Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Exploring novel target structures for manipulating relativistic laser-plasma interaction
No full textAFOSR Basic Research Initiative (BRI) [FA9550-14-1-0085]; DFG (Germany) [Trnsregio TR18]The improved laser-to-pedestal contrast ratio enabled by current high-power laser pulse cleaning techniques allows the fine features of the target survive before the main laser pulse arrives. We propose to introduce the nano-fabrication technologies into laser-plasma interaction to explore the novel effects of micro-structures. We found out that not only laser-driven particle sources but also the laser pulse itself can be manipulated by specifically designed micro-cylinder and -tube targets, respectively. The proposal was supported by full-3D particle-in-cell simulations and successful proof-of-principle experiments for the first time. We believe this would open a way to manipulate relativistic laser-plasma interaction at the micro-size level
Laser performance of a broadband wavelength tunable Yb:germanophosphate glass with direct diode pumping
No full textNational Science Foundation of China (NSFC) [11504394, 61521093, 61378030]The laser performance of a new Yb:germanophosphate (Yb:GP) glass is investigated. A maximum output power of 826 mW at 1063 nm is achieved with direct diode pumping at 976 nm. The wavelength is tuned from 1034.47 to 1070.83 nm, corresponding to a tuning range of 36.36 nm. Thermal lens effects are investigated to optimize the optical cavity
Monte Carlo approach to calculate proton stopping in warm dense matter within particle-in-cell simulations
No full textGerman Academic Exchange Service (DAAD); China Scholarship Council (CSC)A Monte Carlo approach to proton stopping in warm dense matter is implemented into an existing particlein-cell code. This approach is based on multiple electron-electron, electron-ion, and ion-ion binary collision and accounts for both the free and the bound electrons in the plasmas. This approach enables one to calculate the stopping of particles in a more natural manner than existing theoretical treatment. In the low-temperature limit, when "all" electrons are bound to the nucleus, the stopping power coincides with the predictions from the Bethe-Bloch formula and is consistent with the data from the National Institute of Standard and Technology database. At higher temperatures, some of the bound electrons are ionized, and this increases the stopping power in the plasmas, as demonstrated by A. B. Zylstra et al. [Phys. Rev. Lett. 114, 215002 (2015)]. At even higher temperatures, the degree of ionization reaches a maximum and thus decreases the stopping power due to the suppression of collision frequency between projected proton beam and hot plasmas in the target
Optical multistability and Fano line-shape control via mode coupling in whispering-gallery-mode microresonator optomechanics
No full textNational Basic Research Program of China [2016YFA0301200]; National Natural Science Foundation of China (NSFC) [11574104, 11505131, 11675058]We study a three-mode (i.e., a clockwise mode, a counterclockwise mode, and a mechanical mode) coherent coupling regime of the optical whispering-gallery-mode (WGM) microresonator optomechanical system by considering a pair of counterpropagating modes in a general case. The WGM microresonator is coherently driven by a strong control laser field and a relatively weak probe laser field via a tapered fiber. The system parameters utilized to explore this process correspond to experimentally demonstrated values in the WGM microresonator optomechanical systems. By properly adjusting the coupling rate of these two counterpropagating modes in the WGM microresonator, the steady-state displacement behaviors of the mechanical oscillation and the normalized power transmission and reflection spectra of the output fields are analyzed in detail. It is found that the mode coupling plays a crucial role in rich line-shape structures. Some interesting phenomena of the system, including optical multistability and sharp asymmetric Fano-shape optomechanically induced transparency (OMIT), can be generated with a large degree of control and tunability. Our obtained results in this study can be used for designing efficient all-optical switching and high-sensitivity sensor
Ultra-high speed digital micro-mirror device based ptychographic iterative engine method
No full textNatural Science Foundation of China [11404207, 11647144]; Natural Science Foundation of Jiangsu Province of China [BK2012548, BK20130162]; Fundamental Research Funds for the Central Universities [JUSRP115A14]; Local Colleges and Universities Capacity Building Program [15110500900, 14110500900]To reduce the long data acquisition time of the common mechanical scanning based Ptychographic Iterative Engine (PIE) technique, the digital micro-mirror device (DMD) is used to form the fast scanning illumination on the sample. Since the transverse mechanical scanning in the common PIE is replaced by the on/off switching of the micromirrors, the data acquisition time can be reduced from more than 15 minutes to less than 20 seconds for recording 12 x 10 diffraction patterns to cover the same field of 147.08 mm(2). Furthermore, since the precision of DMD fabricated with the optical lithography is always higher than 10 nm (1 mu m for the mechanical translation stage), the time consuming positionerror-correction procedure is not required in the iterative reconstruction. These two improvements fundamentally speed up both the data acquisition and the reconstruction procedures in PIE, and relax its requirements on the stability of the imaging system, therefore remarkably improve its applicability for many practices. It is demonstrated experimentally with both USAF resolution target and biological sample that, the spatial resolution of 5.52 mu m and the field of view of 147.08 mm(2) can be reached with the DMD based PIE method. In a word, by using the DMD to replace the translation stage, we can effectively overcome the main shortcomings of common PIE related to the mechanical scanning, while keeping its advantages on both the high resolution and large field of view
Field-free molecular orientation enhanced by tuning the intensity ratio of a three-color laser field
No full textNational Natural Science Foundation of China [61221064, 61078037, 11134010, 61205208, 61521093]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB16]; International S&T Cooperation Program of China [2016YFE0119300]We theoretically study the field-free molecular orientation induced by a three-color laser field. The three-color laser field with a large asymmetric degree can effectively enhance the molecular orientation. In particular, when the intensity ratio of the three-color laser field is tuned to a proper value of I-3 : I-2 : I-1 = 0.09 : 0.5 : 1, the molecular orientation can be improved by similar to 20% compared with that of the two-color laser field at intensity ratio I-2 : I-1 = 1 : 1 for the same total laser intensity of 2 x 10(13) W/cm(2). Moreover, we investigate the effect of the carrier-envelope phase (CEP) on the molecular orientation and use the asymmetric degree of the laser field to explain the result. We also show the influences of the laser intensity, rotational temperature, and pulse duration on the molecular orientation. These results are meaningful for the theoretical and experimental studies on the molecular orientation
High-precision active synchronization control of high-power, tiled-aperture coherent beam combining
No full textNational Natural Science Foundation of China (NSFC) [61378030, 61775223, 61521093]We propose and demonstrate a high-precision active control technique for tiled-aperture coherent beam combining suitable for high-power laser pulses. The method is a hybrid structure based on the near-field interference fringe technique and single-crystal balanced optical cross-correlation, which enables the active loop to exhibit high accuracy, wide dynamic range, and good capacity for resisting energy disturbance. In the proof-of-principle experiment, we realized an adjustable beam combining bandwidth of approximately 100 Hz (limited by the speed of the piezoelectric transducer) and root-mean-square deviation of approximately lambda/51 for two beam channels with a combining efficiency of 93%
Hot-electron refluxing enhanced relativistic transparency of overdense plasmas
No full textResearch Foundation of the National Key Laboratory of Shock Wave and Detonation Physics [9140C670902140C67001]A new phenomenon of an enhanced relativistic transparency of overdense plasmas by the influence of hot-electron refluxing has been discovered via particle-in-cell simulations. When a p-polarized laser pulse, with intensity below the self-induced-transparency (SIT) threshold, obliquely irradiates a thin overdense plasma, the initially opaque plasma becomes transparent after a time interval that is linearly dependent on the thickness of the plasma. This phenomenon can be interpreted as a consequence of hot-electron refluxing, which reduces the effective electron density by longitudinal heating. When the laser intensity is higher than the SIT threshold, the penetration velocity of the laser in the plasma is enhanced when the refluxing is present. Published by AIP Publishing
Investigation of pre-pulse pumping laser for preserving temporal waveform of stimulated Raman scattering
No full textNational Science Foundation of China (NSFC) [11127901, 11134010]; Shanghai Sailing Program [15YF1413500]A modified polarized beam combination technique is proposed for preserving the temporal waveforms of stimulated Raman scattering. 1064 nm pre-pulse pumping lasers prior to the main pumping laser with a delay time are generated and injected into a Ba(NO3)(2) Raman medium to excite the crystal firstly. The influences of pre-pulse lasers with various energy levels on the temporal shapes of Raman lasers are investigated, and it is demonstrated that the temporal waveforms of the Raman laser are distorted once the energies of the pre-pulse are below and above the required energy for preserving the temporal shapes of Stokes radiation. It is also discovered that the temporal shape of the 1197 nm Raman laser cannot be perfectly preserved if the energy of the 1064 nm main laser is too low or the relative delay time is too large. Moreover, the optical conversion efficiency and Stokes laser energy obtained under pumping lasers with single and double intensity peaks are compared
Magetostatic amplifier with tunable maximum by twisted-light plasma interactions
No full textNational Natural Science Foundation of China [11605269, 11674341, 11675245]; Science Challenge Project [TZ2016005]Laser beams with Laguerre-Gaussian (LG) mode carry orbital angular momentum (OAM); however, when interacting with plasmas, the net angular momentum acquired by plasmas is basically zero after interaction. Here, we find when there exists a small magetostatic seed along the laser propagation direction, the barrier would be broken, giving rise to dramatic angular momentum transfer from LG-lasers to plasmas. Hence, the net OAM remaining in the plasmas system would continuously enhance the magetostatic field, until the corresponding Larmor frequency of electrons is comparable to the laser frequency in vacuum. Three-dimensional particle-in-cell simulations are performed to confirm our theory, producing spatial-uniform, temporal-stable and extremely-intense magetostatic fields