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X-ray-assisted nuclear excitation by electron capture in optical laser-generated plasmas
摘要： X-ray-assisted nuclear excitation by electron capture (NEEC) into inner-shell atomic holes in a plasma environment generated by strong optical lasers is investigated theoretically. The considered scenario involves the interaction of a strong optical laser with a solid-state nuclear target leading to the generation of a plasma. In addition, intense x-ray radiation from the X-ray Free Electron Laser (XFEL) produces inner-shell holes in the plasma ions, into which NEEC may occur. As a case study, we consider the 4.85-keV transition starting from the 2.4-MeV long-lived 93mMo isomer that can be used to release the energy stored in this metastable nuclear state. We ?nd that the recombination into 2p1/2 inner-shell holes is most ef?cient in driving the nuclear transition. The generation of inner-shell holes while the plasma is at a temperature of a few hundred eV can allow optimal conditions for NEEC, which are otherwise reached for steady-state plasma conditions in thermodynamical equilibrium only at few keV. The combination of x-ray and optical lasers presents two advantages: First, NEEC rates can be maximized at plasma temperatures where the photoexcitation rate remains low. Second, with mJ-class optical lasers and an XFEL repetition rate of 10 kHz, the NEEC excitation number can reach ≈1 depleted isomer per second and is competitive with scenarios recently envisaged at petawatt-class lasers.
关键词： XFEL,optical laser-generated plasmas,X-ray-assisted nuclear excitation,NEEC,electron capture
更新于2025-09-12 10:27:22
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Photofragmentation laser-induced fluorescence of ozone: an in situ tool for precise mapping of ozone concentration in non-thermal plasmas
摘要： The absolute spatially resolved concentration of ozone has been determined in the near afterglow of a novel type of atmospheric multi-hollow barrier discharge using photofragmentation laser-induced fluorescence. The method consists of two steps: (i) photodissociation of O3 to O(3P) and O2(X3Σg?) with considerable vibrational excitation; (ii) predissociation laser-induced fluorescence of the molecular fragment via the O2(B 3Σu?, v′ = 0 ← X 3Σg?, v″ = 6) transition. Both processes happen during the same laser pulse, requiring the same excitation wavelength (≈248 nm). The fluorescence signal has been calibrated by infrared absorption. The method allows in situ observation before the afterglow chemistry significantly affects the O3 concentration, and is capable of revealing inhomogeneous ozone distributions in the reactor.
关键词： ozone,spatial resolution,non-thermal plasmas,photofragmentation laser-induced fluorescence
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Quasi-Phase Matching in High Harmonic Generation using Structured Plasmas
摘要： High harmonic generation (HHG) is an important process in attosecond science. Its efficiency is, however, limited to values below 10-5 of the incident power into a single harmonic. Phase matching can increase the efficiency but deals with low ionization rates. Furthermore HHG from laser-produced plasmas has shown some promising advantages in increasing the response of the conversion. These are the appearance of resonantly enhanced harmonics or the efficient generation in carbon or nanoparticle containing plasmas. On the contrary laser-produced plasmas inherently possess a high degree of ionization which hampers any phase-matching scheme with these sources. This dilemma can be circumvented by quasi-phase matching (QPM). In this case the conversion process is suppressed when the harmonics are generated out of phase leading to a quadratic growth of the harmonic intensity with interaction distance. Experimentally QPM can be achieved e.g. by applying a structured conversion medium in a focused driving beam geometry. Here, we show how such a scheme is realized with laser-produced plasmas. The idea of using a structured plasma for QPM is not new [1], but in none of these earlier studies QPM has been optimized for maximum efficiency nor controlled for different regions of the harmonic spectrum.
关键词： laser-produced plasmas,quasi-phase matching,attosecond science,High harmonic generation
更新于2025-09-11 14:15:04
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Multiple colliding laser pulses as a basis for studying high-field high-energy physics
摘要： Apart from maximizing the strength of optical electromagnetic fields achievable at high-intensity laser facilities, the collision of several phase-matched laser pulses has been identified theoretically as a trigger of and way to study various phenomena. These range from the basic processes of strong-field quantum electrodynamics to the extraordinary dynamics of the generated electron-positron plasmas. This has paved the way for several experimental proposals aimed at both fundamental studies of matter at extreme conditions and the creation of particle and radiation sources. Because of the unprecedented capabilities of such sources, they have the potential to open up new opportunities for experimental studies in nuclear and quark-gluon physics. We perform here a systematic analysis of different regimes and opportunities achievable with the concept of multiple colliding laser pulses, for both current and upcoming laser facilities. We reveal that several distinct regimes could be within reach of multi-petawatt laser facilities.
关键词： high-field high-energy physics,quantum electrodynamics,multiple colliding laser pulses,electron-positron plasmas,particle and radiation sources
更新于2025-09-11 14:15:04
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Complementary Characterization of Laser-Induced Plasmas by Optical Emission Spectroscopy and Triple Langmuir Probe
摘要： In this article, we study the temporal evolution of the electron density and temperature of carbon laser-produced plasmas (LPP) using a combination of optical emission spectroscopy (OES) and the triple Langmuir probe (TLP) method. OES has been widely used to characterize LPPs but it is limited to distances relatively close to the target. On the other hand, the main advantage of TLP over the single-probe method is that it allows to obtain simultaneous measurements of electron temperature (Te) and density (Ne), without any voltage sweeping. In this article, we compare both techniques; measurements by OES were performed at distances from the target <1 cm, whereas the triple probe was employed for distances >5 cm. The plasma was generated by focusing nanosecond laser pulses onto a high purity graphite target placed inside a vacuum chamber. Our results show that the values of Te measured using both techniques predict decreasing exponential behavior. Ne determined by the spectral line Stark broadening in OES (<1 cm) was two orders of magnitude larger than that measured by the TLP (>5 cm). This difference in the electron density can be explained by radiative recombination and the presence of different kinds of plasma species detected by the TLP technique. The results show that both methods are complementary and their combination can be used to characterize LPP in a wide range of distances and timescales.
关键词： triple Langmuir probe (TLP),optical emission spectroscopy (OES),Laser-induced plasmas
更新于2025-09-11 14:15:04
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Resonance Enhancement in Laser-Produced Plasmas (Concepts and Applications) || Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
摘要： Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
关键词： resonance enhancement,laser-produced plasmas,picosecond pulses,high-order harmonic generation,harmonic generation
更新于2025-09-11 14:15:04
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Independent excitation of inhomogeneous energy density driven instability by electron density gradient
摘要： In this work, we report an experimental observation of the inhomogeneous energy density driven instability (IEDDI) independently excited by the electron density gradient. This was achieved using a novel design which could generate a controllable electron density gradient, while the self-consistent electric ?eld accompanied with the electron density gradient can be simultaneously compensated. Broadband wave mode in the ion cyclotron frequency range was excited, which was further experimentally identi?ed as the IEDDI. This result suggests that the IEDDI can be independently excited by the electron density gradient, which could be extended to explain the satellite observations of the broadband extremely low frequency waves in the auroral plasmas where the strong plasma density inhomogeneities exist.
关键词： IEDDI,auroral plasmas,ion cyclotron frequency,electron density gradient,broadband wave mode
更新于2025-09-10 09:29:36
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A computational tool for simulation and design of tangential multi-energy soft x-ray pin-hole cameras for tokamak plasmas
摘要： A new tool has been developed to calculate the spectral, spatial, and temporal responses of multi-energy soft x-ray (ME-SXR) pinhole cameras for arbitrary plasma densities (ne,D), temperature (Te), and impurity densities (nZ). ME-SXR imaging provides a unique opportunity for obtaining important plasma properties (e.g., Te, nZ, and Z eff) by measuring both continuum and line emission in multiple energy ranges. This technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently. Simulations assuming a tangential geometry and DIII-D-like plasmas (e.g., ne,0 ≈ 8 × 1019 m?3 and T e,0 ≈ 2.8 keV) for various impurity (e.g., C, O, Ar, Ni, and Mo) density pro?les have been performed. The computed brightnesses range from few 102 counts pixel?1 ms?1 depending on the cut-off energy thresholds, while the maximum allowable count rate is 104 counts pixel?1 ms?1. The typical spatial resolution in the mid-plane is ≈0.5 cm with a photon-energy resolution of 500 eV at a 500 Hz frame rate.
关键词： tokamak plasmas,multi-energy soft x-ray,plasma diagnostics,pinhole cameras,x-ray spectra
更新于2025-09-10 09:29:36
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Optical diagnostics of helium recombining plasmas with collisional radiative model
摘要： Optical diagnostics for plasmas has many advantages that allow for the determination and understanding of plasma parameters. A method employing the line intensity ratio (LIR), combined with the collisional-radiative (CR) model considering the radiation trapping effect (RTE), was developed to analyze the recombining helium plasmas. The recombining plasma component and the ionizing plasma components in the He CR-model were evaluated, and the RTEs for from the ground state to n1P states were analyzed. The electron temperature and density of the helium recombining plasmas were determined using seven LIRs with the He CR-model, considering the RTEs of 11S–31P, 11S–41P, and 11S–51P. When the He gas pressure was above 100 mTorr, the electron temperature was less than 0.8 eV and the electron density was more than 1012 cm?3. The determined plasma parameters were compared with those obtained by the continuum method and in reasonable agreement with those by the continuum method.
关键词： helium recombining plasmas,optical diagnostics,collisional radiative model,radiation trapping effect,line intensity ratio
更新于2025-09-10 09:29:36
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Linear Analyses of Langmuir and EM Waves in Relativistic Hot Plasmas
摘要： The linear Langmuir and electromagnetic (EM) waves in relativistic hot plasmas are discussed, and the dispersion relations are obtained based on the covariant Maxwell’s and ?uid equations. When kBT =mc2 > 1, the e?ective mass of electrons will be increased obviously. As the results, many other in?uences are induced, such as the decrease of the plasmas frequency and the critical frequency, the reduction of the electron sound velocity and the electrons’ oscillation velocity, and so on. Numerical results show that these in?uences can a?ect the dispersion relations of Langmuir and EM waves seriously even in linear regime.
关键词： relativistic hot plasmas,dispersion relation,Langmuir wave,electromagnetic wave
更新于2025-09-09 09:28:46