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.
The paper demonstrates initial results of measuring the retardance of waveplates using a variable wavelength interferometer. The instrument utilizes a continuously variable interference bandpass filter placed in a specially designed intermediate image plane. The fringe field, created by the Wollaston prism, is processed and analysed only once, which speeds up the measuring procedure. In this application a reflected-light mode configuration is presented. The solution is suitable also for transmitted-light systems. The interferometer provides the user the spectral characteristic of retardance of the waveplate across the visible spectrum. The instrument is based on a classical microscope with the Kӧhler illumination system.
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