In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser,we have numerically investigated the dynamics and structure of strong self-generated magnetic f...In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser,we have numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments.Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current,Weibel-like instability and resistivity gradient between two solid layers.Using particle-in-cell simulations,we observe the effect of varying the laser and target parameters,including laser intensity,focal size,incident angle,preplasma scale length,target thickness and material and experimental geometry.The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency.The recent commissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser(XFEL),such as European XFEL-HED,LCLS-MEC and SACLA beamlines,provides unprecedented opportunities to probe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatial and temporal resolution.We expect that this systematic numerical investigation will pave the way to design and optimize near future experimental setups to probe the magnetic fields in such experimental platforms.展开更多
In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then re...In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then related to recent experiments performed on the GEKKO XII laser facility. The RS generated in a xenon gas cell propagates towards a solid obstacle that is ablated by radiation coming from the shock front and the radiative precursor, mimicking processes occurring in astrophysical phenomena. The model presented here calculates the dynamics of the obstacle expansion,which depends on several parameters, notably the geometry and the temperature of the shock. All parameters required for the model have been obtained from experiments. Good agreement between experimental data and the model is found when spherical geometry is taken into account. As a consequence, this model is a useful and easy tool to infer parameters from experimental data(such as the shock temperature), and also to design future experiments.展开更多
The collective response of electrons in an ultrathin foil target irradiated by an ultraintense(~6×10^(20)W cm^(-2)) laser pulse is investigated experimentally and via 3D particle-in-cell simulations. It is shown ...The collective response of electrons in an ultrathin foil target irradiated by an ultraintense(~6×10^(20)W cm^(-2)) laser pulse is investigated experimentally and via 3D particle-in-cell simulations. It is shown that if the target is sufficiently thin that the laser induces significant radiation pressure, but not thin enough to become relativistically transparent to the laser light, the resulting relativistic electron beam is elliptical, with the major axis of the ellipse directed along the laser polarization axis. When the target thickness is decreased such that it becomes relativistically transparent early in the interaction with the laser pulse, diffraction of the transmitted laser light occurs through a so called ‘relativistic plasma aperture', inducing structure in the spatial-intensity profile of the beam of energetic electrons. It is shown that the electron beam profile can be modified by variation of the target thickness and degree of ellipticity in the laser polarization.展开更多
Inverse Bremsstrahlung absorption(IBA) of an intense laser field in plasma containing Maxwellian and nonMaxwellian(with Kappa and q-nonextensive distribution functions) electrons is studied analytically. Our results s...Inverse Bremsstrahlung absorption(IBA) of an intense laser field in plasma containing Maxwellian and nonMaxwellian(with Kappa and q-nonextensive distribution functions) electrons is studied analytically. Our results show that IBA decreases with an increase in temperature at high intensities and a decrease in plasma density for all kinds of distribution functions. Another striking result is that IBA is independent of the laser intensity at low intensity but is dependent on it when the intensity is going to rise. Also, it could be find that the behavior of the absorption as the function of laser intensity for the Kappa distribution with κ= 10 at low intensity is close to that for the Maxwellian distribution, but at high intensity it is close to that in the presence of q-nonextensive electrons with q = 0.9. These results provide insights into the inverse Bremsstrahlung absorption in the laser-plasma interactions.展开更多
Laser-plasma physics has developed rapidly over the past few decades as lasers have become both more powerful and more widely available.Early experimental and numerical research in this field was dominated by single-s...Laser-plasma physics has developed rapidly over the past few decades as lasers have become both more powerful and more widely available.Early experimental and numerical research in this field was dominated by single-shot experiments with limited parameter exploration.However,recent technological improvements make it possible to gather data for hundreds or thousands of different settings in both experiments and simulations.This has sparked interest in using advanced techniques from mathematics,statistics and computer science to deal with,and benefit from,big data.At the same time,sophisticated modeling techniques also provide new ways for researchers to deal effectively with situation where still only sparse data are available.This paper aims to present an overview of relevant machine learning methods with focus on applicability to laser-plasma physics and its important sub-fields of laser-plasma acceleration and inertial confinement fusion.展开更多
Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot...Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.展开更多
Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei) is employed to simulate the entire process of Station of Extreme Light(SEL) 100 PW l...Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei) is employed to simulate the entire process of Station of Extreme Light(SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum,ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.展开更多
We present detailed characterization of laser-driven fusion and neutron production(-10^(5)/second) using 8 mJ, 40 fs laser pulses on a thin(<1 μm) D_2O liquid sheet employing a measurement suite. At relativistic i...We present detailed characterization of laser-driven fusion and neutron production(-10^(5)/second) using 8 mJ, 40 fs laser pulses on a thin(<1 μm) D_2O liquid sheet employing a measurement suite. At relativistic intensity(~ 5 × 10^(18)W/cm^(2))and high repetition rate(1 kHz), the system produces deuterium±deuterium(D-D) fusion, allowing for consistent neutron generation. Evidence of D-D fusion neutron production is verified by a measurement suite with three independent detection systems: an EJ-309 organic scintillator with pulse-shape discrimination, a ~3He proportional counter and a set of 36 bubble detectors. Time-of-flight analysis of the scintillator data shows the energy of the produced neutrons to be consistent with 2.45 MeV. Particle-in-cell simulations using the WarpX code support significant neutron production from D-D fusion events in the laser±target interaction region. This high-repetition-rate laser-driven neutron source could provide a low-cost, on-demand test bed for radiation hardening and imaging applications.展开更多
This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel...This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.展开更多
We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying...We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying during the experiment.The laser energy of 72±9 J is directed to a focal spot of approximately 6μm diameter(full width at half maximum)in 30 fs pulse duration,yielding a focused peak intensity around 2.0×10^(21)W/cm^(2).The first laser-proton acceleration experiment is performed using plain copper and plastic targets.High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4μm via target normal sheath acceleration.For plastic targets of tens of nanometers thick,the proton cut-off energy is approximately 20 MeV,showing ring-like or flamented density distributions.These experimental results reflect the capabilities of the SULF-10 PW beamline,for example,both ultrahigh intensity and relatively good beam contrast.Further optimization for these key parameters is underway,where peak laser intensities of 10^(22)-10^(23)w/cm^(2)are anticipated to support various experiments on extreme field physics.展开更多
The development,the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed.Currently,the POLARIS system delivers 4 J energy,144 fs long laser pulses with an...The development,the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed.Currently,the POLARIS system delivers 4 J energy,144 fs long laser pulses with an ultra-high temporal contrast of 5 × 1012 for the ASE,which is achieved using a so-called double chirped-pulse amplification scheme and cross-polarized wave generation pulse cleaning.By tightly focusing,the peak intensity exceeds 3.5 × 1020 W cm-2.These parameters predestine POLARIS as a scientific tool well suited for sophisticated experiments,as exemplified by presenting measurements of accelerated proton energies.Recently,an additional amplifier has been added to the laser chain.In the ramp-up phase,pulses from this amplifier are not yet compressed and have not yet reached the anticipated energy.Nevertheless,an output energy of 16.6 J has been achieved so far.展开更多
Supersonic gas jets generated via a conical nozzle are widely applied in the laser wakefield acceleration of electrons.The stability of the gas jet is critical to the electron injection and the reproducibility of the ...Supersonic gas jets generated via a conical nozzle are widely applied in the laser wakefield acceleration of electrons.The stability of the gas jet is critical to the electron injection and the reproducibility of the wakefield acceleration.Here we discussed the role of the stilling chamber in a modified converging-diverging nozzle to dissipate the turbulence and to stabilize the gas jets.By the fluid dynamics simulations and the Mach-Zehnder interferometer measurements,the instability originating from the nonlinear turbulence is studied and the mechanism to suppress the instability is proposed.Both the numerical and experimental results prove that the carefully designed nozzle with a stilling chamber is able to reduce the perturbation by more than 10% compared with a simple-conical nozzle.展开更多
We study theoretically intense terahertz radiation from multi-color laser pulse with uncommon frequency ratios. Com- paring the two-color laser scheme, of which the uncommon frequency ratio should be set to be a speci...We study theoretically intense terahertz radiation from multi-color laser pulse with uncommon frequency ratios. Com- paring the two-color laser scheme, of which the uncommon frequency ratio should be set to be a specific value, we show that by using multi-color harmonic laser pulses as the first pump component, the lasers as the second pump component can be adjusted in a continuous frequency range. Moreover, these multi-color laser pulses can effectively modulate and enhance the terahertz radiation, and the terahertz yield increases with the increase of the wavelength of the uncommon pump com- ponent and is stable to the laser relative phase. Finally, we utilize the electron densities and velocities of ionization events to illustrate the physical mechanism of the intense terahertz generation.展开更多
文摘In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser,we have numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments.Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current,Weibel-like instability and resistivity gradient between two solid layers.Using particle-in-cell simulations,we observe the effect of varying the laser and target parameters,including laser intensity,focal size,incident angle,preplasma scale length,target thickness and material and experimental geometry.The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency.The recent commissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser(XFEL),such as European XFEL-HED,LCLS-MEC and SACLA beamlines,provides unprecedented opportunities to probe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatial and temporal resolution.We expect that this systematic numerical investigation will pave the way to design and optimize near future experimental setups to probe the magnetic fields in such experimental platforms.
基金supported by the Scientific Council of the Observatoire de Parisby COST(European COoperation in Science and Technology),action MP1208,with a Short-Term Scientific Mission
文摘In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then related to recent experiments performed on the GEKKO XII laser facility. The RS generated in a xenon gas cell propagates towards a solid obstacle that is ablated by radiation coming from the shock front and the radiative precursor, mimicking processes occurring in astrophysical phenomena. The model presented here calculates the dynamics of the obstacle expansion,which depends on several parameters, notably the geometry and the temperature of the shock. All parameters required for the model have been obtained from experiments. Good agreement between experimental data and the model is found when spherical geometry is taken into account. As a consequence, this model is a useful and easy tool to infer parameters from experimental data(such as the shock temperature), and also to design future experiments.
基金supported by EPSRC (grants:EP/J003832/1,EP/M018091/1,EP/L001357/1,EP/K022415/1 and EP/L000237/1)EPSRC grant EP/G054940/1+2 种基金STFC (grant number ST/K502340/1)the US Air Force Office of Scientific Research (grant:FA8655-13-1-3008)the European Unions Horizon 2020 research and innovation programme (grant agreement No 654148 Laserlab-Europe)
文摘The collective response of electrons in an ultrathin foil target irradiated by an ultraintense(~6×10^(20)W cm^(-2)) laser pulse is investigated experimentally and via 3D particle-in-cell simulations. It is shown that if the target is sufficiently thin that the laser induces significant radiation pressure, but not thin enough to become relativistically transparent to the laser light, the resulting relativistic electron beam is elliptical, with the major axis of the ellipse directed along the laser polarization axis. When the target thickness is decreased such that it becomes relativistically transparent early in the interaction with the laser pulse, diffraction of the transmitted laser light occurs through a so called ‘relativistic plasma aperture', inducing structure in the spatial-intensity profile of the beam of energetic electrons. It is shown that the electron beam profile can be modified by variation of the target thickness and degree of ellipticity in the laser polarization.
文摘Inverse Bremsstrahlung absorption(IBA) of an intense laser field in plasma containing Maxwellian and nonMaxwellian(with Kappa and q-nonextensive distribution functions) electrons is studied analytically. Our results show that IBA decreases with an increase in temperature at high intensities and a decrease in plasma density for all kinds of distribution functions. Another striking result is that IBA is independent of the laser intensity at low intensity but is dependent on it when the intensity is going to rise. Also, it could be find that the behavior of the absorption as the function of laser intensity for the Kappa distribution with κ= 10 at low intensity is close to that for the Maxwellian distribution, but at high intensity it is close to that in the presence of q-nonextensive electrons with q = 0.9. These results provide insights into the inverse Bremsstrahlung absorption in the laser-plasma interactions.
基金The authors acknowledge the use of GPT-3[288](text-davinci-003)in the copy-editing process of this manuscript.
文摘Laser-plasma physics has developed rapidly over the past few decades as lasers have become both more powerful and more widely available.Early experimental and numerical research in this field was dominated by single-shot experiments with limited parameter exploration.However,recent technological improvements make it possible to gather data for hundreds or thousands of different settings in both experiments and simulations.This has sparked interest in using advanced techniques from mathematics,statistics and computer science to deal with,and benefit from,big data.At the same time,sophisticated modeling techniques also provide new ways for researchers to deal effectively with situation where still only sparse data are available.This paper aims to present an overview of relevant machine learning methods with focus on applicability to laser-plasma physics and its important sub-fields of laser-plasma acceleration and inertial confinement fusion.
基金funding from EPSRC grants EP/L01663X/1 and EP/L000644/1the Newton UK grant+1 种基金the National Natural Science Foundation of China NSFC/11520101003the LLNL Academic Partnership in ICF
文摘Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.
基金support from the Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDB34030000)the National Key R & D Program of China (No.2022YFA1602404)+2 种基金National Natural Science Foundation of China (No. U1832129)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (No.2017309)the Program for Innovative Research Team (in Science and Technology) in University of Henan Province of China (No.21IRTSTHN011)。
文摘Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei) is employed to simulate the entire process of Station of Extreme Light(SEL) 100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr, Fe, Ag, Ta, Au, Pb, Th and U, as well as 200 nm thick Al and Ca. An obvious stratification is observed in the simulation. The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration, and this phenomenon is understood from the simulated energy spectrum,ionization and spatial electric field distribution. According to the stratification, it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei. Two plasma clusters in the stratification are observed simultaneously, which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.
基金supported by Air Force Office of Scientific Research(AFOSR)Award number 23AFCOR004(PM:Dr.Andrew B.Stickrath)partially supported by DTRANSREC Award number HDTRA-1343332。
文摘We present detailed characterization of laser-driven fusion and neutron production(-10^(5)/second) using 8 mJ, 40 fs laser pulses on a thin(<1 μm) D_2O liquid sheet employing a measurement suite. At relativistic intensity(~ 5 × 10^(18)W/cm^(2))and high repetition rate(1 kHz), the system produces deuterium±deuterium(D-D) fusion, allowing for consistent neutron generation. Evidence of D-D fusion neutron production is verified by a measurement suite with three independent detection systems: an EJ-309 organic scintillator with pulse-shape discrimination, a ~3He proportional counter and a set of 36 bubble detectors. Time-of-flight analysis of the scintillator data shows the energy of the produced neutrons to be consistent with 2.45 MeV. Particle-in-cell simulations using the WarpX code support significant neutron production from D-D fusion events in the laser±target interaction region. This high-repetition-rate laser-driven neutron source could provide a low-cost, on-demand test bed for radiation hardening and imaging applications.
文摘This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16)the National Natural Science Foundation of China(Nos.11875307,11935008,11804348,11705260,11905278 and 11975302)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2021242).
文摘We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying during the experiment.The laser energy of 72±9 J is directed to a focal spot of approximately 6μm diameter(full width at half maximum)in 30 fs pulse duration,yielding a focused peak intensity around 2.0×10^(21)W/cm^(2).The first laser-proton acceleration experiment is performed using plain copper and plastic targets.High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4μm via target normal sheath acceleration.For plastic targets of tens of nanometers thick,the proton cut-off energy is approximately 20 MeV,showing ring-like or flamented density distributions.These experimental results reflect the capabilities of the SULF-10 PW beamline,for example,both ultrahigh intensity and relatively good beam contrast.Further optimization for these key parameters is underway,where peak laser intensities of 10^(22)-10^(23)w/cm^(2)are anticipated to support various experiments on extreme field physics.
基金funding from the European Commission’s (EC) 7th Framework Programme (LASERLAB-EUROPE,grant no.228334)from the Bundesministerium fr Bildung und Forschung (BMBF) (03ZIK445 and 03Z1H531)
文摘The development,the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed.Currently,the POLARIS system delivers 4 J energy,144 fs long laser pulses with an ultra-high temporal contrast of 5 × 1012 for the ASE,which is achieved using a so-called double chirped-pulse amplification scheme and cross-polarized wave generation pulse cleaning.By tightly focusing,the peak intensity exceeds 3.5 × 1020 W cm-2.These parameters predestine POLARIS as a scientific tool well suited for sophisticated experiments,as exemplified by presenting measurements of accelerated proton energies.Recently,an additional amplifier has been added to the laser chain.In the ramp-up phase,pulses from this amplifier are not yet compressed and have not yet reached the anticipated energy.Nevertheless,an output energy of 16.6 J has been achieved so far.
基金funded by the JST-MIRAI program,grant No.JPMJMI17A1.
文摘Supersonic gas jets generated via a conical nozzle are widely applied in the laser wakefield acceleration of electrons.The stability of the gas jet is critical to the electron injection and the reproducibility of the wakefield acceleration.Here we discussed the role of the stilling chamber in a modified converging-diverging nozzle to dissipate the turbulence and to stabilize the gas jets.By the fluid dynamics simulations and the Mach-Zehnder interferometer measurements,the instability originating from the nonlinear turbulence is studied and the mechanism to suppress the instability is proposed.Both the numerical and experimental results prove that the carefully designed nozzle with a stilling chamber is able to reduce the perturbation by more than 10% compared with a simple-conical nozzle.
基金Project supported by the National Natural Science Foundation of China(Grant No.11604205)the Talent Program of Shanghai University of Engineering Science,China
文摘We study theoretically intense terahertz radiation from multi-color laser pulse with uncommon frequency ratios. Com- paring the two-color laser scheme, of which the uncommon frequency ratio should be set to be a specific value, we show that by using multi-color harmonic laser pulses as the first pump component, the lasers as the second pump component can be adjusted in a continuous frequency range. Moreover, these multi-color laser pulses can effectively modulate and enhance the terahertz radiation, and the terahertz yield increases with the increase of the wavelength of the uncommon pump com- ponent and is stable to the laser relative phase. Finally, we utilize the electron densities and velocities of ionization events to illustrate the physical mechanism of the intense terahertz generation.
