The Focusing Properties Of Partially Coherent Beams Passing Through A Lens With Spherical Aberration

Since the laser beam focusing by an optical system is a useful way for achieving higher power density and smaller beam width, it is applied in many areas such as material processing, the storage and disposal of light information, ICF etc. At present, the propagation of the fully coherent beams has been studied extensively, but the results show that the fully coherent beams are inexistent in practice, and all beams are attributed to the partially coherent beams or non-coherent beams. Furthermore, in some practical applications, the partially coherent beams have been demonstrated to possess advantages over the fully coherent beams. It has been shown that the partially coherent beams are less affected by the atmospheric turbulence than the fully coherent ones. Moreover, it has been applied in laser fusion for its advantages, such as low sensitivity to speckle and smoother focused spot etc. Therefore, the research on the partially coherent beams is one of the hottest topics in the field of laser beams.The present thesis is devoted to studying focused intensity distribution and focal switch phenomenon in Gaussian beams and Hollow beams, whose spatial degree of coherence is Bessel function of zero order, passing through a lens with spherical aberration. The main results achieved in this thesis can be summarized as follows:1. Based on the extensive Huygens-Fresnel principle(Collins formula), the on-axis beam intensity distribution and focal shift of the partially coherent hollow beams and the partially coherent Gaussian beams whose spatial degree of coherence is Bessel function of zero order propagating through a lens with spherical aberration have been investigated.2.Based on the propagation expression of partially coherent Gaussian beams passing through a spherical aberrated lens, it is shown that flat-topped beams or bottle beams can be acquired by changing spectral degree of coherence or spherical aberration efficient. The real focal plane is related to the spherical aberration coefficient and the spectral coherent degree.3.We investigate the focusing properties of partially coherent hollow beams passing through a lens with spherical aberration, and the influence of spherical aberration coefficient, spatial coherent length, and Fresnel number on the focal shift and focal switch. The focal shift is proportional to the absolute value of spherical aberration coefficient and the spectral degree of coherence. Otherwise, the focal switch is related to the Fresnel number, spherical aberration coefficient and spatial coherent length in the non-diaphragm optical system.