GB1307894A - Method and an apparatus for the information transmitting capabili ties of image forming systems - Google Patents

Abstract

1307894 Diffraction processes BAYER A G 5 March 1970 [8 March 1969] 10586/70 Heading G2J [Also in Divisions H3-5] In an imaging process the transmitted information is increased by transforming the spatial frequencies of the structure to be imaged into a smaller range of spatial frequencies by the diffraction of subwaves (defined), the diffraction being effected either by illuminating the object with sub-waves or by illuminating the object with homogeneous waves and thereafter diffracting the sub-waves produced at the object on an analyser grating. In one embodiment sub-waves of spatial frequency kg are produced by illuminating a grating 2 with laser light 1, the grating constant being small compared to the wavelength of the light. (Alternatively they may be formed by total reflection). The sub-waves are diffracted by an object 3, of spatial frequency k a , within their range to produce homogeneous waves of spatial frequency K b = k a - k s . A lens 4 produces a Fourier transform of spectrum k b at 5, but in its image plane 6 it forms a distorted magnified image of object 3. A Fourier transform 8 of this distorted image is formed and its zero and negative order frequencies masked out. A final magnified image 14 is formed by lens 10 which is not distorted because the zero order is restored direct from laser 1. This zero order has an effective point source 13 in the same plane as transform 8. If desired the final image may be formed as a hologram 15 Fig.3 by interference between the first order from transform 8 plus displaced zero order from point 13 and a reference beam 16. Reconstruction from this hologram via a lens gives the final image 14. Using holography a plurality of images of different spatial frequency can be formed. In a further embodiment the object is illuminated by homogeneous waves, and sub-waves of spatial frequency k a are formed by diffraction at the object. The subwaves are directed to an analyser grating of period k s to form homogeneous waves of spatial frequency k b = k a - k s . In a modification of this embodiment the sub-waves generated by the object are recorded holographically, the hologram being reconstructed by sub-waves to give the homogeneous waves of spatial frequency k b . In the first embodiment the grating 2 may have either a phase or an amplitude structure. In other applications the laser is replaced by other sources fo radiation such as electrons, sonic or ultrasonic radiation or X-rays.