US2479458A - Image receiving cathodic tube - Google Patents

Description

Aug. 16, 1949. R. BARTHELEMY IMAGE RECEIVING CATHODIC TUBE Filed March 1, 1946 INVENTOR Rene Burthelgmy ATTORNEYS Patented Aug. 16, 1949 IMAGE RECEIVING carnomc TUBE Ren Barthelemy, Fontenay aux Roses, France, assignor to Compagnie pour la Fabrication des Compteurs et Materiel dUsines a Gaz, Montrouge, France Application March 1, 1946, Serial No. 651,401 In France December 15, 1942 7 Section 1, Public Law 690, August a, 1946 Patent expires December 15, 1962 2 Claims. (01. 250-164) The present invention relates to a cathodic tube for receiving images; this new cathodic tube, also called cathode-ray or cathode-beam tube permits of receiving images transmitted at a distance.

This tube can be utilized in two ways according to conditions of working, either as a relay of light interposed between a powerful source of light and a screen, in order to insure reception on a large screen of televised animated images, transmitted in a known manner; or as a receiver delivering a persistent image, with an eye to special applications, such as safeguarding the secret of transmitted images The invention is characterized by the utilization, instead of the fluorescent screen of the cathode-ray tubes, of an opaque and very thin layer of a volatile substance and in particular an alkali metal, for instance caesium.

The whole of the cathodic tube-excepting the surface swept by the cathode-beam in a known manner-is placed in a drying oven brought up to a temperature approximately between 100 and 200 centigrades-degrees. In the absence of any scanning, the volatile and opaque substance (for instance the caesium contained in the tube) is bound to condense as an opaque and non-uniform layer upon the non-heated portion, that may eventually be cooled by air or water circulation.

When the said caesium layer is impinged by the cathode-beam which issues from the electronic gun of the cathodic tube, the momentary evaporation of the caesium at the point of impact is brought about. The greater the power of the beam, modulated by the Wehnelt cylinder, the more intense is the evaporation. In this manner there is formed a surface, the opacity of which varies in every point, according to the modulation applied to the tube, the said modulation being possibly effected, for instance, by a television receiver. By interposing this surface at the right place in the path of a beam of light, emitted from a powerful source, there is formed on a screen, a brilliant image of a large size. The mean power of the beam and the temperatures of the drying oven and cooled surface are so regulated, that the rate of re-condensation of caesium corresponds to the duration of one image.

The invention may be utilized for obtaining persistent images, for instance for the secret transmission of written messages. It is only necessary therefor to adjust the conditions of working, i. e. power of the beam and temperatures, to have for the caesium a long recondensa- 2 1. tion time, to wit, of the order of severalmicroseconds. To blot out the image entirely and to build again an uniform layer of caesium, requires only a thorough scanning by means of 'apowerful beam, in order to evaporate momentarily all the caesium that is bound to condense back again uniformly a few seconds after. j

The nature of the invention and its working areexplained in the description'following hereinafter and by means of the annexed drawing in which. 7 V

Figure 1 is an embodiment of a device according to the inventionr Figure 2 is a schematic drawing showing the formation of the image in the case of a modulation in diameter of the cathode-beam;

Figures 3 and 4 are two devices to project the enlarged image of the image formed on the receiving surface of the cathodic tube.

According to Fig. 1, where the glass tube l is sealed by an even plate-glass 2 of little thickness, to make thermic exchanges between the two sides easier, the said tube I encloses an electronic gun 3 with its two pairs of deflecting plates 4 and 5. The whole apparatus is void of air and treated according to the classical methods used for cathodic tubes. At the end of the pumping, there is introduced into the tube a small quantity of an alkali-metal, e. g. caesium.

The whole of the tube, excepting a rectangle of the plate-glass 2 that corresponds to the size of the image to be received, is shut up in a drying oven 6 where a temperature of about to 200 degrees centigrade can be attained. The rectangle non-enclosed in the oven may eventually be cooled by air or water circulation I.

In the absence of cathode-beam, all the caesium contained in the tube has to condense as an opaque and uniform layer 8 upon the cold rectangle of plate-glass 2.

Then, when this surface is actually impinged by the cathodic beam 9, some caesium is evaporated in a quantity corresponding to the power of the incident beam, and there is obtained in this manner, a variation of opacity from one point to another, according to a fixed law.

It is also possible to cause the beam to vary its diameter, without varying its intensity, by applying, for instance, the modulation at the electrode of concentration of the cathodic tube. Thus, at every line, the beam evaporates a furrow of caesium equal to its diameter at every point, as is schematically represented in Figure 2 where a and b are two successive lines. In this manner, there is obtained a system of modulation analogous to the method of registering sound films, called with constant opacity and variable elongation.

As wasgalrea'dysexpiained, the-speed of recondensation of caesium depends upon the temperature of the drying oven and the means of cooling. For animated images, the duration of recondensae tion has to be slightly less than the durationof one image. In the case ofsarfixed.image-a message, for instance-thisiduration:fmayebeof several seconds. In the lattericase, theiimage may be blotted out by sweeping plate-glass 2 by the non-modulated beam. The layer of: caesium is rebuilt afterwards uniformly.

The image formed upon plate-glass 2 may be observed directly or proj ected to be enlarged. figs. 3 and 4 show two instances of devices according to the invention, wherein the surface containing the layer of condensedrcaesium is interposed in the path ,of, a powerful beam of.light. In. these l twoijfi uresg numbersihavel the :same .meaning as jSflisa luminous source, C a condenser, O an"'objec assjE a 'screen. In the device acv. colfdi l ".tog". la"ig.i3, the "variation of opacity of the .Eufiacejisntilizedto.produce an image on screen Inthe device accoifding.v-tofFig. 4, the variaof,.reflei lqn ofythe said surface is utilized. Wh ti la m. 3 LA fdevice for receiving "images, comprising a cathO'de -beam tube, a transparent receiving surtacein thesaid, tube anopaque. and uniformlayer or a volatile substance 'disposedron the saidsurriiace and vvolatilizedbyithetipassage of the .said

Number 4 beam in order to cause the image to become visible by variation of opacity of the said surface and-Ma ,heated chamber where 'the said tube is placediinssuch alf manrier that the said receiving surface is exterior to the said chamber so as to 1 adjust the conditions of volatilization and condensationof the said volatile substance.

2. aadevicefor receiving images, comprising a =cathode-beam:=tube,;:a transparent receiving surface-i-n the said tube, an opaque and uniform layer :Ofia V0 atllSlIbStalnC8 disposed on the said surface and vola tilizedtby the passage of the said beam in '.order-to. ..cause,the image to become visible by -variation-of opacity of the said surface, a heated chamber where the said tube is placed in such a *manner that Ethe'said receiving surface is exterior tothe 'said'chamber, and means for cooling the said; receiving surface, the said chamber and the said means being used to adjust the conditions .of -vo1atilizat-i0n -=and condensation-of -the:said volatile substance.

,RENE BARTHELEMY.

REFERENCES CITED The following referencesare i of I record in the 'filei of this patent:

STATES PATENTS U Name Date $2,242,644 SIDeBo'er g May 20,1941 "2,281,637 Sukum'lyn .May 5, 1942 "23151113 Farnswoithe-se-m-n Mar. 30, 1943

Images