A New Approach to Optical Microscopy of Sub-Wavelength Diffraction Structures: Shape Reconstruction from Ellipsometric Back-Focal-Plane Data

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The objective of the proposed project is to use computer simulation to study the feasibility of a new type of optical microscope for measuring the sizes and shapes of three-dimensional objects whose dimensions are smaller than the wavelength of the light employed. Conventional optical microscope based on measurement of the intensity distribution on the image plane is not capable of resolving spatial details much smaller than about one wavelength. The proposed optical microscope, however, is based on ellipsometric measurements of the electric field scattered by an object onto the back focal plane of the objective lens. The ellipsometric data allow the relative phases among different components of the Jones matrix of the optical system to be computed. This phase information is then used to determine the shape of the object by solving an electromagnetic inverse problem.The proposed microscope idea should be of great scientific interest, since the technique of using the phase information obtained from back-focal-plane ellipsometric measurements for object shape reconstruction is novel. Also, the proposed method is insensitive to positioning and focus errors of the sample, which is an important consideration if the method is to be applied to solving metrology problems in industry.The proposed feasibility study will consist of using computer simulation to generate hypothetical data, which will then he used to test the convergence and robustness of various numerical algorithms for solving the electromagnetic inverse problem of shape reconstruction from the hypothetical data. In the process of carrying out the feasibility study, the graduate student involved will gain in-depth knowledge of optical imaging theory and firsthand experience with various numerical methods of electromagnetic. As such, the proposed project should be of great value in the education of graduate students interested in working in an interdisciplinary area involving both optics and electromagnetics. Also, if the results of the feasibility study appear promising, future research projects may he initiated to test the proposed microscope idea experimentally