Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Monte Carlo approach to calculate ionization dynamics of hot solid-density plasmas within particle-in-cell simulations
No full textGerman Academic Exchange Service (DAAD); China Scholarship Council (CSC)A physical model based on a Monte Carlo approach is proposed to calculate the ionization dynamics of hot-solid-density plasmas within particle-in-cell (PIC) simulations, and where the impact (collision) ionization (CI), electron-ion recombination (RE), and ionization potential depression (IPD) by surrounding plasmas are taken into consideration self-consistently. When compared with other models, which are applied in the literature for plasmas near thermal equilibrium, the temporal relaxation of ionization dynamics can also be simulated by the proposed model. Besides, this model is general and can be applied for both single elements and alloys with quite different compositions. The proposed model is implemented into a PIC code, with (final) ionization equilibriums sustained by competitions between CI and its inverse process (i.e., RE). Comparisons between the full model and model without IPD or RE are performed. Our results indicate that for bulk aluminium at temperature of 1 to 1000 eV, (i) the averaged ionization degree increases by including IPD; while (ii) the averaged ionization degree is significantly over estimated when the RE is neglected. A direct comparison from the PIC code is made with the existing models for the dependence of averaged ionization degree on thermal equilibrium temperatures and shows good agreements with that generated from Saha-Boltzmann model and/or FLYCHK code
Next Generation Driver for Attosecond and Laser-plasma Physics
No full textDFG [Transregio TR18]; Munich Centre for Advanced Photonics (MAP); Laserlab-Europe [284464]; Euratom research and training programme within EUROfusion Consortium [633053]The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 10(20)W/cm(2) with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources
Probing the effective length of plasma inside a filament
No full textNational Natural Science Foundation of China (NSFC) [61221064, 11127901, 11404354]; National 973 Project [2011CB808103]; Strategic Priority Research Program [XDB16]; Key Project from Bureau of International Cooperation Chinese Academy of Sciences [GJHZ1759]; State Key Laboratory of High Field Laser Physics, 100 Talents Program of Chinese Academy of SciencesWe present a novel method based on plasma-guided corona discharges to probe the plasma density longitudinal distribution, which is particularly good for the weakly ionized plasmas (similar to 10(14) cm(-3)). With this method, plasma density longitudinal distribution inside both a weakly ionized plasma and a filament were characterized. When a high voltage electric field was applied onto a plasma channel, the original ionization created by a laser pulse would be enhanced and streamer coronas formed along the channel. By measuring the fluorescence of enhanced ionization, in particular, on both ends of a filament, the weak otherwise invisible plasma regions created by the laser pulse were identified. The observed plasma guided coronas were qualitatively understood by solving a 3D Maxwell equation through finite element analysis. The technique paves a new way to probe low density plasma and to precisely measure the effective length of plasma inside a filament
Strong configuration interactions in Be-like ions
No full textNSFC [11374315, 61475168]Strong configuration interactions are observed in Be-like ions between 1s(1)2s(2)nl(1) and 1s(1)2p(2)nl(1). Such configuration interactions not only make a remarkable and systematic difference to the k-shell transition from 1s(1)2p(2)nl(1) to 1s(2)2p(1)nl(1), but they also change the order of the spectral positions between the transitions 1s(1)2p(2)nl(1) - 1s(2)2p(1)nl(1) and 1s(1)2s(1)2p(1)nl(1) - 1s(2)2s(1)nl(1). Including or not including the configuration interaction of 1s(1)2s(2)nl(1) can result in an energy difference of about 6 eV for the 1s(1)2p(2)nl(1) - 1s(2)2p(1)nl(1) transitions of Be-like aluminum. This phenomenon reveals the physical reason behind the existence of differences between the experimental transmission and the theoretical transmission for aluminum plasma in the paper by Zhang et al (2009 Phys. Rev. E 79 016401). For two configurations (KLMf)-L-i-M-j... and (KLMf'')-L-i'-M-j'..., the strongest configuration interactions may appear when the number of electrons in each shell is the same and the parity for each shell is the same
Ultrafast multi-MeV gamma-ray beam produced by laser-accelerated electrons
No full textNational Natural Science Foundation of China [11335013, 11505264, 11374317]; Chinese Academy of Sciences [1701521X00, XDB16]; Ministry of Science and Technology of the People's Republic of China [2016YFA0401102]Ultrafast multi-MeV high-flux gamma-ray beams have been experimentally produced via bremsstrahlung radiation of laser-accelerated energetic electrons through millimeter-thick copper targets. By optimizing the electron bunches to the charge of 10 nC in a clustering argon gas target, the obtained gamma-ray beam significantly increases to 10(10) photons per shot. The gamma-ray beam spectrum has been measured using a differential filtering detector and has a broad spectrum up to 15 MeV, which is approximately consistent with the Geant4 simulation. The generated high-flux high-energy gamma-ray beams are promising sources for photonuclear reaction, non-destructive inspection and clinical applications. Published by AIP Publishing
Decreasing the uncertainty of atomic clocks via real-time noise distinguish
No full textNational Natural Science Foundation of China [61275204, 91336105]The environmental perturbation on atoms is a key factor restricting the performance of atomic frequency standards, especially in the long-term scale. In this Letter, we perform a real-time noise distinguish (RTND) to an atomic clock to decrease the uncertainty of the atomic clock beyond the level that is attained by the current controlling method. In RTND, the related parameters of the clock are monitored in real time by using the calibrated sensors, and their effects on the clock frequency are calculated. By subtracting the effects from the error signal, the local oscillator is treated as equivalently locked to the unperturbed atomic levels. In order to perform quantitative tests, we engineer time-varying noise much larger than the intrinsic noise in our fountain atomic clock. By using RTND, the influences of the added noises are detected and subtracted precisely from the error signals before feeding back to the reference oscillator. The result shows that the statistical uncertainty of our fountain clock is improved by an order of magnitude to 2 x 10(-15). Besides, the frequency offset introduced by the noise is also corrected, while the systematic uncertainty is unaffected
Time-energy analysis of above-threshold ionization in the transverse direction of the linearly polarized laser pulses
No full textNational Key program for S&T Research and Development [2016YFA0401100]; National Basic Research Program of China [2013CB922201]We use a Wigner-distribution-like function based on the strong field approximation to study the photoelectrons emitted in the direction perpendicular to the laser field polarization in the linearly polarized laser pulses with different pulse durations. The calculated time-energy distributions for few-cycle laser pulses show distinct interference structures with regular energy separation of 2 omega, which are consistent with the corresponding energy spectra. Analysis shows that these interference structures can be attributed to the intracycle interference between electrons emitted at times when the laser field is close to its extreme, which is the main reason for the carpet-like pattern in the momentum spectrum. For the longer laser pulse, the energy spectrum shows a much more complicated structure consisting of main peaks with energy separation of 2 omega and many subpeaks in between the main peaks. The time-energy distribution indicates that the main peaks and subpeaks are ascribed to intracycle and intercycle interferences
A robust red-emitting phosphor-in-glass (PiG) for use in white lighting sources pumped by blue laser diodes
No full textKAKENHI [15K06448]; National Natural Science Foundation of China [61177050, 51572232, 61575182, 51272259]; China Postdoctoral Science Foundation [2016M601654]; Application Research Program of Commonweal Technology of Zhejiang Province [2015C31102]A red-emitting phosphor-in-glass (PiG) material was synthesized by dispersing CaAlSiN3:Eu2+ phosphor powders in a ZnO-B2O3-BaO-Al2O3 glass matrix. A fully densified translucent CaAlSiN3:Eu2+ PiG material was achieved at 650 degrees C for 40 min with an external quantum efficiency (QE) of 43%, transmittance of 30% at 640 nm and thermal conductivity of 1.12 Wm(-1)K(-1). The CaAlSiN3:Eu2+ particles were distributed in the glass matrix uniformly, and no serious interfacial reactions occurred between the glass matrix and the contained phosphor particles. Under the excitation of blue laser, the maximum luminous flux of CaAlSiN3:Eu2+ PiG sample is 39 lm at the laser flux density of 0.5 W/mm(2). Although luminous saturation was observed at high laser incident density, the PiG material would be a promising red color converter for use in white lighting sources pumped by blue laser diodes. (C) 2017 Elsevier B.V. All rights reserved
Structural evolution of axial intensity distribution during hot image formation
No full textThe structural evolution of the axial intensity distribution during hot image formation perturbed by a small circular optical obscuration is investigated in detail under different conditions. An analytic expression is derived for the axial intensity distribution around the conjugate plane by assuming the thickness of the nonlinear medium to be infinitely small. In view of the analysis of the axial intensity oscillation, the expression can be extensively utilized to characterize the intensity maxima for a nonlinear medium with a finite thickness. The nonlinear medium thickness and obscuration size both have great influence on the magnitudes and distributed features of the intensity maxima, which initially vary from multiple ones with comparable intensities to ultimately a maximum of one obviously remaining. The reason for this phenomenon is that the nonlinear medium acts like a low-pass filter to the scattering field, and optical interference exists between the scattering and background field. Furthermore, a fixed expression of nonlinear medium thickness and obscuration size is obtained to determine the dividing point of the alterations of the hot image intensity distribution. (C) 2017 Optical Society of Americ
Characterization of ultrashort pulses by time-frequency conversion and temporal magnification based on four-wave mixing at 1 mu m
No full textNational Natural Science Foundation of China (NSFC) [11604350, 61205103, 61405211]In order to characterize ultrashort pulses in real time at 1 mu m wavelength, a temporal imaging structure based on the four-wave mixing effect in highly nonlinear fibers is implemented and analyzed both theoretically and experimentally. It is found that both time-frequency transfer and the temporal magnification process can be realized approximately in one structure. The pulse widths of the signal laser measured by the time-frequency transfer and the temporal magnification process are 3.2 ps and 3.1 ps, respectively, which are nearly the same and are in agreement with the result of the autocorrelator. The temporal magnification factor is 33, and the temporal resolution is 380 fs. The method based on the temporal magnification process is inherently real time and single shot, which makes it suitable for applications in the measurement of high-power ultrashort pulses. The four-wave mixing time lens promises future applications in the characterization of the single-shot high-power short laser. (C) 2017 Optical Society of Americ