Qiguang Zheng

Publications (6)6.57 Total impact

• Article: Nonlinear absorption in CuPc-doped PMMA thin film in the femtosecond regime: experimental and theoretical studies.

  Fang Li, Peixiang Lu, Hua Long, Guang Yang, Yuhua Li, Qiguang Zheng
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  ABSTRACT: The nonlinear absorption (NLA) properties of copper phthalocyanine (CuPc)-doped polymethylmethacrylate (PMMA) thin film in the femtosecond regime were investigated both experimentally and theoretically. The open-aperture (OA) Z-scan measurements of the film were carried out by femtosecond laser pulse. A transition from saturable absorption (SA) to reverse saturable absorption (RSA) was observed as the excitation intensity is increased. The rate equation analysis based on an developed efficient energy level model was performed and the intensity dependence of level populations was obtained, which reveals the source of NLA. The results show that the transition from SA to RSA is ascribed to the fifth-order effect of excited-state absorption (ESA) induced by two-photon absorption (TPA) process. Furthermore, it is found that the CuPc-doped PMMA thin film possesses a large fifth-order coefficient (beta((5))) of 0.24 x 10(-21)cm(3)/W(2). It indicates that the CuPc-doped PMMA thin film could be a promising candidate for optical limiting material.
  Optics Express 10/2008; 16(19):14571-81. · 3.59 Impact Factor
• Article: Femtosecond laser-induced sub-wavelength modification in lithium niobate single crystal

  Benhai Yu, Peixiang Lu, Nengli Dai, Yuhua Li, Xinlin Wang, Ying Wang, Qiguang Zheng
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  ABSTRACT: The microstructural modification of lithium niobate (LiNbO3) single crystal ablated by an 800 nm femtosecond laser pulse has been investigated. The ablation spots have been examined by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman microscopy systems. Sub-wavelength spots in an LiNbO3 crystal ablated by a femtosecond laser focused with a 20 × microscope objective (NA = 0.5) have been achieved. The spot size is 400 and 800 nm with 170 nJ single-pulse and 100 nJ 17-pulse ablation, respectively. The periodic ripples on the bottom of the ablation spot were found, and it has a width of 100 nm and a period of roughly 200 nm between troughs. The results show that the sub-wavelength structures may be formed by the multiple-photon excitation, and the femtosecond laser ablation is an innovative tool for manufacturing LiNbO3-based optical devices.
  Journal of Optics A Pure and Applied Optics 02/2008; 10(3):035301. · 1.92 Impact Factor
• Article: Noncrystalline micromachining of amorphous alloys using femtosecond laser pulses

  Xinlin Wang, Peixiang Lu, Nengli Dai, Yuhua Li, Changrui Liao, Qiguang Zheng, Lin Liu
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  ABSTRACT: Femtosecond laser micromachining of a Zr-based amorphous alloy in air, including measuring the ablation threshold, micro-drilling and trenching, was investigated. The threshold of ablating this amorphous alloy was determined by experiment. Laser-induced ablation and associated damage were examined by means of optical microscope, scanning electron microscopy, transmission electron microscopy and electron diffraction diagram. The results show that conventional processing method induced defects in the vicinity of machined area, such as crystallization, molten trace and spatter, were absent in femtosecond laser ablation area with selected parameters. This indicates that femtosecond laser ablation is a promising method for micromachining amorphous alloys without crystallization.
  Materials Letters. 61(21):4290-4293.
• Article: Single-phase β-FeSi2 thin films prepared on Si wafer by femtosecond laser ablation and its photoluminescence at room temperature

  Peixiang Lu, Youhua Zhou, Qiguang Zheng, Guang Yang
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  ABSTRACT: Single-phase β-FeSi2 thin films were prepared on Si(100) and Si(111) wafers by using femtosecond laser deposition with a FeSi2 alloy target for the first time. X-ray diffraction (XRD), field scanning electron microscopy (FSEM), scanning probe microscopy (SPM), electron backscattered diffraction pattern (EBSD), and Fourier-transform Raman infrared spectroscopy (FTRIS) were used to characterize the structure, composition, and properties of the β-FeSi2/Si films. The orientation of β-FeSi2 grains was found to depend on the orientation of the Si substrates, and photoluminescence at wavelength of 1.53 μm was observed from the single-phase β-FeSi2/Si thin film at room temperature (20 °C).
  Physics Letters A. 350:293-296.
• Article: Optical characterization of β-FeSi2 thin films prepared on fused quartz by femtosecond laser ablation

  Youhua Zhou, Peixiang Lu, Guang Yang, Hua long, Qiguang Zheng
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  ABSTRACT: Single-phase β-FeSi2 thin films have been grown on quartz substrates using femtosecond laser deposition (800 nm, 50 fs, 1 KHz) under gas pressure of 3.0×10−4 Pa. X-ray diffraction (XRD) and field-emission scanning electron microscopy (SEM) were used to determine the structural properties and surface images of the films. Typical XRD patterns of the film showed that no other diffraction peak except β-FeSi2 was found. The SEM results indicated that the films were composed of well-distributed grains, in the range 50–150 nm in diameter. In addition, normal incidence spectral transmittance and reflectance data suggested that the β-FeSi2 film has a direct energy gap of about 0.85 eV. The thickness of the layer and the refractive index of the film were determined by performed calculation in the wavelength range 1.9–2.7 μm. Furthermore, the Raman spectra of the films were also discussed.
  Physica B Condensed Matter 399(1):33-37. · 1.06 Impact Factor
• Article: Molecular structure and visible absorption maximum of cobalt phthalocyanine: Quantum calculations via semi-empirical methods

  Fang Li, Qiguang Zheng, Guang Yang, Peixiang Lu
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  ABSTRACT: The geometrical molecular structure of cobalt phthalocyanine was first optimized using the semi-empirical PM3 method and the electronic spectrum was then calculated using the ZINDO/S method. The results showed that the visible absorption maximum of cobalt phthalocyanine was precisely predicted by setting the π–π overlap weighting factor parameter in the ZINDO/S method at 0.793. Furthermore, the study of molecular orbitals indicates that the visible absorption maximum corresponds to electronic transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital. The splitting of the visible absorption maximum is related to the splitting of the doubly degenerated eg molecular orbital.
  Dyes and Pigments.