Analysis Of Fringe Patterns For Nano Displacement Measurement

Today nanotechnology is playing an important role in the development of our society. Nano-measurement is part of nanotechnology, and it is in a leading position in the development of nanotechnology. Nano-measurement technology deals with the measurements of nano-precision dimensions, nano displacements, nano surface structures, and other physical and chemical properties at nano-scale. Nanotechnology would not develop well without nano-measurement technology.This dissertation discusses interference fringe analysis techniques for nano displacement measurement. In the work, a CCD was used as the fringe position sensor instead of the conventional photodetectors for nano displacement measurement. Interference intensity correlation curves were obtained by the correlation calculations of captured fringe patterns, and the precision measurement of nano displacement was achieved by interpolation. The advantage of this method is the reduction of noise by using an array of sensing elements of a CCD and the correlation calculation. The experiment shows that the method can also be used to analyze the quality of nano-structured surface patterns (the uniformity of pattern parameters) produced by laser interference nanolithography.In the dissertation, Matlab was used for programming and for performing fringe pattern correlation and interpolation calculations for the determination of phase differences between fringe patterns. Two image patches with the same size were selected from two equi-spaced fringe patterns, and auto-correlation and cross-correlation were done separately. The phase differences were calculated by interpolation methods from the correlation function or phase curves. The experimental results have shown that this approach is useful for the determination of phase difference between two equi-spaced fringe patterns in interferometry, and it has the advantages of high precision of nano displacement measurement and high resistance to noise.