The Research On Design Methods And Key Fabricating Technologies Of Flat-field Holographic Concave Gratings

As a part of the National Key Technologies R&D Program for the 11th Five-year Plan, in this paper, the research is mostly focused on design methods and key fabricating technologies of flat-field holographic concave gratings. Firstly, concerning the optimization of flat-field holographic concave gratings, two optimization functions are introduced, which are based on geometric aberration coefficients and spot diagrams, respectively. The effect of optimization function on design result is analyzed. It is found that better imaging property for both tangential and sagittal rays can be achieved when the optimization function based on spot diagrams is used. Secondly, the design method of flat-field holographic concave gratings which is based on flat sagittal focal field is proposed. It is shown with the image evaluation that gratings designed by this method serve good imaging property on both tangential and sagittal directions. The spectral resolution can be as good as gratings which are designed by the conventional method. And the astigmatism is eliminated over the entire wavelength range, so that the energy density of the spectrum image can be greatly increased. As the result, the throughput of flat-field spectrometer can be improved. Thirdly, concerning the study on application of optimization theory, the design method for double-grating flat-field holographic concave grating spectrometer is proposed. The double-grating spectrometer can give better spectral resolution and higher throughput than conventional single grating spectrometer with the same mounting size. Fourthly, in the aspect of error analysis of flat-field holographic concave gratings, the effect of curvature radius error, recording parameter error, and use parameter error on spectral resolution is studied. It is discovered that, for a large parameter error range, the parameter errors bring two effects on the tangential focal curve, displacement and tilt. Numerical calculation results indicate that, in a large neighborhood around the design point, the parameter errors can be compensated by each other. It is shown that the spectral resolution can be as good as designed after compensation of the errors. This error compensation theory gives guidelines for design, fabrication and application of flat-field holographic concave gratings. Fifthly, exposure and development models are proposed for simulating the formation of holographic gratings in the case of asymmetric exposure. This theory can give theoretical guidance to the fabrication technics of the flat-field holographic concave gratings. Sixthly, numerical simulation and experimental demonstration of the in-situ monitoring curve is carried out by using the exposure and development models. The results indicate that the monitoring curves of asymmetric exposure are the same with that of symmetrical exposure. This theoretical model can give explanation for character of the in-situ monitoring curves, and information for end point of exposure and development. As the result, the fabrication technics could be well controlled.