FREQUENCY MODULATION AND SPATIAL FILTERING APPLIED TO PHOTOGRAPHING OF PHASE OBJECTS

IT is not possible to photograph a transparent phase object placed against uniform background. The phase object is visible only insofar as it modifies the appearance of other objects in its vicinity (Fig. 1). It is possible, however, to make the phase object visible in a beam of spatially coherent light: Foucault or schlieren methods, defocusing1, phase contrast2, or interferometric methods3, and so on, may be used. A special process for diffusing surfaces described recently4 consists of forming interference fringes on the object to be studied, its relief being shown by the changes in the shape of the fringes. The method described in this communication differs from the latter method in two important features. © 1969 Nature Publishing Group.