Mr. Liang Shi Profile

Liang Shi

at Electronic Engineering Institute

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Publications (4)

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Proceedings Article | 4 December 2024 Paper

Research on surface plasma characteristics of CaF2 and MgF2 windows induced by laser

Liang Ren, Liang Shi, Xinyan Yang, Xi Wang

Proceedings Volume 13283, 132830O (2024) https://doi.org/10.1117/12.3033898

KEYWORDS: Plasma, Signal intensity, Windows, Calcium, Laser radiation, Chemical species, Temperature metrology, Magnesium, Ions, Spectral density

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Fluoride optical windows with low refractive index and good transparency have been widely used in photoelectric systems, laser systems and optical protective windows. The temperature and the electron number density of surface plasma of fluoride windows induced by 355 nm laser was calculated. The Saha-Boltzmann plot method was used for the calculation of the temperature of plasma. The approximate linear relationship between the electron number density and the Stark broadening of independent spectral lines was used for the calculation of the electron number density. The polynomial function was used to fit the background radiation intensity to solve the peak intensity and the signal-to-background radiation ratio of the emission spectrum. The effect of different laser fluence on the temperature of plasma and electron number density was analyzed. The temperature of plasma of CaF₂ and MgF₂ reached about 5178 K and 7230 K and the electron number density of CaF₂ and MgF₂ reached 6.052 x 10¹⁷ cm^-3 and 5.127 x 10¹⁶ cm^-3 at a laser fluence of 98.2 J/cm² . The signal-to-background radiation intensity ratio of the calcium atom emission spectrum of plasma of CaF₂ induced by 355 nm laser was between 0.2 and 0.5, while the calcium ion emission spectrum after one ionization showed a ratio of approximately 1.19.

Proceedings Article | 31 January 2020 Paper

Projections reconstruction in laser reflective tomography imaging through the use of basic wave pulse

Liang Shi, Lei Wang, Shilong Xu, Yong Wang, Yihua Hu

Proceedings Volume 11427, 114270E (2020) https://doi.org/10.1117/12.2549292

KEYWORDS: Reflectivity, Tomography, Image quality, Image processing

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Range-resolved laser reflective tomography is of great potential application in obtaining image information about an object with non-imaging laser radar system. The resulting time-dependent return signal which collected by non-imaging laser radar system provides one-dimensional raw projection data for reconstructing target image. However, this return signal can be regarded as the multi-convolution between the distribution function of target reflectivity, atmospheric transmission, detection circuit response and acquisition circuit response with the emitted laser pulse signal. In order to efficiently improve the reconstructed target image quality using short pulse laser, this paper presents a method used to restore the impulse response of target reflectivity modulation from the resulting time-dependent return signal so as to improve the reconstructed target image quality. This method is based on sending the laser and making it vertically irradiate to a profile of target in the front view to obtain basic wave pulse, then used it to recover the response of target reflectivity modulation. The experiment results show that this method is feasible and efficient.

Proceedings Article | 19 October 2016 Paper

Research on effect of reconstructed image quality in laser reflective tomography imaging

Liang Shi, Yi-hua Hu, Nan-xiang Zhao, Lei Yu

Proceedings Volume 10155, 101551P (2016) https://doi.org/10.1117/12.2246633

KEYWORDS: Reconstruction algorithms, Reflectivity, Tomography, Image filtering, Image quality, Laser imaging, Optical filters, Image restoration

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As a novel imaging method, laser reflective tomography imaging can be used for long-range, high-resolution target imaging, with advantages that its spatial resolution is unrelated with the imaging distance, but related with laser pulse-width, bandwidth of detectors and noise. And it can also be easily realized in technology. The principle of range resolved laser reflective tomography imaging was firstly introduced in this paper. The experiment system of laser reflective tomography imaging was established and the projection data acquired by the experiment system was then analyzed and discussed. In the view of the quality of reconstructed image which used filtered back projection algorithm, the influences on reconstructed image quality that those factors such as filter type and projection data cause were compared, and the most critical factor that effect constructed image quality was found out. Experiment results showed that projection data quality is the key factor to reconstructed image quality in laser reflective tomography, Projection data reconstruction which means extracting target range-resolved data from laser echo was useful to improve reconstructed image quality.

Proceedings Article | 19 October 2016 Paper

Numerical simulation research on wind field disturbance detecting with coherent laser

Lei Yu, Yihua Hu, Shilong Xu, Le Li, Liang Shi

Proceedings Volume 10155, 101551K (2016) https://doi.org/10.1117/12.2246598

KEYWORDS: Numerical simulations

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In order to grasp the information of wind field and disturbance in the airport in real time, and to ensure the safety of flight, a method of detecting wind field disturbance using coherent laser is presented. A model to solve the vector velocity of the wind field disturbance is established in this paper. Based on the radial velocity simulation of coherent laser echo signal, a reliable and effective radial velocity data is provided for inversing the vector velocity of the wind field disturbance. Actually, the radial wind velocity appears relatively large fluctuations due to the distribution inhomogeneity of aerosol particles and sensor noise in actual measurement. Therefore, the purpose of adding random noise into the above-mentioned inversion of the radial wind velocity is to simulate the measured radial wind velocity data. In the case of noise interference, the damping least square algorithm is proposed to solve the numerical optimal vector velocity of the wind field disturbance to verify the solving model. In addition, the vector velocity of the wind field disturbance is compared and analyzed under different scanning azimuth interval. Through the simulation results, it shows that the mean square error(MSE) of inversion result is smaller with the decrease of scanning azimuth interval. When the scanning azimuth interval is less than 60°, the mean squared error of the vector velocity of the wind field disturbance is less than 1.14m/s, horizontal direction disturbance quantity is less than 4°, which lays a good theoretical basis for the follow-up field tests.

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