Design Of Diffractive Optical Elements For Laser Beam Shaping

Recently, laser technology has been widely applied in many fields, such as industry, agriculture, medical and health, national defense, and scientific research. It is difficult to find a field which is not connected with the laser technology. However, some properties of laser beams limit its further application. For example, its intensity distribution is Gaussian profile, not uniform one. And propagation path is hyperbolic line, not straight line. In order to extend the application field and improve application level of laser technology, it is very necessary to shape laser beams for meeting the demands of different occasions.Diffractive optical elements have many advantages, such as small size, light weight, replicating easily, low cost, high diffraction efficiency, many design variables, wide range of optional materials, peculiar chromatic dispersion performances, and so on. Therefore they can implement some new functions, for example microminiatrue, array, integration and arbitrary wave transformation, which are difficult for traditional optical elements to realize. Diffractive optical elements have wide application prospect in laser beam shaping.Design methods of diffractive optical elements for beam shaping are investigated in this dissertation, which mainly include the improvement of algorithms based on scalar model, the design of sub-wavelength diffractive optical elements based on vector model, and the design of lens axicon for simulating the axicon performance and diffractive optical elements for achieving long depth of focus and small spot by ZEMAX. The main works contained in this dissertation are as follows:1. The GSGA hybrid algorithm, the profile-smoothing algorithm, and fuzzy control iterative algorithm are proposed for designing diffractive optical elements for laser beam shaping in the scalar domain. Computer-designed results show the validity of those algorithms. Especially fuzzy control iterative algorithm, applying the fuzzy control theory to design DOE, can intellectively choose the optimization path by fuzzy decision, which will enable it to avoid being trapped into local optimum solution.2. The design of finite aperture aperiodic sub-wavelength DOEs is studied. Based on Mansuripur's vector diffractive model, vector fuzzy control iterative algorithm is put forward for the designing of sub-wavelength DOEs for beam shaping. To validate the method, the design results are discussed and the FDTD is further used. Moreover, because the assumption in the Mansuripur's model is somewhat subject, an improved scheme is proposed. The updated vector diffraction formula is deduced, a revised model is built and a sub-wavelength diffractive optical element is designed. 3. Base on the ray model, the lens axicon for stimulating axicon performance and diffractive optical elements with long depth of focus and small spot are designed by ZEMAX. The design works are achieved by rationally designing object function, editing the extend programs and depending on the optimization ability of ZEMAX. In the process of design, in order to trade-off the uniform distribution of light intensity on the axis and the spot keeping unchanged, a weighted method of designing object function is proposed, which makes the results more desirable.