| 摘要 |
1,202,562. Cathode-ray tubes. EIDOPHOR A.G. 10 Nov., 1967 [16 Nov., 19661, No. 51357/67. Heading H1D [Also in Division H4] In a schlieren-optical system in which a modulated electron beam is scanned across a deformable light-modulating surface, the electrostatic charge deposited at each individual image point is confined to the area of the image point, and a secondary or neutralizing charge is deposited on the surface in the area surrounding each image point in order that images that are traced in single lines or that are built up of an arbitrary sequence of spots may be optically reproduced. The complete scanning cycle for forming the image is repeated at a constant repetition frequency and the surface deformation at each image point neutralized or at least substantially reduced during the interval between successive scans. The neutralizing charge travels at least substantially incidently with the image tracing charge which is preferably deposited intermittently. The neutralizing charge is necessary because the electrostatic pressure generated by the arbitrarily deflected electron beam would by itself cause the oil film modulation to disperse at the image points since the overall electrostatic surface charge produced when the oil film is raster scanned and which prevents the oil film from laterally yielding to the transient pressure when the individual image points in a line are traversed by the electron beam are absent. The neutralizing charge may be generated by defocusing the electron beam which also deposits the image forming charge. Preferably the neutralizing charge is generated by alternately underfocusing and overfocusing the image-forming beam. As described with reference to Fig. 3 (not shown) this alternating underfocusing and overfocusing may be effected by a trapezoidal voltage applied to a focus modulating system in the cathode-ray tube, the focus of the electron beam passing through the image plane at a speed determined by the steepness of the flank of the trapezoidal voltage. The magnitude of the neutralizing field and the charge density in the neutralizing field are varied by controlling the amplitude of the trapezoidal voltage. The frequency of the trapezoidal voltage is so chosen that it has no common submultiple with the image repetition frequency. Besides stabilizing the oil film against lateral spreading of the deformation at the image point, the neutralizing charge also assists in the smoothing out of the image point deformation by the surface tension of the oil film. If the image is formed by a plurality of differently positioned writing cycles, then the tracing and neutralizing electron beam is blanked out during the positioning cycles. |
