Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Dissociative ionization of CH2Br2 in 800 and 400 nm femtosecond laser fields
No full textNational Natural Science Fund [11604046, 11474096]; Natural Science Foundation of Shanghai [16ZR1448100]; Chenguang Program; Shanghai Education Development Foundation; Shanghai Municipal Education Commission [16CG38]; Shanghai-International Scientific Cooperation Fund [16520721200]We experimentally demonstrate the dissociative ionization of CH2Br2 molecules irritated by 800 and 400 nm femtosecond laser fields using time-of-flight mass spectra and dc-sliced ion imaging technology. Our results show that in both laser fields, CH2Br2 can ionize to CH2Br2+, then CH2Br2+ break one C-Br bond to produce fragments CH2Br(+) and Br(+). The charge assignment is determined by the ionization energy of the fragments. Additionally, in 400 nm laser fields, the CH2Br2+ can overpass a transition state to form an intermediate CH2Br-Br+, then the intermediate break C-Br bond to produce Br-2 or Br-2(+) via elimination channel
Dissociative photoionization of 1,2-dichloroethane in intense near-infrared femtosecond laser field
No full textNatural Science Foundation of Shanghai [16ZR1448100]; National Natural Science Fund [11604046, 51132004, 11474096]We experimentally demonstrate the dissociative photoionization of 1,2-C2H4Cl2 molecules in femtosecond laser field by time-of-flight mass spectrum and dc-slice imaging technology. Our results show the low kinetic energy components are from the dissociative ionization process of singly charged molecular ions, and the positive charge assignment are greatly influenced by the appearance energy of the fragment ions. The high kinetic energy components result from Coulomb explosion of multi-charged molecular ions, and the different angular distribution of these fragments along C-C and C-Cl bond dissociation can be explained by the potential energy surfaces of the molecular ions. (C) 2016 Elsevier B.V. All rights reserved
Highly compact CsPbBr3 perovskite thin films decorated by ZnO nanoparticles for enhanced random lasing
No full textNational Natural Science Foundation of China (NSFC) [61404017, 61475169]; Chongqing Postdoctoral Science Research Special Funded Project [Xm2016017]; Natural Science Foundation of Chongqing [cstc2017jcyjB0273]; 100 Talents Program of Chinese Academy of Sciences (CAS); Strategic Priority Research Program of CAS [XDB1603]Inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, I) have attracted enormous attention as a novel optoelectronic material with enhanced stability. However, the perovskite CsPbX3 thin films fabricated by onestep spin-coating method contain the defects of voids or pinholes, seriously affecting their amplified spontaneous emission (ASE) or lasing performance. To solve this issue, herein, we demonstrate that by simply introducing ZnO nanoparticles (NPs) into the CsPbBr3 precursor solution, the CsPbBr3:ZnO films synthesized by one-step spin-coating method exhibit enhanced crystallization, improved photoluminescence (PL) intensity and prolonged lifetime. Introducing the ZnO NPs can provide an effective route for CsPbBr3 nucleation during the spin-coating and annealing process, contributing to compact and smooth thin films with no obviously large voids or pinholes. Under the one-photon (400 nm) and two-photon (800 nm) femtosecond laser excitation, the ASE of CsPbBr3 and CsPbBr3:ZnO films have been investigated at room temperature, respectively. After the film compactness, surface smoothness and crystal size are modified by the ZnO additive, both the emission efficiency and the ASE threshold of the CsPbBr3:ZnO films have been improved in comparison with the pure CsPbBr3 films
Numerical investigations of signal-spectrum shaping based on conformal profile theory in optical parametric chirped pulse amplification
No full textNational Natural Science Foundation of China (NSFC) [61378030, 61521093]We proposed a theoretical description and numerical model of signal-spectrum shaping based on conformal profile theory and the three-dimensional coupling wave equations for improving the performance of optical parametric chirped pulse amplification (OPCPA). Using our model, we executed quantitative simulations of signal-spectrum shaping and compared the differences of spatiotemporal amplification characteristics between a shaped signal-spectrum and Gaussian signal-spectrum of an OPCPA based on LiB3O5 near 800 nm. By comparison, we found that the conversion efficiency from pump to signal can be dramatically boosted via signal-spectrum shaping. Meanwhile the amplified-spectrum profile, as well as the Fourier-limited pulse, can be improved significantly. We also found that the spatial spot profiles, for injecting a shaped signal or a Gaussian signal in OPCPA, are nearly the same before the saturation regime and at the maximum conversion efficiency or output energy
Propagation dynamics of radially polarized pulses in a gas-filled hollow-core fiber
No full textNational Natural Science Foundation of China (NSFC) [11604351, 11204328, 61521093, 61078037, 11127901, 11134010, 61205208]; National Basic Research Program of China [2011CB808101]The propagation dynamics of radially polarized (RP) pulses in a gas-filled hollow-core fiber (HCF) is numerically studied. It is found that the stable transverse mode of RP pulse in HCF is not TM01 mode, nor any eigenmodes in terms of Bessel functions. Compared with linearly polarized (LP) pulses, the RP pulses with the same initial pulse duration and energy have higher transmission efficiency, more uniform spectral broadening, and cleaner temporal profile after highly nonlinear propagation in HCF and better focusing properties. These results suggest that energetic few-cycle RP pulses can be generated more efficiently by directly spectral broadening the RP pulses in HCF followed by temporal compression. (C) 2016 Optical Society of Americ
Waveform control of enhanced THz radiation from femtosecond laser filament in air
No full textStrategic Priority Research Program of the Chinese Academy of Sciences [XDB160104]; Key Project from Bureau of International Cooperation Chinese Academy of Sciences [181231KYSB20160045]; State Key Laboratory Program of the Chinese Ministry of Science and Technology; 100 Talents Program of Chinese Academy of Sciences; Laval University, Quebec City, CanadaWe report on a waveform control of enhanced THz radiation along a femtosecond laser filament in air with a high voltage technique. By applying a DC high-voltage electric field from two sharp electrodes in a direction parallel to the laser filament and scanning it along the filament, the longitudinal evolution of amplified THz emission was demonstrated. By changing the position of the pair of electrodes along the laser filament, different waveforms of THz radiation were obtained. Due to the change of the plasma density distribution at the leading and trailing ends of a laser filament, the enhanced THz waveforms could have a phase shift of similar to pi. The technique is very simple. It could help to understand the THz generation process through external electric field assisted laser filamentation. Published by AIP Publishing
Real-time characterization of FM-AM modulation in a high-power laser facility using an RF-photonics system and a denoising algorithm
No full textFM-AM modulation of high-power lasers significantly affects laser performance. Therefore, precise measurement of the FM-AM modulation depth is necessary. The subsequent FM-AM modulation generated by group velocity dispersion when the laser pulse propagates through a fiber affects the measurement accuracy. In order to eliminate this effect, a waveform-acquisition module is proposed that converts a broad-spectrum pulse of 1053 nm to a narrow-spectrum pulse of 1550 nm, without affecting the waveform. In addition, a signal-processing algorithm based on the orthogonal matching pursuit method is implemented to remove the sampling noise from the wave-form. In this way, the signal-to-noise ratio of the measurement can be readily improved. Both theoretical and experimental results indicate that the proposed FM-AM modulation detection system is effective and economical. It can measure the FM-AM modulation depth precisely, and therefore shows considerable promise for future applications in high-power lasers. (C) 2017 Optical Society of Americ
Strong magnetic fields generated with a metal wire irradiated by high power laser pulses and its effect on bow shock
No full text强激光照射金属线圈后,会在打靶点附近的背景等离子体中诱发冷电子的回流,在金属丝内形成强电流源,从而产生强磁场.本文利用神光II高功率激光器产生的强激光照射金属丝靶,产生了围绕金属丝的环形强磁场.利用B-dot对局域磁感应强度进行了测量,根据测量结果,结合三维模拟程序,反演得到磁场的空间分布.再利用强激光与CH平面靶相互作用产生的超音速等离子体撞击该金属丝,产生了弓激波.通过光学成像手段研究了磁场对冲击波的影响,发现磁场使得弓激波的轮廓变得不明显并且张角变大.同时,通过实验室天体物理定标率,将金属丝表面等离子参数变换到相应的天体参数中,结果证明利用该实验方法可以在实验室中产生类似太阳风的磁化等离子体.National Basic Research Program of China [2013CBA01501]; National Natural Science Foundation of China [11135012, 11375262, 11520101003, 11503041]; Science Challenge Project [TZ2016005]Laboratory astrophysics is a rapid developing field studying astrophysical or astronomical processes on a high-power pulsed facility in laboratory. It has been proved that with the similarity criteria, the parameters in astrophysical processes can be transformed into those under laboratory conditions. With appropriate experimental designs the astrophysical processes can be simulated in laboratory in a detailed and controlled way. Magnetic fields play an important role in many astrophysical processes. Recently, the generation of strong magnetic fields and their effects on relevant astrophysics have attracted much interest. According to our previous work, a strong magnetic field can be induced by a huge current formed by the background cold electron flow around the laser spot when high power laser pulses irradiate a metal wire. In this paper we use this scheme to produce a strong magnetic field and observe its effect on a bow shock on the Shenguang II (SG II) laser facility. The strength of the magnetic field is measured by B-dot detectors. With the measured results, the magnetic field distribution is calculated by using a three-dimension code. Another bunch of lasers irradiates a CH planar target to generate a high-speed plasma. A bow shock is formed in the interaction of the high-speed plasma with the metal wire under the strong magnetic condition. The effects of the strong magnetic field on the bow shock are observed by shadowgraphy and interferometry. It is shown that the Mach number of the plasma flow is reduced by the magnetic field, leading to an increase of opening angle of the bow shock and a decrease of the density ratio between downstream and upstream. In addition, according to the similarity criteria, the experimental parameters of plasma are scaled to those in space. The transformed results show that the magnetized plasma around the wire, produced by X-ray emitted from the laser-irradiated planar target in the experiment, is suitable for simulating solar wind in astrophysics. In this paper, we provide another method to produce strong magnetic field, apply it to a bow shock laboratory astrophysical study, and also generate the magnetized plasma which can be used to simulate solar wind in the future experiments
Colloidal PbS quantum dot-AlPO4 nanoporous glass composites: Controllable emission and nonlinear absorption
No full textNational Natural Science Foundation of China [61275208]; Research Complex at Harwell, UKIn recent years, near-infrared (NIR) materials beyond the visible region (700-2500 nm) has emerged as a promising research field with applications toward telecommunications, photovoltaic, in-vivo imaging, etc. Such technologies will benefit greatly from the advantageous properties of NIR materials including broadband tunable emission, nonlinear optical properties, photostability, and simple chemical processing. Here, we report a facile approach to fabricate high stable and controllable luminescent NIR-emitting composites by confining PbS colloidal quantum dots (CQDs) in sol-gel nanoporous AlPO4 glasses. The transmission electron microscopy images combined with X-ray photoelectron spectra in different depth of PbS-AlPO4 composites (PACs) reveal the successful solidification of CQDs in nanoporous structure of glasses. The controllable luminescence of PACs is dependent on the size of PbS CQDs in solution and glass pore size. We show that the broadband (270 nm) and bimodal emission of PACs are tailored by designing different composited strategies on the incorporation of colloidal quantum dots in AlPO4 nanoporous glasses. Ultrafast nonlinear optical properties of PACs were investigated using an open-aperture Z-scan technique with 515 nm 340 fs pulses. The PACs exhibited obvious reverse saturable absorption in our experiments, with a nonlinear absorption coefficient of 7.17 x 10(-2) cm/GW. Furthermore, the stability of PACs is investigated by emission spectra from a few days to 180 days. The results imply PACs has a better stability than other regular PbS-solid materials such as PbS-Al2O3 films and close packed PbS-filter paper systems
Covalent-linked porphyrin/single-walled carbon nanotube nanohybrids: synthesis and influence of porphyrin substituents on nonlinear optical performance
No full textNational Natural Science Foundation of China [51432006, 51172100]; Ministry of Education; State Administration of Foreign Experts Affairs for the 111 Project [B13025]; Ministry of Education of China for the Changjiang Innovation Research Team [IRT14R23]; 100 Talents Program of CAS; Ministry of Science and Technology of China for International Science Linkages Program [2011DFG52970]; Australian Research CouncilElectron-withdrawing 4-cyanophenyl-, electronically innocent phenyl-, and electron-donating 4-dimethylaminophenyl-functionalized porphyrin/single-walled carbon nanotube (SWCNT) nanohybrids have been synthesized and characterized by ultraviolet-visible absorption, steady-state fluorescence, Fourier transform infrared, and Raman spectroscopies, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. Nonlinear optical (NLO) studies using the Z-scan technique revealed that both the cyano (CN) and the dimethylamino (DMA) substituents have a positive effect in optimizing the optical limiting performance of the SWCNT-porphyrin nanohybrids, owing to increased reverse saturable absorption (RSA) of the porphyrin moieties after functionalization by CN or DMA. In comparison with CN, the DMA group has a more positive influence on the porphyrin excited states and thereby the RSA and NLO activity. (C) 2017 Elsevier Ltd. All rights reserved