Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Corona discharge induced snow formation in a cloud chamber
No full textNational Basic Research Program of China [2011CB808100]; Shanghai Science and Technology Talent Project [12XD1405200]; 100 Talents Program of Chinese Academy of Sciences; Shanghai Pujiang Program; Laval University, Quebec City, CanadaArtificial rainmaking is in strong demand especially in arid regions. Traditional methods of seeding various Cloud Condensation Nuclei (CCN) into the clouds are costly and not environment friendly. Possible solutions based on ionization were proposed more than 100 years ago but there is still a lack of convincing verification or evidence. In this report, we demonstrated for the first time the condensation and precipitation (or snowfall) induced by a corona discharge inside a cloud chamber. Ionic wind was found to have played a more significant role than ions as extra CCN. In comparison with another newly emerging femtosecond laser filamentation ionization method, the snow precipitation induced by the corona discharge has about 4 orders of magnitude higher wall-plug efficiency under similar conditions
Coulomb interaction-induced jitter amplification in RF-compressed high-brightness electron source ultrafast electron diffraction
No full textNational Natural Science Fund [51132004, 11474096]; Shanghai Municipal Science and Technology Commission [14JC1401500]We have theoretically and experimentally demonstrated an RF compression-based jitter-amplification effect in high-brightness electron source ultrafast electron diffraction (UED), which degrades the temporal resolution significantly. A detailed analysis and simulations reveal the crucial role of the longitudinal and transverse Coulomb interaction for this jitter-amplification effect, which accord very well with experimental results. An optimized compact UED structure for full compression has been proposed, which can suppress the jitter by half and improve the temporal resolution to sub-100 fs. This Coulomb interaction-induced jitter amplification exists in nearly the whole ultrafast physics field where laser-electron synchronization is required. Moreover, it cannot be suppressed completely. The quantified explanation for the mechanism and optimization provides important guidance for photocathode accelerators and other compression-based ultrashort electron pulse generation and precise control
High-order dispersion control of 10-petawatt Ti:sapphire laser facility
No full textNational Basic Research Program of China [2011CB808101]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB16]; International S&T Cooperation Program of China [2016YFE0119300]; National Natural Science Foundation of China (NSFC) [61521093, 10734080, 60921004, 60908008, 61078037]A grism pair is utilized to control the high-order dispersion of the Shanghai Superintense Ultrafast Lasers Facility, which is a large-scale project aimed at delivering 10-PW laser pulses. We briefly present the characteristics of the laser system and calculate the cumulative B-integral, which determines the nonlinear phase shift influence on material dispersion. Three parameters are selected, grism separation, angle of incidence and slant distance of grating compressor, to determine their optimal values through an iterative searching procedure. Both the numerical and experimental results confirm that the spectral phase distortion is controlled, and the recompressed pulse with a duration of 24 fs is obtained in the single-shot mode. The distributions and stabilities of the pulse duration at different positions of the recompressed beam are also investigated. This approach offers a new feasible solution for the high-order dispersion compensation of femtosecond petawatt laser systems
Nonlinear dynamics investigation in few-cycle laser seeding of quantum cascade lasers: role of permanent dipole moment
No full textNational Natural Science Foundation of China (NNSF) [11374318, 11674312]; Chinese Academy of Sciences and Department of Human Resources and Social Security of ChinaThe ultrafast dynamics in the few-cycle laser seeding of quantum cascade laser (QCL) is numerically investigated via the exact solution of the full-wave Maxwell-Bloch equations. It is found that, with or without taking permanent dipole moment (PDM) into account, the QCL emission is quite different: beyond the fundamental frequency band, additional high and low bands occur for that with PDM, which forms an ultra broad quasi-comb. The origin for this is closely related to the generation of second order harmonic and direct current components as a result of PDM breaking down the parity symmetry. Moreover, the carrier-envelope phase (CEP) of laser seed is locked to the QCL output, no matter with or without PDM, and this phase controlled QCL maybe has more wide and convenient applications in related fields
Self-Tuning Mode-Locked Fiber Lasers Based on Prior Collection of Polarization Settings
No full textNational Natural Science Foundation of China [11434005, 11404211]; National Instrumentation Program [2012YQ150092]; Shanghai Science and Technology Commission [14JC1401600]; China Postdoctoral Science Foundation [2015M581634]; Hujiang Foundation of China [D15014]We present a method to discriminate stable mode-locked states of an all fiber erbium-doped laser based on nonlinear polarization rotation mechanism. The method has a balance between the accuracy and rapidness of the pulses discrimination. Mode-locked states are distinguished and confirmed by an amplitude discriminator, which reflects the repetition rate information of the pulses. An electronic polarization controller is used to precisely adjust the intracavity polarization states. The driving voltages of the electronic polarization controller at those mode-locked states are recorded as populations, and it is benefit to reduce the build-up time for mode locking. The populations are also recorded at operation temperature covering from 20 degrees C to 50 degrees C, which exhibits the repeatability and stability of the mode-locked states. Rapid self-tuning mode-locked fiber lasers could be achieved by the repeatability of the polarization settings under the stable temperature environment
Spectral modulation observed in artificial photosynthetic complexes by real-time vibrational spectroscopy
No full text100 Talents Program of Chinese Academy of Sciences (CAS), Strategic Priority Research Program of CAS [XDB1603, 61475169, 61521093, 11127901]; Japan Science and TechnologyBy real-time vibrational spectroscopy using 6.8 fs pulses, real-time vibronic coupling in stair-like zinc chlorin aggregates was studied. Besides the observed fast excitonic relaxation, amplitudes of coherent molecular vibrations are found to be linearly dispersed from the resonant peak as a function of their own vibrational frequencies. In addition, the initial phases of the molecular vibrations exhibiting clear pi phase jump have been observed. All these results indicate that coherent vibrations in the artificial chlorosome intermediate energy exchange between the laser fields around the resonant peak and those separated from it by photon energy equal to the vibrational frequencies
The controllable electron-heating by external magnetic fields at relativistic laser-solid interactions in the presence of large scale pre-plasmas
No full textNational Natural Science Foundation of China [11605269, 11674341, 11675245]; National Basic Research Program of China [2013CBA01504]; National Key Research and Development Program of China [2016YFA0401101]The two-stage electron acceleration/ heating model (Wu et al 2017 Nucl. Fusion 57 016007 and Wu et al 2016 Phys. Plasmas 23 123116) is extended to the study of laser magnetized-plasmas interactions at relativistic intensities and in the presence of large-scale preformed plasmas. It is shown that the electron-heating efficiency is a controllable value by the external magnetic fields. Detailed studies indicate that for a right-hand circularly polarized laser, the electron heating efficiency depends on both strength and directions of external magnetic fields. The electronheating is dramatically enhanced when the external magnetic field is of B equivalent to omega(c) /omega(0) > 1. When magnetic field is of negative direction, i.e. B < 0, it trends to suppress the electron heating. The underlining physics-the dependences of electron-heating on both the strength and directions of the external magnetic fields-is uncovered. With -infinity < B < 1, the electron-heating is explained by the synergetic effects by longitudinal charge separation electric field and the reflected 'envelop-modulated' CP laser. It is indicated that the 'modulation depth' of reflected CP laser is significantly determined by the external magnetic fields, which will in turn influence the efficiency of the electron-heating. While with B > 1, a laser front sharpening mechanism is identified at relativistic laser magnetized-plasmas interactions, which is responsible for the dramatical enhancement of electron-heating
Solitons in One-Dimensional Bose-Einstein Condensate with Higher-Order Interactions
No full textNational Natural Science Foundation of China [11791240178, 11674338, 11547024]We model a one-dimensional Bose-Einstein condensate with the one-dimensional Gross-Pitaevskii equation (1D GPE) incorporating higher-order interaction effects. Based on the F-expansion method, we analytically solve the 1D GPE, identifying the typical soliton solution under certain experimental settings within the general wave-like solution set, and demonstrating the applicability of the theoretical treatment that is employed
Spin dynamics of high-spin fermions in optical superlattices
No full textNational Key Research and Development Program of China [2016YFA0301504]We investigate the spin dynamics, starting from the initial band-insulating state, of fermionic high-spin atoms in optical superlattices. Through numerical simulations and analytical calculations, we determine the time evolution behavior of the system. When the spin-changing strength and tunneling strength are comparable, the spin dynamics feature a spin-changing oscillation with the amplitude modulated by the superexchange interaction. When the double-well potential is very shallow, the spin dynamics feature a simple harmonic oscillation with the oscillation frequencies related only to the spin-changing strength, which can be properly explained with the perturbation model
State Preparation in a Cold Atom Clock by Optical Pumping
No full textMinistry of Science and Technology of China [2013YQ09094304]; Youth Innovation Promotion Association of Chinese Academy of SciencesWe implement optical pumping to prepare cold atoms in our prototype of the Rb-87 space cold atom clock, which operates in the one-way mode. Several modifications are made on our previous physical and optical system. The effective atomic signal in the top detection zone is increased to 2.5 times with 87% pumping efficiency. The temperature of the cold atom cloud is increased by 1.4 mu K. We study the dependences of the effective signal gain and pumping efficiency on the pumping laser intensity and detuning. The effects of sigma transition are discussed. This technique may be used in the future space cold atom clocks