Study On The Focusing Properties Of Beams And The Spreading Of Partially Coherent Beams Propagating Through Turbulent Atmosphere

The propagation of laser beams is a topic that has considerable theoretical and practical interest. The present thesis is devoted to studying the focusing properties of beams and the spreading of partially coherent beams propagating through turbulent atmosphere. The main results achieved in this thesis summarized as follows: Study on Laser Propagation takes a great importance in both theoretical and practical fields. In this thesis we studied two aspects of laser propagation. They are focusing properties of laser beams and partially coherent beams propagating through turbulence atmosphere.1. The focal shift and focal switch of Hermite-cosh-Gaussian(HChG) beams are studied. The axial intensity distribution of HChG beams passing through a system with the aperture and lens separated is studied numerically. It is found that, under certain conditions there exist two intensity maxima along the axis, and an effective permutation of the focal point can take place due to the competition between the two maxima, i.e., focal switch appears. For HChG beams the conditions of focal switch are that the relative separation of the aperture and lens is 1, the beam order is even, the beam parameter is smaller than its corresponding critical value, and the truncation parameter is between its two corresponding critical values. Furthermore, It is shown that the relative transition height and the relative intensity sunken height increase with decreasing the beam parameter, but as the truncation parameter increases there exists a maximum of the relative transition height and the relative intensity sunken height, respectively. The focal switch can be used to focus within a large range, but the focal switch should be avoided in precision focus.