Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ens...Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ensures the distance between the laser and samples.In the present work,we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys.It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum.Nevertheless,the fine quantitation was only realized at the position where the air emission(e.g.O(I)777.4 nm)reached intensity maximum,and also in this way,a repeatable quantitation was successfully achieved even after 120 days.The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser,and spectra-assisted focusing could be a simple way to find the identical condition for different samples’detection.In the future,this method might be applicable in field measurements for LIBS analysis of solids.展开更多
Ultra-intense electromagnetic fields exceeding 10^(23)W∕cm^(2)are enabling breakthroughs in compact laser-driven particle accelerators and revealing new quantum electrodynamics(QED)phenomena.However,conventional lase...Ultra-intense electromagnetic fields exceeding 10^(23)W∕cm^(2)are enabling breakthroughs in compact laser-driven particle accelerators and revealing new quantum electrodynamics(QED)phenomena.However,conventional laser-focusing methods face considerable engineering challenges and require substantial costs.Focusing schemes utilizing plasma optics can produce sub-micrometer focus spots beyond the diffraction limit and substantially enhance the peak intensity;however,owing to significant energy dissipation,they may fail to simultaneously increase the laser fluence.To address these challenges,we propose a focusing scheme employing a near-critical-density hollow plasma fiber(HPF)that utilizes graded refractive index dynamics to boost both laser peak intensity and fluence at the same time.Three-dimensional particle-in-cell simulations demonstrate the HPF’s capability to focus a 4.5-μm-diameter Gaussian beam to a sub-diffraction-limited 0.6-μm-diameter spot.The peak intensity and laser fluence can be enhanced by factors of 22 and 10,respectively,marking a substantial improvement over existing plasma-based focusing schemes.Furthermore,the proposed scheme exhibits wide-range parameter adaptation and high robustness,making it suitable for direct implementation in PW-class ultra-intense laser experiments.展开更多
The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave...The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave, a non-stationary flow was induced in the small space between the parallel plates. The spherical and cylindrical shock propagations were observed with schlieren method. The shock Mach number decreases with time and approaches to unity. As reported in the previous investigations, the shock speed was attenuated in a short distance and time. In the present experiment, It was not found a remarkable difference in the shock speed between the spherical and cylindrical shock experiments. Subsequently, the flow induced by the cylindrical shock wave was studied using PIV technique. A smoke tracer was used in the experiment and its velocity was measured within 100 μs. A numerical simulation was carried out to investigate the momentum relaxation between the gas and smoke particle. A suitable shock initiation model was introduced in the simulation. The experimental results show that a wide acceleration and deceleration zone exist behind the shock wave. Also, the relaxation distance in the experimental data is much longer than that in numerical simulation.展开更多
Accurate prediction of hypersonic boundary-layer transition plays an important role in thermal protection system design of hypersonic vehicles.Restricted by the capability of spatial diagnostics for hypersonic boundar...Accurate prediction of hypersonic boundary-layer transition plays an important role in thermal protection system design of hypersonic vehicles.Restricted by the capability of spatial diagnostics for hypersonic boundary-layer study,quite a lot of problems of hypersonic boundary-layer transition,such as nonlinearity and receptivity,remain outstanding.This work reports the application of focused laser differential interferometer to instability wave development across hypersonic boundary-layer on a flared cone model.To begin with,the focused laser differential interferometer is designed and set up in a Mach number 6 hypersonic quiet wind tunnel with the focal point in the laminar boundary-layer of a 5 degree half-angle flared cone model.Afterwards,instability experiments are carried out by traversing the focal point throughout the hypersonic boundary-layer and the density fluctuation along the boundary-layer profile is measured and analyzed.The results show that three types of instability waves ranging from 10 k Hz to over 1 MHz are co-existing in the hypersonic boundary-layer,indicating the powerful capability of focused laser differential interferometer in dynamic response resolution for instability wave study in hypersonic flow regime;furthermore,quantitative analyses including spectra and bicoherence analysis of instability waves throughout the hypersonic boundary-layer for both cold and heated cone models are performed.展开更多
Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-...Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-color waveform on generation of macroscopic HHG in soft x-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which “short”-or “long”-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of the two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for modification of two-color waveform upon propagation. This work can be used to find better macroscopic conditions for generating soft x-ray HHG by employing two-color optimized waveforms.展开更多
Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of ...Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.展开更多
The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on th...The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on the electron radiation power in the time domain is studied systematically.An asymmetric bimodal structure is found in the time domain in the direction of the maximum radiation.For this special structure,an explanation is given based on the electron dynamics perspective.The structure is compared with the symmetric bimodal structure in the classical theory.The increase in laser intensity,while significantly increasing the radiated power of the electron,exacerbates the asymmetry of the electron radiation.The variation in the initial phase of the laser leads to a periodic variation in the electron motion,which results in a periodic extension of the electron spatial radiation with a period ofπ.Moreover,the existence of jump points with a phase difference ofπin the range of 0-2πis found.The increase in pulse width reduces the radiated power,extends the radiation range,and alleviates the radiation asymmetry.The results in this paper contribute to the study of electron radiation characteristics in intense laser fields.展开更多
By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser ...By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser diffraction,pump depletion,and electron dephasing which are always suffered in usual LWFA.The scheme thus has the potentiality to accelerate electrons to Te V energy in a single acceleration stage.However,the controlled electron injection has not been self-consistently included in such schemes.Only external injection was suggested in previous theoretical studies,which requires other accelerators and is relatively difficulty to operate.Here,we numerically study the actively controlled density transition injection in phase-locked LWFA to get appropriate density profiles for amount of electron injection.The study shows that compared with LWFA driven by lasers with fixed focus,a larger plasma density gradient is necessary.Electrons experience both transverse and longitudinal loss during acceleration due to the superluminal group velocity of the driver and the variation of the wakefield structure.Furthermore,the periodic deformation and fracture of the flying focus laser in the high-density plasma plateau make the final injected charge also depend on the beginning position of the density downramp.Our studies show a possible way for amount of electron injection in LWFA driven by flying focus lasers.展开更多
This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circ...This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.展开更多
A highly focused beam with spot radius of around 1 ktm and enhanced light intensity is obtained by using an open hollow cone. Two-dimensional and three-dimensional finite-difference time-domain simulations are perform...A highly focused beam with spot radius of around 1 ktm and enhanced light intensity is obtained by using an open hollow cone. Two-dimensional and three-dimensional finite-difference time-domain simulations are performed for clarifying light propagation characteristics and the cone geometry dependence of the cone-focused laser light. Two important parameters characterizing the cone-focusing effect are introduced, which are opening angle and cone tip size. By changing these parameters, the laser intensification, field spatial distribution at the cone tip and the near-field transmission can be controlled. Understanding this is quite important in designing the optimum cone shape for fast ignition and determining the basis for using hollow cone targets as devices for generating high energy charged particles.展开更多
A study of the structure of the electric and magnetic fields of ultraintense laser pulses focused by an off-axis parabolic mirror is reported. At first, a theoretical model is laid out, whose final equations integrati...A study of the structure of the electric and magnetic fields of ultraintense laser pulses focused by an off-axis parabolic mirror is reported. At first, a theoretical model is laid out, whose final equations integration allows the space and time structure of the fields to be retrieved. The model is then employed to investigate the field patterns at different times within the optical cycle, for off-axis parabola parameters normally employed in the context of ultraintense laser–plasma interaction experiments. The results show that nontrivial, complex electromagnetic field patterns are observed at the time at which the electric and magnetic fields are supposed to vanish. The importance of this effect is then studied for different laser polarizations, f numbers and off-axis angles.展开更多
We demonstrate a configuration optimization process of an off-axis parabolic mirror to maximize the focused peak intensity based on a precise knowledge of the tight focusing properties by using a full vector-diffracti...We demonstrate a configuration optimization process of an off-axis parabolic mirror to maximize the focused peak intensity based on a precise knowledge of the tight focusing properties by using a full vector-diffraction theory and obtain an optimum configuration scaling rule, which makes it possible to achieve the maximum peak intensity. In addition, we also carry out an assessment analysis of the offset and off-axis angle tolerances corresponding to a 5% drop of the maximum focused peak intensity and present scaling laws for the tolerances of the offset and off-axis angle. Understanding these scaling laws is important to enhance the focusability of a laser beam by an off-axis parabolic mirror in the optimum configuration, in particular, which is valuable for structural design and selection of an off-axis parabolic mirror in ultrashort and ultraintense laser–matter interaction experiments.展开更多
We present the main features of the ultrashort, high-intensity laser installation at the Intense Laser Irradiation Laboratory(ILIL) including laser, beam transport and target area specifications. The laboratory was de...We present the main features of the ultrashort, high-intensity laser installation at the Intense Laser Irradiation Laboratory(ILIL) including laser, beam transport and target area specifications. The laboratory was designed to host laser–target interaction experiments of more than 220 TW peak power, in flexible focusing configurations, with ultrarelativistic intensity on the target. Specifications have been established via dedicated optical diagnostic assemblies and commissioning interaction experiments. In this paper we give a summary of laser specifications available to users,including spatial, spectral and temporal contrast features. The layout of the experimental target areas is presented, with attention to the available configurations of laser focusing geometries and diagnostics. Finally, we discuss radiation protection measures and mechanical stability of the laser focal spot on the target.展开更多
Normal-mode splitting is a hallmark of strong coupling between two coupled harmonic oscillators.Here,we report the realization of strong coupling in the optically-levitated nanoparticle system via feedback.A silica na...Normal-mode splitting is a hallmark of strong coupling between two coupled harmonic oscillators.Here,we report the realization of strong coupling in the optically-levitated nanoparticle system via feedback.A silica nanoparticle is trapped by a tightly focused laser travelling in free space,which is regarded as a harmonic oscillators.An external electric oscillator is then phase-locked to the nanoparticle’s motion as another harmonic oscillator,which is modulated on the trapping laser to feedback and interact with the nanoparticle.Therefore,a highly manipulatable coupled-harmonic oscillator system is built in our platform and the normal-mode splitting is realized with strong coupling in both Hermitian and non-Hermitian cases.Moreover,since the coupling between the two harmonic oscillators induced by the feedback is flexibly manipulated,the normal-mode splitting following the cooling or heating effect is simultaneously observed.This method could be useful for further studying quantum mechanical Hamiltonian and non-Hermitian phenomena of an optically-levitated nanoparticle.展开更多
基金financially supported by the Provincial Key Research and Development Program of Shandong,China(No.2019GHZ010)the Natural Science Foundation of Shandong Province(No.ZR2020MF123)+1 种基金National Natural Science Foundation of China(Nos.61975190 and12174359)the Fundamental Research Funds for the Central Universities(No.202161002)。
文摘Laser-induced breakdown spectroscopy(LIBS)is a capable technique for elementary analysis,while LIBS quantitation is still under development.In quantitation,precise laser focusing plays an important role because it ensures the distance between the laser and samples.In the present work,we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys.It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum.Nevertheless,the fine quantitation was only realized at the position where the air emission(e.g.O(I)777.4 nm)reached intensity maximum,and also in this way,a repeatable quantitation was successfully achieved even after 120 days.The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser,and spectra-assisted focusing could be a simple way to find the identical condition for different samples’detection.In the future,this method might be applicable in field measurements for LIBS analysis of solids.
基金supported by the National Grand Instrument Project(Grant No.2019YFF01014402)the National Key Research and Development Program of China(Grant No.2024YFF0726304)+2 种基金the Guangdong High Level Innovation Research Institute(Grant No.2021B0909050006)the National Natural Science Foundation of China(Grant No.12205008)W.Ma acknowledges support from the National Science Fund for Distinguished Young Scholars(Grant No.12225501)。
文摘Ultra-intense electromagnetic fields exceeding 10^(23)W∕cm^(2)are enabling breakthroughs in compact laser-driven particle accelerators and revealing new quantum electrodynamics(QED)phenomena.However,conventional laser-focusing methods face considerable engineering challenges and require substantial costs.Focusing schemes utilizing plasma optics can produce sub-micrometer focus spots beyond the diffraction limit and substantially enhance the peak intensity;however,owing to significant energy dissipation,they may fail to simultaneously increase the laser fluence.To address these challenges,we propose a focusing scheme employing a near-critical-density hollow plasma fiber(HPF)that utilizes graded refractive index dynamics to boost both laser peak intensity and fluence at the same time.Three-dimensional particle-in-cell simulations demonstrate the HPF’s capability to focus a 4.5-μm-diameter Gaussian beam to a sub-diffraction-limited 0.6-μm-diameter spot.The peak intensity and laser fluence can be enhanced by factors of 22 and 10,respectively,marking a substantial improvement over existing plasma-based focusing schemes.Furthermore,the proposed scheme exhibits wide-range parameter adaptation and high robustness,making it suitable for direct implementation in PW-class ultra-intense laser experiments.
文摘The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave, a non-stationary flow was induced in the small space between the parallel plates. The spherical and cylindrical shock propagations were observed with schlieren method. The shock Mach number decreases with time and approaches to unity. As reported in the previous investigations, the shock speed was attenuated in a short distance and time. In the present experiment, It was not found a remarkable difference in the shock speed between the spherical and cylindrical shock experiments. Subsequently, the flow induced by the cylindrical shock wave was studied using PIV technique. A smoke tracer was used in the experiment and its velocity was measured within 100 μs. A numerical simulation was carried out to investigate the momentum relaxation between the gas and smoke particle. A suitable shock initiation model was introduced in the simulation. The experimental results show that a wide acceleration and deceleration zone exist behind the shock wave. Also, the relaxation distance in the experimental data is much longer than that in numerical simulation.
基金the State Key Laboratory for Turbulence&Complex Systems of Peking University for their support in this studysupport of National Numerical Wind-tunnel(No.2018-ZT1A03)+1 种基金National Natural Science Foundation of China grant(No.11702106)Fundamental Research Funds for the Central Universities(2019kfyXKJC001)。
文摘Accurate prediction of hypersonic boundary-layer transition plays an important role in thermal protection system design of hypersonic vehicles.Restricted by the capability of spatial diagnostics for hypersonic boundary-layer study,quite a lot of problems of hypersonic boundary-layer transition,such as nonlinearity and receptivity,remain outstanding.This work reports the application of focused laser differential interferometer to instability wave development across hypersonic boundary-layer on a flared cone model.To begin with,the focused laser differential interferometer is designed and set up in a Mach number 6 hypersonic quiet wind tunnel with the focal point in the laminar boundary-layer of a 5 degree half-angle flared cone model.Afterwards,instability experiments are carried out by traversing the focal point throughout the hypersonic boundary-layer and the density fluctuation along the boundary-layer profile is measured and analyzed.The results show that three types of instability waves ranging from 10 k Hz to over 1 MHz are co-existing in the hypersonic boundary-layer,indicating the powerful capability of focused laser differential interferometer in dynamic response resolution for instability wave study in hypersonic flow regime;furthermore,quantitative analyses including spectra and bicoherence analysis of instability waves throughout the hypersonic boundary-layer for both cold and heated cone models are performed.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.91950102,12274230,and 11834004)the Funding of Nanjing University of Science and Technology (Grant No.TSXK2022D005)。
文摘Synthesis of multi-color laser pulses has been developed as a promising way to improve low conversion efficiency of high-order harmonic generation(HHG). Here we systematically study the effect of laser focus in a two-color waveform on generation of macroscopic HHG in soft x-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which “short”-or “long”-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of the two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for modification of two-color waveform upon propagation. This work can be used to find better macroscopic conditions for generating soft x-ray HHG by employing two-color optimized waveforms.
基金suported by the National Natural Science Foundation of China (Grant No. 10874242)the National Basic Research Program of China (973 Program) (Grant No. 2007CB815105)Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070290008)
文摘Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10947170/A05 and 11104291)Natural Science Fund for Colleges and Universities in Jiangsu Province (Grant No.10KJB140006)+2 种基金Natural Science Foundation of Shanghai (Grant No.11ZR1441300)Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant No.NY221098)sponsored by the Jiangsu Qing Lan Project and STITP Project (Grant No.CXXYB2022516)。
文摘The nonlinear radiation of the electron is a distinctive feature of the action of tightly focused linearly polarized lasers.In this paper,from the perspective of radiation symmetry,the effect of laser parameters on the electron radiation power in the time domain is studied systematically.An asymmetric bimodal structure is found in the time domain in the direction of the maximum radiation.For this special structure,an explanation is given based on the electron dynamics perspective.The structure is compared with the symmetric bimodal structure in the classical theory.The increase in laser intensity,while significantly increasing the radiated power of the electron,exacerbates the asymmetry of the electron radiation.The variation in the initial phase of the laser leads to a periodic variation in the electron motion,which results in a periodic extension of the electron spatial radiation with a period ofπ.Moreover,the existence of jump points with a phase difference ofπin the range of 0-2πis found.The increase in pulse width reduces the radiated power,extends the radiation range,and alleviates the radiation asymmetry.The results in this paper contribute to the study of electron radiation characteristics in intense laser fields.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11991074,12225505 and12135009)。
文摘By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser diffraction,pump depletion,and electron dephasing which are always suffered in usual LWFA.The scheme thus has the potentiality to accelerate electrons to Te V energy in a single acceleration stage.However,the controlled electron injection has not been self-consistently included in such schemes.Only external injection was suggested in previous theoretical studies,which requires other accelerators and is relatively difficulty to operate.Here,we numerically study the actively controlled density transition injection in phase-locked LWFA to get appropriate density profiles for amount of electron injection.The study shows that compared with LWFA driven by lasers with fixed focus,a larger plasma density gradient is necessary.Electrons experience both transverse and longitudinal loss during acceleration due to the superluminal group velocity of the driver and the variation of the wakefield structure.Furthermore,the periodic deformation and fracture of the flying focus laser in the high-density plasma plateau make the final injected charge also depend on the beginning position of the density downramp.Our studies show a possible way for amount of electron injection in LWFA driven by flying focus lasers.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10947170/A05 and 11104291)the Natural Science Fund for Colleges and Universities in Jiangsu Province (Grant No.10KJB140006)+2 种基金the Natural Sciences Foundation of Shanghai (Grant No.11ZR1441300)the Natural Science Foundation of Nanjing University of Posts and Telecommunications (Grant No.NY221098)the Jiangsu Qing Lan Project for their sponsorship。
文摘This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings,when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.
基金supported by the National Basic Research Program of China(Grant No.61359020101-3)the National High Technology ResearchDevelopment Program for Inertial Confinement Fusion of China
文摘A highly focused beam with spot radius of around 1 ktm and enhanced light intensity is obtained by using an open hollow cone. Two-dimensional and three-dimensional finite-difference time-domain simulations are performed for clarifying light propagation characteristics and the cone geometry dependence of the cone-focused laser light. Two important parameters characterizing the cone-focusing effect are introduced, which are opening angle and cone tip size. By changing these parameters, the laser intensification, field spatial distribution at the cone tip and the near-field transmission can be controlled. Understanding this is quite important in designing the optimum cone shape for fast ignition and determining the basis for using hollow cone targets as devices for generating high energy charged particles.
基金support from the EU’s Horizon 2020 research and innovation programme through the project ‘EuPRAXIA’(grant agreement No.653782)from the Italian Ministry of Education,University and Research(MIUR)through the PRIN project‘Preclinical Tool for Advanced Translational Research with Ultrashort and Ultraintense xray Pulses’(prot.20154F48P9)from the MIUR through the research network funding ELI-Italy(‘Attoseconds’)
文摘A study of the structure of the electric and magnetic fields of ultraintense laser pulses focused by an off-axis parabolic mirror is reported. At first, a theoretical model is laid out, whose final equations integration allows the space and time structure of the fields to be retrieved. The model is then employed to investigate the field patterns at different times within the optical cycle, for off-axis parabola parameters normally employed in the context of ultraintense laser–plasma interaction experiments. The results show that nontrivial, complex electromagnetic field patterns are observed at the time at which the electric and magnetic fields are supposed to vanish. The importance of this effect is then studied for different laser polarizations, f numbers and off-axis angles.
基金supported by the Science Foundation for the Youth Scholars of Minjiang University (No. Mj9n201602)the National Science and Technology Major Project of the Ministry of Science and Technology of China。
文摘We demonstrate a configuration optimization process of an off-axis parabolic mirror to maximize the focused peak intensity based on a precise knowledge of the tight focusing properties by using a full vector-diffraction theory and obtain an optimum configuration scaling rule, which makes it possible to achieve the maximum peak intensity. In addition, we also carry out an assessment analysis of the offset and off-axis angle tolerances corresponding to a 5% drop of the maximum focused peak intensity and present scaling laws for the tolerances of the offset and off-axis angle. Understanding these scaling laws is important to enhance the focusability of a laser beam by an off-axis parabolic mirror in the optimum configuration, in particular, which is valuable for structural design and selection of an off-axis parabolic mirror in ultrashort and ultraintense laser–matter interaction experiments.
基金The ILIL-PW upgrade was established in the framework of the Italian Research Network on Extreme Light Infrastructure(ELI-Italy)funded by CNRfinancial contribution from the Eu PRAXIA project of the EU Horizon 2020 Research and Innovation Program under Grant Agreement No.653782the Line for Laser Light Ion Acceleration(L3IA)project funded by INFN,Italy。
文摘We present the main features of the ultrashort, high-intensity laser installation at the Intense Laser Irradiation Laboratory(ILIL) including laser, beam transport and target area specifications. The laboratory was designed to host laser–target interaction experiments of more than 220 TW peak power, in flexible focusing configurations, with ultrarelativistic intensity on the target. Specifications have been established via dedicated optical diagnostic assemblies and commissioning interaction experiments. In this paper we give a summary of laser specifications available to users,including spatial, spectral and temporal contrast features. The layout of the experimental target areas is presented, with attention to the available configurations of laser focusing geometries and diagnostics. Finally, we discuss radiation protection measures and mechanical stability of the laser focal spot on the target.
基金supported by National Natural Science Foundation of China(Grant No.11234008,11361161002,61975101,61571276,11654002).
文摘Normal-mode splitting is a hallmark of strong coupling between two coupled harmonic oscillators.Here,we report the realization of strong coupling in the optically-levitated nanoparticle system via feedback.A silica nanoparticle is trapped by a tightly focused laser travelling in free space,which is regarded as a harmonic oscillators.An external electric oscillator is then phase-locked to the nanoparticle’s motion as another harmonic oscillator,which is modulated on the trapping laser to feedback and interact with the nanoparticle.Therefore,a highly manipulatable coupled-harmonic oscillator system is built in our platform and the normal-mode splitting is realized with strong coupling in both Hermitian and non-Hermitian cases.Moreover,since the coupling between the two harmonic oscillators induced by the feedback is flexibly manipulated,the normal-mode splitting following the cooling or heating effect is simultaneously observed.This method could be useful for further studying quantum mechanical Hamiltonian and non-Hermitian phenomena of an optically-levitated nanoparticle.
