The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and...The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.展开更多
Applying the classical Lie symmetry approach to the barotropic and quasi-geostrophic potential vorticity equation without forcing and dissipation on a β-plane channel, we find a new symmetry, which is not presented i...Applying the classical Lie symmetry approach to the barotropic and quasi-geostrophic potential vorticity equation without forcing and dissipation on a β-plane channel, we find a new symmetry, which is not presented in a previous work [F. Huang, Commun. Theor. Phys. （Beijing, China） 42 （2004） 903]. A general finite transformation group is obtained based on the full Lie point symmetry, Furthermore, two new types of similarity reduction solutions are obtained.展开更多
The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching.Our main focus here is on the production o...The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching.Our main focus here is on the production of free-standing,thin foil targets,such as diamond-likecarbon foils,carbon nanotube foams(CNFs),plastic,and gold foils.The presented methods comprise cathodic arc deposition for DLC targets,chemical vapor deposition for CNFs,a droplet and spin-coating process for plastic foil production,as well as physical vapor deposition that has been optimized to provide ultrathin gold foils and tailored sacrifice layers.This paper reviews our current capabilities,which are a result of a close collaboration between target production processes and experiment,using high-power chirped pulse amplification laser systems over the past eight years.展开更多
The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optic...The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber technology: a fixed-wavelength pump laser pulse is converted into a spectrally very broadband output, from which the required resulting wavelength is then optically filtered. Unfortunately, this process is associated with an inherently poor noise figure, which often precludes many realistic applications of such supercontinuum sources. Here, we show that by adding only one passive optical element—a tapered photonic crystal fiber—to a fixed-wavelength femtosecond laser, one can in a very simple manner resonantly convert the laser emission wavelength into an ultra-wide and continuous range of desired wavelengths, with very low inherent noise, and without mechanical realignment of the laser. This is achieved by exploiting the double interplay of nonlinearity and chirp in the laser source and chirp and phase matching in the tapered fiber. As a first demonstration of this simple and inexpensive technology, we present a femtosecond fiber laser continuously tunable across the entire red–green–blue spectral range.展开更多
We report on a target system supporting automated positioning of nano-targets with a precision resolution of 4 μm in three dimensions. It relies on a confocal distance sensor and a microscope. The system has been com...We report on a target system supporting automated positioning of nano-targets with a precision resolution of 4 μm in three dimensions. It relies on a confocal distance sensor and a microscope. The system has been commissioned to position nanometer targets with 1 Hz repetition rate. Integrating our prototype into the table-top ATLAS 300 TW-laser system at the Laboratory for Extreme Photonics in Garching, we demonstrate the operation of a 0.5 Hz laser-driven proton source with a shot-to-shot variation of the maximum energy about 27% for a level of confidence of 0.95. The reason of laser shooting experiments operated at 0.5 Hz rather than 1 Hz is because the synchronization between the nano-foil target positioning system and the laser trigger needs to improve.展开更多
Modern chirped pulse amplification laser systems with continuously improving controllability and increasing power are about to reach intensities of up to 10^(22) W cm^(-2) and have proven their potential to accelerate...Modern chirped pulse amplification laser systems with continuously improving controllability and increasing power are about to reach intensities of up to 10^(22) W cm^(-2) and have proven their potential to accelerate ions out of plasma to several tens percent of the speed of light. For enabling application, one important step is to increase the repetition rate at which ion bunches are at the disposal. In particular, techniques used so far for thin foil target production can require several days of preparing reasonable amounts for a single campaign. In this paper we describe the reasonably droplet method which we have tested and improved so that the emerging foils with thicknesses of a few nanometres up to micrometre can be used as targets for laser ion acceleration. Their quality and performance can compete with so far employed techniques thereby enabling the production of hundreds of targets per day.展开更多
Color screening and parton inelastic scattering modify the heavy-quark antiquark potential in mediums consisting of particles from quantum chromodynamics(QCD),leading to the suppression of quarkonium production in rel...Color screening and parton inelastic scattering modify the heavy-quark antiquark potential in mediums consisting of particles from quantum chromodynamics(QCD),leading to the suppression of quarkonium production in relativistic heavy-ion collisions.Owing to the small charm/anti-charm(cc)pair production number in proton-nucleus(pA)collisions,the correlation between different cc pairs is negligible,which makes the Schrödinger equation viable for tracking the evolution of only one cc pair.We employ the time-dependent Schrödinger equation with an in-medium cc potential to study the evolution of charmonium wave functions in a hydrodynamic-like QCD medium produced in pA collisions.We explore different parametrizations of real and imaginary parts of the cc potential and calculate the nuclear modification factors(R_(pA))of J/ψ and ψ(2S)in √s_(NN)=5.02 TeV energy p-Pb collisions at the Large Hadron Collider(LHC).Comparing strong and weak screening scenarios with experimental data in this approach,we arrive at the conclusion that color screening is weak at temperatures close to the deconfined phase transition.Moreover,the imaginary part of the potential is crucial in describing the experimental data,which is consistent with widely studied semi-classical approaches,where dissociation rates are essential.展开更多
基金supported by NNSA cooperative agreement DE-NA0002008the Defense Advanced Research Projects Agency's PULSE program(12-63-PULSE-FP014)the Air Force Office of Scientific Research(FA9550-14-1-0045).
文摘The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.
基金The project supported by the Alexander von Humboldt Foundationthe Youth Foundation of Shanghai Jiao Tong UniversityNational Natural Science Foundation of China under Grant No.10475055
文摘Applying the classical Lie symmetry approach to the barotropic and quasi-geostrophic potential vorticity equation without forcing and dissipation on a β-plane channel, we find a new symmetry, which is not presented in a previous work [F. Huang, Commun. Theor. Phys. （Beijing, China） 42 （2004） 903]. A general finite transformation group is obtained based on the full Lie point symmetry, Furthermore, two new types of similarity reduction solutions are obtained.
文摘The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching.Our main focus here is on the production of free-standing,thin foil targets,such as diamond-likecarbon foils,carbon nanotube foams(CNFs),plastic,and gold foils.The presented methods comprise cathodic arc deposition for DLC targets,chemical vapor deposition for CNFs,a droplet and spin-coating process for plastic foil production,as well as physical vapor deposition that has been optimized to provide ultrathin gold foils and tailored sacrifice layers.This paper reviews our current capabilities,which are a result of a close collaboration between target production processes and experiment,using high-power chirped pulse amplification laser systems over the past eight years.
基金Teknologi og Produktion,Det Frie Forskningsrad(FTP,DFF)(ALFIE)Research Executive Agency(REA)(EU Career Integration Grant 334324LIGHTER)+2 种基金H2020 European Research Council(ERC)(ERC-617521 NLL)National Cancer Institute(NCI)(1 R01 CA166309)Max-Planck-Gesellschaft(MPG)
文摘The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber technology: a fixed-wavelength pump laser pulse is converted into a spectrally very broadband output, from which the required resulting wavelength is then optically filtered. Unfortunately, this process is associated with an inherently poor noise figure, which often precludes many realistic applications of such supercontinuum sources. Here, we show that by adding only one passive optical element—a tapered photonic crystal fiber—to a fixed-wavelength femtosecond laser, one can in a very simple manner resonantly convert the laser emission wavelength into an ultra-wide and continuous range of desired wavelengths, with very low inherent noise, and without mechanical realignment of the laser. This is achieved by exploiting the double interplay of nonlinearity and chirp in the laser source and chirp and phase matching in the tapered fiber. As a first demonstration of this simple and inexpensive technology, we present a femtosecond fiber laser continuously tunable across the entire red–green–blue spectral range.
基金supported by the DFG Cluster of Excellence Munich-Centre for Advanced Photonics (MAP)the Centre for Advanced Laser Applications and China Scholarship (no. 201508080084)
文摘We report on a target system supporting automated positioning of nano-targets with a precision resolution of 4 μm in three dimensions. It relies on a confocal distance sensor and a microscope. The system has been commissioned to position nanometer targets with 1 Hz repetition rate. Integrating our prototype into the table-top ATLAS 300 TW-laser system at the Laboratory for Extreme Photonics in Garching, we demonstrate the operation of a 0.5 Hz laser-driven proton source with a shot-to-shot variation of the maximum energy about 27% for a level of confidence of 0.95. The reason of laser shooting experiments operated at 0.5 Hz rather than 1 Hz is because the synchronization between the nano-foil target positioning system and the laser trigger needs to improve.
基金supported by the DFG funded Cluster of Excellence Munich Centre for Advanced Photonics and the Transregio 18
文摘Modern chirped pulse amplification laser systems with continuously improving controllability and increasing power are about to reach intensities of up to 10^(22) W cm^(-2) and have proven their potential to accelerate ions out of plasma to several tens percent of the speed of light. For enabling application, one important step is to increase the repetition rate at which ion bunches are at the disposal. In particular, techniques used so far for thin foil target production can require several days of preparing reasonable amounts for a single campaign. In this paper we describe the reasonably droplet method which we have tested and improved so that the emerging foils with thicknesses of a few nanometres up to micrometre can be used as targets for laser ion acceleration. Their quality and performance can compete with so far employed techniques thereby enabling the production of hundreds of targets per day.
基金Supported by the National Natural Science Foundation of China (NSFC)(12175165, 11705125)support from U.S. Department of Energy,Office of Science,Office of Nuclear Physics,(DE-FG88ER40388)support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the CRC-TR 211’Strong-interaction matter under extreme conditions’–project number 315477589–TRR 211
文摘Color screening and parton inelastic scattering modify the heavy-quark antiquark potential in mediums consisting of particles from quantum chromodynamics(QCD),leading to the suppression of quarkonium production in relativistic heavy-ion collisions.Owing to the small charm/anti-charm(cc)pair production number in proton-nucleus(pA)collisions,the correlation between different cc pairs is negligible,which makes the Schrödinger equation viable for tracking the evolution of only one cc pair.We employ the time-dependent Schrödinger equation with an in-medium cc potential to study the evolution of charmonium wave functions in a hydrodynamic-like QCD medium produced in pA collisions.We explore different parametrizations of real and imaginary parts of the cc potential and calculate the nuclear modification factors(R_(pA))of J/ψ and ψ(2S)in √s_(NN)=5.02 TeV energy p-Pb collisions at the Large Hadron Collider(LHC).Comparing strong and weak screening scenarios with experimental data in this approach,we arrive at the conclusion that color screening is weak at temperatures close to the deconfined phase transition.Moreover,the imaginary part of the potential is crucial in describing the experimental data,which is consistent with widely studied semi-classical approaches,where dissociation rates are essential.
