Study On Nonparaxial Propagation Characteristic Of Laser Beam

For most of the optical diffraction and the light beam transmission problems, the solution to the paraxial scalar diffraction theory can accurately reflect the real situation. With the development of laser technology, especially in recent years, semiconductor laser beam(with large divergence angle) is widely used, and the near field optical field has developed rapidly. Many traditional paraxial scale diffraction theory is no longer set up, so that people began to study transfer characteristic of the non-paraxial beam. The earliest is pioneered by Lax, after the work of Davis, Agrawal, Wunsche et al., they set up several main methods of non-paraxial beam propagation including the perturbation method, the angular spectrum method, the diffraction integral method. The main work of this dissertation is summarized as follows:In the review based on the scalar solution to the paraxial, the transmission methods of the non-paraxial beam are summarized, including the perturbation method, the angular spectrum method, the Rayleigh-Sommerfeld diffraction integral method, the operator method, the virtual point source method, Wigner distribution function method and the optical flow model. This paper introduces the core idea and the basic principle of each method, and meanwhile comparative analysis their merits and demerits.The accurate definition of non-paraxial vectorial beam intensity is presented in detail. Then a simple comparison with the definition of paraxial scalar beam intensity and of non- paraxial scalar beam intensity is made.Theory of angular spectrum method is studied, it is proved that this method has equivalent properties with the first Rayleigh-Sommerfeld diffraction integral method. Also, this paper has presented the approximate form of the angular spectrum solution in different approximate condition. And with Gaussian beam as an example, according to the different divergence angle, this paper has analyzed the variation of light intensity, confirmed that the non-paraxial solution is more accurate.Through the analysis of the waveguide mechanism of semiconductor lasers, the beam divergence angle is large, which belongs to non-paraxial beam. Followed by the emitting surface light field of the semiconductor laser, boundary conditions are determined. Then find out the expression of the half space of light field using the Rayleigh-Sommerfeld diffraction integral method. And through these two different methods, the direct integration and the stationary phase approximation, the far field vector expression of semiconductor lasers is derived. The calculated results show the vectorial theory is more precise, and the component along the optical field propagation direction can not be ignored.