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 Select A 1-kHz Single Frequency Nd:YAG Ring Laser by Injection Seeding Xue-Zhe Cao, Pei-Lin Li, Zai-Yuan Wang, Qiang Liu Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124201 Abstract   HTML   PDF (720KB) We report on an injection seeded 1 kHz single frequency pulsed Nd:YAG ring laser with pulse energy of 5.2 mJ and pulse width of 9.9 ns. The ramp-fire technique is used to maintain single frequency operation and the cavity length is modulated by an intracavity RbTiOPO$_{4}$ (RTP) crystal. The frequency stability (rms) of the output pulse is 1.99 MHz over 1 min and the linewidth is 64 MHz.
 Select Photoexcited Blueshift and Redshift Switchable Metamaterial Absorber at Terahertz Frequencies Zong-Cheng Xu, Liang Wu, Ya-Ting Zhang, De-Gang Xu, Jian-Quan Yao Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124202 Abstract   HTML   PDF (904KB) We propose a design and numerical study of an optically blueshift and redshift switchable metamaterial (MM) absorber in the terahertz regime. The MM absorber comprises a periodic array of metallic split-ring resonators (SRRs) with semiconductor silicon embedded in the gaps of MM resonators. The absorptive frequencies of the MM can be shifted by applying an external pump power. The simulation results show that, for photoconductivity of silicon ranging between 1 S/m and 4000 S/m, the resonance peak of the absorption spectra shifts to higher frequencies, from 0.67 THz to 1.63 THz, with a resonance tuning range of 59%. As the conductivity of silicon increases, the resonance frequencies of the MM absorber are continuously tuned from 1.60 THz to 1.16 THz, a redshift tuning range of 28%. As the conductivity increases above 30000 S/m, the resonance frequencies tend to be stable while the absorption peak has a merely tiny variation. The optical-tuned absorber has potential applications as a terahertz modulator or switch.
 Select A V-Folded Digital Laser for On-Demand Vortex Beams by Astigmatic Transformation of Hermite–Gaussian Modes Sen-Sen Liu, Xu-Dong Chen, Ji-Xiong Pu, Zhi-Li Lin, Zi-Yang Chen Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124203 Abstract   HTML   PDF (891KB) A V-folded digital laser using a spatial light modulator (SLM) for intra-cavity loss shaping is exploited to generate Hermite–Gaussian modes with on-demand mode order. With a $\pi$/2 astigmatic mode converter, vortex beams carrying on-demand orbital angular momentum (OAM) with a tunable range from $-11\hbar$ to $12\hbar$ are obtained. The mode order of the HG mode, hence the OAM of the vortex beam, is digitally switched by changing the phase pattern imposed on the SLM without requiring any mechanic alignment of the cavity. This work has great potential applications in various OAM-tunable vortex beams.
 Select Landau–Zener–Stückelberg Interference in Nonlinear Regime Tong Wu, Yuxuan Zhou, Yuan Xu, Song Liu, Jian Li Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124204 Abstract   HTML   PDF (1631KB) Landau–Zener–Stückelberg (LZS) interference has drawn renewed attention to quantum information processing research because it is not only an effective tool for characterizing two-level quantum systems but also a powerful approach to manipulate quantum states. Superconducting quantum circuits, due to their versatile tunability and degrees of control, are ideal platforms for studying LZS interference phenomena. We use a superconducting Xmon qubit to study LZS interference by parametrically modulating the qubit transition frequency nonlinearly. For dc flux biasing of the qubit slightly far away from the optimal flux point, the qubit excited state population shows an interference pattern that is very similar to the standard LZS interference in linear regime, except that all bands shift towards lower frequencies when increasing the rf modulation amplitude. For dc flux biasing close to the optimal flux point, the negative sidebands and the positive sidebands behave differently, resulting in an asymmetric interference pattern. The experimental results are also in good agreement with our analytical and numerical simulations.
 Select Terahertz Lens Fabricated by Natural Dolomite Si-Bo Hao, Zi-Li Zhang, Yuan-Yuan Ma, Meng-Yu Chen, Yang Liu, Hao-Chong Huang, Zhi-Yuan Zheng Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124205 Abstract   HTML   PDF (2982KB) Optical operations have served as the basis of spectroscopy and imaging in terahertz regimes for a long time. Available lenses are practical tools for modulations. We fabricate a kind of biconvex lens from the natural dolomite cluster. The lens works well at 0.1 THz based on the relatively high refractive index and low absorption coefficients. Compared with the lens fabricated by a dolomite stone, such a lens can focus dispersive terahertz beam efficiently in terahertz imaging systems, which indicates that natural minerals hold promising applications in terahertz optics.
 Select Generation of Femtosecond Laser Pulse at 1.43GHz from an Optical Parametric Oscillator Based on LBO Crystal Jia-Jun Song, Xiang-Hao Meng, Zhao-Hua Wang, Xian-Zhi Wang, Wen-Long Tian, Jiang-Feng Zhu, Shao-Bo Fang, Hao Teng, Zhi-Yi Wei Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124206 Abstract   HTML   PDF (758KB) A femtosecond LBO optical parametric oscillator (OPO) with widely adjustable repetition rate by fractionally decrement of the cavity length is demonstrated. The repetition rate of 755 MHz to 1.43 GHz at an interval of 75.5 MHz is realized, which is 10 to 19 times that of the pump laser. The properties of output signal at 750 nm at different repetition rates are studied. The power of signal decreases with increasing the repetition rate. The maximum power of 194 mW at the repetition rate of 755 MHz and the minimum power of 22 mW at repetition rate of 1.43 GHz for the signal at 750 nm are obtained for the pump power of 3 W.
 Select Identifying the Symmetry of an Object Based on Orbital Angular Momentum through a Few-Mode Fiber Zhou-Xiang Wang, Yu-Chen Xie, Han Zhou, Shuang-Yin Huang, Min Wang, Rui Liu, Wen-Rong Qi, Qian-Qian Tian, Ling-Jun Kong, Chenghou Tu, Yongnan Li, Hui-Tian Wang Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124207 Abstract   HTML   PDF (724KB) In recent years, orbital angular momentum (OAM), as a new usable degree of freedom of photons, has been widely applied in both classical optics and quantum optics. For example, digital spiral imaging uses the OAM spectrum of the output beam from the object to restore the symmetry information of the object. However, the related experiments have been carried out in free space so far. Due to the poor anti-noise performance, limited transmission distance and other reasons, the practicability is seriously restricted. Here, we have carried out a digital spiral imaging experiment through a few-mode fiber, to achieve the identification of the symmetry of object by measuring the OAM spectrum of the output beam. In experiment, we have demonstrated the identification of the symmetry of amplitude-only and phase-only objects with the two-, three- and four-fold rotational symmetries. We also give the understanding of the physics. We believe that our work has greatly improved the practical application of digital spiral imaging in remote sensing.
 Select Emergent Quantum Dynamics of Vortex-Line under Linear Local Induction Approximation Gui-Hao Jia, Yu Xu, Xiao Kong, Cui-Xian Guo, Si-Lei Liu, Su-Peng Kou Chin. Phys. Lett.    2019, 36 (12): .   DOI: 10.1088/0256-307X/36/12/124701 Abstract   HTML   PDF (5143KB) Using the linear local induction approximation, we investigate the self-induced motion of a vortex-line that corresponds to the motion of a particle in quantum mechanics. Provided Kelvin waves, the effective Schrödinger equation, physical quantity operators, and the corresponding path-integral formula can be obtained. In particular, the effective Planck constant defined by parameters of vortex-line motion shows the mathematical relation between the two fields. The vortexline–particle mapping may help in understanding particle motion in quantum mechanics.
 Select Mid-IR Laser Generating Ultrasound in a Polyetheretherketone Polymer Ye Zhang, Gao-You Liu, Yi Chen, Chuan-Peng Qian, Ben-Rui Zhao, Bao-Quan Yao, Tong-Yu Dai, Xiao-Ming Duan Chin. Phys. Lett.    2019, 36 (11): .   DOI: 10.1088/0256-307X/36/11/114201 Abstract   HTML   PDF (740KB) We demonstrate laser ultrasonic generation in polyetheretherketone (PEEK). A middle infrared ZnGeP$_{2}$ optical parametric oscillator (ZGP-OPO) pumped by a Q-switched Ho:YAG laser is employed as the ultrasonic excitation source. The ZGP-OPO has a spectral range of 3.2–3.4 μm. At an output wavelength of 3.4 μm, the maximum average output power of ZGP-OPO is 3.05 W with a pulse width of 24.3 ns, corresponding to a peak power of approximately 127.5 kW. The ultrasound is generated by the laser converted from 3.2 to 3.4 μm in the PEEK composite. The maximum ultrasonic signal amplitude in PEEK is 33 mV under the condition of thermoelastic excitation at 3.4 μm. Ablation occurs in the CPRF sample when the energy fluence is over 122.45 mJ/cm$^{2}$. PEEK has a stronger absorption at 3.4 μm and laser-ultrasound generation is influenced by the wavelength of the laser.
 Select High-Repetition-Rate and High-Beam-Quality Laser Pulses with 1.5MW Peak Power Generation from a Two-Stage Nd:YVO$_{4}$ Amplifier Qiu-Run He, Jing Guo, Bao-Fu Zhang, Zhong-Xing Jiao Chin. Phys. Lett.    2019, 36 (11): .   DOI: 10.1088/0256-307X/36/11/114202 Abstract   HTML   PDF (802KB) We develop a two-stage end-pumped Nd:YVO$_{4}$ amplifier seeded by a passively Q-switched microchip laser. An average output power of 13.5 W with repetition rate up to 7 kHz and pulse duration of $\sim$1.24 ns is obtained, corresponding to a pump extraction efficiency of 16.1% (19.5% for the second stage) and peak power of $\sim$1.5 MW. The beam quality factors at maximum output power are measured to be $M_{x}^{2}=1.56$ and $M_{y}^{2}=1.48$. We introduce an analytical model to estimate gain and beam quality after amplification. This model focuses on the influence of ratio of seed spot radius to pump spot radius when designing an amplifier. Moreover, our experiments reveal that the re-imaging system in the double-pass configuration can be used to enhance the beam quality.
 Select Label-Free Microscopic Imaging Based on the Random Matrix Theory in Wavefront Shaping Li-Qi Yu, Xin-Yu Xu, Zhen-Feng Zhang, Qi Feng, Bin Zhang, Ying-Chun Ding, Qiang Liu Chin. Phys. Lett.    2019, 36 (11): .   DOI: 10.1088/0256-307X/36/11/114203 Abstract   HTML   PDF (724KB) Wavefront shaping technology has mainly been applied to microscopic fluorescence imaging through turbid media, with the advantages of high resolution and imaging depth beyond the ballistic regime. However, fluorescence needs to be introduced extrinsically and the field of view is limited by memory effects. Here we propose a new method for microscopic imaging light transmission through turbid media, which has the advantages of label-free and discretional field of view size, based on transmission-matrix-based wavefront shaping and the random matrix theory. We also verify that a target of absorber behind the strong scattering media can be imaged with high resolution in the experiment. Our method opens a new avenue for the research and application of wavefront shaping.
 Select Detection and Location of a Target in Layered Media by Snapshot Time Reversal and Reverse Time Migration Mixed Method Hong-Juan Yang, Jian Li, Xiang Gao, Jun Ma, Jun-Hong Li, Wen Wang, Cheng-Hao Wang Chin. Phys. Lett.    2019, 36 (11): .   DOI: 10.1088/0256-307X/36/11/114301 Abstract   HTML   PDF (2249KB) A target in layered medium can be located by the ridge-like distribution time reversal and reverse time migration (TR-RTM) mixed method. However, this method cannot distinguish between acoustic field distributions of the interface and target for the wider acoustic pulse signals, which may result in inaccurate location of the target. A snapshot TR-RTM mixed method is proposed to solve this problem. The principle of snapshot TR-RTM mixed method is first given. Experiments are then carried out, and a mountain-like acoustic field distribution is obtained by processing experimental data. The results show that the location of the peak is that of the target, and the ratio of the scattered signal and interface reflection signal (signal-to-interference ratio) is improved by about four times after processing. Furthermore, this method can effectively suppress the interface reflection signal and enhance the target scattering signal. Therefore, it can achieve effective detection and location of a target in a layered medium.
 Select Acoustic Vortex Beam Generation by a Piezoelectric Transducer Using Spiral Electrodes Han Zhang, Yang Gao Chin. Phys. Lett.    2019, 36 (11): .   DOI: 10.1088/0256-307X/36/11/114302 Abstract   HTML   PDF (973KB) We propose an innovative method to generate acoustic vortex waves based on a disc piezoelectric transducer that is coated with multi-arm coiled electrodes. Finite element simulation results for single-arm to four-arm coiled electrodes indicate that the method could modulate amplitude and phase spatial distribution of the acoustic waves near the acoustic axis by acoustic field synthesis principle, making the waves rotate spirally in space and form stable focused vortex beams. Compared with the traditional method that requires electronic control of an array consisting of a large number of transducers, this method provides a more effective and compact solution.
 Select III–V/Si Hybrid Laser Array with DBR on Si Waveguide Yan-Ping Li, Li-Jun Yuan, Li Tao, Wei-Xi Chen, Bao-Jun Wang, Jiao-Qing Pan Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/104201 Abstract   HTML   PDF (603KB) We report an eight-channel silicon evanescent laser array operating at continuous wave under room temperature conditions using the selective-area metal bonding technique. The laser array is realized by evanescently coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector gratings. The lasers have emission peak wavelengths in a range of 1537–1543 nm with a wavelength spacing of about 1.0 nm. The thermal impedances $Z_{\rm T}$ of these hybrid lasers are evidently lower than those DFB counterparts
 Select Optically Modulated Tunable O-Band Praseodymium-Doped Fluoride Fiber Laser Utilizing Multi-Walled Carbon Nanotube Saturable Absorber H. Ahmad, M. F. Ismail, S. N. Aidit Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/104202 Abstract   HTML   PDF (1772KB) A tunable and optically modulated fiber laser utilizing a multi-walled carbon nanotube based saturable absorber is demonstrated for operation in the O-band region. A praseodymium-doped fluoride fiber is used as the gain medium and the system is capable of generating modulated outputs at 1300 nm. Pulsed output is observed at pump powers of 511 mW and above, with repetition rates and pulse widths that can be tuned from 41 kHz and 3.4 μs to 48 kHz and 2.4 μs, respectively, at the maximum pump power available. A maximum average output power of 100 $\mu$W with a corresponding single pulse energy of 2.1 nJ is measured, while the tunability of the proposed laser is from 1290 nm to 1308 nm. The output is stable, with peak power fluctuations of $\sim$4 dB from the average value.
 Select Quantifying Process Nonclassicality in Bosonic Fields Shuang-Shuang Fu, Shun-Long Luo Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/104203 Abstract   HTML   PDF (449KB) Nonclassicality of optical states, as a key characteristic of bosonic fields, is a valuable resource for quantum information processing. We investigate the generation of nonclassicality in quantum processes from a quantitative perspective, introduce three information-theoretic measures of nonclassicality for quantum-optical processes based on the Wigner–Yanase skew information and coherent states, and illustrate their physical significance through several well-known single-mode quantum processes.
 Select Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions Jin-Ming Chen, Jin-Ping Yao, Zhao-Xiang Liu, Bo Xu, Fang-Bo Zhang, Yue-Xin Wan, Wei Chu, Zhen-Hua Wang, Ling-Ling Qiao, Ya Cheng Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/104204 Abstract   HTML   PDF (1219KB) We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense 800 nm laser pulse and a weak 400 nm laser pulse. It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap. In comparison, the spectral broadening in argon is less pronounced, although argon atoms and nitrogen molecules have comparable ionization potentials. We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.
 Select A Photon-Counting Full-Waveform Lidar Bing-Cheng Du, Zhao-Hui Li, Guang-Yue Shen, Tian-Xiang Zheng, Hai-Yan Zhang, Lei Yang, Guang Wu Chin. Phys. Lett.    2019, 36 (9): .   DOI: 10.1088/0256-307X/36/9/094201 Abstract   HTML   PDF (1132KB) We present the results of using a photon-counting full-waveform lidar to obtain detailed target information with high accuracy. The parameters of the waveforms (i.e., vertical structure, peak position, peak amplitude, peak width and backscatter cross section) are derived with a high resolution limit of 31 mm to establish the vertical structure and scattering properties of targets, which contribute to the recognition and classification of various scatterers. The photon-counting full-waveform lidar has higher resolution than linear-mode full-waveform lidar, and it can obtain more specific target information compared to photon-counting discrete-point lidar, which can provide a potential alternative technique for tomographic surveying and mapping.
 Select Design of an Acoustic Levitator for Three-Dimensional Manipulation of Numerous Particles Di Wu, De-Yao Yin, Zhi-Yuan Xiao, Qing-Fan Shi Chin. Phys. Lett.    2019, 36 (9): .   DOI: 10.1088/0256-307X/36/9/094301 Abstract   HTML   PDF (4169KB) We present a design of an acoustic levitator consisting of three pairs of opposite transducer arrays. Three orthogonal standing waves create a large number of acoustic traps at which the particles are levitated in mid-air. By changing the phase difference of transducer arrays, three-dimensional manipulation of particles is successfully realized. Moreover, the relationship between the translation of particles and the phase difference is experimentally investigated, and the result is in agreement with the theoretical calculation. This design can expand the application of acoustic levitation in many fields, such as biomedicine, ultrasonic motor and new materials processing.
 Select Phase Transition and Critical Phenomenon Occurring in Granular Matter Yao-Dong Feng, Tao Su, Qing-Fan Shi, Gang Sun Chin. Phys. Lett.    2019, 36 (9): .   DOI: 10.1088/0256-307X/36/9/094501 Abstract   HTML   PDF (541KB) We investigate the granular flow states in a channel with bottleneck by molecular dynamics simulations. Our study is restricted only on a selected key area rather than on the whole system to focus on the flow properties of a single granular state. A random force field is introduced to control the granular temperature. It is also pointed out that the flow rate in the granular flow can be correlated with the pressure, which leads us to carry out a comprehensive study similar to the classical study for general liquid-gas phase transition. Our results show that the dilute flow state and the dense flow state of the granules are similar to the gas state and the liquid state of general substances, respectively, and the properties of phase transition and critical phenomenon are also similar to those occurring in general substances.
 Select High-Brightness Low-Divergence Tapered Lasers with a Narrow Taper Angle Zhong-Hao Chen, Hong-Wei Qu, Xiao-Long Ma, Ai-Yi Qi, Xu-Yan Zhou, Yu-Fei Wang, Wan-Hua Zheng Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084201 Abstract   HTML   PDF (569KB) High-brightness tapered lasers with photonic crystal structures are designed and fabricated. A narrow taper angle is designed for the tapered section. The device delivers an output power of 3.3 W and a maximum wall-plug efficiency of 43%. The vertical beam divergence is around 11$^{\circ}$ at different currents. Nearly diffraction-limited beam qualities for the vertical and lateral directions are obtained. The lateral beam quality factor $M^{2}$ is below 2.5 and the vertical $M^{2}$ value is around 1.5 across the whole operating current range. The maximum brightness is 85 MW$\cdot$cm$^{-2}$sr$^{-1}$. When the current is above 3.3 A, the brightness is still above 80 MW$\cdot$cm$^{-2}$sr$^{-1}$.
 Select A Silicon Shallow-Ridge Waveguide Integrated Superconducting Nanowire Single Photon Detector Towards Quantum Photonic Circuits Lingjie Yu, Heqing Wang, Hao Li, Zhen Wang, Yidong Huang, Lixing You, Wei Zhang Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084202 Abstract   HTML   PDF (671KB) A silicon shallow-ridge waveguide integrated superconducting nanowire single photon detector is designed and fabricated. At the bias current of 11.6 $\mu$A, 4% on-chip detection efficiency near 1550 nm wavelength is achieved with the dark count rate of 3 Hz and a timing jitter of 75 ps. This device shows the potential application in the integration of superconducting nanowire single photon detectors with a complex quantum photonic circuit.
 Select Preparation and 1.06μm Fluorescence Decay of Nd$^{3+}$-Doped Glass Ceramics Containing NaYF$_{4}$ Nanocrystallites Xing-Yong Huang, Da-Qin Chen, Bi-Zhou Shen, Hai-Zhi Song Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084203 Abstract   HTML   PDF (742KB) Considered to be a candidate for large-size bulk materials used in lasers and other fields, Nd$^{3+}$-doped glass ceramics containing NaYF$_{4}$ nanocrystallites are prepared. Using x-ray diffraction and transmission electron microscopy, we show that pure cubic NaYF$_{4}$ is well precipitated in the glass matrix. To obtain the optical property of this material at 1.06 μm, the fluorescence decay of $^{4}\!F_{3/2}$ energy levels is measured and analyzed. It is found that the fluorescence lifetime decreases first and then increases with the increasing dopant concentration due to the existing but finally weakening energy dissipation. As a result, a long radiation lifetime of about 191–444 μs is obtained at 1.06 μm in the prepared material. It is thus revealed that Nd$^{3+}$-doped glass ceramic containing NaYF$_{4}$ nanocrystallites is a potential candidate as a near-infrared laser material.
 Select Wavelength-Locked 878.6nm In-Band Pumped Intra-Cavity 2.1μm Optical Parametric Oscillator Shuang Wu, Yong-Ji Yu, Yue Li, Yu-Heng Wang, Jing-Liang Liu, Guang-Yong Jin Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084204 Abstract   HTML   PDF (1175KB) We report herein a high-power folded intra-cavity 2.1 μm optical parametric oscillator (ICOPO) which is the first example of an ICOPO that utilizes a wavelength-locked 878.6 nm in-band pumped Nd:YVO$_{4}$ laser as the pump source. The thermal effect of PPMgLN crystal and the divergence angle of the incident laser are considered comprehensively to determine the 2128 nm degenerate temperature. In the experiment, the functions of different output coupler transmittances and different repetition rates on the parametric laser output power are studied, respectively. The temperature versus parametric laser output power in an in-band pumped non-wavelength-locked 880 nm laser diode (LD) and in a wavelength-locked 878.6 nm LD is compared. A maximum output power of 5.87 W is obtained at the pump power of 56.9 W when the repetition rate is 80 kHz. The corresponding conversion efficiency is 14.55%, with a linewidth of 73.65 nm and pulse width of 3.62 ns. The wavelength-locked 878.6 nm LD in-band pumping technology can stabilize the 2.1 μm laser output power of Nd:YVO$_{4}$ crystal effectively in the environment of intense temperature change.
 Select Influence of Coating Layer on Acoustic Wave Propagation in a Random Complex Medium with Resonant Scatterers Hang Yang, Xin Zhang, Jian-hua Guo, Fu-gen Wu, Yuan-wei Yao Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084301 Abstract   HTML   PDF (1713KB) We investigate the influence of coating layer on acoustic wave propagation in a dispersed random medium consisting of coated fibers. In the strong-scattering regime, the characteristics of wave scattering resonances are found to evolve regularly with the properties of the coating layer. By theoretical calculation, frequency gaps are found in acoustic excitation spectra in a random medium. The scattering cross section results present the evolution of scattering resonances with the properties of the coating layer, which offers a good explanation for the change of the frequency gaps. The velocity of the propagation quasi-mode is also shown to depend on the filling fraction of the coating layer. We use the generalized coherent potential-approximation approach to solve acoustic wave dispersion relations in a complicated random medium consisting of coating-structure scatterers. It is shown that our model reveals subtle changes in the behavior of the acoustic wave propagating quasi-modes.
 Select Oscillation and Migration of Bubbles within Ultrasonic Field Wen-Hua Wu, Peng-Fei Yang, Wei Zhai, Bing-Bo Wei Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/084302 Abstract   HTML   PDF (730KB) The oscillation and migration of bubbles within an intensive ultrasonic field are important issues concerning acoustic cavitation in liquids. We establish a selection map of bubble oscillation mode related to initial bubble radius and driving sound pressure under 20 kHz ultrasound and analyze the individual-bubble migration induced by the combined effects of pressure gradient and acoustic streaming. Our results indicate that the pressure threshold of stable and transient cavitation decreases with the increasing initial bubble radius. At the pressure antinode, the Bjerknes force dominates the bubble migration, resulting in the large bubbles gathering toward antinode center, whereas small bubbles escape from antinode. By contrast, at the pressure node, the bubble migration is primarily controlled by acoustic streaming, which effectively weakens the bubble adhesion on the container walls, thereby enhancing the cavitation effect in the whole liquid.
 Select Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields Li Zhao, Zhi-Jing Chen, Hai-Bo Sang, Bai-Song Xie Chin. Phys. Lett.    2019, 36 (7): .   DOI: 10.1088/0256-307X/36/7/074101 Abstract   HTML   PDF (786KB) Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray, in which a high radiation power per solid angle as $\sim$$10^{11}$ a.u. can be obtained.
 Select A 1kHz Fe:ZnSe Laser Gain-Switched by a ZnGeP$_{2}$ Optical Parametric Oscillator at 77K Ying-Yi Li, Ke Yang, Gao-You Liu, Li-Wei Xu, Bao-Quan Yao, You-Lun Ju, Tong-Yu Dai, Xiao-Ming Duan Chin. Phys. Lett.    2019, 36 (7): .   DOI: 10.1088/0256-307X/36/7/074201 Abstract   HTML   PDF (671KB) We demonstrate a Fe:ZnSe laser gain-switched by a 2.9 μm ZnGeP$_{2}$ optical parametric oscillator under pulse repetition frequency of 1 kHz at liquid nitrogen temperature of 77 K. The maximum output power is 63 mW with pulse duration of 34.4 ns. The wavelength covers 3686.6–4088.6 nm and centers at 3897.7 nm. The output power decreases with increasing the temperature of the crystal in 77–222 K.
 Select Generation of Gaussian-Shape Single Photons for High Efficiency Quantum Storage Jian-Feng Li, Yun-Fei Wang, Ke-Yu Su, Kai-Yu Liao, Shan-Chao Zhang, Hui Yan, Shi-Liang Zhu Chin. Phys. Lett.    2019, 36 (7): .   DOI: 10.1088/0256-307X/36/7/074202 Abstract   HTML   PDF (892KB) We report the generation of heralded single photons with Gaussian-shape temporal waveforms through the spatial light modulation technique in an atomic ensemble. Both the full width at half maximum and the peak position of the Gaussian waveform can be controlled while the single photon nature holds well. We also analyze the bandwidth of the generated single photons in frequency domain and show how the sidebands of the frequency spectrum are modified by the shape of the temporal waveform. The generated single photons are especially suited for the realization of high efficiency quantum storage based on electromagnetically induced transparency.
 Select Nanosecond Pulses Generation with Samarium Oxide Film Saturable Absorber N. F. Zulkipli, M. Batumalay, F. S. M. Samsamnun, M. B. H. Mahyuddin, E. Hanafi, T. F. T. M. N. Izam, M. I. M. A. Khudus, S. W. Harun Chin. Phys. Lett.    2019, 36 (7): .   DOI: 10.1088/0256-307X/36/7/074203 Abstract   HTML   PDF (2112KB) Nanosecond pulse generation is demonstrated in a mode-locked erbium-doped fiber laser (EDFL) utilizing a samarium oxide (Sm$_{2}$O$_{3}$) film. The Sm$_{2}$O$_{3}$ film exhibits a modulation depth of 33%, which is suitable for mode-locking operation. The passively pulsed EDFL operates stably at 1569.8 nm within a pumping power from 109 to 146 mW. The train of generated output pulses has a pulse width of 356 nm repeated at a fundamental frequency of 0.97 MHz. The average output power of 3.91 mW is obtained at a pump power of 146 mW, corresponding to 4.0 nJ pulse energy. The experimental result indicates that the proposed Sm$_{2}$O$_{3}$ saturable absorber is viable for the construction of a flexible and reliably stable mode-locked pulsed fiber laser operating in the 1.5 μm region.
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