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    Wyświetlanie 1-7 z 7
    Tytuł:
    Laser frequency stability estimation and velocity measurement in the atmosphere with self-heterodyne
    Autorzy:
    Zhang, H.
    Wang, H.
    Zhao, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/174066.pdf
    Data publikacji:
    2016
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    frequency stability
    atmospheric propagation
    self-heterodyne
    Doppler velocity
    Opis:
    We present a novel method of self-heterodyne for laser frequency stability estimation in the atmosphere. At the same time, it is used in the Doppler velocity measurement for moving targets in the atmosphere. The transmission range is 16.2 km (round-trip propagation with 8.1 km) in the horizontal atmospheric path, and the measuring results showed that the frequency stability of the whole laser detection system is 53.4 kHz with 20.7 kHz stand deviation. This frequency stability is the integrated influence with the whole detection system not just for the laser, but it can be considered as the estimation of the laser’s frequency stability. It is much more practical for the heterodyne detection in the atmosphere. At last, the method of self-heterodyne was used for 16.2 km round trip velocity measurement. It is showed that the velocity absolute error is less than 1.5 cm/s in the turbulent atmosphere, and the relative error is not higher than 5%.
    Źródło:
    Optica Applicata; 2016, 46, 2; 305-316
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Abruptly autofocusing property of circular Pearcey vortex beams with different initial launch angles in harmonic potentials
    Autorzy:
    Liu, Xianglian
    Zhang, Di
    Zhao, Lijiao
    Li, Pu
    Zhang, Jianguo
    Liu, Yi
    Powiązania:
    https://bibliotekanauki.pl/articles/2172824.pdf
    Data publikacji:
    2022
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    autofocusing beam
    optical vortices
    Pearcey
    Opis:
    We have studied and explored the influence of different launch angles on the circular Pearcey beams (CPBs) without vortex or with vortex for the first time. Although launch angles can manipulate the focal length and the contrast of peak intensity of the CPBs, the shape and propagation trajectory of the CPBs maintain invariant. When the vortex is considered, the focal pattern and the contrast of peak intensity of the circular Pearcey vortex beams (CPVBs) can be changed by adjusting the magnitude of topological charges and the position of vortex. In addition, we have deliberated the propagation of the CPVBs under the action of double opposite optical vortices.
    Źródło:
    Optica Applicata; 2022, 52, 3; 417--428
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Digital watermarking algorithm based on 4-level discrete wavelet transform and discrete fractional angular transform
    Autorzy:
    Li, Jing-You
    Zhao, Chun-Hui
    Zhang, Guang-Da
    Powiązania:
    https://bibliotekanauki.pl/articles/2033921.pdf
    Data publikacji:
    2021
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    digital watermarking algorithm
    mix optical bistability
    Harris feature point detection
    discrete wavelet transform
    discrete fractional angular transform
    singular value decomposition
    Opis:
    Nowadays, there are many watermarking algorithms based on wavelet transform. The simple one is to insert directly the watermark into the wavelet transform coefficients. However, most of the existing watermarking schemes can only resist traditional signal processing attacks, such as image compression, noise and filtering. When the watermarked image is subject to geometric transformations, especially rotation attack, it is hard to detect the watermark successfully. In this paper, a digital watermarking algorithm is proposed based on 4-level discrete wavelet transform and discrete fractional angular transform. To enhance the security of the algorithm, the watermark is scrambled with the simplicity of Arnold transform and chaos-based mix optical bistability model, since the chaos is pseudorandom and sensitive to the initial values. And the watermark is embedded into the medium frequency sub-band of the 1-level wavelet decomposition according to the Harris feature point detection. Simulation results show that the proposed digital watermarking algorithm by combining 4-level discrete wavelet transform with discrete fractional angular transform could resist rotation attack and other common attacks.
    Źródło:
    Optica Applicata; 2021, 51, 4; 605-619
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of dispersion order on the spectral degree of polarization of stochastic electromagnetic pulsed beams
    Autorzy:
    Wang, H.
    Ding, C.
    Zhang, Y.
    Zhao, Z.
    Pan, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/173625.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    stochastic electromagnetic Bessel–Gauss pulsed beams
    dispersive aperture lens
    pulse
    duration
    temporal coherence length
    Opis:
    The analytical expression for the cross-spectral density function of stochastic electromagnetic Bessel–Gauss pulsed beams through a dispersive aperture lens is derived and used to study the changes in the spectral degree of polarization in an optical focus system. The changes in the spectral degree of polarization at the focal plane and on the z-axis are performed in the case of dispersion-free, dispersion of the first, second, and higher orders, respectively. It is shown that the dispersion affects the peak value of the spectral degree of polarization, and the higher order dispersion leads to a more obvious effect on the peak value of the spectral degree of polarization at the focal plane. On the z-axis, the spectral degree of polarization in the dispersion-free case is different form that in the dispersion case, however, the dispersion of different orders almost has the same effect on the spectral degree of polarization. The results obtained in this paper may be crucial for high precision laser detection.
    Źródło:
    Optica Applicata; 2014, 44, 1; 147-158
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Polarization properties of Gaussian–Schell model quantization field in a turbulent marine-atmosphere
    Autorzy:
    Zhao, Y.
    Xia, M.
    Wang, Q.
    Li, Y.
    Hu, Z.
    Sun, H.
    Zhang, Y.
    Powiązania:
    https://bibliotekanauki.pl/articles/173639.pdf
    Data publikacji:
    2016
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    polarization fluctuation
    Gaussian–Schell model
    marine-atmosphere
    Kolmogorov turbulence
    Opis:
    Polarization properties of Gaussian–Schell model quantization field propagating through the Kolmogorov turbulence of a marine-atmosphere channel are studied based on the degree of quantum polarization. The effective photon annihilation and creation operators of Gaussian–Schell model quantization field propagation in a marine-atmosphere are developed by making use of the extended Huygens–Fresnel integral of quantum field. The effects of the outer scale on the degree of polarization can be neglected. As the source transverse coherent width, the number of received photons, the inner scale of turbulent eddies, and the source transverse radius decrease or the re- fractive index structure parameter increases, the degree of polarization decreases. In theory, we find that the polarization fade of marine-atmosphere turbulence channels is larger than that of terrene-atmosphere turbulence channels under same transport parameters and the channel with a stronger turbulence strength will possess a larger detection area of a polarization signal, which have potentially important implications for free-space quantum key distribution.
    Źródło:
    Optica Applicata; 2016, 46, 3; 335-345
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Low atmospheric density measurement based on Rayleigh scattering of an ultraviolet laser
    Autorzy:
    Wang, R
    Yao, J.
    Zhong, K.
    Miao, Y.
    Cui, H.
    Zhao, X.
    Zhang, C.
    Powiązania:
    https://bibliotekanauki.pl/articles/174910.pdf
    Data publikacji:
    2013
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    atmospheric density measurement
    Rayleigh scattering
    ultraviolet laser
    Opis:
    The qualitative measurement of low atmospheric density in the air flow field has been investigated in this paper. The supersonic flow field with Mach number of 1.5 around the NACA0006 aerofoil has been numerically simulated and the transient slight pressure and low density atmosphere have been experimentally determined based on Rayleigh scattering of a 266 nm ultraviolet laser. The scattering patterns have been effectively captured under different atmospheric pressure of 4.5, 92, 470 and 710 Pa with laser energy of only 0.5 mJ. It has been demonstrated that in the pressure range from 4.5 to 1100 Pa, corresponding to the atmospheric density from 4.8105×10–5 kg/m3 to 1.279×10–2 kg/m3, the scattering intensity of an ultraviolet laser is linear to the pressure and density with the slope coefficient of 0.00968 a.u./Pa and 0.83226 a.u./(kg/m3×10–3). It has been proved that Rayleigh scattering is a promising technology for observation of instantaneous and multidimensional distribution of a supersonic flow field.
    Źródło:
    Optica Applicata; 2013, 43, 3; 597-605
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Colloidal crystal cladded microfiber for refractive index sensing
    Autorzy:
    Yan, H. T.
    Zhao, X Y
    Zhang, Ch.
    Zhen, Z Q
    Li, Q Z
    Cao, J X
    Xia, L X
    Powiązania:
    https://bibliotekanauki.pl/articles/174902.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    microfibers
    colloidal crystals
    refractive index sensing
    Opis:
    We investigate the evanescent field of a microfiber wrapped by colloidal crystals. The microfiber has the diameter of about 1 μm that is drawn from a single-mode fiber with an alcohol lamp. The colloidal spheres are further attached to the microfiber through thermal evaporation, then they self-assemble to crystal-like structures. The 400 nm, 590 nm, and 710 nm-diameter SiO2 colloidal spheres are used, respectively. The spectral responses are studied theoretically and experimentally, and the results agree with each other. It is revealed that the evanescent field of a microfiber could be modulated by the photonic band-gap of colloidal crystals. This characteristic is very useful in refractive index sensing for liquids.
    Źródło:
    Optica Applicata; 2014, 44, 2; 309-315
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-7 z 7

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