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The Transmission Characteristic of Light in Random Medium with Non-spherical Scatters

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Tutor: LiZhiQuan
School: Yanshan University
Course: Detection Technology and Automation
Keywords: laser physics,random medium,shapes of scattering particles,finite different time
CLC: O436.2
Type: Master's thesis
Year:  2012
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Abstract:
Based on the laser physics and the electromagnetic fields of light, this thesisstudies the relevant issues of the phenomenon of laser radiation in random medium inrecent years. With the discovery of the laser phenomenon in random medium, expertsand scholars of related areas did many experimental and theoretical researches,theyalso discussed the factors may influence its characteristics extensively and obtainedappropriate results.According to the random laser theory, the multiple scattering of light waves inrandom medium causes the stimulated emission of radiation in gain medium, whichgenerates the laser. However, the scattering particles randomly distributed in two-dimensional model are usually equivalent to spherical in the theoretical research,which is a great simplification but ignores the function of the scattering particle shape.In view of this situation, the paper discussed the impact of the change of the scatteringparticle shape on the transmission of wave lights in the two- dimensional randommedium system. Based on the model of holistic scattering effect, we established thetwo-dimensional random medium model that non-spherical particles as scatteringparticles in it. Accordingly, we constructed the corresponding Maxwell equation.Using finite difference time domain (FDTD) method to solve Maxwell equation andrate equation, we got the transmission and spatial distribution of wave lights in thetwo-dimensional random medium model that non-spherical particles as scatters in it.By the spectrum transform of simulation data through Fourier transform(FFT), lightemission spectrum in frequency domain is obtained.Compared with previous studies, the simulation results show that the lightintensity in the non-spherical particle system is different from the intensity inspherical particle system, the former may result in oscillations as the concentration ofscattering particles increases. This means high energy can also be captured in thenon-spherical particle system of lower concentration if we choose appropriately, andthe threshold can be decreased. The emission spectrum shows mode competes innon-spherical particles systems are stronger than the spherical particle systems and areeasier to realize mode selection.
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