A Study On The Focusing Properties Of Laser Beams Passing Through An Astigmatic Lens

The focal switch phenomena of focusing properties in light field are topics of current interest, which play important roles in the development of the modern optics theory and laser technologies.First, a comprehensive review of the progress and the background of the research for the focal switch is given in the thesis. Then, the basic theories and analytical methods for the focal switch in beam propagation are introduced. The models of beams related to this thesis are also introduced. The main works of this thesis are as follows:1. The propagation formula of cosine-Gaussian beams passing through astigmatic ABCD optical system without aperture is derived by using the general Huygens-Fresnel diffraction integral formula. Based on this formula, the focal switch is found in the analyze of beams focusing properties and focal shift research. the influence of parameters on the axis intensity and the focal switch effect of cosine-Gaussian beams passing through an astigmatic lens are investigated in detail. The results of numerical calculations show that the focal switch of cosine-Gaussian beams passing through an astigmatic lens is dependent on the optical system parameter. For the first time, the research of focal switch shows that: the focal switch effect occurs not only when the optical system parameter is 1.0 as usual, but also when the optical system parameter takes other values, i.e. the focal switches could occur at both sides of the geometric focus. The dependence of the relative focal shift on the astigmatic parameterαis examined at different optical system parameter for a particular beam parameter. The value range of the astigmatic parameter a for the emergences of the optical switches is given when the optical system parameter does not equal to 1.0. The results also indicate that the more focal switches will excited by changing the Fresnel number.2. Based on the propagation theory of partially coherent beams, the axial intensity distributions of partially coherent modified Bessel-Gauss beams passing through an aperture astigmatic lens are studied. The influences of Fresnel number, truncation parameter, astigmatic parameter and spectral degree of coherence on the intensity distributions are investigated. Numerical results show that, multi-focal switches of partially coherent modified Bessel-Gauss beams can be found by altering the astigmatic parameter or changing the spectral degree of coherence on particular conditions. The multi-focal switches phenomenon is found in some special situations. The process and conditions for the multi-focal switches phenomenon and the conditions of focal switches are represented.3. The focal switch effect of Hermite-cosine-Gaussian beams passing through an astigmatic lens is investigated in detail based on the general Huygens-Fresnel diffraction integral formula. The results of numerical calculations show that the multi-focal switches are found in the analyze of beams focusing properties and focal shift research. The relative focal shift for the different astigmatic parameter and Fresnel number are examined at different optical system parameter for a particular beam parameter. The intensities of Hermite-cosine-Gaussian beams with different modulus passing through an astigmatic lens are discussed. The effect of modulus on axis intensity distribution and space intensity distribution of HCsG beams is examined. The results indicate that the astigmatic parameter is determinant in multi-focal switches phenomenon.