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Browse Prior Art Database

Cathodochromic Tube with High Writing Speed

IP.com Disclosure Number: IPCOM000079979D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Kazan, B: AUTHOR

Abstract

One of the limitations of cathodochromic (dark-trace) tubes is their limited writing speed. Because of the fundamental limitations of the materials employed, it is not expected that any major increase in sensitivity can easily be obtained by improvement of the materials. However, by use of a special focusing grid near the screen, the current density at local areas can be greatly increased, thus increasing the writing speed.

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Cathodochromic Tube with High Writing Speed

One of the limitations of cathodochromic (dark-trace) tubes is their limited writing speed. Because of the fundamental limitations of the materials employed, it is not expected that any major increase in sensitivity can easily be obtained by improvement of the materials. However, by use of a special focusing grid near the screen, the current density at local areas can be greatly increased, thus increasing the writing speed.

A general arrangement proposed is shown in cross-section. A focusing grid of fine wires is shown, spaced a short distance away from the cathodochromic screen. In conventional cathodochromic tubes this grid is absent, resulting in a spot of diameter A-A' on the cathodochromic screen, equal in diameter to the electron beam. If the focusing grid shown is included and its potential held at about 1/4 the final anode voltage, it causes a focusing action whereby the electrons passing through the spaces between the grid wires are converged to narrow elliptical spots, elongated in the direction of the grid wires. Since the width of the elliptical spots can be about 1/10 of the spacing between wires, a current density increase of about 10 can be obtained in the bombarded areas of the screen. (It should be noted that instead of a focusing grid consisting of wires, a focusing mask with round holes, for example, could be used, thus causing convergence of the electron beam into fine round spots, instead of elliptical spots, producing a much higher increase in current density.)

In general, it is assumed that the grid wires have a spacing which is smaller than the electron beam, so that the electron beam arriving at the grid covers one or more openings of the grid. The beam is shown covering three spacings, resulting in three high-density spots at the screen. Presumably, at normal viewing distances the individual high-density spots would not be resolved by the eye.

Since most of the area of the cathodochromic screen remains unbombarded, the contrast of a recorded image viewed, for example, by transmitted light would be very low. To avoid this, opaque strips are provided between the cathodochromic screen and the transport support layer, with these strips being in register with the wires of the focusing grid. The flooding light will now pass through the screen only at local areas where the electron beam can land. If the opaque strips appear black as seen from the observer'...