Design And Fabrication Of Variable-Line-Space Gratings And Its Application To Position Sensor

Diffraction gratings are wide used to disperse light, which is to disperse incident light into angular directions corresponding to the wavelength of incident light. At the end of the 19th century Henry Rowland invented the ruling machine of diffraction gratings and the concave grating mounting, henceforth diffraction gratings have replaced prisms in most fields of spectral analysis. Subsequent production of high quality gratings led to significant advances in analytical spectroscopy. It has found a wide application from the fundamental research to the application study.Theoretic analysis show that the changes of groove density, line-profile and grating substrate(blank) shapes endow gratings the ability of focusing and reducing aberration, so the amount of reflective mirrors are decreased, the efficiency and resolving power of instruments are improved. The flat CCD is used in modern spectrograph. VLS gratings give the spectrum on a flat field, which is more suitable for CCD array instruments.Although variable-line-space gratings (VLS gratings) are wide used in spatial spectrum and synchrotron radiation devices, but the design and fabrication methods of them are difficult. Some abroad scholars studied VLS gratings year after year, but only a few papers about VLS gratings have been found in China. The test, fabrication, principle and applications of VLS gratings need more research. This dissertation is engaged in the study on design and fabrication of holographic VLS gratings and its application to position sensor.In chapter 2, the principal of diffraction grating and its application are introduced.In chapter 3, the geometry theory of aspheric wave-front recording optics is briefly described. The genetic algorithm is introduced to the recording parameters optimization of holographic VLS gratings; the integral expression of the merit function is also derived to improve the efficiency of calculation. Design example of holographic variable-line-space gratings is given to demonstrate the capability of this method, the groove density error curves are also given. The line-profiles of VLS plane gratings with two spherical wave-front recording are a family of confocal hyperbola, while the line-profiles of VLS plane gratings with spherical and aspheric wave-front recording are very complex. VLS plane gratings with the same grooves distribution maybe have different line-profiles. The merit function of the curve tendency is derived. Design example of holographic VLS plane gratings is given to demonstrate the capability of our method, which shows that the curve tendency is in very good agreement with the merit function. We analyze the relationship between the recording parameters and the coefficients of groove density distribution of VLS plane gratings. The curve by optimizing the groove density error with genetic algorithm is given, which validates the theory analysis.