Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
Not a member yet
13355 research outputs found
Sort by
Generalized non-separable two-dimensional Dammann encoding method
No full textWe generalize for the first time, to the best of our knowledge, the Dammann encoding method into non separable two-dimensional (2D) structures for designing various pure-phase Dammann encoding gratings (DEGs). For examples, three types of non-separable 2D DEGs, including non-separable binary Dammann vortex gratings, non-separable binary distorted Dammann gratings, and non-separable continuous-phase cubic gratings, are designed theoretically and demonstrated experimentally. Correspondingly, it is shown that 2D square arrays of optical vortices with topological charges proportional to the diffraction orders, focus spots shifting along both transversal and axial directions with equal spacings, and Airy-like beams with controllable orientation for each beam, are generated in symmetry or asymmetry by these three DEGs, respectively. Also, it is shown that a more complex-shaped array of modulated beams could be achieved by this non-separable 2D Dammann encoding method, which will be a big challenge for those conventional separable 2D Dammann encoding gratings. Furthermore, the diffractive efficiency of the gratings can be improved around 10% when the non-separable structure is applied, compared with their conventional separable counterparts. Such improvement in the efficiency should be of high significance for some specific applications. (C) 2016 Elsevier B.V. All rights reserved
Attosecond chirp effect on the transient absorption spectrum of laser-dressed helium atom
No full textNational Natural Science Foundation of China [61690223, 11561121002, 61521093, 11127901, 11227902, 11404356, 11574332]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB16]; Shanghai Commission of Science and Technology Sailing Project [14YF1406000]; Shanghai Institute of Optics and Fine Mechanics Specialized Research Fund [1401561J00]; Youth Innovation Promotion Association CASWe theoretically investigate the attosecond transient absorption spectrum of helium atom in the presence of an infrared-dressed laser pulse upon scanning their relative delay, with the particular emphasis on the chirp effect of the attosecond pulse. By numerically solving the fully three-dimensional time-dependent Schrdinger equation, we identify the attoscecond chirp can induce the temporal shift of the absorption spectrogram along the delay axis. Additionally, it is found that the extent of the temporal shift is dependent on both the position of the absorption line and the infrared pulse wavelength, which is well confirmed and reproduced by a three-level model. Moreover, we demonstrate that the observed features can be quantitatively explained in terms of the indirect two-photon absorption processes through some virtual states. This effect might provide a way to measure the chirp of attosecond pulse in an all-optical way. (C) 2017 Optical Society of Americ
Electron localization of H-3(+) and HeH2+ in an ultrashort ultraviolet laser field
No full textNational Natural Science Foundation of China [11127901, 61521093, 11134010, 11227902, 11222439, 11274325]; National 973 Project [2011CB808103]Electron localization in the dissociation of the molecular ions H-3(+) and HeH2+ in an intense ultrashort ultraviolet laser pulse is studied with the Schrdinger equation. Two different dissociation channels, H-3(+) + n gamma -> H-2 + p and H-3(+) + n gamma -> H-2(+) + H, and HeH2++ n gamma -> He+ + p and HeH2++ n gamma -> alpha + H, for H-3(+) and HeH2+, are investigated, respectively. The numerical and analytical results both show that, for a molecular ion with an asymmetric double-well Coulomb potential, most electrons of the 1s sigma(g) state are localized at the potential well with lower energies. For electrons of the 2p sigma u state, most are localized at the potential well with higher energies when in a single ultraviolet laser pulse. Therefore, for H-3(+), most electrons of the dissociation state are stabilized at the potential well with higher energies (H+), for the lowest dissociation state is the 2p sigma(u) state. Most of the electrons of the dissociation state of HeH2+ are captured by the potential well with lower energies (He2+), because the lowest dissociation state is the 1ssg state and the 2p sigma(u) state is bounded
Identifying the source of super-high energetic electrons in the presence of pre-plasma in laser-matter interaction at relativistic intensities
No full textNational Natural Science Foundation of China [11304331, 11174303, 61221064]; National Basic Research Program of China [2013CBA01504, 2011CB808104]; USDOE at UCSD [DENA0001858]The generation of super-high energetic electrons influenced by pre-plasma in relativistic intensity laser-matter interaction is studied in a one-dimensional slab approximation with particle-in-cell simulations. Different pre-plasma scale lengths and laser intensities are considered, showing an increase in both particle number and cut-off kinetic energy of electrons with the increase of pre-plasma scale length and laser intensity, the cut-off kinetic energy greatly exceeding the corresponding laser ponderomotive energy. A two-stage electron acceleration model is proposed to explain the underlying physics. The first stage is attributed to the synergetic acceleration by longitudinal electric field and counter-propagating laser pulses, and a scaling law is obtained with efficiency depending on the pre-plasma scale length and laser intensity. These electrons pre-accelerated in the first stage could build up an intense electrostatic potential barrier with maximal value several times as large as the initial electron kinetic energy. Some of the energetic electrons could be further accelerated by reflection off the electrostatic potential barrier, with their finial kinetic energies significantly higher than the values pre-accelerated in the first stage
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
Moving toward optoelectronic logic circuits for visible light: a chalcogenide glass single-mode single-polarization optical waveguide switch
No full textNational Natural Science Foundation of China (NSFC) [11374316]In this paper, we propose an arsenic trisulfide (As-S) optical waveguide switch-based logic gate mainly comprised of a photorefractive Sn1As20S79 waveguide core and a LiNbO3 crystal substrate. In combination with the unique optical stopping effect of Sn1As20S79, this device can realize logical operations on an electrical signal and an optical signal, holding promises to be applied in optoelectronic logic circuits. While most of the previous research on As-S has focused on applications in the infrared regime, this device operates at the visible wavelengths of 632.8 and 441.6 nm, which are the specific wavelengths for optical stopping. As the kernel part of this logic gate, an optical waveguide switch based on an electro-optic coupler is employed to control optical signals by electrical signals, providing a solid foundation of operation for an electro-optic logic function. Some crucial design specifications of the switch are optimized by means of simulation analysis. It is found that less than 10 V of applied voltage is sufficient to realize a satisfactory function of the switch. A coupling efficiency of 90% and an extinction ratio of greater than 10 dB are achieved by simulating the lightwave propagation in the waveguide switch. Since the waveguide structure of the switch has no upper cladding, it is different from that of a ridge waveguide or a buried waveguide, and is, thus, convenient to fabricate by only using UV exposure without etching. Our work will open new possibilities for photoelectric hybrid logical operation in visible light, and, thus, provide fertile ground for applications in programmable optical chips. (C) 2017 Optical Society of Americ
The phosphorescence and excitation-wavelength dependent fluorescence kinetics of large-scale graphene oxide nanosheets
No full textNational Science Foundation of China [61108077, 61178085, 61008003, 61275147]; Key Project of Science and Technology of Shandong Province of China [2010GGX10127]; Shandong Province Natural Science Foundation of China [ZR2012AL11, ZR2013EML006]In this study, phosphorescence emission and a strong excitation-wavelength dependent fluorescence has been found in large-scale graphene oxide (GO) nanosheets. GO was covalently functionalized with triphenylamine (GO-CONH-TPA) in order to enhance the GO fluorescence quantum yield to 18%. The intersystem crossing (ISC) dynamics were studied using a femtosecond transient absorption technique, which appeared in the same timescale as the fluorescence dynamics of GO-CONH-TPA in both a polar solvent and solid film. Therefore, both, the solvation (several hundreds of picoseconds) and the intersystem crossing (ISC) gave rise to the strong excitation-wavelength dependent fluorescence. Moreover, the phosphorescence emission of the GO-CONH-TPA film at room temperature has been described for the first time in this report, and the lifetime of phosphorescence was found to be 6.95 ms. The fluorescence kinetics of GO-CONH-TPA were attributed to the aromatic hydrocarbon-carboxylic domain structure of GO
Wavelength scaling of atomic nonsequential double ionization in intense laser fields
No full textNational Basic Research Program of China Grant [2013CB922201]; NNSF of China [11334009, 11425414, 11527807]Experimental and theoretical investigations of the wavelength dependence of the nonsequential double ionization (NSDI) process of the xenon atom in intense laser fields are reported. The observed wavelength dependence of the ratio Xe2+/Xe+ deviates significantly from the prediction of the three-step model of ionization (sometimes called the "simple-man" model), both in the slope of the overall decrease with increasing wavelength and in the existence of some pronounced humps. A semiclassical model calculation reproduces the changing slope of the overall decrease, which is due to the interplay of wave-packet diffusion, Coulomb focusing, and a closely related Coulomb defocusing effect of the liberated electron. The hump is beyond the scope of the semiclassical model
Shearing interferometric electron beam imaging based on ptychographic iterative engine method
No full text提出了基于Mollenstedt电子双棱镜的电压扫描剪切干涉全场ptychographic iterative engine (PIE)显微成像技术.从低到高逐步改变电子双棱镜的电压,并同时记录所形成的剪切干涉条纹,待测样品透射电子束的强度和相位分布就可以用PIE算法得以快速重建,而且双棱镜的方向、位置和实际电场强度分布等诸多实验中不可避免地偏差都可以在迭代过程中自动得以更正.所提技术能够克服现阶段用电子束进行PIE成像的诸多技术困扰,从而有望推动PIE技术在电子显微成像领域的发展和应用.National Natural Science Foundation of China [11647144]; Natural Science Foundation of Jiangsu Province, China [BK2012548]Ptychographic iterative engine (PIE) method can provide high-resolution amplitude and phase distributions in short-wavelength imaging, such as electron beam and X-ray imaging. Traditional PIE relies on the sub field of view (sub-FoV) scanning, and the coincidence between these adjacent sub-FoVs is required in order to ensure the high accuracy in sample information retrieval. However, in the applications of electron beam imaging, attachments or contaminants on the sample surface will be dragged with the probe light during the sub-FoV scanning due to the adsorption of charges, and the inevitable attachment and contaminant shifting will change the probe light, therefore generating inconsistent probe light, and reducing the imaging resolution and accuracy, since the deteriorated probe light destroys the PIE scanning demands. In order to maintain the high resolution and accuracy in the electron beam imaging, the attachment and contaminant shifting during the sub-FoV scanning should be avoided. Here, a shearing interference based PIE using Mollenstedt biprism is proposed in this paper. Mollenstedt biprism is widely used in the electron beam imaging, and by applying the voltage to the wire, the generated electrical field can control the deflection of the electron beam, working similarly to a biprism modulating the wavefront passing through it. In the proposed approach, setting the Mollenstedt biprism after the sample, and changing the voltage on the Mollenstedt biprism, the beam deflection angle proportional to the added voltage can generate a series of interferograms with different fringe densities. Because the traditional sub-FoV scanning is replaced by wide-field scanning by changing the voltage on the Mollenstedt biprism, the proposed method can maintain the stable probe light, avoiding the inevitable attachment and contaminant shifting, and both the amplitude and phase can be retrieved from these interferograms by using a modified PIE algorithm. In order to verify the proposed PIE method, besides the theoretical analysis, numerical calculations are provided. The biprism phase distribution is adopted to simulate the electron beam deflection caused by the Mollenstedt biprism. Additionally, by changing the voltage on the wire, different biprism phase distributions are generated to produce various interferograms. By the modified PIE method, accurate amplitude and phase distribution within error less than 0.2% can be obtained through using less than 50 iterations, indicating a rapid convergence rate. Moreover, the errors in the imaging system, such as phase deviation, position shifting, and rotation are also quantitatively analyzed. Numerical computation proves that the direction of the biprism can be precisely determined according to the frequency distribution of the fringe, and the accurate sample information can still be retrieved even with a deviation of 30% in phase deviation and 30 mu m in position shifting, proving the deviations of the direction and position of the Mollenstedt biprism, as well as the phase distribution can be corrected automatically in the iterative process. Finally, the modified PIE relying on the lensfree configuration can reach the resolution of the diffraction limit in imaging similar to those PIE approaches. The proposed technique can overcome difficulties of current PIE in using electron beam, thus promoting the development and application of PIE in electron microscopy
Single-Shot Full-Field Characterization of Short Pulses by Using Temporal Annealing Modified Gerchberg-Saxton Algorithm
No full textNational Natural Science Foundation of China [61205103]The dispersive Fourier transform is suitable for characterizing short pulses. However, the traditional temporal Gerchberg-Saxton (GS) algorithm suffers from the timing error of measured dispersed waveforms, which limits the measurement performance of the temporal phase. An annealing modified GS algorithm that can simultaneously retrieve the temporal profile and phase is proposed. The inevitable timing error in the measurement can be accurately recovered by the algorithm, which significantly improves the retrieval performance. Based on the annealing modified GS algorithm, an experimental structure is proposed to achieve single-shot full-field measurement. The algorithm is analyzed numerically and the temporal waveform and phase of short pulses can be retrieved successfully in the experiment. The results indicate that this single-shot full-field measurement method is free from timing error, which is important for real applications. The simple single-shot method promises future applications to measure the temporal profile and temporal phase of short pulses with high accuracy simultaneously