Abstract
A new device for observing phase-object is introduced. Its optical system is similar to a schlieren system having a small circular disk or a thin straight wire as a spatial filter instead of a knife edge. A monochromatic point source of coherent and highly bright light is required and a relatively large aperture (blank space or “margin”) which is uniform in refractive index is needed around the object.
A portion of the light beam which is transmitted through and refracted by the phase-object reaches the image plane keeping away from and therefore without being affected by the spatial filter. However, the other portion which passes through the “margin” is partially shaded by the spatial (high-pass) filter. Then, the image of the “margin” is distorted and some components fall on the image of the object and interference fringes appear. When the reference light function D defined in this paper has an absolute value of about unity, and when D remains approximately constant, the fringes have high contrast and coincide with the phase-contours.
As an example, calculations and experiments were carried out in case of a circular phaseobject placed at the center of a circularr field. The calculations predicted that the above conditions could be realized in certain cases and some experiments actually presented clear fringes coincident with the phase-contours.
