bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Si and Y co-doping on stability and oxidation resistance of γ-TiAl based alloys
Authors: Song Qing-Gong , Wang Li-Jie , Zhu Yan-Xia , Kang Jian-Hai , Gu Wei-Feng , Wang Ming-Chao , Liu Zhi-Feng ,   Institute of Low Dimensional Materials and Technology, College of Science, CivilAviation University of China, Tianjin 300300, China,   Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin 300300, China
Published: December 2020

Improving the oxidation resistance of TiAl-based alloys at high temperature has great significance for expanding their application fields. Adding ternary and quaternary elements is one of the effective ways to solve the oxidation problem of this kind of alloys materials. The first-principles method based on density functional theory was used to study the Si and Y substitution co-doping effects on the oxidation resistance of γ-TiAl based alloys from the aspects of atomic average formation energy and elastic constant of system, as well as the formation energies of interstitial O atom, Ti vacancy and Al vacancy in the system. The results indicate that the atomic average formation energies of the Si and Y dual-doped systems are all negative, which imply they possess energy stability and can be prepared by experiments. In addition, the elastic constants of most Si and Y substitution co-doping γ-TiAl systems satisfy the mechanical stability criterion. For the mechanical stable systems, the analysis results about the formation energies of the interstitial O atom, Ti vacancy and Al vacancy reveal that the Ti6SiYAl8 series, in which both Si and Y substitute Ti, have obvious promotion effect on the improvement about oxidation resistance; system Ti7YAl7Si, in which Y substitutes Ti and Si substitutes Al, and system Ti7SiAl7Y, in which Si substitutes Ti and Y substitutes Al, have uncertain influence on improving oxidation resistance; system Ti8Al6SiY, in which both Si and Y substitute Al, is harmful to the improvement about oxidation resistance of the γ-TiAl based alloys. Therefore, the preparation conditions should be controlled moderately so that both Si and Y substitute Ti at the same time to form a large proportion configurations of Ti6SiYAl8 series in the materials. In these configurations, the outward diffusion of Ti atoms and the inward diffusion of interstitial O atoms are suppressed, meanwhile the outward diffusion of the Al atoms is facilitated. In this way, the production of α-Al2O3 is promoted and that of TiO2 is weakened on the surface of co-doping γ-TiAl based alloys. Thus, a scale rich in α-Al2O3, i. e., a continuous, dense, and protective oxide scale can be grown on the surface of Si and Y substitution co-doping γ-TiAl alloys.
First-principles prediction of carbon monoxide nanotube bundles in low pressure phase
Authors: Zhou Hong-Cai , Huang Shu-Lai , Li Gui-Xia , Yu Gui-Feng , Wang Juan , Bu Hong-Xia ,   Science and Information College, Qingdao Agricultural University, Qingdao 266109, China,   College of Physics and Electronic Engineering, Qilu Normal University, Jinan 250200, China
Published: December 2020

The crystal structure of carbon monoxide has been studied for more than half a century. The internal structures of low-pressure carbon monoxide crystals have been investigated by means of infrared analysis and Raman analysis, and the internal structure of carbon monoxide has also been studied through computational analysis. Previous studies showed that carbon monoxide can produce different phase transitions at different pressures, and thus forming new polymers with new physical properties such as electrical, optical and mechanical properties. In this paper, from first-principles calculations, we propose six nanotube structures made of carbon monoxide, named Tube-3–Tube-8. The nanotubes are packed into the nanotube bundles, and carbon monoxide nanotube bundle structures that are similar to carbon nanotube bundles are constructed by first-principles calculation. We study the structural, energy and electronic properties of the nanotubes and nanotube bundles. In order to evaluate the relative stability of the predicted nanotubes, we calculate the cohesive energy and phonon spectrum, and we also carry out the molecular dynamics analysis. The results show that there are three nanotubes (Tube-4–Tube-6) that are relatively stable, of which Tube-5 nanotube is the most stable phase. We attribute the stability of Tube-5 to sp3-hybridized C atoms being nearest to the hybridized atoms of diamond. Then we investigate nanotube bundles from the three stable nanotubes, and accordingly name them Bundles-4–Bundles-6. We calculate the enthalpy function under pressure and compare it with the enthalpy function of several known carbon monoxide molecular crystal and chain crystal, which are the most stable structures according to the current studies. More pleasingly, we find that these nanotube bundles are more stable than these carbon monoxide molecular crystal and chain crystal at low pressure. In addition, by calculating the energy bands of Tube-4–Tube-6, we can deduce that these nanotube bundles (Bundles-4– Bundles-6) are all wide band gap semiconductors, which are entirely different from molecular and chain crystals that are metals. We expect that the discovery of nanotube bundle structures will increase the diversity of carbon monoxide crystal under low pressure, and provide a new understanding of exploring the internal structure of carbon monoxide crystal.
Theoretical study on the hydrogen storage properties of (MgO)4 under external electric field
Authors: Yin Yue-Hong , Xu Hong-Ping ,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronics Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

MgO is a typical ionic compound with strong polarity. Hydrogen absorbed by MgO materials subjected to an external electric field is a potential method to store hydrogen. However, the method requires an extremely high intensity of electric field, which is difficult to achieve. Therefore, reducing field intensity has become a key problem in the field of hydrogen storage. In this paper, the hydrogen storage properties of an (MgO)4 cluster under an external electric field are investigated. The results show that under the external electric field, (MgO)4 keeps the frame of cube structure but with little distortion, which implies that (MgO)4 cluster can sustain the strong electric field. The (MgO)4 is also polarized by the external electric field and its dipole momentum increases to 1.67 and 3.33 Debye when the field intensity is 0.005 and 0.010 a.u., respectively. H2 can be adsorbed on a single Mg/O atom: H2 is adsorbed at lateral position of Mg atom, while at the top of O atom. The adsorption strength is substantially enhanced under an external electric field. Under only 0.010 a. u. of electric field, the adsorption energy of H2 on the Mg or O atoms increases from –0.118 eV to –0.225 eV or from –0.060 eV to –0.150 eV, respectively. The electric field required is significantly lower than that of a large (MgO)9 cluster. This result suggests that reducing the size of material is a possible method toreduce the electric field for hydrogen storage in polarizable materials. The weak interaction between H2 and (MgO)4 is analyzed by the quantum theory of atoms in molecules. The results indicate that under an electric field, (MgO)4 and H2 are effectively polarized, and the electrostatic interaction between them is subsequently enhanced. Meanwhile, the small cluster is easily polarized because most of the atoms are in the surface and have low coordination. Therefore, the electric field required can be substantially reduced. Moreover, (MgO)4 adsorbs 16 H2 molecules at most. The corresponding mass density of hydrogen storage reaches 16.7 wt%, indicating that (MgO)4 can be used as a hydrogen storage material under an electric field.
First principles study of structural, electric, and magnetic properties of fluoride perovskite NaFeF3
Authors: Song Rui , Feng Kai , Lin Shang-Jin , He Man-Li , Tong Liang ,   Department of General Education, Army Engineering University of People’ Liberation Army, Nanjing 211101, China
Published: December 2020

On the basis of first-principles calculations, the systematic researches of the structural, electronic and magnetic properties of NaFeF3 are carried out in the present work. The influences of anion substitution and strain effect are taken into consideration in the reaearch.

First, the basic properties of the NaFeF3 bulk are determined. The fully relaxed structure exhibits a distinct GdFeO3-type distortion and a relatively weak Jahn-Teller distortion. The band gap is estimated at 3 eV from our DFT calculations with Hubbard U correction. Moreover, the magnetic structure is of G-type antiferromagnetism (G-AFM). This intrinsic G-AFM magnetic state is robust, and cannot be easily destroyed by small perturbations, includinganion doping and epitaxial strain.

Secondly, we study the oxygen doping effect on the properties of material with considering the fact that the radius of oxygen anion is very close to that of fluoride anion, and the oxygen substitution can be accommodated by the further oxidation of iron cation from divalent to trivalent state. According to our energy comparison calculations, when one of the twelve F sites in the NaFeF3 unit cell is taken up by an oxygen anion, whose corresponding doping concentration is approximately 8.3%, the O ion is more likely to occupy the in-plane site of the FeF6 octahedron. This low concentration doping may induce unequal Fe—O bonds, which lead to diverse valence states of surrounding Fe cations, and therefore result in local polarization and non-zero net magnetic moment. The local dipole and magnetic moment are inherently correlated with each other due to the common origin, i.e., the incoordinate Fe—O bonds. Therefore, the net magnetic moment together with the local polarization may be reversed simultaneously by an external electric field. However, when the doping concentration is further increased to 33%, the overall iron valence will rise to a higher state where the local charge order and the net moment disappear.

In addition, the electronic properties of NaFeF3 also show obvious change due to the influence of biaxial strain. Specifically, the energy gap decreases monotonically as the in-plane stress gradually changes from compression to extension. However, the band structure does not change significantly. The top of the valence band and the bottom of the conduction band are both located at the Gamma point, thus making it a direct bandgap semiconductor material with an adjustable energy gap.

These findings may promote further theoretical and experimental research on fluoride family and introduce a new candidate to the multiferroic field.
Influence of Raman laser sidebands effect on the measurement accuracy of cold atom gravimeter
Authors: Wu Bin , Cheng Bing , Fu Zhi-Jie , Zhu Dong , Wu Li-Ming , Wang Kai-Nan , Wang He-Lin , Wang Zhao-Ying , Wang Xiao-Long , Lin Qiang ,   Institute of Optics, College of Science, Zhejiang University of Technology, Hangzhou 310023, China,   Institute of Optics, Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The technology of electro-optic modulation is one of the several methods of generating the Raman beams. The experimental system based on this method is simple and much easier to implement, and the environmental adaptability is strong as well. However, this kind of modulation technology will produce additional laser lines, which may affect the measurement accuracy of cold atom gravimeter. Based on a homemade transportable cold atom gravimeter, the influence of Raman sideband effect on the accuracy of cold atom gravimeter is investigated in this paper. We analyze in detail the relationship between Raman sideband effect and some experimental parameters, such as the height of Raman retro-reflection mirror, the time of free fall of the atoms, the detuning of Raman laser, etc. It is found that those parameters have a dominant influence on the measured gravity resulting from Raman sideband effect. Besides, it is also found that the gravity measurements will be sensitive again to some experimental parameters in the case of Raman sideband effect while these parameters are usually insensitive in case of laser system without sideband effect. Finally, we investigate the relationship between Raman sideband effect and Raman detuning, and presente a method of evaluating the gravity induced by Raman sideband effect. The experimental results in this paper can provide a reference for reducing the influence of Raman sideband effect on the accuracy evaluation of cold atomic gravimeter.
Phase-composition design of high-hardness and high-electric-conductivity Cu-Ni-Si Alloy
Authors: Li Dong-Mei , Han Jing-Yu , Dong Chuang ,   Key Laboratory of Materials Modification by Laser, Iron, and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China,   Inner Mongolia University For Nationalities, Tongliao 028000, China
Published: December 2020

Cu-Ni-Si alloy has good electrical conductivity, thermal conductivity, high strength, and high hardness, and is widely used in electronic components and other fields. When the compositions of the Cu-Ni-Si alloy are designed, the determination of the phase component is critical. In this work, the composition of Cu-Ni-Si alloy is designed according to the "precipitation phase" by cluster-plus-glum-atom model. Following the cluster selection criteria, the δ-Ni2Si, γ-Ni5Si2 and β-Ni3Si phase clusters are determined, respectively, and the corresponding cluster formulas are [Ni-Ni8Si5]Ni,[Si-Ni10]Si3, and [Si-Ni12]Si3. the compositions of a series of Cu-Ni-Si alloys are designed according to the different precipitated phases of δ-Ni2Si, γ-Ni5Si2, and β-Ni3Si each with Cu atom content being 93.75%, 95%, 95.8%, 96.7% and 97.5%, respectively. The alloy raw material is melted into alloy ingot in an argon-filled vacuum arc furnace. The ingots undergoes solid-solution at 950 ° C for 1 hour and water quenching then aging treatment at 450 ° C for 4 hour and water quenching. The conductivity and Vickers hardness of the alloy are tested by conductivity meter and hardness meter, respectively. The microstructure of the alloy is characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In general, the electrical conductivity of Cu-Ni-Si is the main consideration in the design of alloy composition, the content values of matrix Cu atoms are in the ranges of 90%-95.63% and 95.63%-97.5% respectively, the precipitated phases are designed according to δ-Ni2Si and γ-Ni5Si2 respectively; the content of matrix Cu atoms is over 97.5%, it can be designed according to any phase of δ-Ni2Si, γ-Ni5Si2 and β-Ni3Si, with no difference in electrical conductivity among them. If the strength of the alloy is the main factor in the composition design, the content values of Cu atoms in the matrix are in the ranges of 90% — 93.93%, 93.93% — 94.34%, 94.34%— 95.63%, and 95.63%—96.12% respectively, according to the composition intervals the precipitated phases are designed as δ-Ni2Si, γ-Ni5Si2, β-Ni3Si, and γ-Ni5Si2, respectively. Once the content of Cu in the matrix is greater than 96.12%, the precipitated phase can be designed according to any of the phases of δ-Ni2Si, γ-Ni5Si2 and β-Ni3Si.
Advances in surface-enhanced optical forces and optical manipulations
Authors: Wang Han-Cong , Li Zhi-Peng ,   Fujian Key Laboratory of Automotive Electronics and Electric Drive, School of Information Science and Engineering, Fujian University of Technology, Fuzhou 350108, China,   The Beijing Key Laboratory for Nano-Photonics and Nano-Structure (NPNS), Department of Physics, Capital Normal University, Beijing 100048, China
Published: December 2020

The localized surface plasmons in metal nanostructures under optical excitation will lead to near-field localization and enhancement, which have shown important applications in surface enhancement spectroscopy, ultra-sensitive sensing, microfluidic chip, enhanced optical force, etc. The plasmon resonance and the resulting electric field enhancement strongly depend on wavelength and structure geometry. As a result, the optical force will be closely related to the field distribution, that is, the optical force can be used to manipulate and sort plasmonic metal structures. The large near-field enhancement and gradient of metal nanoparticle aggregates can also be used as a " plasmonic tweezer” to manipulate other particles. Furthermore, in the case of changing the incident polarization and even for a new type of structured laser beam, the optical manipulation has a higher degree of freedom. In this review, having briefly introduced the plasmon-enhanced optical force, we focus on the recent advances in the following three aspects: 1) the manipulation of plasmonic nanoparticles by optical tweezer, 2) the manipulation of other particles by plasmonic tweezer, and 3) dependence of plasmonic optical force on the polarization, optical angular momentum, structured light and the structured chirality. Comparing with other topics of plasmon- enhanced light-interactions, there is plenty of room for further developing the plasmon-enhanced optical force and optical manipulation. Several research trends can be foreseen. 1) More precise optical manipulating and sorting of nanoparticles (even sub-nanometer). For example, more sensitive special resonant modes (e.g. Fano resonance) of plasmonic nanostructure can be utilized. For some nanostructures with small feature sizes, especially when the gap size is close to 1 nm, the non-local effect has a certain effect on the plasmon resonance. Therefore, when calculating the optical force in this case, non-local effects and possibly other quantum effects should be considered. 2) Richer laser fields, that is, using various new structured fields and chiral structures provides a higher degree of freedom for the optical forces and optical manipulation. Also, the localized surface plasmons can be combined with propagating surface plasmons. 3) Wider applications of plasmonic optical forces, especially in combination with other effects and even interdiscipline, e.g. enhanced spectroscopy, enhanced single particle chemical reactions, nonlinear optical effects, and photothermal manipulations.
Influence of momentum ratio and its throttling method on spray characteristics of pintle injector
Authors: Chen Hui-Yuan , Li Qing-Lian , Cheng Peng , Lin Wen-Hao , Li Chen-Yang ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The spray characteristics of a liquid-liquid pintle injector under different momentum ratios are investigated experimentally in this paper. Water is used as a simulant medium for both the fuel and the oxidizer. By increasing the mass flow rate of the oxidizer or reducing the mass flow rate of the fuel, the local momentum ratio is increased from 0.16 to 0.99, wherein the responding total momentum obtained by the former throttling method is relatively high due to the higher mass flow rate of the fluid. The outer and inner spray boundary, droplet size distribution and the velocity field are studied by high-speed camera and phase Doppler anemometry (PDA). It is indicated that the spray pattern is affected by the operating conditions directly. The spray pattern is divided into the solid cone and the hollow-solid cone, generally. Furthermore, the spray pattern influences the other spray characteristics. Under the same local momentum ratio with different throttling methods, the spray angle is almost consistent, while the spray boundary in the far field is wider under the higher total momentum. With the increase of the mass flow rate of the outer injector, a hollow structure is generated in the near field of the spray, and its range expands with the increase of the local momentum ratio. The value of SMD increases with the local momentum ratio increasing. Under the same local momentum ratio, the variation range of SMD is wider under the higher total momentum. The variation trend of SMD in the radial direction differs from the spray pattern, too. The SMD of the hollow-solid spray displays as an " N” shape along the radial direction, and reaches its peak at the outer boundary. By contrast, the SMD of the solid spray decreases slightly in the radial direction and varies on a small scale. The value of the resultant velocity is determined by the total momentum, and the curves of all the resultant/axial/radial velocity display as an inverted " V” in the radial direction. Nevertheless, the trend of axial velocity in the radial direction is mainly decreasing, and the increasing stage only exists at the central spray. However, the radial velocity undergoes a slight decrease or levels off directly after reaching the peak. The higher the local momentum ratio, the larger the radial velocity is, while the lower the axial velocity. In addition, the velocity field below the hollow field is dominated by the liquid film, which is explained by analyzing the impinging process of the neighboring cloaks in this paper.
Molecular dynamics study of trapping and detrapping process of hydrogen in tungsten vacancy
Authors: Fu Bao-Qin , Hou Qing , Wang Jun , Qiu Ming-Jie , Cui Jie-Chao ,   Key Laboratory for Radiation Physics and Technology, Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China
Published: December 2020

Tungsten (W) alloys and W-based alloys are the primary candidate materials for plasma-facing components in future fusion reactors (e.g. ITER and CFETR). One of the critical issues still to be clarified in the design of the fusion reactor materials is the retention of hydrogen (H) isotopes in W, when the plasma-facing materials are supposed to sustain high-flux plasma and high-energy neutron. The dynamical behaviours of H in W with radiation defects (e.g. vacancy) are of serious concerns for understanding the mechanism of H capture, retention and permeation in W. In this work, a new model to extract the effective capture radius (ECR) and dissociation coefficient simultaneously is presented through coupling the trapping process and detrapping process of H in W vacancy. In the new model, the quantity ratio of vacancy to H atom in vacancy-H complex (VHx+1) in the molecular dynamics (MD) simulations is described as a function of time, while the exact occurrence time of corresponding event is not required. This new model, combined with extensive MD calculations, enables the simultaneous determining of the ECR and dissociation coefficient of H in W vacancy. It is found that the parameters are dependent not only on the event type but also on temperature. The dissociation energy of H from vacancy-H complex decreases gradually with the increase of the trapped number of H atoms in the vacancy-H complex. It is also found that the common assumption (i.e. the ECR is equal to one lattice constant and the pre-exponential factor is equal to 1013 s–1) in the long-term simulation methods (e.g. kinetic Monte Carlo and rate theory) is not always valid, since these calculated dynamical parameters are dispersive. The new model to obtain more reliable results with lower cost of computing resources can be easily extended into the other similar kinetic processes (e.g. H/He trapping and detrapping processes in other materials systems). These calculated dynamical parameters should be potentially helpful in supplying the initial input parameters for the long-term simulation methods.
Research progress of coherent control of terahertz spin waves and strong coupling in rare-earth orthoferrites
Authors: Jin Zuan-Ming , Ruan Shun-Yi , Li Ju-Geng , Lin Xian , Ren Wei , Cao Shi-Xun , Ma Guo-Hong , Yao Jian-Quan ,   Department of Physics, Shanghai University, Shanghai 200444, China,   College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300110, China
Published: December 2020

Antiferromagnets (AFM) are promising for future spintronic applications due to their advantageous properties. Antiferromagnets produce no stray fields and are insensitive to external magnetic field perturbations. Furthermore, antiferromagnets show intrinsic high terahertz (THz) frequency dynamics. The THz pulses are a direct and general probe of ultrafast spin dynamics in insulating antiferromagnets. In this review article, we discuss the excitation and control of the antiferromagnetic spin resonances in rare-earth orthoferrites (RFeO3, R indicates Y and rare-earth element) with the THz electromagnetic pulsetime-domain spectroscopy. We believe that this approach is general and can be applied to a broad range of materials with different AFM spin alignments, giving a novel non-contact approach to probing AFM order with ps temporal resolution. We summarize different quasi-ferromagnetic modes (qFM) and quasi-antiferromagnetic modes (qAFM), as well as the spin reorientation transition temperatures of RFeO3. Coherent control of spin waves at THz frequency promises fruitful applications in ultrafast magnetization control and has received increasing attention. It is demonstrated that not only the delay time between the excitation and control THz pulses arriving DyFeO3, but also the intrinsic dielectric anisotropy of YFeO3 in the THz range allow the coherent control of both the amplitude and the phase of the excited spin waves. Moreover, we outline the current observation of Dicke cooperativity in magnetic interaction of ErxY1－xFeO3, which presents a route to understanding, controlling, and predicting novel phases of condensed matter by using the concepts and tools available in quantum optics. Finally, magnon-polaritonsare demonstrated to play a key role in preparing the THz waves through TmFeO3.
Optical design of X-ray focusing telescope
Authors: Qiang Peng-Fei , Sheng Li-Zhi , Li Lin-Sen , Yan Yong-Qing , Liu Zhe , Zhou Xiao-Hong ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Xi'an 710119, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

X-ray focusing telescope is one of the most important equipment for X-ray space observation, which is designed based on the grazing incidence principle. The purpose of x-ray observation is to detect the black holes of various sizes in outer space, and the data obtained by X-ray telescope conduces to investigating the basic physical law under the condition of extreme gravity and magnetic field, In this article, multi-layer telescope is designed to satisfy the demand for enhanced X-ray timing and polarimetry mission. in which the telescope is designed based on Wolter-I telescope. The Monte Carlo method and power spectral density are used when the relationship between mirror profile and roughness with angular resolution is investigated. We analyze the relationship between angular resolution and mirror profile, and the result shows that the higher mirror profile possesses higher angular resolution. When the root mean square(RMS) of mirror profile is 0.04 μm, PV is 0.2 μm and roughness is 0.4 nm, the mirror angular resolution is 6.3" and it will change to 30.6" when the RMS of mirror profile is 0.2 μm, PV is 1 μm and roughness is 0.4 nm. The angular resolution out of focus is also investigated in this article, and the more defocusing amount gives rise to the worse angular resolution because defocusing spot will be larger than that of focal plane. So the maximum defocusing amount of 5 mm is required when the focal plane detector is installed. The relationship between effective area with film structure and layers number is also investigated. The film with Au mixed with C has a higher reflectivity than the film with only Au, because the mixed film will generate an interference effect and enhance the intensity of reflecting X-ray. When the telescope layers increase, the effective area and telescope weight are both improved, the requirement for effective area of satellite can be satisfied when the number of nesting layers is 45. However, when the number of nesting layers further increase, the effective area will be improved with a low speed, but the weight of telescope will increase with a high speed. The field of view of this telescope is 16′, which is more than the required value of 12′. Finally, the X-ray focusing telescope with 5.25 m focal length, 45 nesting layers, effective area 842 cm2 at 2 keV, 563 cm2 at 6 keV is obtained.
Design of a multimode interference waveguide semiconductor laser combining gain coupled distributed feedback grating
Authors: Qiu Cheng , Chen Yong-Yi , Gao Feng , Qin Li , Wang Li-Jun ,   State Key Laboratory of Luminescence and Application, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130010, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Semiconductor laser is one of the most critical components in the field of modern communication. Research and development of single-mode semiconductor laser with high stability, high power, high beam quality and narrow line width is an important research area in this field. In this paper, A novel edge-emitting semiconductor laser diode structure is proposed. In the structure an active multimode interference waveguide structure serves as a main gain region. To modulate the longitudinal mode of the laser, a gain-coupled distributed feedback(DFB) laser based on high order surface gain coupled grating is introduced into the structure as well. The novel structure is then fabricated and compared with an conventional DFB laser. The experimental results show that higher slope efficiency and output power are achieved with the proposed structure than those with the conventional distributed feedback semiconductor lasers. The novel structure is also compared with conventional MMI laser with only Fabry-Parot(FP) cavity. The result shows that the proposed structure has higher beam quality and better stability than the FP cavity multimode interference waveguide lasers. To enhance the gain contrast in the quantum wells without introducing the effective index-coupled effect, the groove length and depth are well designed. Our device provides a single longitudinal mode with the maximum CW output power up to 53.8 mW/facet at 981.21 nm and 400 mA without facet coating, 3 dB linewidth < 13.6 pm, and SMSR > 32 dB. Optical bistable characteristic is observed with a threshold current difference. Meanwhile, by using high-order distribution feedback grating formed by shallow surface etching in the process of chip design and fabrication, the proposed structure of laser diode can realize regrowth freely and only micron-scale precision i-line lithography is required. Such a structure with simple fabrication process and low manufacturing cost has great potential for commercial mass production.
Mechanism of contrast-enhancement in ultrasound-modulated laser feedback imaging with ultrasonicmicrobubble contrast agent
Authors: Zhou Bo-Rui , Tan Yi-Dong , Shen Xue-Ju , Zhu Kai-Yi , Bao Li-Ping ,   Department of Electronic and Optical Engineering, Army Engineering University of PLA, Shijiazhuang 050051, China,   State Key Laboratory of Precision Measurement Technology and Instrument, Tsinghua University, Beijing 100084, China,   Department of Ultrasound, Peking University Cancer Hospital, Beijing 100042, China
Published: December 2020

Ultrasound-modulated optical imaging technology is a new type of biological tissue optical detection technology, and sensitive to the change of scattering coefficient and absorption coefficient of biological tissue. This technology is a non-ionizing and non-invasive pathological detection method, which has great potential application in early detection of cancer. However, ultrasound-modulated optical imaging technology is insufficient in signal-to-noise ratio (SNR) and imaging contrast. Frequency-shifted laser feedback technology with microchip laser is a new type of highly sensitive interference technology, whose gain coefficient for weak optical signal can reach 106. This technology can greatly improve the SNR of imaging. Combined with the high sensitive laser feedback technology, the ultrasound-modulated laser feedback technology is proposed. The SNR of this technology is better than that of the traditional ultrasound-modulated optical imaging technology. The increase in SNR can achieve greater depth of detection in biological tissue imaging, but there is no significant improvement in imaging contrast. In order to improve the contrast of biological tissue imaging and achieve high resolution imaging of thick biological tissue, we use ultrasound microbubble contrast agent in ultrasound-modulated laser feedback imaging technology. We establish a Monte Carlo photon transport model with microbubbles in order to study the mechanism of contrast enhancement in ultrasound-modulated laser feedback imaging with microbubbles. Finally, we establish an experimental system to verify the correctness of the simulation results. Experimental and simulation results show that in the transparent solution, the ultrasonic microbubble contrast agent can enhance the ultrasound-modulated laser feedback signal and generate harmonic modulation, which can improve the imaging contrast by detecting the enhancement of the fundamental and harmonic signals of the feedback. In the scattering medium, the ultrasonic microbubble contrast agent can significantly attenuate the ultrasound modulated laser feedback signal, and the imaging contrast can be improved by detecting the attenuation of the fundamental and harmonic signal.
Molecular structure and electronic spectrum of MoS2under external electric field
Authors: Du Jian-Bin , Feng Zhi-Fang , Zhang Qian , Han Li-Jun , Tang Yan-Lin , Li Qi-Feng ,   School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China,   College of Science, Langfang Normal University, Langfang 065000, China,   College of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

A variety of new materials have improved the production and life of human beings. Two-dimensional nano materials have become a research hotspot due to their unique physical and chemical properties. Molybdenum disulfide (MoS2) is representative of transition metal sulfide, with excellent mechanical properties and chemical stability. In order to study the influence of external electrical field on the molecular structure and spectrum, here in this work, the density functional theory with the hybrid B3LYP at Def2-TZVP level is employed to calculate the geometrical parameters of the ground state of MoS2 molecule under external electric fields ranging from 0 to 0.1 a.u. (0−5.1423 × 1010 V/m). Based on the optimized structures, the time-dependent density functional theory at the same level as the above is adopted to calculate the absorption wavelengths and the molar absorption coefficients for the first ten excited states of MoS2 molecule under external electric fields. The results show that the most strongest absorption band is located at 483 nm with a molar absorption coefficient of 461 L·mol–1·cm–1 in the UV-Vis absorption spectrum. The intramolecular charge transfers as a whole with the enhancement of the external electric field. The electric dipole moment increases with the external electric field rising, while the total molecular energy decreases with external electric field increasing. With the enhancement of the external electric field, the absorption peaks show a significant redshift. When the electric field increases to 0.1 a.u., the redshift is obvious. This can be explained as follows. When the external electric field is weaker, the electron transfer in the molecule is not significant. However, with the augment of the external electric field, the electron transfer in the molecule occurs as a whole. This makes the electron interaction between Mo and S weaker, thus the electron transition is more likely to occur. The energy required for excitation is reduced, and the wavelength of the excited state becomes longer, that is, the absorption peak takes a redshift. With the enhancement of the external electric field, the molar absorption coefficient increases obviously. This is because the overall transfer of the external electric field to the electron makes the electron cloud density of the MoS2 molecule increase and the number of electrons in transition augment. This work provides a theoretical basis for the utilization and improvement of MoS2 photoelectric properties, and also enlightens the application research of other photoelectric materials.
Design and analysis of new meminductor model based on Knowm memristor
Authors: Zhu Lei-Jie , Wang Fa-Qiang ,   State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

In the past, the memristor model and its application research have mainly focused on constructing and analyzing the memristor model and its equivalent circuit model based on the basic concept of memristor, while the research based on commercial memristive devices in the market has been rare. According to the theoretical relationship between meminductor and memristor, a new model of meminductor is constructed based on Knowm memristor, the first commercial memristor chip in the world, combined with the second-generation current conveyor and transconductance operational amplifier. By adjusting the frequency and the amplitude of the input voltage and the transconductance gain of the transconductance operational amplifier, the continuous adjustment of the meminductance can be effectively achieved in the circuit. The LTspice circuit model and hardware experimental circuit of the proposed meminductor are designed. The validity of the new meminductor model and the correctness of the design method are verified by LTspice simulations and circuit experiments.
Analysis of main parameters of spectral interferometry ranging using optical frequency comb and animproved data processing method
Authors: Chen Jia-Wei , Wang Jin-Dong , Qu Xing-Hua , Zhang Fu-Min ,   State Key Laboratory of Precision Measurement Technology and Instruments, Tianjin University, Tianjin 300072, China
Published: December 2020

With the rapid development of modern technology, high-precision absolute distance measurement is playing an important role in many applications, such as scientific research, aviation and industry measurement. Among the above various measurement methods, how to realize higher-accuracy, larger-scale, and faster-speed measurement is particularly important. In the traditional technique for long-distance measurement, the emergence of optical frequency comb (OFC) provides a breakthrough technology for accurately measuring the absolute value of distance. The OFC can be considered as a multi-wavelength source,whose phase and repetition rate are locked. The OFC is a very useful light source that can provide phase-coherent link between microwave and optical domain, which has been used as a source in various distance measurement schemes that can reach an extraordinary measurement precision and accuracy. A variety of laser ranging methods such as dual-comb interferometry and dispersive interferometer based on femtosecond laser have been applied to the measuring of absolute distance.

In this paper, the factors affecting the resolution and the non-ambiguous range of spectral interferometry ranging using OFC are particularly discussed. We also analyze the systematic errors and the limitations of traditional transform methods based on Fourier transform, which can conduce to the subsequent research.

To address the problem caused by low resolution and unequal frequency interval, we propose a data processing method referred to as equal frequency interval resampling. The proposed method is based on cubic spline interpolation and can solve the error caused by the frequency spectrum broadening with the increase of distance. Moreover, we propose a new method based on least square fitting to calibrate the error introduced by the low resolution of interferometry spectrum obtained with fast Fourier transform (FFT). With the proposed method, the simulation results show that the systematic error is less than 0.2 μm in the non-ambiguity range and the system resolution is greatly improved. Finally, anabsolute distance measurement system based on Michelson interferometer is built to verify theproposed method. The measurement results compared with those obtained by using a high-precision commercial He-Ne laser interferometer show that the distance measurement accuracy is lower than 3 μm at any distancewithin the non-ambiguity range. The experimental results demonstrate that our data processing algorithm is able to increase the accuracy of dispersive interferometry ranging with OFC.
Light rays in Fourier domain
Authors: Zhang Shu-He , Shao Meng , Zhang Sheng-Zhao , Zhou Jin-Hua ,   Department of Biomedical Engineering, Anhui Medical University, Hefei 230032, China
Published: December 2020

Establishing a universal model to characterize the relationship between light rays and optical waves is of great significance in optics. The ray model provides us with an intuitive way to study the propagation of beams as well as their interaction between objects. Traditional ray model is based on the normal of a beam wave front. The normal vector is defined as the direction of ray. However, it fails to describe the relationship between light ray and optical wave in the neighborhood of focus or caustic lines/surface since light ray in those regions are no longer perpendicular to the wavefront. In this work, the ray model of a light beam is built according to its Fourier angular spectrum, where the positions of rays can be determined by the gradient of the phase of the Fourier angular spectrum. On the other hand, the Fourier angular spectrum of a light beam can be reconstructed through the ray model. Using Fourier angular spectra, we construct the ray model of two typical beams including the Airy beam and the Cusp beam. It is hard to construct ray model directly from the optical field of these beams. In this ray model, the information about ray including direction and position involves the propagation properties of light beams such as self-accelerating. In addition, we demonstrate that the optical field of the focused plane wave can be reconstructed by the ray model in Fourier regime, and the optical field in spatial domain can be obtained by inverse Fourier transform. Simulation results are consistent with the results from Debye’s method. Finally, the high-dimensional ray model of light beams is elaborated in both spatial and spectral regime. Combined with focused plane wave, Airy beam and rays in quadratic gradient-index waveguide, our results show that the ray model actually carries the information about optical field in both spatial and Fourier domain. Actually, the traditional ray model is just a spatial projection of the high-dimensional ray model. Hence, when traditional ray model fails at the focus or caustic lines/surface, it is able to obtain the spectrum of the corresponding optical field from the Fourier domain, and then obtain the field distribution in spatial domain by inverse Fourier transform.
Energy conversion of multi-optical parametric oscillation based on time-dependent split-step integration methods in MgO:APLN
Authors: Liu Hang , Yu Yong-Ji , Wang Yu-Heng , Liu He-Yan , Li Lu-Jie , Jin Guang-Yong ,   Jilin Key Laboratory of Solid Laser Technology and Application, School of Science, Changchun University of Science and Technology, Changchun 130022, China,   Changchun China Optical Science and Technology Museum, Changchun 130117, China
Published: December 2020

In a multi-optical parametric oscillator by pulse pumping, energy conversion process for 1.57 μm and 3.84 μm parametric light can be expressed by time-dependent wave equations. The split-step integration method is used to solve the equations. By analyzing the simulation results of the output waveform for the multi-optical parametric amplifier, it is confirmed that back conversion and mode competition are the important factors affecting the multi-optical parametric oscillation. The 1.57 μm and 3.84 μm parametric light in an external cavity multi-optical parametric oscillator are simulated under different output mirror transmittances, crystal working lengths and cavity lengths. The conversion efficiency of 1.57 μm and 3.84 μm increase with the output mirror transmittance increasing, which means that the conversion efficiency can be adjusted by changing the parametric light transmittance of the output mirror. There exist an optimal crystal working length and a cavity length in the external cavity multi-optical parametric oscillator. The experiment on external cavity multi-optical parametric oscillator is carried out. The conversion efficiency of 1.57 μm and 3.84 μm parametric light are consistent with the theoretical values. The energy conversion process in the multi-optical parametric oscillator can be simulated by this method, which could be used for optimizing the multi-optical parametric oscillator and increasing the parametric conversion efficiency.
Isolated attosecond pulse generation from a double optical gating scheme based on orthogonal polarization field
Authors: Lü Xiao-Yuan , Zhu Ruo-Bi , Song Hao , Su Ning , Chen Gao ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Isolated attosecond pulses make it possible to study and control the ultrafast electron processes in atoms and molecules. High order harmonic generation (HHG) is the most promising way to generate such pulses, benefiting from the broad plateau structure of the typical HHG spectrum. In previous HHG studies on the polarization gating scheme, atomic ionization caused by the laser cycles before the polarization gate not only places a limit on the pulse width and intensity of the driving laser, but also affects the phase matching of harmonics generated in a polarization gate. According to these, in this paper we propose a new double optical gating scheme, in which the polarization of the laser pulse changes from linear to elliptical and back to linear again. Thus, only the linearly polarized field in the leading of the pulse contributes to high harmonic generation. By using a strong field approximation theory, we first simulate high order harmonic and attosecond pulse generation from helium atom irradiated by a double optical gating pulse based on the orthogonal polarization field. Here the orthogonal polarization field consists of two linearly polarized pulses with a certain time delay, orthogonal polarization directions and equal amplitudes. And for the double optical gating pulse, the second harmonic of the driving field is added to an orthogonal polarization field with an appropriate phase and energy. It is found that the high harmonic spectrum with higher efficiency and supercontinuum plateau is obtained by reasonably adjusting the parameters of the combined pulse. After inverse Fourier transform, an isolated 143-as pulse with higher intensity can be realized by superposing supercontinuum harmonics from the 50th to the 150th order. Compared with the double optical gating scheme proposed by Chang et al. (Zhao K, Zhang Q, Chini M, Wu Y, Wang X, Chang Z 2012 Opt. Lett. 37 3891), our scheme not only overcomes the limit on the pulse duration and intensity of the incident pulse laser, but also avoids the harmonic phase mismatching in the process of the propagation due to unwanted ionization of the gas target caused by the laser cycles before the polarization gate.