Investigation On The Optimization Design Method And Fabricating Technique For Toroidal Holographic Gratings

Toroidal holographic grating(THG), as a typical spectroscopic unit for monochromator, exhibits great advantages such as chromatic dispersion, imaging, aberration correction and so on. Since the invention of THG, it has played an important role in the high-resolution monochromator in the soft X-ray and extreme ultraviolet(EUV) region. Although the surface shape features and groove distribution of THG result in a good ability of eliminating aberration, such complicated structure makes it difficult to be fabricated as well. Therefore, in this thesis, we systematically investigated the optimization design method and fabricating technique for the toroidal holographic gratings.Firstly, we deduced the optical path function aberration theory and ray tracing spot graph theory of THG according to Fermat’s Principle. We further improved the traditional optimization function in the optical path function aberration theory, and proposed a new design method for THG with introducing weighing coefficient. The root mean square optimization function of spot diagram was derived based on the ray tracing spot graph of THG. Combined with the optical path function aberration theory and ray tracing spot graph theory of THG, we proposed a new optimazation design method, namely the aberration-balance optimization design method. This method employed a combination of genetic algorithm and local optimization algorithm to optimize the design of the grating, which enhanced the computation efficiency and improved the performance of an established grating spectrometer. Additionally, we further used this aberration-balance optimization design method to design three kinds of gratings for different purposes. The results proved that the new method is suitable for parameter optimization design of THG recorded by two spherical waves, which build the theoretical basis for the design of high-resolution THG.Secondly, in order to theoretically guide the key link of spin coating technique in the fabricating process of THG, we analyzed the spin coating process from the point of view of hydrodynamics and thermodynamics. The function of an approximate radius of curvature for the surface of THG and the thickness distribution model of photoresist spin-coating under non-lubrication condition had been proposed. The laboratory coefficient for spin-coating model had been provided by combining experimental induction and polynomial fitting. We further testified this model with experiments and made the comparison and analysis by employing different technique parameters. The thickness distribution model of photoresist spin-coating on plane substrate and concave spherical substrate(CSS) were derived under lubrication and non-lubrication conditions. The results indicated that the theoretically calculated values were well consistent with the experimental results measured with various rotational speeds and liquid concentrations at steady state. Therefore, both our experimental results and theoretical analysis provide the guidance for photoresist dilution and pave the way for THG fabrication in the future.Thirdly, in order to analyze the effect of different parameter error formed during the THG fabricating process on the spectral resolution, we established a function to evaluate the integrated spectral properties of THG. This function nont only can be utilized to make a systematically analysis on the image height, image width and spectral properties of ray tracing spot graph of THG, but also analyze in depth the impact of use parameter error, recording parameter error, substrate surface error, and spin coating parameter error on the integrated spectral properties of THG. Numerical calculation results indicated that, in a large neighborhood around the design point, the parameter errors can be compensated by each other. It is also proved that the integrated spectral properties can be repaired as we use another single parameter to do the compensation. This error compensation theory gives guidelines for design, fabrication and application of THG.Fourthly, we systematically introduced the fabrication techniques of THG, and analyzed the disadvantages of the spin coating technique and how to solve them. We combined with the fabrication technique of THG, the design of spherical wave interference light path and the real-time asymmetric exposure imaging technique to introduce the detailed fabricating technique of THG used in the high-resolution and wide-region monochromator. The results have provided theoretical guidance and experimental evidence for fabricating THG products.