Chen Bai-Hui, Shi Bao-Chang, Wang Lei, Chai Zhen-Hua
In this study, we utilize the lattice Boltzmann method to investigate the flow behavior in a two-dimensional trapezoidal cavity, which is under two-sided driving on the upper and lower walls. Our calculations have been accelerated through GPU-CUDA software. We have conducted an analysis of the flow field mode using proper orthogonal decomposition. The effects of various parameters such as Reynolds number (Re) and driving direction on the flow characteristics are examined through numerical simulations. The results show that:(1) for the upper wall drive (T1a), the flow field remains stable within the range of Re from 1000 to 8000. However, when Re=8500, the flow field becomes periodic yet unstable. The velocity phase diagram at the monitoring point is a smooth circle, and the energy of the first two modes has dominated the energy of the whole field. Once Re exceeds 10000, the velocity phase diagram turns irregular and the flow field becomes aperiodic and unsteady. (2) As for the lower wall drive (T1b), the flow is stable within Re 1000-8000, yet when Re=11500, the flow field becomes periodic yet unsteady. The energy of the first three modes appears relatively large. When Re is greater than 12500, the flow field becomes aperiodic and unsteady. At this time, the phase diagram exhibits a smooth circle, with the energy of the first two modes almost entirely dominating the entire energy. (3) For the case of upper and lower walls moving in the same direction with the same speed (T2a), the flow field remains stable when Re changes from 1000 to 10000. When Re is between 12500 to 15000, the flow becomes periodic yet unstable. The velocity phase diagram continues to be a smooth circle, with the first two modes still occupying a large portion of the energy. Once Re surpasses 20000, the energy proportion of the first three modes significantly decreases, and the flow becomes aperiodic and unsteady. (4) For the case in which the upper and lower walls are driven in opposite directions with the same velocity (T2b), the flow field remains stable within Re changes from 1000 to 5000. When Re=6000, the energy of the first mode accounts for 86%, and the flow field becomes periodic yet unstable. When Re surpasses 8000, the energy proportion of the first three modes decreases significantly, and the flow field becomes aperiodic and unsteady.
{"title":"Lattice Boltzmann simulation and analysis of two-dimensional trapezoidal cavity flow based on GPU","authors":"Chen Bai-Hui, Shi Bao-Chang, Wang Lei, Chai Zhen-Hua","doi":"10.7498/aps.72.20230430","DOIUrl":"https://doi.org/10.7498/aps.72.20230430","url":null,"abstract":"In this study, we utilize the lattice Boltzmann method to investigate the flow behavior in a two-dimensional trapezoidal cavity, which is under two-sided driving on the upper and lower walls. Our calculations have been accelerated through GPU-CUDA software. We have conducted an analysis of the flow field mode using proper orthogonal decomposition. The effects of various parameters such as Reynolds number (Re) and driving direction on the flow characteristics are examined through numerical simulations. The results show that:(1) for the upper wall drive (T1a), the flow field remains stable within the range of Re from 1000 to 8000. However, when Re=8500, the flow field becomes periodic yet unstable. The velocity phase diagram at the monitoring point is a smooth circle, and the energy of the first two modes has dominated the energy of the whole field. Once Re exceeds 10000, the velocity phase diagram turns irregular and the flow field becomes aperiodic and unsteady. (2) As for the lower wall drive (T1b), the flow is stable within Re 1000-8000, yet when Re=11500, the flow field becomes periodic yet unsteady. The energy of the first three modes appears relatively large. When Re is greater than 12500, the flow field becomes aperiodic and unsteady. At this time, the phase diagram exhibits a smooth circle, with the energy of the first two modes almost entirely dominating the entire energy. (3) For the case of upper and lower walls moving in the same direction with the same speed (T2a), the flow field remains stable when Re changes from 1000 to 10000. When Re is between 12500 to 15000, the flow becomes periodic yet unstable. The velocity phase diagram continues to be a smooth circle, with the first two modes still occupying a large portion of the energy. Once Re surpasses 20000, the energy proportion of the first three modes significantly decreases, and the flow becomes aperiodic and unsteady. (4) For the case in which the upper and lower walls are driven in opposite directions with the same velocity (T2b), the flow field remains stable within Re changes from 1000 to 5000. When Re=6000, the energy of the first mode accounts for 86%, and the flow field becomes periodic yet unstable. When Re surpasses 8000, the energy proportion of the first three modes decreases significantly, and the flow field becomes aperiodic and unsteady.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"96 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73683908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xu Meng-min, Li Xiao-qing, Tang rong, Ji xiao-ling
The influence of thermal blooming on orbital angular momentum (OAM) and phase singularity of dual-mode vortex beams under different wind direction and wind speed has been studied in this paper. Due to the different symmetries of dual-mode vortex beams superimposed by different modes, the impact of thermal blooming on them not only depends on wind speed, but also on wind direction. Based on the scalar wave equation and the hydrodynamic equation, a 4D computer code to simulate the time-dependent propagation of dual-mode vortex beams in the atmosphere is devised by using the multiphase screen method and finite difference method. It is found that, for certain wind direction, the value of OAM increases with the decreasing wind speed because the thermal blooming becomes more serious, i.e., the thermal blooming effect promotes the OAM of dual-mode vortex beam growth. For an example, when the angle between the wind direction and the beam is 0＜θ＜50°, the OAM of the dual-mode vortex beams with a topological charge difference of 2 increases with decreasing wind speed, and there is an optimal angle (θ≈20°) to maximize OAM. Therefore, for certain wind direction and wind speed, the OAM of dual-mode vortex beam propagating in the atmosphere could be larger than that in free space, and could be larger than the OAM of single-mode vortex beam. The dual-mode vortex beam with higher modes requires smaller wind speed to make its OAM larger than the OAM in free space. In addition, the larger the topological charge difference between the two element beams of a dual-mode vortex beam is, the more stable the OAM of the dual-mode vortex beam is. On the other hand, the evolution of linear edge dislocation singularity under atmospheric thermal blooming are also investigated in this paper. When the wind direction is perpendicular to the dislocation line, the linear edge dislocation singularity disappears. If the wind direction is parallel to the dislocation line, the linear edge dislocation singularity always exists. At other angles, the linear edge dislocation singularity will evolve into optical vortex pairs. The results obtained in this paper are useful to laser propagating in the atmosphere and optical communication.
{"title":"Influence of wind-dominated thermal blooming on orbital angular momentum and phase singularity of dual-mode vortex beams","authors":"Xu Meng-min, Li Xiao-qing, Tang rong, Ji xiao-ling","doi":"10.7498/aps.72.20230684","DOIUrl":"https://doi.org/10.7498/aps.72.20230684","url":null,"abstract":"The influence of thermal blooming on orbital angular momentum (OAM) and phase singularity of dual-mode vortex beams under different wind direction and wind speed has been studied in this paper. Due to the different symmetries of dual-mode vortex beams superimposed by different modes, the impact of thermal blooming on them not only depends on wind speed, but also on wind direction. Based on the scalar wave equation and the hydrodynamic equation, a 4D computer code to simulate the time-dependent propagation of dual-mode vortex beams in the atmosphere is devised by using the multiphase screen method and finite difference method. It is found that, for certain wind direction, the value of OAM increases with the decreasing wind speed because the thermal blooming becomes more serious, i.e., the thermal blooming effect promotes the OAM of dual-mode vortex beam growth. For an example, when the angle between the wind direction and the beam is 0＜θ＜50°, the OAM of the dual-mode vortex beams with a topological charge difference of 2 increases with decreasing wind speed, and there is an optimal angle (θ≈20°) to maximize OAM. Therefore, for certain wind direction and wind speed, the OAM of dual-mode vortex beam propagating in the atmosphere could be larger than that in free space, and could be larger than the OAM of single-mode vortex beam. The dual-mode vortex beam with higher modes requires smaller wind speed to make its OAM larger than the OAM in free space. In addition, the larger the topological charge difference between the two element beams of a dual-mode vortex beam is, the more stable the OAM of the dual-mode vortex beam is. On the other hand, the evolution of linear edge dislocation singularity under atmospheric thermal blooming are also investigated in this paper. When the wind direction is perpendicular to the dislocation line, the linear edge dislocation singularity disappears. If the wind direction is parallel to the dislocation line, the linear edge dislocation singularity always exists. At other angles, the linear edge dislocation singularity will evolve into optical vortex pairs. The results obtained in this paper are useful to laser propagating in the atmosphere and optical communication.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"10 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74741807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The low-frequency Alfvénic fluctuations in the kinetic thermal-ion gap frequency range have been of research interest since they can interact with both thermal and energetic particles. In this work, linear wave properties of the low-frequency shear Alfvén waves excited by energetic and/or thermal particles observed in tokamak experiments with reversed magnetic shear are theoretically investigated and delineated in the theoretical framework of the generalized fishbone-like dispersion relation (GFLDR). Since these low-frequency shear Alfvén waves are closely related to the dedicated experiment of energetic ion-driven low-frequency instabilities conducted on DIII-D in 2019, this work demonstrates, by adopting the representative experimental equilibrium parameters of DIII-D, that the experimentally observed lowfrequency modes and beta-induced Alfvén eigenmodes (BAEs) are, respectively, the reactive-type and dissipative-type unstable modes with dominant Alfvénic polarization, thus the former being more precisely called low-frequency Alfvén modes (LFAMs). More specifically, due to diamagnetic and trapped particle effects, the LFAM can be coupled with the beta-induced Alfvén-acoustic mode (BAAE) in the low-frequency region (frequency much less than the thermal-ion transit and/or bounce frequency); or with the BAE in the high frequency region (frequency higher than or comparable to the thermal-ion transit frequency); resulting in reactive-type instabilities. Moreover, due to different instability mechanisms, the maximal drive of BAEs occurs, in comparison to LFAMs, when the minimum of the safety factor (qmin) deviates from a rational number. Meanwhile, the BAE eigenfunction peaks at the radial position of the maximum energetic particle pressure gradient, resulting in a large deviation from the qmin surface. The ascending frequency spectrum patterns of the experimentally observed BAEs and LFAMs can be theoretically reproduced by varying qmin and also be well interpreted based on the GFLDR. In particular, it is confirmed that the stability of the BAAE is not affected by energetic ions, which is consistent with the first-principle-based theory predictions and simulation results. The present analysis illustrates the solid predictive capability of the GFLDR and its practical usefulness in enhancing the interpretative capability of both experimental and numerical simulation results.
{"title":"Theoretical Studies of Low-frequency Shear Alfvén Waves in Reversed Shear Tokamak Plasmas","authors":"Ma Rui-Rui, Chen Liu, Qiu Zhi-Yong","doi":"10.7498/aps.72.20230255","DOIUrl":"https://doi.org/10.7498/aps.72.20230255","url":null,"abstract":"The low-frequency Alfvénic fluctuations in the kinetic thermal-ion gap frequency range have been of research interest since they can interact with both thermal and energetic particles. In this work, linear wave properties of the low-frequency shear Alfvén waves excited by energetic and/or thermal particles observed in tokamak experiments with reversed magnetic shear are theoretically investigated and delineated in the theoretical framework of the generalized fishbone-like dispersion relation (GFLDR). Since these low-frequency shear Alfvén waves are closely related to the dedicated experiment of energetic ion-driven low-frequency instabilities conducted on DIII-D in 2019, this work demonstrates, by adopting the representative experimental equilibrium parameters of DIII-D, that the experimentally observed lowfrequency modes and beta-induced Alfvén eigenmodes (BAEs) are, respectively, the reactive-type and dissipative-type unstable modes with dominant Alfvénic polarization, thus the former being more precisely called low-frequency Alfvén modes (LFAMs). More specifically, due to diamagnetic and trapped particle effects, the LFAM can be coupled with the beta-induced Alfvén-acoustic mode (BAAE) in the low-frequency region (frequency much less than the thermal-ion transit and/or bounce frequency); or with the BAE in the high frequency region (frequency higher than or comparable to the thermal-ion transit frequency); resulting in reactive-type instabilities. Moreover, due to different instability mechanisms, the maximal drive of BAEs occurs, in comparison to LFAMs, when the minimum of the safety factor (qmin) deviates from a rational number. Meanwhile, the BAE eigenfunction peaks at the radial position of the maximum energetic particle pressure gradient, resulting in a large deviation from the qmin surface. The ascending frequency spectrum patterns of the experimentally observed BAEs and LFAMs can be theoretically reproduced by varying qmin and also be well interpreted based on the GFLDR. In particular, it is confirmed that the stability of the BAAE is not affected by energetic ions, which is consistent with the first-principle-based theory predictions and simulation results. The present analysis illustrates the solid predictive capability of the GFLDR and its practical usefulness in enhancing the interpretative capability of both experimental and numerical simulation results.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"68 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74760861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-order harmonic generation (HHG) from the molecular ions stretched to large internuclear distances is studied numerically and analytically in this work. We focus on the fine structure of the HHG spectrum related to the contribution of short electron trajectory. In our numerically solving the time-dependent Schrodinger equation (TDSE), we use a trajectory-dependent filtering procedure to separate the short-trajectory contribution from other contributions of long trajectory and multiple returns. Our TDSE results reveal that the short-trajectory HHG spectra of molecular ion with larger internuclear distance show some complex interference structures characterized by some remarkable dips, and that the position of the dip is sensitive to the laser parameters. With a developed model arising from strong-field approximation (SFA), we are able to identify the physical origins of the complex interference structures. In this model considered is the charge-resonance effect which induces the strong coupling between the ground state and the first excited state of the molecular ion at large internuclear distance. In this model, the well-known effect of two-center interference occurs in the form of the canonical momentum instead of the momentum related to the instantaneous velocity of the electron in the general SFA. It is shown that some dips in TDSE results arise from two-center interference of the electronic wave between these two atomic cores of the molecule in the ionization process, while others come from that in the recombination process. These ionization and recombination dips alternately appear in the HHG spectra from the formed complex interference structures. The main differences between the interference effects in the ionization process and the recombination process are twofold. Firstly, in the ionization process, the destructive two-center interference strongly suppresses the forming of the continuum wavepacket, while in the recombination process, the recombination of the rescattering electron with other bound eigenstates with small weights can also contribute to HHG bedsides the recombination of the ground state with the first excited state with large weights. As a result, in TDSE results, the ionization dips are deeper and more remarkable than the recombination ones. Secondly, in the recombination process, the Coulomb acceleration remarkably changes the de Broglie wavelength of the rescattering electron and therefore changes the position of the interference-induced dip. While in the ionization process, the Coulomb potential plays a small role in the interference effect. As a result, the interference dips in the ionization process and the recombination process differ from each other.
{"title":"Physical origins of complex interference structures in harmonic emission from molecular ions stretched to large internuclear distances","authors":"Weiyan Li, Na Liu, Shang Wang","doi":"10.7498/aps.72.20222410","DOIUrl":"https://doi.org/10.7498/aps.72.20222410","url":null,"abstract":"High-order harmonic generation (HHG) from the molecular ions stretched to large internuclear distances is studied numerically and analytically in this work. We focus on the fine structure of the HHG spectrum related to the contribution of short electron trajectory. In our numerically solving the time-dependent Schrodinger equation (TDSE), we use a trajectory-dependent filtering procedure to separate the short-trajectory contribution from other contributions of long trajectory and multiple returns. Our TDSE results reveal that the short-trajectory HHG spectra of molecular ion with larger internuclear distance show some complex interference structures characterized by some remarkable dips, and that the position of the dip is sensitive to the laser parameters. With a developed model arising from strong-field approximation (SFA), we are able to identify the physical origins of the complex interference structures. In this model considered is the charge-resonance effect which induces the strong coupling between the ground state and the first excited state of the molecular ion at large internuclear distance. In this model, the well-known effect of two-center interference occurs in the form of the canonical momentum instead of the momentum related to the instantaneous velocity of the electron in the general SFA. It is shown that some dips in TDSE results arise from two-center interference of the electronic wave between these two atomic cores of the molecule in the ionization process, while others come from that in the recombination process. These ionization and recombination dips alternately appear in the HHG spectra from the formed complex interference structures. The main differences between the interference effects in the ionization process and the recombination process are twofold. Firstly, in the ionization process, the destructive two-center interference strongly suppresses the forming of the continuum wavepacket, while in the recombination process, the recombination of the rescattering electron with other bound eigenstates with small weights can also contribute to HHG bedsides the recombination of the ground state with the first excited state with large weights. As a result, in TDSE results, the ionization dips are deeper and more remarkable than the recombination ones. Secondly, in the recombination process, the Coulomb acceleration remarkably changes the de Broglie wavelength of the rescattering electron and therefore changes the position of the interference-induced dip. While in the ionization process, the Coulomb potential plays a small role in the interference effect. As a result, the interference dips in the ionization process and the recombination process differ from each other.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"194 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75027004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiang Xing-Cheng, Ma Hai-Bei, Wang Lei, Tian Da, Zhang Wei, Zhang Cai-Hong, Wu Jing-Bo, Fan Ke-Bin, Jin Biao-Bing, Chen Jian, Wu Pei-heng
A metamaterial sensor using sample traps based on terahertz electromagnetically-induced-transparency-like（EIT-like） effect is proposed. The basic unit structure of the sensor is composed of a metal wire and a pair of split-ring resonators(SRRs), which are coupled to produce EIT-like effect. A transparency peak with a full width at half maximum (FWHM) of 178 GHz is obtained at 1.067 THz, and the maximum transmittance of the transparency peak is 89.71%. The sensing characteristics of the structure are studied, and the sensitivity is 178 GHz/(RIU·mm3). It is found that the electric field at gaps of the SRRs on both sides is the strongest by analyzing electric field distribution at the resonant frequency point of the metamaterial. Sample traps are constructed at the gaps, where the electric field is strongest. The photoresist was filled into the sample traps as the object to be measured, and 50 GHz frequency offset was successfully measured, which verified that the sample trap structure can be applied to sensing. After research and analysis, by placing samples in the sample traps, the sample volume is reduced to the ultra-micro level, and the sensitivity is increased to 5538 GHz/(RIU·mm3), which is 31 times higher than before. The successful identification of water, human skin and rat skin samples shows that the metamaterial sensor using sample traps has potential application value in the field of ultra-micro detection.
{"title":"Ultramicro-sensing of terahertz metamaterials using sample traps","authors":"Xiang Xing-Cheng, Ma Hai-Bei, Wang Lei, Tian Da, Zhang Wei, Zhang Cai-Hong, Wu Jing-Bo, Fan Ke-Bin, Jin Biao-Bing, Chen Jian, Wu Pei-heng","doi":"10.7498/aps.72.20230080","DOIUrl":"https://doi.org/10.7498/aps.72.20230080","url":null,"abstract":"A metamaterial sensor using sample traps based on terahertz electromagnetically-induced-transparency-like（EIT-like） effect is proposed. The basic unit structure of the sensor is composed of a metal wire and a pair of split-ring resonators(SRRs), which are coupled to produce EIT-like effect. A transparency peak with a full width at half maximum (FWHM) of 178 GHz is obtained at 1.067 THz, and the maximum transmittance of the transparency peak is 89.71%. The sensing characteristics of the structure are studied, and the sensitivity is 178 GHz/(RIU·mm3). It is found that the electric field at gaps of the SRRs on both sides is the strongest by analyzing electric field distribution at the resonant frequency point of the metamaterial. Sample traps are constructed at the gaps, where the electric field is strongest. The photoresist was filled into the sample traps as the object to be measured, and 50 GHz frequency offset was successfully measured, which verified that the sample trap structure can be applied to sensing. After research and analysis, by placing samples in the sample traps, the sample volume is reduced to the ultra-micro level, and the sensitivity is increased to 5538 GHz/(RIU·mm3), which is 31 times higher than before. The successful identification of water, human skin and rat skin samples shows that the metamaterial sensor using sample traps has potential application value in the field of ultra-micro detection.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"65 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75252250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Parity-time (PT)symmetric is not a necessary condition for achieving a real spectrum and some studies about realizing real spectra in non-PT-symmetric systems with arbitrary gain–loss profiles have been presented recently. By tuning the free parameters in non-PT-symmetric potentials, phase transition could also be induced. Above phase transition point, discrete complex eigenvalues bifurcate out from continuous real eigenvalues in the interior of the continuous spectrum. In this work, we investgate the existence and stability of solitons in nonlocal nonlinear couplers with non-PT-symmetric complex potentials both below and above phase transition. There are several discrete eigenvalues in the linear spectra of the non-PT-symmetric system used here. With the square-operator iteration method, we find that different continuous families of solitions can bifurcate from different discrete linear eigenvalues. Moreover, linear-stability analysis collaborated with direct numerical propagation simulations demonstrates that the nonlocal solitions can be stable in a range of parameter values. we first address the cases below the phase transition. To be specific,when we fix the coupling coefficient and vary the degree of nonlocality, it’s found that fundamental solitons, dipole solitons, tripolar solitons, quadrupole solitons bifurcate from the largest,the second-largest, the third-largest and the fifth-largest discrete eigenvalue, respectively. These nonlocal solitons are all stable in the low power region. With an increase of the degree of nonlocality, the stability region shrinks for the fundamental solitons while it widens for the dipole and multiplole solitons. At the same time, the power of all the stable solitons increases with the increase of the degree of nonlocality. By varying the coupling coefficient, the arrangement of soliton families emerging in the discrete interval of the linear spectrum can be changed. For example, the dipole solitons bifurcate from the third-or fourth-largest discrete eigenvalue while the tripolar solitons bifurcate from the fifth largest discrete eigenvalue. Above phase transition,the fundamental solitons are unstable in the low and high power region but are stable in the moderate power region. The stability region shrinks with the increasing degree of nonlocality. We also find the the family of dipole solitons bifurcates from the second-largest discrete eigenvalue, but all the dipole solitons are unstable. In addition,we find that the eigenvalues in linear-stability spectra of solitons emerge as conjugation pairs.
{"title":"Nonlocal soliton in non-parity-time-symmetric coupler","authors":"Jiang Hong-Fan, Lin Ji, Hu Bei-Bei, Zhang Xiao","doi":"10.7498/aps.72.20230082","DOIUrl":"https://doi.org/10.7498/aps.72.20230082","url":null,"abstract":"Parity-time (PT)symmetric is not a necessary condition for achieving a real spectrum and some studies about realizing real spectra in non-PT-symmetric systems with arbitrary gain–loss profiles have been presented recently. By tuning the free parameters in non-PT-symmetric potentials, phase transition could also be induced. Above phase transition point, discrete complex eigenvalues bifurcate out from continuous real eigenvalues in the interior of the continuous spectrum. In this work, we investgate the existence and stability of solitons in nonlocal nonlinear couplers with non-PT-symmetric complex potentials both below and above phase transition. There are several discrete eigenvalues in the linear spectra of the non-PT-symmetric system used here. With the square-operator iteration method, we find that different continuous families of solitions can bifurcate from different discrete linear eigenvalues. Moreover, linear-stability analysis collaborated with direct numerical propagation simulations demonstrates that the nonlocal solitions can be stable in a range of parameter values. we first address the cases below the phase transition. To be specific,when we fix the coupling coefficient and vary the degree of nonlocality, it’s found that fundamental solitons, dipole solitons, tripolar solitons, quadrupole solitons bifurcate from the largest,the second-largest, the third-largest and the fifth-largest discrete eigenvalue, respectively. These nonlocal solitons are all stable in the low power region. With an increase of the degree of nonlocality, the stability region shrinks for the fundamental solitons while it widens for the dipole and multiplole solitons. At the same time, the power of all the stable solitons increases with the increase of the degree of nonlocality. By varying the coupling coefficient, the arrangement of soliton families emerging in the discrete interval of the linear spectrum can be changed. For example, the dipole solitons bifurcate from the third-or fourth-largest discrete eigenvalue while the tripolar solitons bifurcate from the fifth largest discrete eigenvalue. Above phase transition,the fundamental solitons are unstable in the low and high power region but are stable in the moderate power region. The stability region shrinks with the increasing degree of nonlocality. We also find the the family of dipole solitons bifurcates from the second-largest discrete eigenvalue, but all the dipole solitons are unstable. In addition,we find that the eigenvalues in linear-stability spectra of solitons emerge as conjugation pairs.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"81 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75299975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Li Gao-Fang, Yin Wen, Huang Jing-Guo, Cui Hao-Yang, Ye Han-Jing, Gao Yan-Qing, Huang Zhi-Ming, Chu Jun-hao
In this paper, the conductivity of intrinsic GaSe, S doped 2.5 mass% GaSe, and S doped 7 mass% GaSe crystals, in the range of 0.3-2.5 THz, was measured by transmission terahertz time-domain spectroscopy, and fitted well with Drude-Smith-Lorentz model which was introduced lattice vibration effect. It was found that the real part of conductivity decreased with S doping, which was caused by the gradual shift of the Fermi energy level of GaSe crystals to the charge neutrality level due to the generation of substitution impurities and gap impurities by S doping, resulting in the reduction of carrier concentration. The intrinsic GaSe and S doping 2.5 mass% GaSe had a clear lattice vibration peak at about 0.56 THz, while GaSe: S 7% had no lattice vibration peak near 0.56 THz, which was mainly due to the S doping increased the structural hardness of the crystal and reduced the interlayer rigidity vibration of the crystal. All three samples had obvious narrow lattice vibration peaks at about 1.81 THz, and the intensity first decreased and then increased with S doping, which mainly due to a small amount of S doping reduced the local structural defects of GaSe and weakened the intensity of the narrow lattice vibration peak, while excessive S doping generated β-type GaS crystals, increased the local structural defects of the crystals and the intensity of the narrow lattice vibration peak. With the increase of S doping, the intensity of the broad lattice vibration peak of GaSe crystal weakened or even disappeared at about 1.07 THz and 2.28 THz, mainly due to the S doping resulting in S substitution impurities and GaS gap impurities, which reducing the fundamental frequency phonon vibration intensity, thereby weakening the lattice vibration caused by the second-order phonon difference mode of the crystal. The results show that the appropriate concentration of S doping can effectively suppress the lattice vibration of GaSe crystal, reduce the conductivity and power loss in the THz band. This study provides important data support and theoretical basis for the design and fabrication of low loss THz devices.
{"title":"Conductivity in sulfur doped gallium selenide crystals measured by terahertz time-domain spectroscopy","authors":"Li Gao-Fang, Yin Wen, Huang Jing-Guo, Cui Hao-Yang, Ye Han-Jing, Gao Yan-Qing, Huang Zhi-Ming, Chu Jun-hao","doi":"10.7498/aps.72.20221548","DOIUrl":"https://doi.org/10.7498/aps.72.20221548","url":null,"abstract":"In this paper, the conductivity of intrinsic GaSe, S doped 2.5 mass% GaSe, and S doped 7 mass% GaSe crystals, in the range of 0.3-2.5 THz, was measured by transmission terahertz time-domain spectroscopy, and fitted well with Drude-Smith-Lorentz model which was introduced lattice vibration effect. It was found that the real part of conductivity decreased with S doping, which was caused by the gradual shift of the Fermi energy level of GaSe crystals to the charge neutrality level due to the generation of substitution impurities and gap impurities by S doping, resulting in the reduction of carrier concentration. The intrinsic GaSe and S doping 2.5 mass% GaSe had a clear lattice vibration peak at about 0.56 THz, while GaSe: S 7% had no lattice vibration peak near 0.56 THz, which was mainly due to the S doping increased the structural hardness of the crystal and reduced the interlayer rigidity vibration of the crystal. All three samples had obvious narrow lattice vibration peaks at about 1.81 THz, and the intensity first decreased and then increased with S doping, which mainly due to a small amount of S doping reduced the local structural defects of GaSe and weakened the intensity of the narrow lattice vibration peak, while excessive S doping generated β-type GaS crystals, increased the local structural defects of the crystals and the intensity of the narrow lattice vibration peak. With the increase of S doping, the intensity of the broad lattice vibration peak of GaSe crystal weakened or even disappeared at about 1.07 THz and 2.28 THz, mainly due to the S doping resulting in S substitution impurities and GaS gap impurities, which reducing the fundamental frequency phonon vibration intensity, thereby weakening the lattice vibration caused by the second-order phonon difference mode of the crystal. The results show that the appropriate concentration of S doping can effectively suppress the lattice vibration of GaSe crystal, reduce the conductivity and power loss in the THz band. This study provides important data support and theoretical basis for the design and fabrication of low loss THz devices.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"22 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82233700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Luo Yu-Xuan, Cheng Yong-Zhi, Chen Fu, Luo Hui, Li Xiang-Cheng
In this paper, a dual passband filter with spoof surface plasmon polaritons (SSPPs) and interdigital capacitance structure loaded on a coplanar waveguide (CPW) is proposed. Firstly, the hourglass-shaped SSPP unit-cell structure and the interdigital capacitor structure are introduced on the coplanar waveguide transmission line to obtain high fractional bandwidth and low insertion loss passband characteristics. Then, a dual passband filter is formed by loading the interdigital capacitor loop resonator to excite the trapped waves. The simulation results show that the proposed dual passband filter has excellent upper sideband rejection and dual passband filtering performance. The fractional bandwidths of the two passbands of the design are 46.8% (1.49-2.40 GHz) and 15.1% (2.98-3.63 GHz), respectively, which can achieve more than -40 dB rejection in the range of 4.77-7.48 GHz. The upper and lower cutoff frequencies of the two passbands can be independently regulated by changing the structural parameters of the proposed filter. In order to gain a deeper understanding of the operating principle of the dual passband filter, the corresponding dispersion curves and electric field distribution, LC equivalent circuit analysis are given. Finally, the prototype of the designed filter is fabricated according to the optimized parameter values. The experimental results are in good agreement with the simulation ones, indicating that the proposed dual-passband filter is of great importance in microwave integrated circuit applications.
{"title":"Dual-band filter design based on hourglass-shaped spoof surface plasmon polaritons and interdigital capacitor structure","authors":"Luo Yu-Xuan, Cheng Yong-Zhi, Chen Fu, Luo Hui, Li Xiang-Cheng","doi":"10.7498/aps.72.20221984","DOIUrl":"https://doi.org/10.7498/aps.72.20221984","url":null,"abstract":"In this paper, a dual passband filter with spoof surface plasmon polaritons (SSPPs) and interdigital capacitance structure loaded on a coplanar waveguide (CPW) is proposed. Firstly, the hourglass-shaped SSPP unit-cell structure and the interdigital capacitor structure are introduced on the coplanar waveguide transmission line to obtain high fractional bandwidth and low insertion loss passband characteristics. Then, a dual passband filter is formed by loading the interdigital capacitor loop resonator to excite the trapped waves. The simulation results show that the proposed dual passband filter has excellent upper sideband rejection and dual passband filtering performance. The fractional bandwidths of the two passbands of the design are 46.8% (1.49-2.40 GHz) and 15.1% (2.98-3.63 GHz), respectively, which can achieve more than -40 dB rejection in the range of 4.77-7.48 GHz. The upper and lower cutoff frequencies of the two passbands can be independently regulated by changing the structural parameters of the proposed filter. In order to gain a deeper understanding of the operating principle of the dual passband filter, the corresponding dispersion curves and electric field distribution, LC equivalent circuit analysis are given. Finally, the prototype of the designed filter is fabricated according to the optimized parameter values. The experimental results are in good agreement with the simulation ones, indicating that the proposed dual-passband filter is of great importance in microwave integrated circuit applications.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"51 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87867105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liu Huizhen, Liu Bei, Dong Jiabin, Li Jianpeng, Cao Zixiu, Liu Yue, Meng Rutao, Zhang Yi
Efficient copper based thin film solar cells usually use inorganic n-type semiconductor material CdS as the buffer layer. Therefore, the interface quality and energy band matching between the buffer layer and the absorption layer are crucial to the collection and utilization of carriers. Heat treatment can promote the mutual diffusion of interface elements, the migration of ions in the material and the change of defect state, and the proper temperature will change the degree of Cu-Zn ordering in the absorption layer, so as to improve the efficiency of the solar cells. Based on the optimization of CdS basic process, the strategy of annealing CdS/copper-based thin film heterojunction in sulfur atmosphere further improves the quality of CdS thin film, and applies it to copper-based solar cells to regulate the p-n heterojunction energy band gap matching of copper-based thin film cells. The results show that the annealing of CdS film in sulfur-containing inert atmosphere can effectively improve the crystal quality of CdS film and inhibit the non-radiative recombination loss caused by defect trapping at the interface of CZTS/CdS heterojunction, and the open-circuit voltage of the device can be significantly increased, up to 718 mV. In addition, annealing CZTS/CdS heterojunction in S/Ar atmosphere can effectively improve the p-n heterojunction energy band gap matching, which not only improves the electron transmission, but also reduces the carrier recombination, thus improving the Voc and FF of devices. Besides, the oxygen element in CdS film can be replaced by sulfur element in sulfur atmosphere to improve the quality of CdS film and thus enhance the short-wave absorption of solar cell devices. Therefore, In terms of device efficiency, the efficiency of CZTS solar cell based on sputtering method has increased from 3.47% to 5.68%, which is about twice that of non-annealing treatment, Its device structure is Glass/Mo/CZTS/CdS/i-ZnO/Al:ZnO/Ni/Al, providing a reliable process window for copper based thin film solar cell devices to achieve high open-circuit voltage. Meanwhile, this study strongly demonstrates the importance of annealing atmosphere selection for CdS quality and energy band matching of CZTS/CdS heterojunction. In addition to interface interdiffusion, the composition and crystallinity of thin film materials are controlled.
{"title":"Study on the regulation of solar cell performance by cadmium sulfide/copper-based thin film heterojunction annealing under different atmospheres","authors":"Liu Huizhen, Liu Bei, Dong Jiabin, Li Jianpeng, Cao Zixiu, Liu Yue, Meng Rutao, Zhang Yi","doi":"10.7498/aps.72.20230105","DOIUrl":"https://doi.org/10.7498/aps.72.20230105","url":null,"abstract":"Efficient copper based thin film solar cells usually use inorganic n-type semiconductor material CdS as the buffer layer. Therefore, the interface quality and energy band matching between the buffer layer and the absorption layer are crucial to the collection and utilization of carriers. Heat treatment can promote the mutual diffusion of interface elements, the migration of ions in the material and the change of defect state, and the proper temperature will change the degree of Cu-Zn ordering in the absorption layer, so as to improve the efficiency of the solar cells. Based on the optimization of CdS basic process, the strategy of annealing CdS/copper-based thin film heterojunction in sulfur atmosphere further improves the quality of CdS thin film, and applies it to copper-based solar cells to regulate the p-n heterojunction energy band gap matching of copper-based thin film cells. The results show that the annealing of CdS film in sulfur-containing inert atmosphere can effectively improve the crystal quality of CdS film and inhibit the non-radiative recombination loss caused by defect trapping at the interface of CZTS/CdS heterojunction, and the open-circuit voltage of the device can be significantly increased, up to 718 mV. In addition, annealing CZTS/CdS heterojunction in S/Ar atmosphere can effectively improve the p-n heterojunction energy band gap matching, which not only improves the electron transmission, but also reduces the carrier recombination, thus improving the Voc and FF of devices. Besides, the oxygen element in CdS film can be replaced by sulfur element in sulfur atmosphere to improve the quality of CdS film and thus enhance the short-wave absorption of solar cell devices. Therefore, In terms of device efficiency, the efficiency of CZTS solar cell based on sputtering method has increased from 3.47% to 5.68%, which is about twice that of non-annealing treatment, Its device structure is Glass/Mo/CZTS/CdS/i-ZnO/Al:ZnO/Ni/Al, providing a reliable process window for copper based thin film solar cell devices to achieve high open-circuit voltage. Meanwhile, this study strongly demonstrates the importance of annealing atmosphere selection for CdS quality and energy band matching of CZTS/CdS heterojunction. In addition to interface interdiffusion, the composition and crystallinity of thin film materials are controlled.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"106 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88107704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tao Chen-Yu, Lei Jian-Ting, Yu Xuan, Luo Yan, Ma Xin-wen, Zhang Shao-Feng
In the past two decades,the development of laser technology has made attosecond science become a cutting-edge research field,providing various novel perspectives for the study of quantum few-body ultrafast evolution.The attosecond pulses prepared in the current laboratory are widely used in experimental research in the form of isolated pulses or pulse trains.The ultrafast changing light field allows people to control and track the motion of electrons at the atomic-scale,and realizes real-time tracking of electron dynamics on the sub-femtosecond time-scale.This review focuses on the progress in the study of ultrafast dynamics of atoms and molecules,which is an important part of attosecond science.Firstly,the generation and development of attosecond pulses are reviewed,mainly including the principle of high-order harmonic and the separation method of single-attosecond pulses.Then the applications of attosecond pulses are systematically introduced,including photo-ionization time delay,attosecond charge migration,non-adiabatic molecular dynamics and so on.Finally,the summary and outlook of the application of attosecond pulses are presented.
{"title":"Development of Attosecond Pulse and Application in Ultrafast Dynamics of Atoms and Molecules","authors":"Tao Chen-Yu, Lei Jian-Ting, Yu Xuan, Luo Yan, Ma Xin-wen, Zhang Shao-Feng","doi":"10.7498/aps.72.20222436","DOIUrl":"https://doi.org/10.7498/aps.72.20222436","url":null,"abstract":"In the past two decades,the development of laser technology has made attosecond science become a cutting-edge research field,providing various novel perspectives for the study of quantum few-body ultrafast evolution.The attosecond pulses prepared in the current laboratory are widely used in experimental research in the form of isolated pulses or pulse trains.The ultrafast changing light field allows people to control and track the motion of electrons at the atomic-scale,and realizes real-time tracking of electron dynamics on the sub-femtosecond time-scale.This review focuses on the progress in the study of ultrafast dynamics of atoms and molecules,which is an important part of attosecond science.Firstly,the generation and development of attosecond pulses are reviewed,mainly including the principle of high-order harmonic and the separation method of single-attosecond pulses.Then the applications of attosecond pulses are systematically introduced,including photo-ionization time delay,attosecond charge migration,non-adiabatic molecular dynamics and so on.Finally,the summary and outlook of the application of attosecond pulses are presented.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"7 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88169816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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