Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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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
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
Fabrication of polarization-independent waveguides deeply buried in lithium niobate crystal using aberration-corrected femtosecond laser direct writing
No full textNational Basic Research Program of China [2014CB921300]; National Natural Science Foundation of China [61590934, 11134010, 21375139, 61327902]; Youth Innovation Promotion Association of Chinese Academy of SciencesWriting optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1400 mu m, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing
Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface
No full textNational Natural Science Foundation of China [61307130, 11374316]; Shanghai Municipal Education Commission [14YZ077]; Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education MinistryWe present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of < 100 >-oriented semi-insulating gallium arsenide (SIGaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n- type GaAs at the surface of SI-GaAs. These n- type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy
Visible perfect reflectors realized with all-dielectric metasurface
No full textScience and Technology Development Fund of CAEP [2014A0302014]Highrefractive index dielectric material with negligible absorption loss can offer strong confinement of light, providing a potential alternative to plasmonic materials at optical frequencies. Here, we demonstrate perfect reflectors with unit reflection (over 99%), by utilizing the Mie resonances of high index amorphous titanium dioxide (alpha TiO2) metasurface arrays. Full-wave simulation and realistic optical constants analysis show that, these perfect reflectors exhibiting (magnetic or electric) dipole resonance can produce a perfect magnetic conductor (PMC) or a perfect electric conductor (PEC). Specifically, such a PMC mirror does not reverse the phase (phi, = 0) of the reflected electric field, resulting in the standing wave close to the mirror has an enhanced maxima field. Therefore, an object placed closely to the surface of a PMC will have a significant stronger interaction with electric field than that placed to a PEC. This unique PMC metasurface serving as back reflectors may enhance light absorption in devices with thin active films, such as solar cells, light-emitting diodes and biosensor devices
High-order exceptional points in optomechanics
No full textNSFC [11474087]; ARO [W911NF-16-1-0339]; RIKEN iTHES Project; MURI Center for Dynamic Magneto-Optics via the AFOSR [FA9550-14-1-0040]; JST, CRESTWe study mechanical cooling in systems of coupled passive (lossy) and active (with gain) optical resonators. We find that for a driving laser which is red-detuned with respect to the cavity frequency, the supermode structure of the system is radically changed, featuring the emergence of genuine high-order exceptional points. This in turn leads to giant enhancement of both the mechanical damping and the spring stiffness, facilitating low-power mechanical cooling in the vicinity of gain-loss balance. This opens up new avenues of steering micromechanical devices with exceptional points beyond the lowest-order two
Ptychographic phase microscope based on high-speed modulation on the illumination beam
No full textChinese Academy of Sciences (CAS) [902012312D1100101]; CAS [29201431151100301]A type of ptychography-based phase microscope was developed by integrating a spatial light modulator (SLM) into a commercial wide-field light microscope. By displaying a moving pattern on the SLM to change the sample illumination and record the diffraction intensities formed, both the modulus and phase of the transmission function of the sample could be accurately reconstructed with formulas similar to those of common ptychography. Compared with other kinds of phase microscopes, the developed microscope has several advantages, including its simple structure, high immunity to coherent noise, and low requirement for quality optics. In addition, defects in the illumination beam are also removed from the reconstructed image. Further, this microscope's fast data acquisition ability makes it highly suitable for many applications where highly accurate quantitative phase imaging is important, such as in living cells or other fragile biological samples that cannot sustain continuous imaging over a long period of time. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE
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
Spectrally and angularly resolved measurements of three-halves harmonic emission from laser-produced plasmas
No full textNational Science and Technology Innovation Foundation of Chinese Academy of Sciences [CXJJ-15S114, CXJJ-16S042]Spectra of three-halves harmonic emissions (3 omega(0)/2) from laser-produced plasmas were measured at different angles, including both forward and backward sides, from the direction of incident laser beams. The 3 omega(0)/2 emitted from carbon-hydrogen (CH) targets was observed to be larger than that from aluminum (Al) targets with the same incident laser intensity, which supports the argument that the two-plasmon decay (TPD) instability could be inhibited by using medium-Z ablator instead of CH ablator in direct-drive inertial confinement fusion. Besides, the measured 3 omega(0)/2-incident intensity curves for both materials suggest relatively lower threshold of TPD than the calculated values. In experiments with thin Al targets, the angular distribution of the blue-and red-shifted peaks of 3 omega(0)/2 spectra were obtained, which shows that the most intense blue-and red-shifted peaks may not be produced in paired plasmons, but the spectra produced by their 'twin' plasmons were not observed. Because 3 omega(0)/2 may have been influenced by other physical processes during their propagation from their birth places to the detectors, the mismatches on emission angle, wavelength shift, and threshold may be qualitatively explained through the assumption that small-scale light filaments widely existed in the corona of laser-produced plasmas
Temporally Modulated Phase Retrieval Method for Weak Temporal Phase Measurement of Laser Pulses
No full textNational Natural Science Foundation of China [61205103]We propose a simple iterative algorithm based on a temporally movable phase modulation process to retrieve the weak temporal phase of laser pulses. This unambiguous method can be used to achieve a high accuracy and to simultaneously measure the weak temporal phase and temporal profile of pulses, which are almost transform-limited. A detailed analysis shows that this iterative method has valuable potential applications in the characterization of pulses with weak temporal phase