GB2129606A - Electron beam addressed liquid crystal light valve and method for construction thereof - Google Patents

Abstract

A twisted nematic liquid crystal cell comprises nematic liquid crystal material 34 sandwiched between a transparent faceplate 24 having a transparent electrode 26, and a transparent, dielectric target plate 30. A writing gun 16 directs electrons at the target plate, a flood gun 18 directs a cloud of electrons at the target for restoring the potential thereof, and secondary emission and free flood gun electrons are collected 20, the writing gun, flood gun, and collector being disposed outside a field of view 22 through the cell. A projection system utilizes polarizing material in front of and behind the cell, and an optical system for directing light through the cell. The cell is constructed by coating one side of a glass faceplate with a transparent electrode and forming alignment surfaces on the electrode and target plate. An inlet and an outlet through the faceplate are provided. The target plate is placed over the transparent electrode, separated therefrom by a spacer. The space is evacuated, and degassed liquid crystal material is forced through the inlet until the cell is filled, at which point the inlet is sealed off. Thereafter, pressure on the outside of the target plate is increased until it is parallel to the faceplate, the outlet tube is then pinched off. <IMAGE>

Description

SPECIFICATION Electron beam addressed liquid crystal light valve and method for construction thereof BACKGROUND OF THE INVENTION This invention relates to display devices and their construction, particularly to electron beam addressed liquid crystal light modulators.

There are many applications in which it would be desirable to modulate light to produce an image based upon information provided by an electrical signal. Among such applications are the projection of television pictures or computer generated data or graphics onto a screen.

Projection apparatus which utilize interactive light valve technology generally fall into two categories: (1) those in which the light modulator is coupled by means of a photoconductor to the addressing system; and (2) those in which the light modulator is directly addressed, usually by an electron beam or laser. An example of the first mentioned type is a liquid crystal light valve referred to in J. Grinberg, et al., "Photoactivated Birefringent Liquid Crystal Light Valve for Color Symbology Display," IEEE Trans. Elec. Dev., Vol. ED-22, No. 9, p. 775 (1975) and W.

Bleha, et al., "Application of Liquid Crystal Light Valve to Real-Time Optical Data Processing," Opt. Eng., Vol. 17, No. 4, p. 371 (1978). In the aforementioned device a field is applied across a reflective liquid crystal cell by a photoconductor activated by light impinging thereon from one side, which causes the cell to modulate light entering the cell from the other side and be reflected back therethrough. However, this type of device employs a complex layered structure and complex optics, and for a practical liquid crystal cell thickness its switching speed and contrast ratio are unsatisfactory for some pertinent applications.

Examples of the second type of light modulator are oil film devices referred to in T. True, "Recent Advances in High Brightness and High Resolution Color Light Valve Projector." 10 SID Symposium Digest Vol. 10, p. 20 (1979); a deformagraphic mirror device described in Wohl et al. U.S. Patent 3,626,084 issued December 7, 1971 for "Deformographic Storage Display Tube;" a thermally addressed smectic liquid crystal light valve described in H. Dewey, et al., "Laser-Addressed Liquid Crystal Projection Displays," SID Proceedings, Vol. 19, No. 1, p. 1 (1978) and M. Smith, et al., "Ultra High Resolution Graphic Data Terminal," SPIE, Vol. 200, p. 171 (1979); a mirror matrix device described in R. Thomas, et al., "The Mirror Matrix Tube: A Novel Light Valve for Projection Displays," Westinghouse Scientific Paper, 74-1 G7-Mirro-P1 (ES 481), November 1974, in G.Guldberg, etal., "An Aluminum/SiO2/Silicon on Saphire Light Valve Matrix for Projection Displays," Applied Physics Letters, Vol. 26, No. 7, p. 391 (1975), and in L. Hornbeck, et al., "Deformable Mirror Projection Display" 11 SID Digest, Vol.

11, p. 229 (1980); and a pockels effect device referred to in G. Marie and J. Donjon, "Single Crystal Ferroelectrics and Their Application in Light Valve Display Devices," Proc. of the IEEE, Vol. 6, No. 7 (1973).

The aforementioned devices in the second category have various drawbacks. The oil film, deformographic mirror, thermally addressed, and matrix mirror devices all require Schlieren optics, which are complex and optically inefficient. In addition, these, as well as the pockels effect device, are all reflective devices. The oil film devices, wherein an image is written by an electron beam onto a thin film of oil, requires high maintenance and complex mechanics due to degradation of the oil film and a cathode by the electron beam. The deformographic, thermally addressed and matrix mirror devices are all storage devices which utilize modulation media with switching speed limitations that restrict their use in other applications.The deformographic device, which utilizes a flexible membrane to modulate the light, has no low frequency spatial response and develops failures due to flexing of the membrane. The thermally addressed device exhibits low sensitivity. The pockels effect device, wherein light is modulated by a KDP crystal written on by an electron beam, is a complex device which requires a cooling system and whose resolution is limited by the small size of a practical crystal.

Liquid crystal materials are attractive for image projection devices because of their selectively controllable light modulation properties. However, one limitation to their use heretofore has been the lack of a satisfactory addressing scheme. It would be desirable to address a liquid crystal cell directly with an electron beam since cathode ray tube (hereinafter "CRT") technology is highly advanced. In fact, a reflective type liquid crystal CRT television display is described in J. VanRaalte, Proc. of the IEEE, Vol. 56, No. 12, p. 2146 (1968). However, in that case the electron beam was coupled to the liquid crystal cell by a plurality of metallic pins, resulting in a variety of problems, including low resolution and pin-to-pin cross taik. Electron beam scanning of a liquid crystal material for storage of information has also been disclosed in J. Hansen and R.Schneeberg, "Liquid Crystal Media for Electron Beam Recording," IEEE Trans. on Elec. Dev., Vol. ED-1 5, No. 11, p. 896 (1968), though the device disclosed therein employs a cholesteric liquid crystal material whose response time is slow and switching requires a high electric field, resulting in low sensitivity. In addition, the possible use of a liquid crystal cell in an electron beam addressed direct view storage display has been mentioned in I. Chang and W.

Pennebaker, "Bi-stable Storage Tube With AC Controlled Display," 1973 SID Symposium Digest of Technical Papers, p. 102.

However, none of the devices described in the aforementioned references provides a fast response device which modulates light passing through the device for satisfactory projection, without the use of complex optics, of rapidly changing images, such as those produced by television. Accordingly, there has heretofore been a need for development of such a device.

SUMMARY OF THE INVENTION The present invention meets the aforementioned need and overcomes the aforementioned drawbacks of previous devices used for image projection by providing a liquid crystal light valve which modulates light as it is transmitted through the light valve and is directly addressable by a scanning electron beam as in a CRT. The light valve of the invention can be used with a simple transmissive optical system to project rapidly changing images, exhibits high resolution, contrast and sensitivity, and is believed to provide greater reliability than prior art devices. The invention also provides for the construction of a projection system employing a CRT having windows through which light is passed for modulation and thereafter projected onto a screen. The invention further provides a novel method for constructing such a light valve.

A twisted nematic liquid crystal cell is constructed using a suitable liquid crystal material sandwiched between a transparent faceplate having a transparent electrode formed thereon and a transparent target plate, the central portion of the cell defining a window through which light may be transmitted for modulation. A writing electron gun is provided for directing a narrow beam of electrons to selectable locations on the target plate to change the target surface electric potential at those locations. One or more flood guns are provided for directing a broad, unfocused beam, or cloud, of electrons at the target plate for restoring the target surface potential to the potential of the flood gun cathode.A collector is placed adjacent the periphery of the target plate for collecting secondary electrons emitted from, and flood gun electrons repelled by, the target, the collector potential being maintained just below the first crossover of the characteristic secondary emission curve of the target so that the target may be written on and refreshed at high speed by the writing gun. The writing gun, flood gun and collector are placed outside a predetermined field of view of the liquid crystal cell window so the light may be transmitted toward the target plate through the cell for modulation.

A projection system is constructed by providing a CRT with a writing gun, a flood gun, a collector and the liquid crystal cell, the faceplate of the liquid crystal cell forming the faceplate of the CRT. An entry window is formed at the back of the CRT so that light may be transmitted into the entry window and directed out through the liquid crystal cell. Polarizing material is placed in front of the entry window and in front of the faceplate so that the liquid crystal cell can be used to modulate the intensity of the light by varying the polarization of light passing through it. A lens system is provided for directing light from a light source through the CRT and projecting the emerging light.

The light valve is constructed by a procedure that results in an isostatic liquid crystal cell. The faceplate is prepared by depositing an indium-tin oxide coating on one surface to form the transparent electrode and providing an inlet and an outlet through the faceplate, the outlet being connected to a collection chamber. The target plate is placed over and attached at its perimeter to the faceplate, the target plate being separated from the electrode by a peripheral spacer. The space within and surrounding the cell is evacuated, after which thoroughly degassed liquid crystal material is forced by pressure through the inlet until the cell is entirely filled, at which point the inlet is sealed off. Thereafter, pressure on the outside of the target plate is increased until the target plate is substantially parallel to the faceplate, at which point the outlet is sealed off.It has been determined that nematic liquid crystal material with high birefringence, low dielectric anisotropy, and low viscosity at room temperature is particularly suitable.

It is therefore a principal objective of the present invention to provide a new and improved electron beam addressable liquid crystal light valve and method for construction thereof.

It is another objective to provide such a light valve wherein light is modulated as it passes through the valve.

It is another objective of the present invention to provide such a light valve which is suitable for use in a high speed write and refresh application.

It is yet another objective of the invention to provide an image projection system employing the aforementioned light valve.

It is a further objective to provide a method for construction of the aforementioned light valve which results in an isostatic liquid crystal cell.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side, schematic view of a light valve according to the present invention.

Figure 2 is a graph of the secondary emission characteristic of an exemplary electron beam target employed in the light valve shown in Fig. 1, illustrating the relationship of writing gun and collector potentials to secondary emission.

Figure 3 illustrates waveforms of writing gun current and electric potential produced at a written region of the aforementioned target.

Figure 4 is a side, schematic view of the light valve shown in Fig. 1 employed in a projection system according to the present invention.

Figure 5 is a side, schematic view of the construction of a light valve according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to Fig. 1 of the drawing, the electron beam addressed liquid crystal light valve comprises a liquid crystal cell 10, having a front surface 1 2 and a back surface 14, a writing electron gun 1 6 for directing a beam of electrons to selectable locations on the back surface of the cell to change the electric potential at those selectable locations, one or more flood electron guns 1 8 for directing a broad, unfocused beam of electrons at and over the back surface of the cell, and a collector electrode 20 disposed adjacent the periphery of the back surface of the cell for collecting secondary electrons emitted from, and electrons repelled by, the back surface of the cell.The writing gun, flood gun and collector electrodes, which must be at least partially contained within a substantially evacuated space along with the back surface of the liquid crystal cell, are disposed in respective positions outside a predetermined field of view of a window defined through the liquid cell as represented by lines 22. This permits light to be transmitted unobstructively through the liquid crystal cell and modulated thereby, ordinarily entering the cell window from the back surface 1 4 and exiting out the front surface 1 2 of the cell.

The liquid crystal cell itself has a faceplate 24 of transparent material, preferably, but not necessarily, glass, one side of the faceplate comprising the front surface 1 2 of the liquid crystal cell. A transparent faceplate electrode 26 is formed on the other, back surface 28 of the faceplate. The transparent electrode suitably is a thin film of indium-tin oxide (ITO) deposited in a conventional manner on the surface 28. A target plate 30 of transparent, dielectric material is disposed parallel to the faceplate at a predetermined distance D from the transparent electrode 26 as determined by a spacer 32, the back, or exterior, surface of the target plate comprising the back surface 14 of the liquid crystal cell. Filling the gap between the transparent faceplate electrode 26 and the target plate 30 is a layer of nematic-type liquid crystal material 34.The liquid crystal material is prevented from escaping by a seal 35 of an epoxy compound or other suiable material extending around the periphery of the cell. The surfaces of electrode 26 and target plate 30 in contact with the liquid crystal layer are treated in a suitable manner to provide a parallel (homogeneous) boundary orientation, with the orientations of the two surfaces being at right angles to provide a 90 twist in the nematic liquid crystal material. Such surface orientation preferably is provided in a known manner by vacuum-depositing a transparent film of silicon monoxide (SiO) onto the surfaces at an angle of approximately 5" relative to the surface.

It has been found that float glass is a suitable material for the faceplate, and that a taut transparent dielectric membrane of a material such as mica, polyimide or glass is suitable for the target plate, though other materials might satisfactorily be used. The material of target plate 30 must have, or must be treated to have, a secondary electron emission ratio (8) greater, and preferably substantially greater, than unity when struck by electrons from a writing electron gun.

Spacer 32 suitably is formed of polyester film (such as that sold under the designation Mylar, a trademark of E.l. du Pont de Nemours 8 Co.) or glass frit.

In the assembled cell, the molecules of the nematic liquid crystal material 34 are ordered such that plane polarized light passing through the cell is, in the absence of an applied electric field, rotated 90 . When a voltage is applied across a region of the material the molecular axes of the liquid crystal molecules in that region tend to orient themselves parallel to the applied field, thereby decreasing the angle of rotation of the polarized light passing through that region of the cell. Thus, the liquid crystal material modulates the light by shifting its polarization. If sufficient voltage is applied, the polarized light passes through the "switched" region of the cell unchanged.

Commercially available nematic liquid crystal materials suitable for use in cell 10 include E.

Merck's Nematic Phase 11 32TNC, a mixture of three phenyl cyclohexane single components and one biphenyl cyclohexane single substance, and BDH Chemical's E7, a eutectic mixture of 4-cyano-4'-n-pentabiphenyl, 4-cyano-4"-n-pentyl-terphenyl, 4-cyano-4'-n-heptyl-biphenyl and 4cyano-4'-n-octoxybiphenyl. Ideally, the nematic liquid crystal material should have high birefringence (i.e., An > 0.15), low dielectric anisotropy, and low viscosity at room temperature.

Materials having such characteristics are preferred because they minimize the writing beam current required to switch the cell at speeds adequate for standard monochromatic television image displays. Liquid crystal compositions having such a combination of physical and electrical properties are the subject of a contemporaneously-filed U.S. patent application entitled "Light Transmissive Liquid Crystal Materials for Use in Electro-Optical Display Devices," in the names of Robert L Hubbard and Jason C. H. Liang, the disclosure of which is incorporated herein by reference.By way of example, however, a preferred nematic material having a An > 0.1 6, an e || < 13, an ej < 6, and a viscosity < 40 cp at 20"C, consists essentially of an admixture containing 80 wt% of a eutectic of BDH Chemical's K1 5 and E. Merck's S1103, and 20 wt% of E. Merck's S1544.

The writing electron gun 1 6 may be configured in a variety of ways suitable for CRT, as is well known in the display technology industry. Similarly, the flood guns 1 8 may also be configured in a variety of ways, as is well known in the display technology industry for the production of storage-type CRT displays.

The collector configuration of the light valve is particularly important, as it is necessary to provide an electrode for collecting secondary emission electrons from, and flood gun electrons repelled by, the back surface 14 of the dielectric target plate 30, while simultaneously permitting light to be transmitted unobstructively through the liquid crystal cell 10 and an electric potential image to be written on the back surface 14 of the target plate. It is preferred that the collector be formed of a conductive ring 20 placed around the periphery of the liquid crystal cell with its center axis extending away from the faceplate 24 thereof as shown in Fig. 1, the target plate 30 of the cell being circular.This places the collector electrode outside the field of view of the cell window, represented by lines 22, while providing a reasonably uniform electric field associated with the collector around the periphery of the cell.

In operation, the back surface 1 4 of the target plate 30 is ordinarily maintained at the same potential Vfg as the cathode of flood gun 18, since the flood gun continuously directs a cloud of electrons at and over the back surface of the target. Regions of the back surface which are at the same potential Vfg as the flood gun repel flood gun electrons, while regions of the back surface that are positive with respect to Vfg attract flood gun electrons until such regions reach Vfg, extra free electrons being attracted to the collector 20.The target plate 30 acts as a capacitor, as does the liquid crystal material 24; consequently, the voltage across a given region of the liquid crystal material, and hence its polarization switching effect, is a function of Vfgt the transparent faceplace electrode 26 potential Vfp, and the capacitance of the target plate relative to the capacitance of the liquid crystal material in that region. Typically, the flood gun cathode would be electrically connected to the transparent electrode so that the transparent electrode and back surface of the target would ordinarily be at the same potential, Vfgx thereby maintaining the liquid crystal material in an unswitched, unbiased state.However, in some circumstances it may be desired to impose a bias across the cell, and in that case the flood gun cathode and electrode 26 would not be connected together.

The writing gun cathode 1 6 is operated at a very high negative potential Vwg with respect to the flood gun cathode potential Vfg, typically about 4.5 kV, so that when the writing beam strikes the back surface 14 of the target more electrons are emitted than are absorbed, as shown by the secondary emission curve of Fig. 2. Consequently, the region of the target struck by electrons from the writing gun takes on a positive potential which is capacitively coupled to a corresponding region of the liquid crystal, thereby switching that region.

Since the target plate material is dielectric, a collector must be provided in its vicinity to provide a return path for the writing and flood guns. To perform this function the collector would necessarily have to be at a positive potential with respect to both the writing and flood gun cathodes, though in order to permit the flood guns to restore to Vfg regions which have been struck by the writing gun beam, rather than stabilize at the collector potential Vcoi, the collector potential must be less than the first crossover potential VCrW of the target, that is, the lowest potential corresponding to electron energy at which the secondary emission ratio 8 is one. This permits the light valve to be used in a fast response write and refresh operation, rather than as a storage device.

Referring to Fig. 3, when a region of the back surface 14 of the target is struck by the writing gun beam, the potential at that region rises toward, but cannot exceed, the collector potential VcO,. Since the collector potential is less than Vac,,, more flood gun electrons are thereafter absorbed than emitted, so the potential at that region drops back down to Vfg after the writing gun current at that region has stopped. In this manner, a potential image may be written on the target by the writing gun, thereafter erased by the flood gun, and subsequently rewritten by the writing gun. This image is capacitively coupled to the liquid crystal, which modulates the light passing therethrough in accordance with the image.

It has been found that using the aforementioned preferred nematic liquid crystal material placed in a cell with a separation distance D of 10-7 M a display satisfactory for projection of a monochromatic television image at a wavelength of 0.6 X 10-6 M can be obtained. Using a writing gun providing a beam current of 14.7 X 10-6 amp and a beam width of 4.4 mils, and a taut mica target, the following results may be obtained: Display switching speed 25 msec Contrast ratio 59::1 Resolution 225 lines per inch Writing speed 1 64 cm/msec Turning now to Fig. 4, a projection apparatus employing a light valve according to the present invention further includes an evacuated chamber 36 containing the writing gun 16, flood guns 18, and a collector electrode 20, the liquid crystal cell 10 being attached to the front of the chamber with the back surface 14 facing inwardly.Preferably an entry window 38, comprising an aperture covered by a transparent material, is placed at the back of the chamber 36 and the writing gun 1 6 is placed off axis so that there is an unobstructed field of view through the entry window 38 and the window defined through the liquid crystal cell 1 0. A first polarizer 40 is placed behind the entry window for polarizing light entering the entry window and a second polarizer, or analyzer, 42 is placed in front of the cell 10 for preventing all but light of a selected polarity from passing therethrough without a reduction in intensity. The polarizer 40 and the analyzer 42 may be made from commercially available polarizing sheet materials.

The intensity of light passing through the analyzer from a given region of the liquid crystal cell will depend upon the extent to which that region has been switched "on" by the writing gun, since the intensity of the light passing through the analyzer is a function of the relative polarization of the analyzer and the light impinging on it. Consequently, the polarization modulation produced by the twisted nematic liquid crystal cell is converted by the polarizer and analyzer to intensity modulation. With the analyzer polarization oriented with the polarizer the resultant image intensity will increase with the intensity of the electron beam writing gun, while with the analyzer polarization oriented 90 to the polarization of the polarizer the image intensity will decrease with increased intensity of the electron beam writing gun.

A lens 44 is provided for directing light from a source, such as a lamp 46, through the entry window 38 and through the window of the liquid crystal cell 10. Another lens 48 is provided for focusing the image produced by the liquid crystal cell onto a viewing surface, such as the surface of screen 50, thereby projecting onto the screen the image represented by an electrical input signal to the writing gun. While a simple optical system represented by lenses 44 and 48 is illustrated here, it is recognized that more complex optics might be used depending upon the particular application in which the light valve is used.

It has been found that a suitable light valve can be constructed as shown in Fig. 5. A faceplate 52 of float glass, or some other suitable transparent material, is prepared by first depositing a layer of indium-tin oxide (ITO) on one surface in a conventional manner, forming a transparent electrode 54, and thereafter depositing a thin, transparent alignment film of silicon monoxide (not shown) on the surface of ITO electrode 54. The alignment film can be deposited by vacuum evaporating silicon monoxide at 5" from the plate surface by a process such as the one described by J. Janning in Appl. Phys. Lett., Vol. 21, No. p 1 73 (1972). An inlet aperture 56 and an outlet aperture 58 are formed in the faceplate, and inlet and outlet tubes 60 and 62 are sealingly attached to the faceplate in communication with their respective apertures.A glass vacuum ampoule, or chamber, 64 is sealingly attached to the remaining end of the outlet tube.

This configuration is arranged with faceplate oriented horizontally and a target plate 66 is then placed over the transparent ITO electrode 54, resting on a peripheral spacer 68 and attached at its perimeter to the coated faceplate by a seal 70 using an epoxy compound or other suitable sealant. Target plate 66 includes a transparent silicon monoxide alignment film on its inner surface, oriented at 90 to the alignment film on electrode 54.

Thereafter, the space between the target plate 66 and the transparent electrode 54 is filled with liquid crystal material. This is accomplished by first evacuating the space immediately surrounding and interior to the faceplate, target plate, inlet tube, outlet tube and ampoule. Then the free end of the inlet tube 60 is placed into thoroughly degassed liquid crystal material and the pressure on the liquid crystal material is increased, which causes it to enter the cell through the inlet tube 60, fill the space between the faceplate 52 and target plate 66, and flow out the outlet tube 62 and into the ampoule 64.After the space between the faceplate and target plate is entirely filled, the inlet tube 60 is pinched off by conventional means at an appropriate point 72 and the pressure on the outside surface of the target plate 66 is increased until the target plate rests solidly on the peripheral spacer 68 and is substantially parallel to the faceplate.

Thereafter, the outlet tube 62 is pinched off at an appropriate point 74 to seal the liquid crystal material in the cell. By performing the aforementioned process utilizing a thoroughly degassed liquid crystal material, an isostatic liquid crystal cell is produced, thereby ensuring uniform plate separation and structure stability in a high vacuum.

A suitable fixture 76 for forcing liquid crystal material into the cell is shown in Fig. 5. The inlet tube 60 is sealingly attached to an upper portion 77 of the fixture by a threaded cap 78, washer 80 and resilient O-ring 82, the inlet tube extending downwardly through an upper chamber 84 and lower chamber 86 of the upper portion of the fixture.

Once the cell and surrounding space have been evacuated, a lower portion 88 of the fixture, holding a container 90 of liquid crystal material 92, is threaded upwardly into the lower chamber 86 of the upper portion of the fixture until it covers ports 94, provided for evacuating the interior of the fixture, and is lodged against a stop 96, an O-ring 98 providing a pressure seal, thereby placing the inlet tube into the liquid crystal material. Pressure on the liquid crystal material 92 is increased to force it into the inlet tube 60 by introducing a gas into the upper chamber 84 through an inlet port 100. Preferably such a gas should be inert and have low soluability in liquid crystal material, and argon has been found to bs most suitable, though others might be used without departing from the principles of the invention.

Initial evacuation of the cell and surrounding space can be accomplished by placing the assembly in a bell jar and evacuating the bell jar. Once the cell is entirely filled with liquid crystal material, the pressure in the bell jar is then increased in order to increase the pressure on the outside surface of the target plate 66, as previously discussed.

Once the liquid crystal cell has been constructed it may be attached to, or integrated into, some appropriate structure having a writing gun, a flood gun and a collector electrode and being adopted to operate the valve in a vacuum, such as a CRT.

Alternatively, where the cell is to be used as the faceplate of a CRT it is attached to the funnel 102 of the CRT prior to placement in the bell jar. In this case the pressure on the outside of the target plate 66 is increased by increasing the pressure inside the CRT, preferably with an inert gas such as argon. The CRT is heat treated in a conventional manner to remove gases, particularly water vapor, before it is sealed. The cell is attached to the funnel 102 by an epoxy, though other conventional attachment means might be used, and this epoxy, as well as others used in construction of the valve should, in this case, be chosen from commercially available epoxies capable of withstanding for a short period of time the high temperature, on the order of 300or, necessary for heat treatment of the CRT.

The twisted nematic liquid crystal cell employed in the light valve of the present invention is not restricted to the type of cell described above. Other twisted nematic cells that may be used include flow-assisted cells of the type described by R. Hubbard and D. Bos in "Optical-Bounce Removal and Turnoff-Time Reduction in Twisted-Nematic Displays." IEEE Trans. Elec. Dev., Vol.

ED-28, No. 6, p 723 (1981). Also usable are dual-frequency addressable twisted nematic cells made using liquid crystal materials of the type described in a paper by R. Hubbard et al. titled "Development of Dual-Frequency Addressable Liquid Crystals," which was presented at the Fourth Annual Symposium on Liquid Crystals and Ordered Fluids on April 1, 1982, at Las Vegas, Nevada.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention of the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims (10)

1. An electron beam addressed liquid crystal light valve for modulating transmitted light in an image projection system, comprising: (a) a liquid crystal cell having a transparent faceplate including a transparent electrode disposed on one surface thereof, a transparent target plate disposed on the same side of said faceplate as said transparent electrode and substantially parallel to and at a predetermined distance from said transparent electrode, said target plate having a target surface on the side thereof opposite said transparent electrode, liquid crystal material disposed between said target plate and said transparent electrode, and sealing means for containing said liquid crystal material between said target plate and said transparent electrode, a portion of said cell defining a window through said faceplate, transparent electrode and target plate;; (b) writing gun means for altering the electric potential at selectable locations on said target surface by directing a beam of electrons onto said target surface; (c) flood gun means for restoring the electric potential of said target surface to a predetermined value by directing a cloud of electrons toward said target surface; and (cub) collector means disposed adjacent the periphery of said target table for collecting electrons emitted by and repelled from said target surface, said flood gun means, writing gun means and collector means being disposed outside a predetermined field of view through said cell window.

2. The light valve of claim 1 wherein said liquid crystal material is a nematic type material.

3. The light valve of claim 2 wherein said nematic liquid crystal material is characterized by having high birefringence, low dielectric an isotropy, and low viscosity at room temperature.

4. The light valve of claim 1 wherein said liquid crystal material modifies the polarization of light passing therethrough in response to an electric field applied thereto, and further comprising polarizer means for polarizing light prior to passing through said window of said cell and analyzer means for receiving light which has passed through said window and transmitting said light with an intensity dependent upon the polarization of said received light.

5. The light valve of claim 4, further comprising optical system means for receiving light from a light source, directing said light through said polarizer means, thereafter through said window of said cell, and thereafter through said analyzer means, and projecting the light passing through said analyzer means.

6. The light valve of claim 1 further comprising a first alignment film disposed on said transparent electrode and a second alignment film disposed on said target plate, both said films being in contact with said liquid crystal material, for ordering said liquid crystal material, said first and second alignment films having a predetermined orientation with respect to each other.

7. The light valve of claim 1 further comprising a substantially evacuated chamber attached to said liquid crystal cell, said target surface of said target plate facing inwardly toward said chamber, said flood gun means and said writing gun means emitting electrons within said chamber, said collector means having an electron-collecting electrode disposed within said chamber adjacent the periphery of said cell, and said chamber having an entry window for receiving light from outside said chamber and transmitting said light toward said target surface.

8. The light valve of claim 1 further comprising means associated with said collector means and said flood gun means for producing a positive potential at said collector means with respect to said flood gun means, said potential being less than the first crossover potential of the secondary electron emission curve of said target plate.

9. The light valve of claim 1 wherein said target plate comprises a taut dielectric membrane.

10. An electron beam addressable liquid crystal light valve substantially as hereinbefore described with reference to the accompanying drawings.