The various instruments to be described are based on the following principle: a wave front which has been deformed by optical path difference variations in the object is doubled into two identical wave fronts by means of a birefringent system. The interference phenomena between these two wave fronts bring out the path difference variations in the object. By this means the transparent object is made visible. The birefringent systems employed are mainly of the Savart polariscope and Wollaston prism types. They can be equally well used in microscopy or macroscopy. These instruments can be used, by means of adequate modifications, without any collimation. In the latter case they are extremely luminous. They are of particular interest in microscopy where they permit the measure of refractive indexes and of thicknesses of small details in preparations. We shall describe a very simple differential observation method which places in evidence the gradient of the optical path. The sensitivity of the method depends on the width of the object. It is of the order of λ/50 for an object 1 mm wide. This sensitivity can therefore be very large for very small objects.
© 1957 Optical Society of AmericaFull Article | PDF Article
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