Developing a High-Speed Electronic Speckle Pattern Interferometer: Innovation from Integrating Laser Doppler Interferometry and Time-stepped Phase Shifting Method

With the rapid advancement of nanotechnology, many industries have focused their research efforts to products of miniature size. It is to be noted that high-precision metrology is the driving force that propels miniature product forward. To further advance this line of research, there is an imminent need to develop a metrology system that can perform dynamic measurement through a microscopic system. In other words, the goal of this research is to develop an optical metrology system that can measure full-field and dynamic nanometer vibrations. By integrating an innovative optical configuration and a newly developed signal algorithm, the above-mentioned goals were completed successfully during the course of this research.
In this dissertation, electronic speckle pattern interferometry (ESPI) with high speed CCD camera was adopted to achieve full-filed deformation measurement. By means of short exposure time and precise time control, a series of transient information could be obtained. Image processes including (5,1) phase shifting technology, direct correlation method, noise reduction median filter, and path-independent phase unwrapping method were all integrated to reconstruct surface profile of specimen. Moreover, based on circular polarization interferometer and quadrature signal phase decoded method, laser Doppler interferometry was combined with ESPI system successfully to pursue multi-functional optical metrology system. Besides, an innovative time-stepped phase shifting method has also been proposed. This newly developed process essentially circumvents the de-correlation problem faced by incorporating ESPI technology into microscopic system. The newly developed time-stepped quadrature phase shifting method can even remove the phase shifting device so as to thoroughly improve the accuracy.
With regard to the experimental achievements, the optimal optical configuration has been constructed according to the optical simulation results. In addition, the complete experimental process control system and signal/image analysis interface have also been developed. In summary, the vibration measurement results obtained from a piezoelectric plate verifies the performance of the innovative optical metrology system disclosed and accuracy of the newly developed algorithm adopted.