US1954025A - Electrooptical system - Google Patents

Description

April 10, 1934. F w. EYNOLDS 1,954,025

ELECTROOPTICAL SYSTEM Filed Jan. 22. 1929 F W HEYNOL D5 Patented Apr. 10, 1934 UNITED vSTATES PATENT OFFICE ELECTBOOPTICAL SYSTEM Frederick W. Reynolds, Grantwood, N. J., as-

signor to American Telephone and Telegraph Company, a corporation of New York Application January 22, 1929, Serial No. 334,337

11 Claims. (Cl. 176-122) This invention relates to electro-optical sysbattery 8. The vessel 5 is illled with a suitable tems and more particularly to a variable light gas at such a pressure that a luminous dissource for such systems. charge occurs throughout substantially the In accordance with the present invention an whole length of the tube except for a short cathimproved gaseous discharge device is provided ode dark space. This discharge illuminates an w 5 to produce light ilux varying in accordance with aperture 9 in an opaque screen 10. For recorda variable magnetic eld. ing purposes, as in a picture transmission sys- An arrangement illustrative of the invention tem, for example, an image f the aperture 9 iS comprises a gasfllled tube of the arc discharge formed by a lens 11 on a drum mounted light type having a hot cathode in which the arc sensitive record blank 12. Helium gas preferably o 0 discharge and therefore the intensity of the is used within the chamber 5 at a pressure of useful illumination of the positive column is between 2 and 5 millimeters 0f mercurycontrolled by focusing the emitted electrons with The intensity of illumination 0f the aperturek the magnetic field of an external concentric 9 is controlled by the magnetic iield prOduced coil. In one speciiic form of the invention the by a coil 13 cooperating With a baule 14 ccntain- 70 15 control coil is located at the end of the tube ing asmail hole 15 through which electrons from adjacent to the cathode. A bame or nrst anode the cathode 6 pass before producing the posiis located between this coil and the anode and tive column to the right of the baille 14. The contains a. small hole through which the elecbaiiie 14 may also serve as a first anode. in which trons pass before entering the positive column. case a portion only 0f the Voltage 0f battery 8 u 2 The light emerging from the anode end of the is impressed thereon. Separate sources may of tube varies with the current through the concourse be used. In an image or picture protrol coil. In a modified arrangement the conducing System the energizing current for the trol coil extends substantially the whole length eOil 13 iS Supplied by image 0r picture current of the tube. An indirectly heated oxide coated producing apparatus 16. cathode is preferably employed with low values "It iS not necessary t0 describe in greater deof cathode to anode vo1tage so that the control tail the apparatus 16 and its cooperation with coil eld strength may be kept Smau. the drum mounted light sensitive record blank These devices are particularly adapted to serve l2 for image or picture production in view of the as the light sources at the receiving terminals HOrtOn-IVcS-Lcng Patent N0. 1,606,227, issued 85 of picture or image producing systems, the vary- November 9, 1926 With Which the apparatus 0f ing image currents being impressed upon the Fig-11S readily combinable. conti-01 coils, The aperture 15in the baille 14 should be small,

A more detailed description of the invention compared t0 the diameter 0f the tube, in Order follows having reference to the accompanying that the bafiie may be effective in Screening mOSt drawing. Identical elements in the several iig- 0f the electrons from the pOSitiVe column, when ures are identified by the same reference charn0 current iS applied t0 the fOcuSing c011- There acters. will be some tendency for the electron beam to Figure 1 illustrates one form of an electrobe Self-focusing due t0 the Sheath OfpOSitive optical system according to this invention. gas iOnS which Will be preSent, althOugh this 95 Fig. 2 illustrates a modified form of the ineffect is much less with helium and neon gases vention. than with heavier gas ions such as argon. 'Ihe Fig. 3 shows more in detail an indirectIy heated magnetic field produced axially along the tube by hot cathode suitable for use in the discharge the control coil will cause more electrons to enter tubes of Figs. l and 2. the positive column to the right of bafl'ie 14, thus 100 Fig. 4 illustrates another modiflcation of the localizing the ionization `near the axis of the tube. invention in which an aperture external to the This action 0f the control coil causes electrons tube is employed.V which are moving in directions other than axially Fig. 5 illustrates a further modication wherealong the tube to follow a helical path of diminin the anode serves also as an apertured screen. ishing radius of curvature, thus directing the 105 In the arrangement of Fig. l an enclosing motion of the electrons and to some extent the vessel 5 is provided with a cathode 6 and an positive ions along the axis of the tube and coil. anode'l. The cathode 6 is heated by current The resultant illumination of the aperture 9 at from a battery 31 and a discharge between the the anode end of the tube will therefore vary cathode 6 and the anode 7 is maintained by with the current through the control coil. The 110 sary number of electrons for maintaining the discharge. This permits of reducing the cathode potential drop to the minimum required for ionization of the particular gas used, since for visible as well as for useful photographic illumination from gas lled tubes such as helium, the velocities of the electrons need correspond to only a few volts.

` The distance between the cathode 6 and the rst anode ld which serves also as a bae, may be such that in combination with the voltage applied and the mean free path of the electrons at the pressure of thegas used, no appreciable ionization occurs until the electrons reach the space between the first anode land the anode '7. The ionization in this latter portion of the tube 5 and therefore the illumination of the aperture 9 will increase with the number of electrons entering this space which number is determined by the focusing action of the external concentric coil 13. The intensity of illumination as viewed from the end of the tube will also be greater the longer the column of ionized gas. At pressures from 1 to 5 millimeters of mercury using a gas such as helium, the potential gradient in this portion of the tube will be from l to 2 volts per centimeter depending upon the gas pressure land diameter of the tube. 'Ihe total anode voltage applied will, of course, depend upon the length of the tube and the gas pressure, and for tubes to 40 centimeters long may be as great as 50 to 75 volts without causing disintegration of the electrodes or cathode sputtering. Luminous outputs as great as several thousand lumens may therefore be obtained.

Another advantage of using a hot cathode is that it is possible to use a cathode to anode voltage Well below that which causes disintegration of the cathode by sputtering. A useful tube life of several thousand hours is therefore possible.

The preferred form of cathode 6 is illustrated in Fig. 3 and is an indirectly heated oxide coated cathode. A heated filament 20 located within a capillary tube 21 has external terminals 17 and 18. Surrounding the filament 20 is a hollow cylindrical metallic member 22, the inside surface of which is coated with the oxides of alkali earth metals in a well known manner to produce an electron emitting surface when heated. 'I'he hollow cylinder 22 is surrounded by a tube 23. 'I'he capillary tube 21 and the tube 23 are made of refractory material, such as fused quartz.

An advantage of this type of cathode resides in the fact that substantially no light ilux from the electron emitting surface is incident upon the aperture 9 to affect the intensity of illumination thereof.

In the alternative arrangement of Fig. 2 the control coil 13 is applied to substantially the entire length of the tube 5. A more eiiicient control of the ionization in the positive column results since very few of the emitted electrons travel far from the cathode before causing ionization and are deected by collisions with gas atoms and ions. The presence of the magnetic eld throughout the length of positive column has a greater inuenceupon the nature of the discharge, resulting in a concentration of ionization near the axis of the tube proportional to the current throughout the control coil. Magnetic elds of the order of afew gausses are suiiicient to obtain suflicient variation in the degree of illumination in the aperture 9 for ordinary image or picture producing purposes andI such fields can be ob- 3,954,025 function of the hot cathode is to supply the necestained without introducing an objectionable amount of inductance into the control circuit.

In the arrangement of Fig. 2 the anode 7 is ring shaped, the central opening being somewhat larger than the aperture 9 in screen l0. The type of anode shown in Fig. 1 may, however, be used. Likewise the type of anode shown in Fig. 2 may be used in Fig. 1.

'Ihe illuminated aperture 9 at the anode end of the tube 5 may or may not bel suitable for imaging upon the light sensitive record blank 12. If it is vnot suitable, a second aperture 24 in a screen 25 located near a. lens 26 may be used. A lens 27 forms an image of the aperture 24 on the light sensitive record blank 12 while the lens 26 forms an image of the aperture 9 at some point between the shield 25 and the lens 27, preferably nearer the lens 27. By this arrangement eiiicient gathering of the light ux passing through the aperture 9 is effected and a suitable spot of uniform intensity over its cross section is produced on the light sensitive record blank l2.

The lens system of Fig. 2 may, of course, be embodied in the system of Fig. l or vice versa.- 'I'he system of Fig. 2 may be used for the same purposes as that of Fig. l.

In Fig. 4 there is shown a system in which an aperture 30 in a tube 29 external to the discharge tube 5l is adjustable in a 'casing 28 within which the lens 11 and drum mounted light sensitive record blank 12 is located. The lens system of Fig. 2 may be used in the arrangement of Fig. 4. In some instances the arrangement of Fig. 4 may be preferable to those of Figs. l and 2.

In Fig. 5 the ring shaped anode 7 serves also as j', the apertured light screen. It is preferably located as close as possible to the end of the tube, 5 in order to obviate the production of a luminous discharge to the light of the screen.

For photographic purposes helium, mercury vapor, carbon monoxide or carbon dioxide, rather than neon gas is preferable due to its greater energy distribution in the shorter wave lengths of the visible spectrum. The greater portion of luminous energy from the neon discharge occurs in the red portion of the spectrum for which the ordinary photographic emulsion is comparatively insensitive. Neon is preferable, however, in certain forms of image producing systems, such as television.

Various modications of the illustrated forms of the invention may be made without vdeparting from the purview of the invention as dened in the appended claims.

What is claimed is;

1. A luminous gaseous discharge lamp comprising a gaseous discharge tube containing an anode and a cathode for producing a gaseous discharge having a luminous positive column, and a magnetic control coil concentric with the discharge 135 path between said anode and cathode for varying the cross-section of said positive column.

2. A luminous gaseous discharge lamp comprising a gaseous discharge tube containing an anode and a cathode for producing a gaseous discharge 140 having a luminous positive column, a magnetic control coil concentric with the discharge path between said anode and cathode for varying the cross-section of said positive column, and a secondary light eld energized by light iiux from 145 said positive colunm, the intensity of the light flux emerging therefrom being a function of the cross-section 'of the positive column.

3. A luminous gaseous discharge lamp comprising a gaseous discharge tube containing an anode 150 and cathode for setting up a gaseous discharge having a luminous positive column, and a control coil located concentrically with the dischargepath between said anode and cathode for varying the cross-section of said positive column and extending over the major portion of ,the whole distance therebetween.

4. An electro-optical device comprising a gaseous discharge tube having an anode and a cathode of the thermionic type for producing a gaseous discharge having a luminous positive column, said cathode being so shaped that the light therefrom in the direction of the positive column is negligible, and a magnetic control coil concentric with the discharge path between said anode and cathode to control the light flux emanating from the positive column.

5. An electro-optical device comprising a gaseous discharge tube containing an anode and a cathode for setting up a gaseous discharge having a luminous positive column, said cathode comprising a hollow cylinder coaxial with said positive column, a thermionic electron emitting layer on the insidesurface of said cylinder, and a heating element within said cylinder, and a magnetic control coil concentric with the discharge path between said anode and cathode to control the light ux emanating from the positive column.

6. An electro-optical device comprising a gaseous discharge tube containing an anode and a cathode for setting up a gaseous discharge having a luminous positive column, said cathode comprising a hollow cylinder coaxial with said positive column, a thermionic electron emitting layer of the oxides of alkali earth metals on the inside surface of said cylinder, a fllamentary heater element inside said cylinder but separated from said inner surface and a refractory insulating covering for said filament and the outside surface of said cylinder, and a magnetic control coil concentric with the discharge path between said anode and cathode to control the light flux emanating from the positive column.

'1. A luminousgaseous discharge lamp comprising a gaseous discharge tube having an anode and a cathode for producing a gaseous discharge having a luminous positive column, ionizable gas at low pressure within said tube, the gas ions of which are lighter than those of argon, and a magnetic control coil concentric with the discharge path between said anode and cathode for varying the cross-section of said positive column.

8. A luminous gaseous discharge lamp comprising a gaseous discharge tube having an anode and a cathode for producing a gaseous discharge having a luminous positive column, a filling of helium gas at low pressure for said tube, and a magnetic control coil concentric with the discharge path between said anode and cathode for varying the cross-section of said positive column.

9. A luminous gaseous discharge lamp comprising a gaseous discharge tube containing an anode and a cathode for producing a gaseous discharge having a luminous positive column, a baille between said anode and cathode comprising a small aperture through which said discharge takes place, and a magnetic control coil concentric with the discharge path between said cathode and said baille to vary the cross-section of said positive column to control the light flux emanating from the positive column.

10. A luminous gaseous discharge lamp comprising a gaseous discharge tube containing an anode and an electron emitting cathode for producing a gaseous discharge having a luminous positive column, and a magnetic control coil concentric with the discharge path between said anode and cathode for varying the cross-section of said positive column.

11. A luminous gaseous discharge lamp comprising a discharge tube containing an anode and an lectron emitting cathode for setting up a gaseous discharge having a luminous positive column, and a control coil located concentrically with the discharge path between said anode and cathode for varying the cross-section of said positive column and extending over the maior portion of the whole distance therebetween.

FREDERICK W. REYNOLDS.

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