We investigate the dynamics of convergent shock compression in solid cylindrical targets irradiated by an ultrafast relativistic laser pulse.Our particle-in-cell simulations and coupled hydrodynamic simulations reveal...We investigate the dynamics of convergent shock compression in solid cylindrical targets irradiated by an ultrafast relativistic laser pulse.Our particle-in-cell simulations and coupled hydrodynamic simulations reveal that the compression process is initiated by both magnetic pressure and surface ablation associated with a strong transient surface return current with density of the order of 10^(17) A/m^(2) and lifetime of 100 fs.The results show that the dominant compression mechanism is governed by the plasma β,i.e.,the ratio of thermal pressure to magnetic pressure.For targets with small radius and low atomic number Z,the magnetic pressure is the dominant shock compression mechanism.According to a scaling law,as the target radius and Z increase,the surface ablation pressure becomes the main mechanism generating convergent shocks.Furthermore,an indirect experimental indication of shocked hydrogen compression is provided by optical shadowgraphy measurements of the evolution of the plasma expansion diameter.The results presented here provide a novel basis for the generation of extremely high pressures exceeding Gbar(100 TPa)to enable the investigation of high-pressure physics using femtosecond J-level laser pulses,offering an alternative to nanosecond kJ-laser pulse-driven and pulsed power Z-pinch compression methods.展开更多
In ultra-short laser pulses,small changes in dispersion properties before the final focusing mirror can lead to severe pulse distortions around the focus and therefore to very different pulse properties at the point o...In ultra-short laser pulses,small changes in dispersion properties before the final focusing mirror can lead to severe pulse distortions around the focus and therefore to very different pulse properties at the point of laser±matter interaction,yielding unexpected interaction results.The mapping between far-and near-field laser properties intricately depends on the spatial and angular dispersion properties as well as the focal geometry.For a focused Gaussian laser pulse under the influence of angular,spatial and group-delay dispersion,we derive analytical expressions for its pulse-front tilt,duration and width from a fully analytic expression for its electric field in the time±space domain obtained with scalar diffraction theory.This expression is not only valid in and near the focus but also along the entire propagation distance from the focusing mirror to the focus.Expressions relating angular,spatial and group-delay dispersion before focusing at an off-axis parabola,where they are well measurable,to the respective values in the pulse’s focus are obtained by a ray tracing approach.Together,these formulas are used to show in example setups that the pulse-front tilts of lasers with small initial dispersion can become several tens of degrees larger in the vicinity of the focus while being small directly in the focus.The formulas derived here provide the analytical foundation for observations previously made in numerical experiments.By numerically simulating Gaussian pulse propagation and measuring properties of the pulse at distances several Rayleigh lengths off the focus,we verify the analytic expressions.展开更多
Laser-driven ion sources are a rapidly developing technology producing high energy,high peak current beams.Their suitability for applications,such as compact medical accelerators,motivates development of robust accele...Laser-driven ion sources are a rapidly developing technology producing high energy,high peak current beams.Their suitability for applications,such as compact medical accelerators,motivates development of robust acceleration schemes using widely available repetitive ultraintense femtosecond lasers.These applications not only require high beam energy,but also place demanding requirements on the source stability and controllability.This can be seriously affected by the laser temporal contrast,precluding the replication of ion acceleration performance on independent laser systems with otherwise similar parameters.Here,we present the experimental generation of>60 MeV protons and>30 MeV u-1 carbon ions from sub-micrometre thickness Formvar foils irradiated with laser intensities>1021 Wcm2.Ions are accelerated by an extreme localised space charge field≥30TVm-1,over a million times higher than used in conventional accelerators.The field is formed by a rapid expulsion of electrons from the target bulk due to relativistically induced transparency,in which relativistic corrections to the refractive index enables laser transmission through normally opaque plasma.We replicate the mechanism on two different laser facilities and show that the optimum target thickness decreases with improved laser contrast due to reduced pre-expansion.Our demonstration that energetic ions can be accelerated by this mechanism at different contrast levels relaxes laser requirements and indicates interaction parameters for realising application-specific beam delivery.展开更多
We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute,National Institutes for Quantum Science and Technology.The reflectivity ...We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute,National Institutes for Quantum Science and Technology.The reflectivity of the single plasma mirror system exceeded 80%.In addition,the temporal contrast was improved by two orders of magnitude at 1 ps before the main pulse.Furthermore,the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm^(2).We also present the results of investigating the difference and the fluctuation in energy,pulse width and pointing stability with and without the plasma mirror system.展开更多
文摘We investigate the dynamics of convergent shock compression in solid cylindrical targets irradiated by an ultrafast relativistic laser pulse.Our particle-in-cell simulations and coupled hydrodynamic simulations reveal that the compression process is initiated by both magnetic pressure and surface ablation associated with a strong transient surface return current with density of the order of 10^(17) A/m^(2) and lifetime of 100 fs.The results show that the dominant compression mechanism is governed by the plasma β,i.e.,the ratio of thermal pressure to magnetic pressure.For targets with small radius and low atomic number Z,the magnetic pressure is the dominant shock compression mechanism.According to a scaling law,as the target radius and Z increase,the surface ablation pressure becomes the main mechanism generating convergent shocks.Furthermore,an indirect experimental indication of shocked hydrogen compression is provided by optical shadowgraphy measurements of the evolution of the plasma expansion diameter.The results presented here provide a novel basis for the generation of extremely high pressures exceeding Gbar(100 TPa)to enable the investigation of high-pressure physics using femtosecond J-level laser pulses,offering an alternative to nanosecond kJ-laser pulse-driven and pulsed power Z-pinch compression methods.
基金Center for Advanced Systems Understanding(CASUS)。
文摘In ultra-short laser pulses,small changes in dispersion properties before the final focusing mirror can lead to severe pulse distortions around the focus and therefore to very different pulse properties at the point of laser±matter interaction,yielding unexpected interaction results.The mapping between far-and near-field laser properties intricately depends on the spatial and angular dispersion properties as well as the focal geometry.For a focused Gaussian laser pulse under the influence of angular,spatial and group-delay dispersion,we derive analytical expressions for its pulse-front tilt,duration and width from a fully analytic expression for its electric field in the time±space domain obtained with scalar diffraction theory.This expression is not only valid in and near the focus but also along the entire propagation distance from the focusing mirror to the focus.Expressions relating angular,spatial and group-delay dispersion before focusing at an off-axis parabola,where they are well measurable,to the respective values in the pulse’s focus are obtained by a ray tracing approach.Together,these formulas are used to show in example setups that the pulse-front tilts of lasers with small initial dispersion can become several tens of degrees larger in the vicinity of the focus while being small directly in the focus.The formulas derived here provide the analytical foundation for observations previously made in numerical experiments.By numerically simulating Gaussian pulse propagation and measuring properties of the pulse at distances several Rayleigh lengths off the focus,we verify the analytic expressions.
基金supported by Kakenhi Grant No.16K05506,Grant No.20H00140,Grant No.21KK0049,Grant No.22H00121,JST PRESTO Grant No.JPMJPR16P9,QST President's Strategic Grant(QST) International Research Initiative(AAA98)and Creative Research(ABACS),and by Laserlab Europe V(PRISES,contract no.871124)supported by EU's Horizon 2020 research and innovation program under the Marie Sktodowska-Curie grant agreement No 894679support by JST-Mirai Program Grant Number JPMJMI17A1,Japan.N.P.D.,EJ.D.,G.S.H.,Z.N.acknowledge support from STFC grants ST/P002021/1,STN001639/1.
文摘Laser-driven ion sources are a rapidly developing technology producing high energy,high peak current beams.Their suitability for applications,such as compact medical accelerators,motivates development of robust acceleration schemes using widely available repetitive ultraintense femtosecond lasers.These applications not only require high beam energy,but also place demanding requirements on the source stability and controllability.This can be seriously affected by the laser temporal contrast,precluding the replication of ion acceleration performance on independent laser systems with otherwise similar parameters.Here,we present the experimental generation of>60 MeV protons and>30 MeV u-1 carbon ions from sub-micrometre thickness Formvar foils irradiated with laser intensities>1021 Wcm2.Ions are accelerated by an extreme localised space charge field≥30TVm-1,over a million times higher than used in conventional accelerators.The field is formed by a rapid expulsion of electrons from the target bulk due to relativistically induced transparency,in which relativistic corrections to the refractive index enables laser transmission through normally opaque plasma.We replicate the mechanism on two different laser facilities and show that the optimum target thickness decreases with improved laser contrast due to reduced pre-expansion.Our demonstration that energetic ions can be accelerated by this mechanism at different contrast levels relaxes laser requirements and indicates interaction parameters for realising application-specific beam delivery.
文摘We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute,National Institutes for Quantum Science and Technology.The reflectivity of the single plasma mirror system exceeded 80%.In addition,the temporal contrast was improved by two orders of magnitude at 1 ps before the main pulse.Furthermore,the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm^(2).We also present the results of investigating the difference and the fluctuation in energy,pulse width and pointing stability with and without the plasma mirror system.
