Color deformographic storage target

[57] ABSTRACT

A target assembly for a storage/display deformographic tube comprising a Fabry-Perot type interference filter deposited on a dielectric target material. The filter comprises a deformographic film sandwiched between two mirrors, the inner dielectric mirror comprised of a quarter wavelength stack of alternating layers of materials with greatly differing indexes of refraction and the outer conducting mirror comprising a thin layer of appropriate metal such as silver. The deformographic film should be deposited in a layer which is an integral number of one-half wavelengths.

Claims, 2 Drawing Figures

<img file="US3902012A_D0001.tif" />

3902D12 °R IN J78/7.5D

3.902,012

PATENTED AW 2 61975

IG. 1

<img file="US3902012A_D0002.tif" />

ERASE X INFORMATION

CONTROL T SIGNAL

CIRCUITS X CIRCUITS ,

3,902,012

COLOR DEFORMOGRAPHIC STORAGE TARGET

This invention relates to storage/display tubes used for the visible presentation of information transduced from electrical information bearing signals and more 5 particularly to a deformographic target assembly of the Fabry-Perot type capable of providing a color visual display.

CROSS REFERENCE TO RELATED PATENTS _J0U.S. Pat. No. 3,109,062 to Clauer and Kuehler issued Oct. 29, 1963.

U.S. Pat. No. 3,445,707 to Hershoff and Gilvey issued May 20, 1969.

U.S. Pat. No. 3,626,084 to Wohl, Hawn and Medley 15 issued Dec. 7, 1971.

U.S. Pat. No. 3,676,588 to Kozol and Wohl issued July 11, 1972.

All of these patents relate to storage/display tubes and improvements therein and all are assigned to the 20 assignee of the present invention. U.S. Pat. No. 3,626,084 is specifically incorporated herein by reference.

BACKGROUND OF THE INVENTION

The conventional method of providing a static visual display of information transmitted in the form of electrical signals is by means.of a cathode ray tube having a phosphor coated face on which an electron beam impinges to produce a visible display. The beam carried information by undergoing modulation of either the intensity of the deflection of the electron beam. However, the use of phosphors for displays of the type contemplated herein, that is, storage as well as projection of the display, is not completely satisfactory.

As a consequence, tubes have been developed and are described in the above referenced patents wherein electron beams generated by electron guns of the type used in cathode ray tubes are directed to a dielectric target rather than a phosphor target. Electron depostion on the dielectric target provides an electrostatic charge pattern corresponding to the information which modulates the electron beam. That electrostatic charge pattern is reproduced on the opposite side of the target in a special material which deforms according to the quantity of electrostatic charge deposited on the dielectric surface. The deformed material may then be viewed through reflective or transmissive schlieren optics and visual perception may be maintained satisfactorily for a period of hours after the electron beam generating gun is turned off.

All of these prior art deformographic tubes have provided black and white visual displays and have used schlieren optics. Consequently, it is the general object of this invention to provide a special target assembly which is capable of providing a color visual display and which does away with schlieren optics in black and white or color mode. Other objects and advantages of the invention will become apparent through the following description.

SUMMARY OF THE INVENTION

This invention provides a target assembly based upon Fabry-Perot interference transmission filter techniques. The target assembly comprises a target dielectric material one surface of which is disposed to receive impinging electrons from an information bearing elec tron beam. The opposite surface of the dielectric material is coated with a dielectric mirror which, in turn, is coated with a deformographic material which is coated with a second mirror. The two mirrors sandwich the deformographic material in a structure that provides a Fabry-Perot type of interference transmission so that a light beam directed to the assembly may be broken into its component colors. The result is the capability of providing a background color for projection onto a screen and a second color delineating the deformities in the deformographic material produced in accordance with the information bearing electron beam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly broken away, illustrating a deformographic storage display tube.

FIG. 2 is a cross-sectional partial view of the target assembly of the present invention used in the display system shown in FIG. 1.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 illustrates a general arrangement of a deformographic storage display tube. The tube includes an ₂₅ evacuated envelope 10 of any suitable shape such as that of a conventional cathode ray tube having an electron gun and focusing system at one end and an enlarged transparent faceplate 12 at the other end. Individual write and erase guns are shown in separate necks 30 ^ext^ending from the envelope 10. The write gun 14 includes a cathode 16 and a control grid 18 to which signals are applied to modulate the electron beam intensity in conventional fashion. The modulating input signals may be derived from any suitable source siich as from video information signal circuits 20. The modulated electron beam is scanned across the surface of dielectric target 22 by deflection means such as a deflection yoke 24 disposed around the neck of the envelope 10 and controlled by sweep voltage generator 26. Al40 though a video-type scanning system is shown, selective scanning or other displays may alternatively be generated by digital-type circuits, by character beam-type tubes or by any other circuits appropriate for a particular application.

An erase gun 28 operated by erase control circuits 30 is utilized for erasure of the electrostatic charge distribution pattern on the writing side of the target 22. Erase gun 28 may be mounted in a separate neck of the envelope 10 and directs a dispersed high intensity beam ⁵⁰ onto the target surface. Details of the beam focusing and accelerating system are not shown since they may assume any of a number of conventional forms.

The outer periphery of the target 22 is mounted to _gg tf*^e inner wall of the envelope 10 in appropriate sealed fashion, not shown in detail, to define two separate and independent chambers 32 and 34 within the envelope 10. The sealed chamber 32 on the one side of the dielectric target 22 is called the electron beam chamber because it contains the write gun 14 and the erase gun 28 and associated components. The sealed chamber 34 on the other side of the dielectric target 22 from the chamber 32 extends between the target and the tube faceplate 12 and may be termed a deformographic film chamber since it contains a deformographic filter 36. Filter 36 will be described hereinafter in detail with respect to FIG. 2. It should be noted that two chamber construction is necessary only because of possible con3,902,012 lamination of cathods by gases given off by presently known suitable deformographic materials.

While reflective optics may be used, if desired, the system illustrated in FIG. 1 is a type of transmissive optical system. Light from a source 60, which in this instance comprises a projection lamp, is focused along an optical axis 62 by a condenser comprising a pair of lenses 64, The focused light passes through the tube faceplate 12 to the deformographic filter 36 where it is refracted and diffracted by the deformations therein. Light passing through the filter 36, the target 22, and an optically clear window 68 comprising a flat surface or lens element in the envelope 10 reaches a projection lens 70 for projecting onto screen 74. It is obvious that the tube faceplate 12 must also be of optically clear material and is a part of the lens system.

A normal Fabry-Perot interferometer is composed of two optical flats or etalons coated with semitransparent metals or dielectric films where the spacing between then is varied to produce interference fringes. By “semi-transparent metal” is meant a metal of controlled thickness so as to obtain satisfactory transparency. Reference may be made to the book “Thin Film Optical Filters” by H. A. Macleod, published by the American Elsevier Publishing Company, Inc., New York, 1969 for explanatory information concerning the theory of Fabry-Perot filters. Essentially, the FabryPerot interferometer is used for the examination of the structure of spectral lines. Light is passed from a source through the interferometer producing fringe patterns which give very preceise wave lengths varying as a function of the physical parameters of the filter. FIG. 2 shows, in cross section, the target assembly according to the present invention in which a Fabry-Perot interferometer is incorporated by sandwiching deformographic material 124 between mirrors 123 and 125. For purposes of illustration, a point charge 126 and a uniform charge 127 are shown as being deposited on the surface of the dielectric target 122. These charges result in the deformations 128 and 129 shown in the deformographic material 124. Since the outer mirror 125 is coated on the surface of the deformographic material, these deformations are also included in mirror 125. Additionally, mirror 125 acts as a conductive ground plane for establishing a reference potential plane substantially coextensive with target 22. Reference may be made to U.S. Pat. No. 3,676,588, mentioned above, for a more thorough explanation of the type of ground plane provided herein.

In designing a filter 36 such as shown in FIG. 2, the deformographic material 124 should be coated to a thickness which is an integral one-half wavelength of the frequency of light for which the filter is designed. The dielectric mirror 123 which should be semitransparent in a transmissive optical system, should be comprised of alternating layers of materials with a much different index of refraction. It might, for example, be produced from alternating layers of zinc-sulfide and cryolite. It is necessary to use an odd number of layers and each layer should be optically a quarter wavelength thick. The semi-transparent conductive mirror 125 deposited over the deformographic material must be thin enough not to prevent the deformations from taking place in the deformographic material but must be thick enough to provide the reflectivity necessary for the operation of the filter. Silver with a thick4 ness of 100 to 200 angstroms may provide suitable results.

In operation, the basic color for which the filter is designed might, for example, be blue. With such a target incorporated into the tube shown in FIG. 1, the color blue would be projected upon the screen 74. The information written upon that backround might be red due to the deformations 128 and 128 shown in FIG. 2. In order to gain the necessary color difference from the background color, all that is necessary is to adjust the intensity modulation on the electron gun when the electrostatic charge is deposited on the dielectric target 122.

Thus, there has been described a filtering target assembly for use in a deformographic storage display tube which has color capability. Importantly, it should be noted when a filter of this type is used, schlieren optics are not required, thus substantially reducing the cost and complexity of this display system over the display systems shown in the referenced patents. Other advantages include the fact that complex electronics are not required to produce the color; write gum intensity modulation is the essential difference from conventional black and white display systems. Also, if this tube is used in black and white mode, it has been observed that contrast is enhanced because the two reflecting surfaces of the filter result in more light out than is obtained through the prior art tubes with their complicated schlieren optics.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.