Influence Of Turbulence On The Total Intensity Distribution And Spreading Of Apertured Polychromatic Partially Coherent Beams

Theories and experimental studies have shown that atmospheric turbulence will lead to beam spreading and decreasing. In practice, the propagation of laser beams in atmospheric turbulence is limited by apertures. On the other hand, the polychromatic beam has important applications in atmospheric communication, objective lighting, and so on. And moreover, the practical laser beams exists the partially coherent beams. Therefore, it is very significant to study the propagation properties of apertured polychromatic partially coherent beams. In this thesis, polychromatic Gaussian Schell-model (GSM) beams were taken as the typical examples of polychromatic partially coherent beams. Based on the extended Huygens-Fresnel principle, the influence of turbulence on the total intensity distribution and beam spreading is studied in detail. The main results obtained are summarized as follows:(1)The expression for the total intensity of apertured polychromatic GSM beams propagating through atmospheric turbulence is derived by using the quadratic approximation of the Rytov's phase structure function, strong fluctuation of turbulence model and the method of the window function being expanded into a finite sum of complex-valued Gaussian functions. It is shown that the total intensity of apertured polychromatic GSM beams with smaller beam truncation parameter, beam coherence parameter and bandwidth will be less affected by the turbulence. In particular, apertured polychromatic GSM beams will be less affected by the turbulence than that for the unapertured case, and apertured polychromatic GSM beams will be more affected by the turbulence than that for the quasi-monochromatic case.(2)The expression for the mean squared beam width of apertured polychromatic GSM beams propagating through atmospheric turbulence is derived by using the quadratic approximation of the Rytov's phase structure function,strong fluctuation of turbulence model and the method of the window function being expanded into a finite sum of complex-valued Gaussian functions. It is shown that the mean squared beam width of apertured polychromatic GSM beams with the increases of propagating distance. The apertured polychromatic GSM beams beam spreading in atmospheric turbulence is less affected by the beam parameter than that in free space. In particular, the beam spreading of apertured polychromatic GSM beams with smaller beam truncation parameter, smaller beam coherence parameter and larger bandwidth will be less affected by the turbulence. In addition, apertured polychromatic GSM beams will be less affected by the turbulence than that for the quasi-monochromatic case.