectroscopy. Two electron-like Fermi surfaces around $X(\pi,0)$ are observed, corresponding to the electron doping of 0.23 per Bi site. We clearly resolve anisotropic band splitting along both ${\it \Gamma}$–$X$ and $M$–$X$ due to the cooperative effects of large spin-orbit coupling and interlayer coupling. Moreover, we observe an almost non-dispersive electronic state around $-$0.2 eV between the electron-like bands. This state vanishes after in-situ K evaporation, indicating that it could be the localized surface state caused by defects on the cleaved surface.
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Possible Nodeless Superconducting Gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and YBa$_2$Cu$_3$O$_{7-x}$ Revealed by Cross-Sectional Scanning Tunneling Spectroscopy
Ming-Qiang Ren, Ya-Jun Yan, Tong Zhang, Dong-Lai Feng
Chin. Phys. Lett. 2016, 33 (12):
127402
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DOI: 10.1088/0256-307X/33/12/127402
Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) and YBa$_2$Cu$_3$O$_{7-x}$ (YBCO) along their $c$-axes on a scale shorter than the interlayer spacing. By tunneling into the (100) plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a (110) surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.
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High Lattice Match Growth of InAsSb Based Materials by Molecular Beam Epitaxy
Yang Ren, Rui-Ting Hao, Si-Jia Liu, Jie Guo, Guo-Wei Wang, Ying-Qiang Xu, Zhi-Chuan Niu
Chin. Phys. Lett. 2016, 33 (12):
128101
.
DOI: 10.1088/0256-307X/33/12/128101
High lattice match growth of InAsSb based materials on GaSb substrates is demonstrated. The present results indicate that a stable substrate temperature and the optimal flux ratios are of critical importance in achieving a homogeneous InAsSb based material composition throughout the growth period. The quality of these epilayers is assessed using a high-resolution x-ray diffraction and atomic force microscope. The mismatch between the GaSb substrate and InAsSb alloy achieves almost zero, and the rms surface roughness of InAsSb alloy achieves around 1.7 ? over an area of 28 μm $\times$ 28 μm. At the same time, the mismatches between GaSb and InAs/InAs$_{0.73}$Sb$_{0.27}$ superlattices (SLs) achieve approximately 100 arcsec (75 periods) and zero (300 periods), with the surface rms roughnesses of InAs/InAs$_{0.73}$Sb$_{0.27}$ SLs around 1.8 ? (75 periods) and 2.1 ? (300 periods) over an area of 20 μm$\times$20 μm, respectively. After fabrication and characterization of the devices, the dynamic resistance of the n-barrier-n InAsSb photodetector near zero bias is of the order of 10$^{6}$ $\Omega\cdot$cm$^{2}$. At 77 K, the positive-intrinsic-negative photodetectors are demonstrated in InAsSb and InAs/InAsSb SL (75 periods) materials, exhibiting fifty-percent cutoff wavelengths of 3.8 μm and 5.1 μm, respectively.
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C-Implanted N-Polar GaN Films Grown by Metal Organic Chemical Vapor Deposition
Ying Zhao, Sheng-Rui Xu, Zhi-Yu Lin, Jin-Cheng Zhang, Teng Jiang, Meng-Di Fu, Jia-Duo Zhu, Qin Lu, Yue Hao
Chin. Phys. Lett. 2016, 33 (12):
128102
.
DOI: 10.1088/0256-307X/33/12/128102
C-implantation N-polar GaN films are grown on $c$-plane sapphire substrates by metal organic chemical vapor deposition. C-implantation induces a large number of defects and causes disorder of the lattice structure in the N-polar GaN film. Raman measurements performed on the N-polar GaN film before C-implantation after C-implantation and subsequent annealing at 1050$^{\circ}\!$C for 5 min indicate that after annealing the disordered GaN lattice is almost recovered. High resolution x-ray diffraction shows that after implantation there is an obvious increase of screw-dislocation densities, and the densities of edge dislocation show slight change. Carbon implantation can induce deep acceptors in GaN, thus the background carriers induced by the high oxygen incorporation in the N-polar GaN film will be partially compensated for, resulting in 25 times the resistivity, which is demonstrated by the temperature-dependent Hall-effect measurement.
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Hopf Amplification Originated from the Force-Gating Channels of Auditory Hair Cells
Lin Tian, Yan-Ping Zhang, Zhang-Cai Long
Chin. Phys. Lett. 2016, 33 (12):
128701
.
DOI: 10.1088/0256-307X/33/12/128701
The sense of mammalian hearing exhibits nonlinear phenomena which are most significant to hearing function, such as nonlinear dynamic compression, nonlinear tuning and combination tones. These nonlinear phenomena are suggested to originate from the Hopf amplification within the cochlea, while the mechanism underlying the Hopf amplification remains elusive. According to the experimental results of force-gating channel operation in hair cells, through a theoretic model, this work reveals a velocity-dependent open probability of force-gating channels in auditory hair cells, and a velocity-dependent active force produced by the force-gating channel operating, which makes sensors hear typical Hopf vibrators with nonlinear hearing phenomena.
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33 articles
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