Multi-electron and multi-orbital effects play a crucial role in the interaction of strong laser fields with complex molecules.Here,multi-electron effects encompass not only electron-electron Coulomb interactions and e...Multi-electron and multi-orbital effects play a crucial role in the interaction of strong laser fields with complex molecules.Here,multi-electron effects encompass not only electron-electron Coulomb interactions and exchangecorrelation effects but also the interference between the dynamics of different electron wave packets.展开更多
The low-order harmonic generation of hydrogen molecular ion interacting with a linearly polarized laser field has been investigated theoretically by using a simple two-state model. The validity of the two-state model ...The low-order harmonic generation of hydrogen molecular ion interacting with a linearly polarized laser field has been investigated theoretically by using a simple two-state model. The validity of the two-state model is carefully examined by comparing the harmonic spectra of hydrogen molecular ion obtained from this model with those from the three-dimensional time-dependent Schr¨odinger equation. When combined with the Morlet transform of quantum time-frequency spectrum,the two-state model can be used to study the dynamical origin of the low-order harmonic generation of hydrogen molecular ion driven by low-frequency pulses. In addition, some interesting structures of the time profiles for low order harmonics are obtained.展开更多
We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed ar...We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed around a single type-ⅡWeyl point,especially at zero frequency.Such a remarkable DC signal is proved to have attributions from the intraband transition after spectral decomposition.Under weak pulse electric field,the linear optical response of a nontilted Weyl cone is consistent with the Kubo theory.With extensive numerical simulations,we conclude that the non-zero chemical potential can enhance the even-order generations,from the slightly tilted system to the over-tilted systems.In consideration of dynamical symmetries,type-Ⅰand type-ⅡWeyl cones also show different selective responses under the circularly polarized light.Finally,using a more realistic model containing two pairs of Weyl points,we demonstrate that paired Weyl points with opposite chirality can suppress the overall even-order generations.展开更多
Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation （HHG） of the initial...Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation （HHG） of the initial state separately being the ground and excited states is presented. When the hardness parameter a in the soft Coulomb potential V（x） =-1√x^2＋α is chosen to be small enough, the so-called hard Coulomb potential V（x）=1/｜x｜ can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of - 0.5 and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with a = 2 in the same laser field. Laser-induced non-resonant one-photon emission is also observed.展开更多
The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order ...The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.展开更多
Applying Fourier transform technique to deduction of background and noise on dE/dt-t curve,a new electrochemical method,high order harmonic oscillographic chronopotentiometry is proposed in this paper.
Attosecond light pulses have revolutionized the study of electron dynamics in materials by enabling the observation of ultrafast processes with unprecedented attosecond temporal resolution.They are primarily generated...Attosecond light pulses have revolutionized the study of electron dynamics in materials by enabling the observation of ultrafast processes with unprecedented attosecond temporal resolution.They are primarily generated through the process of high-order harmonic generation.This paper presents a comprehensive setup for attosecond pulse generation and measurement.Using a 900 nm,7 mJ,and 7 fs femtosecond laser with stabilized carrier-envelope phase,we employ polarization gating to generate a near single-cycle,linearly polarized pulse that interacts with neon gas to produce a broadband extreme-ultraviolet continuum with a cutoff photon energy of∼120 eV.The temporal and spectral characteristics of the generated single attosecond pulses are measured using an attosecond streak camera,and the pulse duration is determined to be 59 as through the frequency-resolved optical gating for complete reconstruction of attosecond bursts retrieval algorithm.As part of the Synergetic Extreme Condition User Facility,this setup will facilitate ultrafast research in transient absorption and photoelectron spectroscopy,providing global users with a powerful tool for studying electron dynamics in various materials.展开更多
Generating Bessel-Gauss beams in the extreme ultraviolet(EUV)with attosecond pulse durations poses a significant challenge due to the limitations of conventional transmission optical components.Here,we propose a novel...Generating Bessel-Gauss beams in the extreme ultraviolet(EUV)with attosecond pulse durations poses a significant challenge due to the limitations of conventional transmission optical components.Here,we propose a novel approach to produce such beams by inducing an annular EUV source through high-order harmonic generation(HHG)under nonadiabatic phase-matching conditions.The resulting light pulse maintains temporal coherence and manifests attosecond pulse trains as confirmed by the reconstruction of attosecond beating by interference of two-photon transitions(RABBIT)measurements.Macroscopic HHG calculations reproduce the measured spatiotemporal structures,demonstrating the plasma-induced spatial modulation on the formation of an annular source.Propagation simulations further confirm the feasibility of this approach for generating attosecond Bessel-Gauss beams,presenting exciting prospects for various applications in EUV photonics and attosecond science.展开更多
To measure the signals with high freq u ency(>500 MHz),a sampling frequency down conversion method is introduced.This pa per analyzes the intermodulation signals and figures out the relationship betwee n the interm...To measure the signals with high freq u ency(>500 MHz),a sampling frequency down conversion method is introduced.This pa per analyzes the intermodulation signals and figures out the relationship betwee n the intermodulation signal and intermediate frequenc y signal.Based on the frequency conversion technology,an exclusion algorithm i s proposed a nd the actual implementation of the algorithm is given.The application resu lts show that the exclusion algorithm can identify the intermodulation signal exactly and eliminate the bad influence on the frequency measurement.展开更多
A model of fuel injection adjustment for balancing the 4-stroke six cylinder diesel engine coupling geneset is developed by detecting imbalance in operating engine by the frequency analysis of the crankshaft＇s speed ...A model of fuel injection adjustment for balancing the 4-stroke six cylinder diesel engine coupling geneset is developed by detecting imbalance in operating engine by the frequency analysis of the crankshaft＇s speed variation. In this work, the crankshaft is considered to be a rigid body, so that the variation of its angular speed could be directly correlated to the total gas-pressure torque. By analyzing only the lower harmonic orders, the speed variation spectrum can filter out the distortions produced by the dynamic response of the crankshaft. The information carried by these harmonic orders permits to establish correlations between measurements and the average gas pressure torque of the engine, and to detect imbalance and identify faulty cylinders. Detailed experimental reading are taken on diesel engine coupling genset on the test bed of Greaves Cotton Ltd Pane, India.展开更多
P91 steel is an important bearing material used in nuclear power plants. The study of its mechanical degradation behavior is important for ensuring safe operation. The relationship between the dislocation density of P...P91 steel is an important bearing material used in nuclear power plants. The study of its mechanical degradation behavior is important for ensuring safe operation. The relationship between the dislocation density of P91 steel under different strains and the corresponding nonlinear ultrasonic parameter β was studied. The dislocation density of strained samples was estimated by X-ray diffraction. Nonlinear ultrasonic testing was conducted to evaluate β, showing that this value increased with increasing dislocation density induced by different tensile elongations. It was shown that the ultrasonic secondharmonic generation technique can effectively evaluate the degradation behavior of metallic materials, and the prediction of the residual life of bearing parts in service can be made based on β and the dislocation density.展开更多
Applications using higher orderharmonics (HOH) require knowledge ofthe completeness ofthe HOHfor the diffusion difference equation.This papershowsthatthe set of HOHforthefission sourceis complete ,butthat the setfor...Applications using higher orderharmonics (HOH) require knowledge ofthe completeness ofthe HOHfor the diffusion difference equation.This papershowsthatthe set of HOHforthefission sourceis complete ,butthat the setfortheflux usingthe multi group modelis notcomplete .This paperusesthe assumption thatthe set offlux vectors of HOHfor every group is complete. This assumption can be proven only forthose groups into which noscattering neutrons enter.However,itisalso shownto betrueforseveralpracticalreactor models.Analysisshows thatthe number of HOHwith non zero eigenvaluesis equaltothe numberofdifference meshes withfissile material, and thatthe eigenvalues have positive realvalues.This assumptionis valuablefor HOHapplications,butrequires furthertheoreticalstudyto verify whetheritisuniversally applicable.展开更多
This paper proposes a flux mapping method directly using the higher order harmonics (HOH) of the neutronics equation of the nominal core. The bi-orthogonality and completeness of the HOH set are studied. and they are ...This paper proposes a flux mapping method directly using the higher order harmonics (HOH) of the neutronics equation of the nominal core. The bi-orthogonality and completeness of the HOH set are studied. and they are the theoretical basis for the flux mapping method. Using the bi-orthogonality of HOH and the strict formula for eigenvalue estimation. the process and formulas for HOH calculation called as the source iteration method with source correction are derived. The analysis can predict any order of harmonics for 2-or 3-dimensional geometries.Preliminary verification of the capability for flux mapping is also given. and other applications of HOH for reactor operation analysis and failure diagnosis are underway.展开更多
A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented.The method exploits second-harmonic generation and can be adapted for different laser ...A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented.The method exploits second-harmonic generation and can be adapted for different laser arrays geometries.Experimental and calculated results,presented for negatively coupled lasers formed in a square,honeycomb,and triangular geometries are in good agreement.展开更多
We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were...We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were focused onto an argon filled gas cell.We detected high order harmonics corresponding to a train of 209 as pulses,characterized by the reconstruction of attosecond beating by interference of two-photon transition(RABITT)technique.Compared with the conventional attosecond pulse trains,the broad harmonics in such pulse trains cover more energy range,so it is more efficient in studying some typical cases,such as resonances,with frequency resolved RABITT.As the solid thin plates can support high power supercontinuum generation,it is feasible to tailor the spectrum to have different central wavelength and spectral width,which will make the RABITT source work in different applications.展开更多
The synchrotron radiation spectra of the spherical grating monochromator(SGM)working in the soft X-ray and VUV region are often contaminated by significant amounts of higher order harmonics.They cannot be suppressed c...The synchrotron radiation spectra of the spherical grating monochromator(SGM)working in the soft X-ray and VUV region are often contaminated by significant amounts of higher order harmonics.They cannot be suppressed completely by suitable filters.Higher order contributions in the spectral radiation standard and metrology beamline were researched using transmission grating(made in-house)and IRD AXUV100G(USA)photodiode detector.The exit beam was dispersed with the transmission grating behind the exit slit of the monochromator,and the contributions of the different orders were analyzed.The higher order distributions were quantitatively determined for three gratings with line densities of 1800,600 and 200 l/mm.Experiment results show that in wavelengths between 5 nm and 15 nm the contributions of the higher orders to the detector signal are restricted to less than 7%even without the use of filters.In wavelength regions between 5 nm and 34 nm,the contributions of the higher orders to the detector signal are less than 14%with proper Al,Si_(3)N_(4) and Zr filters,and after being modified by quantum efficiency of the detector,the higher order contributions are restricted to less than 6.5%.The study also shows that higher orders are almost totally suppressed by MgF_(2) filter when the wavelength ranges between 115–140 nm.展开更多
Interferometric measurements of high harmonics induced by multiple laser fields represent a burgeoning field of research,offering prospects for optimized harmonic yield and enabling time-and space-resolved nonlinear s...Interferometric measurements of high harmonics induced by multiple laser fields represent a burgeoning field of research,offering prospects for optimized harmonic yield and enabling time-and space-resolved nonlinear spectroscopy.While most investigations have focused on controlling the time delay between pulses,our study introduces a novel approach.By manipulating an additional parameter—the phase difference between the fields—we unveil detailed insights into the physical mechanisms governing the ultrafast processes underlying high harmonic generation.Leveraging high harmonic 2-dimensional interferograms,our method facilitates the streamlined analysis of attosecond electron dynamics in complex molecules and solids,marking an important advancement in this rapidly evolving field.展开更多
High-order harmonic generation(HHG)in solids—the frequency up-conversion of an optical signal—is governed by symmetries.At terahertz(THz)frequencies,HHG is a key technology to access high-frequency spectral windows ...High-order harmonic generation(HHG)in solids—the frequency up-conversion of an optical signal—is governed by symmetries.At terahertz(THz)frequencies,HHG is a key technology to access high-frequency spectral windows that are usually difficult to cover using conventional solid-state laser technologies.This effect has been recently exploited in graphene,where HHG has been demonstrated,albeit only at odd multiples of the driving frequency owing to its inherent centro-symmetry.In topological insulators(TIs),the combination of spin–orbit interaction and time-reversal symmetry create an insulating bulk state with an inverted band order,inseparably connected with conducting surface states.TIs have been predicted to support unconventional high harmonic generation from the bulk and topological surface,which are usually difficult to distinguish.However,no experimental results have been reported,so far.Here,we exploit the strong optical field amplification provided by an array of single or double split ring resonators,with embedded Bi_(2)Se_(3)or(In_(x)Bi_((1−x)))_(2)Se_(3)/Bi_(2)Se_(3)Van der Waals heterostructures,to achieve up-conversion in the 6.4(even)–9.7(odd)THz frequency range.This results from bulk centro-symmetry(odd states)and symmetry breaking in the topological surface states(odd and even).展开更多
Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,...Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,empowering us to study quantum behaviors of electrons in atoms,molecules,and solids with unprecedented time resolution.Following the cutoff energy law of HHG,the shortest IAP reported so far is driven with short-wavelength infrared(SWIR)pulses,which require additional broadband frequency conversion techniques and raise the bar for attosecond researches.Here,we show that with fewcycle near-infrared(NIR)laser pulses,IAP with pulse duration of 51±4 as is generated during 1-fs linear polarization gate formed by generalized double optical gating(GDOG)technique.The characterization is done with attosecond streak camera,and phase reconstruction is performed with quick phase retrieval by omega oscillation filtering(qPROOF).Furthermore,we show that the IAP generation favors certain carrier envelope phases(CEPs)in the narrow gate,i.e.,IAP is only efficiently produced for certain CEPs,which eliminates the requirement of CEP stabilization.The demonstrated scheme for IAP generation in principle has much higher conversion efficiency than the long-wave driver scheme according to the wavelength scaling law of HHG.Our work suggests an alternative way to generate ultrashort IAPs by applying GDOG on few-cycle free-CEP NIR driving pulses,and is thereby of great importance to facilitate the development of attosecond science and technology.展开更多
Recent advances in selected areas of laser science are briefly reviewed. They include laser technology, coherent control of quantum systems by lasers, X ray generation by ultrashort high intensity laser pulses, and ...Recent advances in selected areas of laser science are briefly reviewed. They include laser technology, coherent control of quantum systems by lasers, X ray generation by ultrashort high intensity laser pulses, and laser spectroscopic studies of surface catalysis in real environment.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFE0134200)the National Natural Science Foundation of China(Grant No.12204214)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.GK202207012)QCYRCXM-2022-241。
文摘Multi-electron and multi-orbital effects play a crucial role in the interaction of strong laser fields with complex molecules.Here,multi-electron effects encompass not only electron-electron Coulomb interactions and exchangecorrelation effects but also the interference between the dynamics of different electron wave packets.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11465016,11674268,and 11764038)
文摘The low-order harmonic generation of hydrogen molecular ion interacting with a linearly polarized laser field has been investigated theoretically by using a simple two-state model. The validity of the two-state model is carefully examined by comparing the harmonic spectra of hydrogen molecular ion obtained from this model with those from the three-dimensional time-dependent Schr¨odinger equation. When combined with the Morlet transform of quantum time-frequency spectrum,the two-state model can be used to study the dynamical origin of the low-order harmonic generation of hydrogen molecular ion driven by low-frequency pulses. In addition, some interesting structures of the time profiles for low order harmonics are obtained.
基金performed at the Chinese Academy of Science Terahertz Science Centersupported by the National Natural Science Foundation of China(Grant No.61988102)
文摘We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed around a single type-ⅡWeyl point,especially at zero frequency.Such a remarkable DC signal is proved to have attributions from the intraband transition after spectral decomposition.Under weak pulse electric field,the linear optical response of a nontilted Weyl cone is consistent with the Kubo theory.With extensive numerical simulations,we conclude that the non-zero chemical potential can enhance the even-order generations,from the slightly tilted system to the over-tilted systems.In consideration of dynamical symmetries,type-Ⅰand type-ⅡWeyl cones also show different selective responses under the circularly polarized light.Finally,using a more realistic model containing two pairs of Weyl points,we demonstrate that paired Weyl points with opposite chirality can suppress the overall even-order generations.
基金Project supported by the National Natural Science Foundation of China （Grant No 10474138） and the National High-Tech Inertial Confinement Fusion Committee in China.
文摘Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation （HHG） of the initial state separately being the ground and excited states is presented. When the hardness parameter a in the soft Coulomb potential V（x） =-1√x^2＋α is chosen to be small enough, the so-called hard Coulomb potential V（x）=1/｜x｜ can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of - 0.5 and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with a = 2 in the same laser field. Laser-induced non-resonant one-photon emission is also observed.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0206004)the National Natural Science Foundation of China(Grant No.11375160)the National Science Instruments Major Project of China(Grant No.2012YQ130125)
文摘The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.
基金supported by the National Natural Science Foundation of Chinaby Special Subject Foundation of Educational Committee of Shanxi Province.
文摘Applying Fourier transform technique to deduction of background and noise on dE/dt-t curve,a new electrochemical method,high order harmonic oscillographic chronopotentiometry is proposed in this paper.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174435,12034020,and 92250303)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-091)the National Key R&D Program of China(Grant No.2022YFA1604200).
文摘Attosecond light pulses have revolutionized the study of electron dynamics in materials by enabling the observation of ultrafast processes with unprecedented attosecond temporal resolution.They are primarily generated through the process of high-order harmonic generation.This paper presents a comprehensive setup for attosecond pulse generation and measurement.Using a 900 nm,7 mJ,and 7 fs femtosecond laser with stabilized carrier-envelope phase,we employ polarization gating to generate a near single-cycle,linearly polarized pulse that interacts with neon gas to produce a broadband extreme-ultraviolet continuum with a cutoff photon energy of∼120 eV.The temporal and spectral characteristics of the generated single attosecond pulses are measured using an attosecond streak camera,and the pulse duration is determined to be 59 as through the frequency-resolved optical gating for complete reconstruction of attosecond bursts retrieval algorithm.As part of the Synergetic Extreme Condition User Facility,this setup will facilitate ultrafast research in transient absorption and photoelectron spectroscopy,providing global users with a powerful tool for studying electron dynamics in various materials.
基金supported by National Natural Science Foundation of China(Grants Nos.12450402,12134005,92250306,11627807,and 12274230)the National Basic Research Program of China(No.2019YFA0307700)+1 种基金Funding of Nanjing University of Science and Technology(NJUST)(No.TSXK2022D005)the Fundamental Research Funds for the Central Universities.
文摘Generating Bessel-Gauss beams in the extreme ultraviolet(EUV)with attosecond pulse durations poses a significant challenge due to the limitations of conventional transmission optical components.Here,we propose a novel approach to produce such beams by inducing an annular EUV source through high-order harmonic generation(HHG)under nonadiabatic phase-matching conditions.The resulting light pulse maintains temporal coherence and manifests attosecond pulse trains as confirmed by the reconstruction of attosecond beating by interference of two-photon transitions(RABBIT)measurements.Macroscopic HHG calculations reproduce the measured spatiotemporal structures,demonstrating the plasma-induced spatial modulation on the formation of an annular source.Propagation simulations further confirm the feasibility of this approach for generating attosecond Bessel-Gauss beams,presenting exciting prospects for various applications in EUV photonics and attosecond science.
文摘To measure the signals with high freq u ency(>500 MHz),a sampling frequency down conversion method is introduced.This pa per analyzes the intermodulation signals and figures out the relationship betwee n the intermodulation signal and intermediate frequenc y signal.Based on the frequency conversion technology,an exclusion algorithm i s proposed a nd the actual implementation of the algorithm is given.The application resu lts show that the exclusion algorithm can identify the intermodulation signal exactly and eliminate the bad influence on the frequency measurement.
基金supported by the BCUD University of Pune,India under Grant No.BCUD/OSD/184 as two year contract & Greaves Cotton Ltd (DEU) Pune
文摘A model of fuel injection adjustment for balancing the 4-stroke six cylinder diesel engine coupling geneset is developed by detecting imbalance in operating engine by the frequency analysis of the crankshaft＇s speed variation. In this work, the crankshaft is considered to be a rigid body, so that the variation of its angular speed could be directly correlated to the total gas-pressure torque. By analyzing only the lower harmonic orders, the speed variation spectrum can filter out the distortions produced by the dynamic response of the crankshaft. The information carried by these harmonic orders permits to establish correlations between measurements and the average gas pressure torque of the engine, and to detect imbalance and identify faulty cylinders. Detailed experimental reading are taken on diesel engine coupling genset on the test bed of Greaves Cotton Ltd Pane, India.
基金Item Sponsored by National Natural Science Foundation of China(61171145,11274226)
文摘P91 steel is an important bearing material used in nuclear power plants. The study of its mechanical degradation behavior is important for ensuring safe operation. The relationship between the dislocation density of P91 steel under different strains and the corresponding nonlinear ultrasonic parameter β was studied. The dislocation density of strained samples was estimated by X-ray diffraction. Nonlinear ultrasonic testing was conducted to evaluate β, showing that this value increased with increasing dislocation density induced by different tensile elongations. It was shown that the ultrasonic secondharmonic generation technique can effectively evaluate the degradation behavior of metallic materials, and the prediction of the residual life of bearing parts in service can be made based on β and the dislocation density.
文摘Applications using higher orderharmonics (HOH) require knowledge ofthe completeness ofthe HOHfor the diffusion difference equation.This papershowsthatthe set of HOHforthefission sourceis complete ,butthat the setfortheflux usingthe multi group modelis notcomplete .This paperusesthe assumption thatthe set offlux vectors of HOHfor every group is complete. This assumption can be proven only forthose groups into which noscattering neutrons enter.However,itisalso shownto betrueforseveralpracticalreactor models.Analysisshows thatthe number of HOHwith non zero eigenvaluesis equaltothe numberofdifference meshes withfissile material, and thatthe eigenvalues have positive realvalues.This assumptionis valuablefor HOHapplications,butrequires furthertheoreticalstudyto verify whetheritisuniversally applicable.
文摘This paper proposes a flux mapping method directly using the higher order harmonics (HOH) of the neutronics equation of the nominal core. The bi-orthogonality and completeness of the HOH set are studied. and they are the theoretical basis for the flux mapping method. Using the bi-orthogonality of HOH and the strict formula for eigenvalue estimation. the process and formulas for HOH calculation called as the source iteration method with source correction are derived. The analysis can predict any order of harmonics for 2-or 3-dimensional geometries.Preliminary verification of the capability for flux mapping is also given. and other applications of HOH for reactor operation analysis and failure diagnosis are underway.
基金supported in part by the Minerva FoundationIsrael Science Foundation (ISF) Bikura foundation
文摘A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented.The method exploits second-harmonic generation and can be adapted for different laser arrays geometries.Experimental and calculated results,presented for negatively coupled lasers formed in a square,honeycomb,and triangular geometries are in good agreement.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFB0405202)the Major Program of the National Natural Science Foundation of China(Grant No.61690221)+1 种基金the Key Program of the National Natural Science Foundation of China(Grant No.11434016)the National Natural Science Foundation of China(Grant Nos.11574384,11674386,and 11774277)
文摘We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were focused onto an argon filled gas cell.We detected high order harmonics corresponding to a train of 209 as pulses,characterized by the reconstruction of attosecond beating by interference of two-photon transition(RABITT)technique.Compared with the conventional attosecond pulse trains,the broad harmonics in such pulse trains cover more energy range,so it is more efficient in studying some typical cases,such as resonances,with frequency resolved RABITT.As the solid thin plates can support high power supercontinuum generation,it is feasible to tailor the spectrum to have different central wavelength and spectral width,which will make the RABITT source work in different applications.
基金This work was supported by the National Natural Science Foundation of China(No.10575097 and 60473133)the 100 Talents Programme of the Chinese Academy of Sciences+1 种基金the National Basic Research Program of China(No.2006CB303102)Specialized Research Fund for the Doctoral Program of Higher Education(No.20060358050).
文摘The synchrotron radiation spectra of the spherical grating monochromator(SGM)working in the soft X-ray and VUV region are often contaminated by significant amounts of higher order harmonics.They cannot be suppressed completely by suitable filters.Higher order contributions in the spectral radiation standard and metrology beamline were researched using transmission grating(made in-house)and IRD AXUV100G(USA)photodiode detector.The exit beam was dispersed with the transmission grating behind the exit slit of the monochromator,and the contributions of the different orders were analyzed.The higher order distributions were quantitatively determined for three gratings with line densities of 1800,600 and 200 l/mm.Experiment results show that in wavelengths between 5 nm and 15 nm the contributions of the higher orders to the detector signal are restricted to less than 7%even without the use of filters.In wavelength regions between 5 nm and 34 nm,the contributions of the higher orders to the detector signal are less than 14%with proper Al,Si_(3)N_(4) and Zr filters,and after being modified by quantum efficiency of the detector,the higher order contributions are restricted to less than 6.5%.The study also shows that higher orders are almost totally suppressed by MgF_(2) filter when the wavelength ranges between 115–140 nm.
基金support from the National Key Research and Development Program of China(grant no.2023YFA1407100)Guangdong Province Science and Technology Major Project(Future functional materials under extreme conditions-2021B0301030005)the Guangdong Natural Science Foundation(General Program project no.2023A1515010871).
文摘Interferometric measurements of high harmonics induced by multiple laser fields represent a burgeoning field of research,offering prospects for optimized harmonic yield and enabling time-and space-resolved nonlinear spectroscopy.While most investigations have focused on controlling the time delay between pulses,our study introduces a novel approach.By manipulating an additional parameter—the phase difference between the fields—we unveil detailed insights into the physical mechanisms governing the ultrafast processes underlying high harmonic generation.Leveraging high harmonic 2-dimensional interferograms,our method facilitates the streamlined analysis of attosecond electron dynamics in complex molecules and solids,marking an important advancement in this rapidly evolving field.
基金funding from the European Union through the FET Open project EXTREME IR(944735)by the Italian Ministry of University and Research through the PNRR project PE0000023-NQSTI+1 种基金the UK Research and Innovation councils through the grant‘NAME’(EP/V001914/1)The samples were grown in the Royce Deposition system at the University of Leeds,which was funded by the Henry Royce Institute,UK,through grant EP/P022464/1.
文摘High-order harmonic generation(HHG)in solids—the frequency up-conversion of an optical signal—is governed by symmetries.At terahertz(THz)frequencies,HHG is a key technology to access high-frequency spectral windows that are usually difficult to cover using conventional solid-state laser technologies.This effect has been recently exploited in graphene,where HHG has been demonstrated,albeit only at odd multiples of the driving frequency owing to its inherent centro-symmetry.In topological insulators(TIs),the combination of spin–orbit interaction and time-reversal symmetry create an insulating bulk state with an inverted band order,inseparably connected with conducting surface states.TIs have been predicted to support unconventional high harmonic generation from the bulk and topological surface,which are usually difficult to distinguish.However,no experimental results have been reported,so far.Here,we exploit the strong optical field amplification provided by an array of single or double split ring resonators,with embedded Bi_(2)Se_(3)or(In_(x)Bi_((1−x)))_(2)Se_(3)/Bi_(2)Se_(3)Van der Waals heterostructures,to achieve up-conversion in the 6.4(even)–9.7(odd)THz frequency range.This results from bulk centro-symmetry(odd states)and symmetry breaking in the topological surface states(odd and even).
基金supported by the National Key Research and Development Program of China(grant no.2019YFA0307703)the Major Research Plan of the National Natural Science Foundation of China(grant no.91850201)the National Natural Science Foundation of China(grant nos.12234020 and 11974426).
文摘Ultrashort laser pulses can serve as fast probes to record instant events.The isolated attosecond pulses(IAPs)generated from high-order harmonic generation(HHG)have been shortened down to about 2 atomic units in time,empowering us to study quantum behaviors of electrons in atoms,molecules,and solids with unprecedented time resolution.Following the cutoff energy law of HHG,the shortest IAP reported so far is driven with short-wavelength infrared(SWIR)pulses,which require additional broadband frequency conversion techniques and raise the bar for attosecond researches.Here,we show that with fewcycle near-infrared(NIR)laser pulses,IAP with pulse duration of 51±4 as is generated during 1-fs linear polarization gate formed by generalized double optical gating(GDOG)technique.The characterization is done with attosecond streak camera,and phase reconstruction is performed with quick phase retrieval by omega oscillation filtering(qPROOF).Furthermore,we show that the IAP generation favors certain carrier envelope phases(CEPs)in the narrow gate,i.e.,IAP is only efficiently produced for certain CEPs,which eliminates the requirement of CEP stabilization.The demonstrated scheme for IAP generation in principle has much higher conversion efficiency than the long-wave driver scheme according to the wavelength scaling law of HHG.Our work suggests an alternative way to generate ultrashort IAPs by applying GDOG on few-cycle free-CEP NIR driving pulses,and is thereby of great importance to facilitate the development of attosecond science and technology.
文摘Recent advances in selected areas of laser science are briefly reviewed. They include laser technology, coherent control of quantum systems by lasers, X ray generation by ultrashort high intensity laser pulses, and laser spectroscopic studies of surface catalysis in real environment.
