Theoretical And Experimental Study Of The Partially Coherent Optical Transmission

Since the emergence of laser, the transmission and the focusing of spatially completely coherent beam have been studied extensively. Recently, considerable interest has been paid to the characteristic of focusing of the partially coherent beams. In practical applications, the partially coherent beams are demonstrated to have advantage over the spatially completely coherent beams. It has been shown that when the partially coherent beams propagate in the atmosphere, it may be less affected by turbulence than are fully coherent ones. Moreover in laser fusion a highly coherent beam is transformed into a partially coherent beam, for reducing the speckle and for getting more smooth focused spot. Besides, high power laser beam with the multi-transverse mode can be described by partially coherent beams. Therefore, the investigation of beam focus of partially coherent beams becomes more and more important research topic. On the other hand, with the developing of laser technology, the beam shaping also becomes interesting. Until now many methods have been proposed to generate the flat-top or bottle beam intensity distribution. This is due to the fact that laser beams with a flat-top profile or other kinds of profiles are desired in various applications, such as in the applications of laser fusion, laser heat treatment and optical data processing etc. Nevertheless most of study on the beam shaping is concentrated on the beam shaping of spatially completely coherent beams. Little work has been done on the beam shaping of partially coherent beams.The present thesis is devoted to studying the intensity distribution of the focused partially coherent beams, especially investigating the focal shift, the focal switch. The generation of partially coherent flat-top beams, partially coherent doughnut spots and partially coherent bottle beams has been investigated. The main results of this thesis can be summarized as follows:1. Based on the Huygens-Fresnel principle, we have derived the propagation expressions of the partially coherent beams passing through an annular lens optical system. The influence of the spectral degree of coherence, Fresnel number and truncated parameter on the focused intensity distribution and focal shift is analyzed.2. According to the Huygens-Fresnel principle, we have derived the propagation expressions of the partially coherent beams passing through dual-focus optical systems and investigated the phenomenon of focal switches of the partially coherent...