Zuoqiang Hao

Changchun University of Science and Technology, Changchun, Fujian, China

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Publications (16)34.32 Total impact

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    ABSTRACT: Evolution of a plasma plume from an Al target ablated with a nanosecond 1064 and 355 nm laser respectively under oblique incidence in air is studied using the time-resolved shadowgraph imaging technique. The characteristics of plasma plume expansion with different focusing conditions (focal point on, ahead of and after the target surface) are experimentally investigated. Experimental results show that the evolution of the plasma plume is strongly influenced by air breakdown which occurs prior to the laser beam reaching the target. Without the occurrence of air breakdown, the temporal evolution of the Al plasma plume with both UV and IR ablation laser wavelengths shows the plume expansion with an ellipsoid-shaped plume front travelling mainly against the incoming laser beam due to the formation of a laser-supported detonation wave at the initial stage of laser ablation, and then the shape of the plume front turns into a sphere. Experimental results also show that a higher portion of the laser pulse energy reaches the target surface at UV laser wavelength than that of an IR laser due to the higher penetrating ability of the UV laser wavelength to the plasma.
    Journal of Physics D Applied Physics 12/2013; 46(48):5207-. · 2.53 Impact Factor
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    ABSTRACT: Microwave guiding along double parallel lines of femtosecond-laser-generated plasma filament has been demonstrated over a distance of about 8 cm in air, corresponding to a maximum microwave signal intensity enhancement more than sixfold the free-space propagation. It is shown that the operating frequency and the line electric width influence the propagation coefficient of microwaves propagating along this transmission line. Based on channeling microwaves along this line and by measuring and comparing the propagated microwave signals, the basic parameters of laser-generated plasma filament, namely, its electron density and conductivity, are obtained.
    Physical Review E 07/2013; 88(1-1):013104. · 2.31 Impact Factor
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    ABSTRACT: Aluminum alloy was analysed by using femtosecond laser-induced breakdown spectroscopy under argon, air and helium environments at pressures ranging from 1 to 80 kPa. The results reveal that both spectra intensity and lines detection are significantly influenced by the ambient conditions. In all ambient gases, as the pressure increases the emitted light initially increases, attains its maximum intensity and then decreases with further increase in pressure. It is also observed that some lines are well detected at low pressures in argon while they are absent at the same pressures in helium. In addition, plasma parameters such as electron densities and electron temperature have been investigated at different pressures in the three gases. Hotter and denser plasma has been observed in argon than that in air and helium. Furthermore, it is noted that plasma parameters at relative low pressures of argon (1 kPa) are similar to those obtained at relative high pressures of helium (80 kPa). The optimum conditions for the use of argon and helium as ambient gases have been determined. In fact, argon provides the best environment of femtosecond laser-induced breakdown spectroscopy only at relative low pressures while helium constitutes a good environment only at relative high pressures.
    Journal of Physics D Applied Physics 06/2013; 46(28):285204. · 2.53 Impact Factor
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    ABSTRACT: We introduce a simple, fast, and non-intrusive experimental method to obtain the basic parameters of femtosecond laser-generated plasma filament. The method is based on the channeling of microwaves along both a plasma filament and a well-defined conducting wire. By comparing the detected microwaves that propagate along the plasma filament and a copper wire with known conductivity and spatial dimension, the basic parameters of the plasma filament can be easily obtained. As a result of the possibility of channeling microwave radiation along the plasma filament, we were then able to obtain the plasma density distribution along the filament length.
    Applied Physics Letters 05/2013; 102(20). · 3.79 Impact Factor
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    ABSTRACT: Characteristics of shock wave as well as its evolution of aluminum plasma produced by nanosecond YAG laser is investigated by time-resolved optical shadowgraph images. Experimental results show that shock wave is strongly influenced by the laser parameters and target arrangement. Shock waves from aluminum plasma and air plasma are observed simultaneously by shadowgraphs when the distance from lens to target surface (DLTS) is longer than the lens focal length, and a narrow bright "line" is observed in the region where shock waves from Al plasma and air plasma meet. The longitudinal expansion velocity of shock wave from Al plasma is largely influenced by DLTS and laser intensity as well, and it increases with laser intensity at the early stage of plasma expansion and reach to a maximum of 8.1×104 m/s.
    Proc SPIE 05/2013;
  • Acner Camino, Zuoqiang Hao, Xu Liu, Jingquan Lin
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    ABSTRACT: Deterministic wavelength-dependent multifilamentation is controlled in fused silica by adjusting the diffraction pattern generated by a loosely focusing 2D periodic lens array. By simply translating the sample along the propagation axis the number and distribution of filaments can be controlled and are in agreement with the results of linear diffraction simulations. The loose focusing geometry allows for long filaments whose distribution is conserved along their propagation inside the sample. The effect of incident energy and polarization on filament number is also studied. Laser filamentation controlled by a microlens array could be a promising method for easy and fast 3D track writing in transparent materials.
    Optics Express 04/2013; 21(7):7908-15. · 3.55 Impact Factor
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    ABSTRACT: A hollow cylindrical plasma waveguide, which cladding consists of a large number of a chaotically distributed plasma filaments induced by the propagation of femtosecond (fs) laser pulses in air, is shown to support guided modes of pulsed infrared (IR) laser radiation. Taking into account the discontinuity and the finiteness of the waveguide cladding, the loss coefficient loss of the laser radiation is calculated for different spatial configurations. We report how the waveguide loss depends on its structural parameters like normalized plasma diameter, distance between filaments, core-radius, cladding's thickness, and filaments' electron density. For typical plasma parameters, the loss of the fs plasma waveguide is found to be lower than that of freely propagating IR laser beams to distances in the order of the filamentation length. This fact allows the delivery of collimated pulsed laser light over long distances in atmospheric air, which is necessary for optical-based remote sensing and the detection of chemical and biological agents.
    Optics Communications 01/2013; · 1.44 Impact Factor
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    ABSTRACT: We have explored here a hollow cylindrical laser plasma multifilament waveguide with discontinuous finite thickness cladding, in which the separation between individual filaments is in the range of several millimeters and the waveguide cladding thickness is in the order of the microwave penetration depth. Such parameters give a closer representation of a realistic laser filament waveguide sustained by a long stable propagation of femtosecond (fs) laser pulses. We report how the waveguide losses depend on structural parameters like normalized plasma filament spacing, filament to filament distance or pitch, normal spatial frequency, and radius of the plasma filament. We found that for typical plasma parameters, the proposed waveguide can support guided modes of microwaves in extremely high frequency even with a cladding consisting of only one ring of plasma filaments. The loss of the microwave radiation is mainly caused by tunneling through the discontinuous finite cladding, i.e., confinement loss, and is weakly dependent on the plasma absorption. In addition, the analysis indicates that the propagation loss is fairly large compared with the loss of a plasma waveguide with a continuous infinite thickness cladding, while they are comparable when using a cladding contains more than one ring. Compared to free space propagation, this waveguide still presents a superior microwave transmission to some distance in the order of the filamentation length; thus, the laser plasma filaments waveguide may be a potential channel for transporting pulsed-modulated microwaves if ensuring a long and stable propagation of fs laser pulses.
    Physics of Plasmas 01/2013; 20(1). · 2.38 Impact Factor
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    ABSTRACT: We theoretically investigated the electromagnetic wave (EMW) transmission along two parallel wires of laser plasma filaments produced by the filamentation of ultrafast laser pulses in air. Many factors, such as wire diameter and separation, electron density, and operating frequency are shown to influence the propagation loss. By taking into consideration the radiation and transmission effects of the wires, the calculations of the two parallel filament wires reasonably agrees with that of the standard commercial twin-lead wire. Specifically, the optimum separation of the two wires is determined for a given frequency and an effective electron density of the wires. When compared with free-space propagation, transmission enhancement of tens dB is obtained using optimized wire configurations. Thus, the two plasma wires may be a potential channel for point to point directed delivery of EM energy or communication of pulsed-modulated EM radiation.
    Applied Physics B 01/2013; 111(3). · 1.78 Impact Factor
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    ABSTRACT: The effects of ambient pressures on the intensity of spectral emission, electron temperature and density of femtosecond laser produced plasma have been investigated. For this purpose, Al targets were ablated by employing a Ti: Sapphire laser system (50fs, 800nm) under various filling pressures of argon gas. The optical emission spectroscopy of Al plasma has been studied using the Laser Induced Breakdown Spectroscopy (LIBS) system. The results indicate that the pressure of the ambient atmosphere is one of the controlling factors of the plasma plume characteristics. The measurements reveal also that some lines which are nearly unresolved at high pressures become well resolved at low pressures.
    Optoelectronics and Microelectronics (ICOM), 2012 International Conference; 08/2012
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    ABSTRACT: Nano- and microscale structures on a material surface formed by femtosecond laser processing have greatly changed optical characteristics, wettability, as well as other properties of the material. In this work, we report the formation of nano- and microscale structures on a spherical Al surface with femtosecond laser filament, and find that the filament-processed surface has a strong light-trapping ability from UV to IR (0.2–2.5 μm). Our result demonstrates that this method can be used to process a spherical surface without the complexity of a 4-axis sample control, and in principle, it is applicable to any non-planar sample.
    Applied Physics Letters 05/2012; 100(20). · 3.79 Impact Factor
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    ABSTRACT: A proposed model for a circular bunch of plasma filaments used as a virtual waveguide for microwave radiation is presented. The virtual circular guiding system is shown to support guided modes of electromagnetic radiation in the millimetre and sub-millimetre wavelength range. Transmission is due to total internal reflection of the wave on the less dense plasma cladding. The energy loss of microwave radiation propagating in such a virtual waveguide is calculated. Optimum spatial configurations of circular plasma filament waveguides are proposed. Plasma filament waveguides are shown to enhance microwave transmission relative to free space propagation of microwave radiation over limited distances.
    Journal of Physics D Applied Physics 01/2012; 45(6):065102. · 2.53 Impact Factor
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    ABSTRACT: The abilities to trigger and guide high-voltage discharge by using single and multiple filaments (MFs) are experimentally studied. It is shown that the discharge voltage threshold can be reduced significantly in both regimes of single and MF; however, the MF does not gain a larger reduction than a single filament. This behavior of the MF is attributed to the single discharge path rather than simultaneous multiple ones as one might expect during the discharge process.
    Optics Letters 01/2012; 37(2):259-61. · 3.39 Impact Factor
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    ABSTRACT: A microwave waveguide that consists of a set of laser plasma filaments produced in air by the propagation of femtosecond laser pulses is investigated according to the hollow conducting waveguide concept. The conductivity, skin depth of the electromagnetic waves in this plasma waveguide and the energy required to excite such a waveguide are calculated for different possible configurations. A hollow conducting plasma waveguide is shown to support guided modes of electromagnetic radiation from millimetre to centimetre wavelength range. Our calculations show that, under the concept of conducting waveguide, it is more suitable to use the TE01 mode rather than TE11 to achieve an extended attenuation length. The attenuation length of the low-loss mode TE01 is shown to be dependent on the geometry of the plasma waveguides, the operating frequency and the plasma effective electron density. The effect of the plasma wall density spread on TE01 propagation is evaluated. Using the hollow conducting plasma waveguide operating in TE01 mode, an enhancement of microwave transmission over both free space propagation and dielectric plasma waveguide is obtained.
    Journal of Physics D Applied Physics 01/2012; 45(26). · 2.53 Impact Factor
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    ABSTRACT: Micro- and nanoscale structures on a material surface formed by femotosecond laser processing have greatly changed its optical characteristics. In this work, the coloring of Al surface has been realized with scanning focused femtosecond laser beam on the Al surface. We further apply femtosecond laser filamentation to form micro- and nano-structures on a spherical Al surface, resulting in a black appearance of the spherical Al. This work opens ways to fabricate strong light-trapping micro- and nano-structure on a non-planar surface without the complexity of a 4-axis sample control.
    Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO), 2012 International Conference on; 01/2012
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    ABSTRACT: We investigated the possibility of Sommerfeld surface waves to propagate along a conducting plasma channel produced by the filamentation of ultrafast laser pulses in air. Using the approximation of a homogenous cylindrical wire of laser plasma filaments, the phase velocity and the propagation loss of different wire configurations are calculated. The phase velocity of the propagating wave proved to be close to the speed of laser pulses, which makes attaching to such instantaneous plasma channel feasible over distances in the order of the filament length. Wire diameter, electron density and operating frequency are appearing to influence the attaching distances and propagation loss. The attenuation of the propagating wave along the plasma wire appears to be lower than that of free space over some distances in the order of the filamentation length, which opens exciting perspectives for short distance point to point wireless transmission of pulsed-modulated microwaves.
    Applied Physics B 108(4). · 1.78 Impact Factor