Micron Moiré Method And Its Correlative Techniques Of Ultrahigh Frequency Grating Fabrication And Digital Image Processing

Development of micro-mechanics requires experimental methods of high sensitivity and high spatial resolution, which should both reach or exceed micron-level. In this dissertation, a high sensitivity, high spatial resolution micron moire method and its correlative techniques of ultrahigh frequency grating fabrication and digital image processing are presented.Techniques of fabricating high diffraction efficiency and ultrahigh frequency gratings by interference of coherent lights are studied. (1) The diffraction property of gratings is adopted to adjust the angle of the two coherent lights, and a grating-fabrication method with multiplying-frequency is realized. (2) Based on multiplying-frequency and conventional refractive index medium grating-fabrication methods, a multiplying-frequency grating-fabrication method using high refractive index medium is proposed. The advantage of this method is that the grating's frequency has no direct relation with the wavelength of the laser and the refractive index of the medium, but equals the grating-fabrication frequency in the air plus twi-frequency of the mother grating. Theoretical analysis of this grating-fabrication method is discussed in detail and the idea is also applied to enhance the sensitivity of moire interferometry. (3) A theoretical model of grating grooves fabricated with positive photo-resist is established, and several factors that affect the grating's diffraction efficiency are gained. Furthermore, a new grating-replication technique is proposed. The gratings fabricated and replicated in the dissertation all have high diffraction efficiencies.Based on classical geometric moire method and microscopic principle, a high spatial resolution and high sensitivity geometric micron-moire method is presented. With a microscopic moire system, the high frequency gratings could be magnified to a low frequency level, so geometric micron-moire patterns can be formed. The sensitivity of micron moire method is determined by the high frequency of original gratings, while the resolution is determined by themagnification of the microscopic system. Experiments show that both the spatial resolution and the sensitivity can reach or exceed micron-level. Compared with other grating-based photo-mechanics methods, micron moire method could provide whole-field moire patterns of both high spatial resolution and high sensitivity. Additionally, some measures are used to enhance the contrast of microscopic moire patterns effectively, e.g., a 4F optical filter system.Fringe center technique and phase analysis technique, the two most important digital processing techniques for automatic fringe patterns analysis, are studied thoroughly. (1) A series of methods are presented in image filtering, fringe center detection, fringe order determination and interpolation, results display, and so on. Especially, a neighborhood-average filtering method with altering-windows is proposed to pre-process the fringe patterns, and a subsection-curve interpolation algorithm is used to ensure the derivative of the fringe order to be continuous. (2) Based on the characteristic of fringe edges, some effective modifications to conventional median-filtering method are proposed. The most important step of phase analysis processing is phase unwrapping, so a bi-directional linear scanning method is proposed. This method can avoid propagating errors, which always exists in traditional path-dependent methods. Furthermore, a tile Cellular Automata phase unwrapping algorithm, a promising path-independent method, is studied.An interface-advanced, powerful and effective software-system of automatic fringe patterns analysis using digital processing techniques is established. The software includes both fringe center technique and phase analysis technique.