Measuring path differences of anisotropic transparent objects - using circular polarisation device with second quarter wave retarder replaceable by compensator

摘要

An object (O) is arranged with any orientation of its main oscillation directions in a circular polarisation device after a first quarter wave retarder (Q1). The polarisation device consists of two parallel linear polarising elements and two, pref. achromatic, quarter wave retarders lying between them. The oscillation ellipse of the object is rotated until maximum contrast is reached. A second retarder (Q2) is then exchanged for a compensator (K) with its main oscillation direction at 45 deg. to the polar retarder oscillation directions and with a measurable, variable path difference. The object's ellipse is rotated by 45 deg. so that its oscillation direction coincides with that of the compensator and the compensation device operated to null the object path difference which can then be derived. ADVANTAGE - Measures path differences of anisotropic transparent objects with any azimuthal orientation and path difference magnitude.