Patent GB-1250333-A (GB)
IPC: H01J37/21
Filed: 1968-10-15
Abstract: 1,250,333. Light modulators. SIEMENS A.G. 15 Oct., 1968 [27 Dec., 1967], No. 48816/68. Heading H4F. [Also in Divisions G2 and H1] The properties of a diffractogram (Fraunhofer diffraction diagram) or a reconstituted hologram are utilized to evaluate (and thus correct) an image in the form of a current density distribution pattern produced by a corpuscular beam e.g. an electron beam, by converting the image into a corresponding phase distribution by means of a coherent beam of visible radiation, which radiation produces the diffractogram or reconstitutes the hologram. The eccentricity of the rings in the diffractogram are taken as an indication or measure of astigmatism in the electron beam lens arrangements used for generation of the image, and the diameters of the rings are taken as a measure of the focussing of the electron beam objective lens. In a first embodiment an electron beam 1 is modulated by video signals obtained by televising the image produced by an electron microscope. The video signals are applied to electrode 3 and the electron beam is focussed by lens 5 after passing through apertured anode electrode 6a, and deflected by means of deflecting systems 7 and 8 in synchronism with the scanning of the image in the electron microscope by the television equipment to scan a phase-shifting layer 9 carried on a circular carrier plate 10 having a metal electrode 12. The charge distribution pattern in the image transmitted by the electron beam locally influences the thickness of the layer 9 in such a way that the current density distribution, i.e. the image, is stored in the form of a distribution of the phase-shifting effect of the layer 9. The phase-shifting layer may alternatively comprise a material whose phase-shifting effect corresponds to the heating effect of the incident electron beam or to the electric field produced thereby. The disc 10 is rotated slowly to allow decay of the charge pattern. An auxiliary condenser 16 is provided to correct the focussing of the electron beam. The coherent visible radiation is produced by a laser 17 and projected via diaphragm 18 and an optical condenser lens 19 on to a deflecting mirror 20 which directs the radiation as a divergent or parallel beam on to layer 9. Where reconstitution of a hologram is concerned, the lens 19 is designed to compensate for any lens aberrations on the part of the electron beam lenses involved in the generation of the hologram. In the production of a diffractogram 23 upon a matt-finished plate 24, two lenses 21 and 22 are provided to produce a diffraction image 25 and project this via mirror 26 on to the plate 24. When a halogram is reconstituted lenses 21 and 22 are not required. All the components may lie within the vacuum-tight chamber 2. The phase-shifting layer should comprise a material (oil or synthetic material) whose electrical conductivity and/or properties of mechanical elasticity ensure storage of the phaseshifting effect until the diffractogram or hologram is rendered visible or is stored in succeeding television equipment. To obtain a clear diffractogram large-area contrast differences are suppressed by differentiation of the video signals applied to electrode 3. Plate 10 which supports the phase-shifting layer instead of being transparent, may reflect the coherent visible radiation. The electron gun and coherent radiation source may be arranged on opposite sides of the phase-shifting layer. In a further embodiment the phase-shifting layer is located in an electron microscope adjacent, or in place of, the final picture screen. An electronic video amplifier is preferably arranged in front of the phase-shifting layer.