Multispectral interferometry for characterizing nano-objects

The paper discusses an alternative approach to the variable wavelength interferometry. The technique is based on specialized composition of two birefringent prisms that are inserted in a classical microscope with the Köhler illumination system. The optical system includes a continuously tuned light source and consists in advanced processing of sequentially recorded images at different wavelengths. The instrument is suitable for both transmitted and reflected-light modes and allows the user to measure optical and geometrical parameters of phase or reflective structures. This paper focuses on the reflected-light mode set-up, and measurements of waveplates and step height standards. The low uncertainty of the optical path difference is obtained by the continuous character of the light source and constitutes a key element of the system. In contrast to some previous presentations on the variable wavelength interferometry this paper demonstrates more profound nature of the phenomenon and a more precise algorithm for the fringe image processing.