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A new kind of contrast for an optical microscope is presented. It can be realized by first imaging a rotating grating onto the object and then imaging the grating together with the object to a second rotating grating positioned in an intermediate image plane. The image of the first grating must be congruent with the second one and the rotating velocities of the two gratings have to be slightly different. Hence a beat frequency will occur in those areas where the contrast of the first grating is not diminished too much by the corresponding object fields. This kind of procedure may be called simultaneous heterodyne detection. The "carrier frequency" is presented by the first grating, which is modulated by the optical properties (reflection, transmission, de-fraction etc.) of the object. After mixing the "carrier wave" with the "reference wave" (presented by the second grating) the image intensity varies with the beat frequency which carries the image information. A video camera is synchronized with the beat frequency so that image pick up will take place only at the maximum and minimum of the image intensity. The difference of the two images will finally form the required image. It is proved within the validity of incoherent approximation that super-resolution is possible.
Burkhard Neumann (Thu,) studied this question.