Design Of Diffractive Optical Elements For Laser Beam Shaping

In recent years, with the optoelectronics industry booming, more frequent application of the laser, the demand for beam shaping is growing. Diffractive optical elements with a thin thickness, light weight,easy to copy and many other advantages, have become a hot research field of the laser beam shaping. Diffractive optical elements for laser beam shaping is based on the principle of light wave diffraction theory. The using of computer-aided design, combined with ultra large scale integrated circuit production process, the diffractive optical elements can be etched with two or more of the depth of relief structures.This article discusses basic theory and methods for the design of diffractive optical elements for laser beam shaping in detail. A preliminary experimental study of Gaussian beam shaping is also taken. In this article, the major contents as follows:Firstly, we introduce the necessary theoretical basis--the scalar diffraction theory, for the design of DOE. we also describe the design principles and evaluation function about the performance of the DOE. Subsequently, the detailed description of how to use the GS algorithm, simulated annealing and genetic algorithms to design the DOE is taken. When the DOE are designed for focusing the incident plane beam a pattern of man, the results of these three methods are compared. The optical experiments comparison are also taken to verify the results obtained by numerical simulation. At last, a hybrid algorithm is described in detail, which combines the genetic algorithms and iterative Fourier transform algorithm. This method is taken to directly design the DOE with quantified phase levels.Secondly, the computer program about the corresponding diffractive optical element design process is written, for the Fraunhofer diffraction system for Gaussian beam shaping. Some phenomenon of the experiments are carried theoretical analysis. In the numerical simulations of the optical diffraction, there exists three methods, Fresnel transformation, convolution, and angular spectrum. The Fresnel transformation employs a single Fourier transform, the convolution employs two and the angular spectrum three. For the Fresnel diffraction system, these three method are all used to design DOE for Gaussian beam shaping and the corresponding experimental results are compared.Finally, in view of the conventional beam shaping technology only has a single output light intensity, and like color images generation,optical tweezers and other applications, we want to get different intensity distribution at different output plane. This chapter first describes a typical serial iterative algorithm to design the DOE for multi-plane reconstruction, and then describes the improved method in detail. The simulation and experimental results of the original serial iterative methods and the improved method are compared. Based on the existing DWL66 laser direct writing system, how to manufacture the DOE is described.