CA1204811A - Electron beam addressed liquid crystal light valve and method for construction thereof - Google Patents

Abstract

ELECTRON BEAM ADDRESSED LIQUID CRYSTAL LIGHT
VALVE AND METHOD FOR CONSTRUCTION THEREOF

ABSTRACT
An electron beam addressed liquid crystal light valve and method for construction. A twisted nematic liquid crystal cell comprises nematic liquid crystal material sandwiched between a transparent faceplate having a transparent electrode, and a transparent, dielectric target plate. A writing gun directs electrons at the target plate for writing thereon, a flood gun directs a cloud of electrons at the target for restoring the potential thereof, and a collector adjacent the target collects secondary emis-sion and free flood gun electrons, the writing gun, flood gun, and collector being disposed outside a field of view through the cell. Collector potential is slightly less than that required to produce a tar-get secondary emission ratio of 1 from flood gun elec-trons. A projection system utilizes polarizing mate-rial disposed in front of and behind the cell, and an optical system for directing light through the cell and polarizing materials. The cell is constructed by coating one side of a glass faceplate with a trans-parent electrode and forming alignment surfaces on the electrode and target plate. An inlet and an outlet through the faceplate are provided, the outlet being connected to a collection chamber. The target plate is placed over the transparent electrode, separated from the electrode by a spacer. The space within and surrounding the assembly is evacuated, after which thoroughly degassed liquid crystal material is forced by pressure through the inlet until the cell is en-tirely 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 substan-tially parallel to the faceplate, at which time the outlet tube is pinched off.

Description

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ELECTRON BEAM ADDRESSED LIQUID CRYSTAL LIGHT
VALVE ~ND 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 sig-nal. Among such applications are the projection of television pictures or comput~r generated data or graphics onto a screen.
Projection apparatus which utilize interac-tive 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 cry~tal 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," ~E~
Eng., Vol. 17, No. 4~ p. 371 (1978). In the aforemen-tioned 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. How-ever, this type of device employs a complex layered structure and complex optics, a~d for a practical liquid crystal cell thickness it~ switching speed and contrast ratio are unsatisfactory for some pertinent applications.

Examples of the second type of light modula-tor are oil film devices referred to in T. True, "Re~
cent 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
Proceedin~s, 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 Projec-tion Displays," Westinghouse Scientific Paper, 74-lG7-Mirro-Pl (ES 481), November 1974, in G. Guldberg, et al., "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, ~5 Proc. of the IEEE, Vol. 6, No. 7 ~1973).
The aforementioned devices in the second cat-agory have various drawbacks. The oil film, deformo-graphic mirror, thexmally addressed, and matrix mirror devices all xequire Schlieren optics, which are com-plex and optically inefficient. In addition, these, as well as ~he pockels effect device, are all reflec-tive devices. ~he oil film devices, wherein an image is written by an electron beam onto a ~hin film of oil, requires high maintenance and complex mechanics due to degradation of ~he oil film and a cathode by 81~

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 util-izes a flexible membrane to modulate the light, has no low frequency spatial respon~e and devlops ~ailures due to flexing of the membrane. The thermally ad-dressed 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 res-olution is limited by the small size of a practical crystal.
Liquid crystal ma~erials are attractive for image projection devices because of their selectively controllable light modulation properties. However, one limitation to their use heretofore haR 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 (herein-after "CRT") technology is highly advanced. In fact, a reflective type liquid crystal CRT television dis-play is described in J. VanRaalte, Proc. of the IEEE, Vol. S6, ~o. 12, p. 2146 (1968). However, in that case the electron beam was coupled to the liquid crys-tal cell by a pluralîty of metallic pins, resulting in a variety of problems, including low resolution and pin-to-pin cro~s talk. 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. EDol5~ No. 11, p. 896 (1968), though the device disclosed therein employs a cholesteric l~quid crystal material whose response time is slow and switching requires a high electric ~z~

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 Con~rolled Display," 1973 SID
Symposium Digest of Technical Papers, p. 102.
However, none of the devices described in the aforementioned references provides a fast response de-vice which modulates light passing through the device for satisfactory projection, without the use of com-plex optics, of rapidly changing images, such as those produced by television. Accordingly, there has here-tofore been a need for development of such a deviceO
SUMMARY OF THE INVENTION
The present invention meets the aforemen-tioned need and overcomes the aforementioned drawbacks of previous devices used for image projection by pro-vidin~ a liquid crystal light valve which modulates light as it is transmitted through the light valve ahd 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 pro-ject rapidly changing images, exhibits high resolu-tion, contrast and sen~itivity, 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 or modulation and thereafter projected onto a ~creen~ The invention further provides a novel method or constructing such a light valve.
A twi~ted nematic liquid crystal cell is constructed using a suitable liquid crystal material sandwiched between a transparent faceplate havin~ a transparent electrode ormed thereon and a transparent target plate, the central portion of the cell definin~

- s -a windo~ 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 5 surface electric potential at tho~e 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 ~he target plate for collecting secondary electrons emitted from, and flood gun electrons repelled by, the target, the col-lector potential beir.g 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 modula-tion.
A projection system is constructed by pro-viding a CRT with a writing gun, a flood gun, a col-lector and the liquid crystal cell, thP faceplate of the liquid crystal cell forming the faceplate of the CRT. An entry window i8 formed at the back of the CRT
50 that light may be transmitted into the entry window and directed out through the liquid crys~al cell.
Polarizing material is placed in front of the entry window and in front of the ~aceplate so that the liquid crys al cell can be used to modulate the inten-sity 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.

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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 eleetrode and providing an inlet and an outlet through the faceplatP, the outlet being connected to a collec-tion 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 peri-pheral spacer. The space within and surrounding the cell is evacuated, after which thoroughly degas~ed 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 ~o 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 -quch a light valve wherein light is modulated as it passes through the valve.
It is another objective of the present inven-~ion 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 aorementioned light valve.
It is a further objective to provid~ a method for construction of the aforementioned light valve which results in an isostatic liquid crystal cell.

~he foregoing and other objectives, eatures, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in con-junction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side, schematic view of a lighk valve according to the present invention.
FIG. 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.
FIG. 3 illustrates waveforms of writing gun current and electric potential produced at a written region of the aforementioned target.
FIG. 4 is a side, schematic view of the light valve shown in FIG. 1 employed in a projection system according to the present invention.
FIG. 5 is a side, schematic view of the construction of a light valve accordin~ to the pre~ent invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 of the drawing, the elec-tron beam addressed liquid crystal light valve com-pri~es a liquid crystal cell 10, having a front sur-face 12 and a back surface 14, a writing electron gun 16 or directing a beam of electrons to selectable locations sn the back ~urface of the cell to change ~he electric potential at those ~electable locations, one or more *lood electron gun~ 18 for directing a broad, unfocused beam of slectrons at and over the i back surface of the cell, and a collector electrode 20 disposea adjacent the periphery of the back surface of : 35 ~he cell for collecting secondary electrons emit~ed from, and electrons rep~lled by, the back sur~ce of , .

the cell. The writing gun, 100d 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 r~espective positions outside a predetermined field of view of a window defined through the liquid cell a~ represented by lines 22. This permits light to be transmitted unob~tructively through the liquid crystal cell and modulated thereby, ordinarily entering the cell window from the back surface 14 and exiting out the front surface 12 of the cell.
The liquid crystal cell itself has a face-plate 24 of transparent material, preferably, but not necessarily, glass, one side of the faceplate compris-ing the front surface 12 of the liquid crystal cell.
A transparent faceplate electrode 26 i9 formed on the other, back surface 28 of the faceplate. The trans-parent electrode suitably i5 a thin film of indium tin oxide (IT0) deposited in a conventional manner on the surface 28. A target plate 30 of transparent, dielec-tric ma~erial is disposed parallel to the faceplate at a predetermined distance D from the transparent elec-trode 26 as determined by a spacer 32, the back, or exterior, surface of the target plate comprising t~e 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 mate-rial is prevented from escaping by a seal 35 of an epoxy compound or other suitable material extending around the periphery of the cell. The surfaces of electrode 26 and target plate 30 in contact wi~h the liquid crystal layer are treated in a suitable manner to provide a parallel (homogeneous) boundary ori~nta~
tion, with the orientations of the two surfa~es being at right angles to provide a 90~ twist in the ne~atic ~o~

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 suit-able material for the faceplate, and that a taut transparent dielectric membrane of a material such as mica, polyimide or glass i5 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 (~ ) 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 designa-tion Mylar, a trademark of E.I. du Pont de Nemours &
Co.) or glass frit.
In the assembled cell, the moleculeq of the nematic liquid crystal material 34 are ordered such that plane polarized light passing through the cell is, in the ab~ence of an applied electric field, ro-tated 9O. When a voltage is applied across a region of the material the molecular axes of the liquid crys-tal molecules in that region tend to orient themselve~
parallel to the applied field, thereby decreasing the angle of rotation of the polarized light passing through that region of the cell. Thus, t'he liquid crystal material modulates the light by shifting it~
polarization~ If sufficient voltage is applied, the polarized light passes through the 'iswitched" region of the cell unchanged.
Commercially available nematic liquid crystal materials suitable for use in cell lO include E. Merck's Nematic Phase 1132TNC, a mixture of three phenyl cyclohexane single components and one biphenyl ~Z~B~i cyclohexane single substance, and BDH Chemical's E7, a eutectic mixture of 4-cyano-4'-n-pentabiphenyl, 4-cyano-4"-n-pentyl-p-terphenyl, 4-cyano-4'-n-heptyl-biphenyl and 4-cyano-4'-n-octoxybiphenyl. Ideally, the nematic liquid crystal material should have high birefringence (i.e., Qn > 0.15), low dielectric aniso-trophy9 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. By way of example, a preferred nematic material having a ~n >0.16, an ~ ~I <13, an ~1 ~6, and a viscosity of ~40 cp at 20C, consists essentially of an admixtu~e containing 80 wt% of a eutectic of BDH
15 Chemical's R15 and E. Merck's S1103, and 20 wt% of E.
Merck's S1544.
The writing electron gun 16 may be configured in ; a variety of ways suitable for a C~T, as is well known in the display technology industry. Similarly, the flood ~0 guns 18 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 trans-mitted unobstructively through the liquid crystal cell 10 and an slectric potential image to be written on the back ~urface 14 of the target plate. It is pre-fer~ed 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 tar-get 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 pro-viding a reasonably uniform electric field associated with ~he collector around the periphery of the cellO
In operation, the back surface 14 of the target plate 30 i5 ordinarily maintained at the same potential Vfg as the cathode of flood gun 18, since the flood gun continuously directs a cloud of elec-trons at and over the back ~urface of the target. Re-gions of the back surface which are at the same poten-tial Vfg as the flood gun repel flood gun electrons, while regions of the back 6urface that are positive wi h respect to Vfg attract flood gun electrons until such re~ions reach V~gr extra free electrons being attracted to the collector 20. The target plate 30 acts as a capacitor, as does the liquid crystal mate-rial 24; consequently, the voltage across a given region of the liquid crystal material, and hence its polarization switching effect, i8 a function of Vfg~
the transparent faceplace electrode 26 potential Vfp, and the capacitance of the target plate relative to the capacitance of ~he li~uid crystal material in that region. Typically, the 100d gun cathode would be electrically connected to the transparent electrode 80 that the transparent electrode and back ~urface of the target would ordinarily be at.the same po~ential~ Vfg, thereby maintaining the liquid crystal material in an unswitched, unbiased state. However, in some circum-stances it may be desired to impose a bias acro~ the cell, and in that case the flood gun cathode and elec-trode 26 would not be connected together.
~ The writing gun cathode 16 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 0 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 xegion of the liquid crystal, thereby switching that region.
Since the target plate material is dielec-tric, 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 necessar~
ily 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 re-gions which have been struck by the writing gun beam, ra her than stabilize at the collector potential V
the collector potential must be le s than the first crossover potential Vcrl of the target, that is, the lowest potential corresponding to electron energy at which ~he secondary emi~sion ratio ~ is one. This permits the light valve to be used in a fast response write and refrèsh 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 exc~ed, the collector potential VcOl.
Since the collector potential is less than V~rl, more flood gun ~lectrons are thereafter absorbed tha~
emitted, 5~ the potential at that region drops back down to Vfg a~ter the writing gun current at that region ha~ 6topped. In this manner, a poten~ial image . 5 may be written on the target by the writing gun, thereafter erased by the flood gun, and ~ub~eque~tly rewritten by the writin~ gun. This image i~ capaci-tiv~ly coupled to the liquid crystal, which modulate~
the light passing here~hrough in accordance with the image.
It has been found that using the af~remen~
tion~d preferred nematic liquid crystal material : placed in a cell with a separation di~tance D of 10-7 M a display satlsfactory for projection of a monochromatic televi~ion im~ge at a wavelength of 0.6x10-6 M ca~ be obtained. Using a wri~ing gun pro-viding a beam current of 14.7xlO-6 amp and a beam width of 4.4 mil~, and a taut mica targetO the following results may be obtai~ed:
Display switching speed 25 msec Con~rast rat~o S9:1 Res~lution 225 lines per inch Writing ~peed 164 cm/m~ec Turning now to FIG. 4, a projection apparatus employing a light valve according to the present invention further includes an evacuated cha~ber 36 containi~g ~he writin~ gun 16, flood guns 18, and a collector electrode 20, the liquid crystal ~ell 10 being attached to the front of the chamber with the back 6urface 14 facing inwardly. Pref~r~bly a~ entry window 38, comprining an aperture covered ~y a tran~;
par2nt mat~rial9 i8 placed at ~e back o t~e chamber 36 ~d the writi~g gun 16 i~ placed of axi~ ~ that th~r~ ie an uno~structed fi~ld of view thro~gh the ~ntry wi~dow 38 ~nd the window d~fined thro~gh t~e liquid ~ry~tal CBll lOo A f~r3~ polari~er ~0 i~

placed behind the entry window for polarizing light entering the entry windo~ and a 3econd polarizer, or analyzer, 42 is placed in front of the cell lO for preventing all but light of a sel0cted polarity from pas~sing therethrough without a reduction in intensity.
The polarizer 40 and the analyzer 42 may be made from commercially available polarizing sheet material~.
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 ana-lyzer and the light impinging on it. Consequently, the polarization modulation produced by the twisted nematic liquid crystal cell is converted by the polar~
izer and analyzer to intensity modulation. With the analyzer polarization oriented with the polarizer the resultant image intensity will increase with the in-tensity of the electron beam writing gun, while with the analyzer polarization oriented 90 to the polari-z~tion 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 lamp 46, through the entry win-i dow 38 and ~hrough the window of the liquid crystal cell lO. Another lens 48 is provided for focusing the image produced by the liquid crystal cell onto a view-ing surface, such as the surface of screen SO, 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 par-ticular 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.
faceplate 52 of float glass, or some other suitable transparent material, is prepared by first depositing S a layer of indium-tin oxide ~IT0) 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 IT0 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 173 (1972). An inlet aperture 56 and an outlet aperture 58 are ormed 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 the faceplate oriented horizontally and a target plate 66 is then placed over the transparent IT0 elec-trode 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 sil-icon 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 5~ is filled with liquid crystal material. This is accomplished by first evacuating the spacs immediately surrounding and interior to the faceplate, target plate, inlet tube, outlet tube and ampoule. Then the ~ree end of the inlet tube 60 is placed into thoroughly degassed liquid crystal material and the pressure on the liquid crystal material in increased, which causes it to ..
. . - .

, . . ., ; .

.

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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 plat~e is entirely filled, the inlet tube 60 is pinched off by conYentional means at an appropxiate point 72 and ~he pressure on the outside surface of the target plate 66 is increased until the target plate rests solidly on the peripheral spacer 68 and ie substan-tially 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 proces~ utilizing a thoroughly degassed liquid crystal material, an isostatic liquid crystal cell is produced, thereby ensuring uniform plate separation and structure sta-bility in a high vacuum.
~ 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 8~ and resilient O-ring 82, the inlet tube ex~ending 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 provid-ing a pressure seal, thereby placing the inl~t tube into the liquid crystal material. Pressure on the liquid crystal material 9~ i~ increased to orce it into the inlet tube 60 by introducing a gas into the ~L2~

upper chamber 84 through an inlet port 100. Prefer-ably~uch a gas should be inert and have low soluabil-i~y in liquid crystal material, and argon has b~en found to be mo~t ~uitabl~, though others might be u3ed without departlng from the principle of t~e invention.
Initial evacuation of the cell and ~urround-i~g space can be accomplished by placing the aR~embly in~a bell jar and evacuating the bell jarO Once the cell i5 entirely f~lled with liquid crystal material, the pressure in ~e bell jar i8 then increa~ed in order to increase the pr~ssure on the outside ~urface of the target plate 66, as previously discusRed.
Once the liquid cry~tal cell ha3 been con-structed it may be attached to, or integrated into, some appropriate ~tructure hav;ng a writing gun, a flood gun and a collector electrode and being adopted to operate the valve in a vacuum, such a~ a CRT.
Alternatively, where the cell is to be used as the faceplate of a CRT it i~ a tached to the funnel 102 of the CRT prior to placemen~ in the bell jar. In ~hi~ ca3e the pre6~ure on the outs~de of the ~arge~
plate 66 i8 increased by increa~ing the pres~ure inside the C~T, preferably with an inert gas such as argonO The CRT is heat treated in a con-ventional manner to remove gases, particularly water vapor, before it is ~ealed. The cell is attached to ~he funnel 10~ by an epoxy, ~hough other conventional ~ttachme~t mean~ might be used~ and this ~poxy, as well as oth~rs used in ~onstruction of ~ valve ~houl~ in thi~ case, be cho~en ~rom commercially available epox~es capable of withs~-anding for a ~hor~
period o time the high temperature, on ~he order of 300~C, nece~ary for hea~ trea~men~ o~ ~he CRT.
The ~wisted nematic liquid cry~tal cell em-ployed i~ the l~ght valve of ~he presen~ anvention i~
not re~trict~d ~o the type o~ cell d~scribed abov~.

~zo~

Other ~wisted nematic cells that may be used include flow-assisted cells oE ~he type described by R. Hub-bard and D. Bos in "Optical-Bounce Remov~l and Turnoff-Time Reduction in Twisted-Mematic Displays."
IEEE Trans. Elec. Dev., Vol. ED-28, No. 6, p ~23 (1981). Also usable are dual-frequency addressable twisted nematic cells made using liquid crystal materials of the type described in a paper by R. Hub-bard et al. titled "Development of Dual-Frequency Addressable Liquid Crystals," which was presented at the Fourth Annual Symposium on Liquid Crystals and Ordered Fluid~ 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 (9)

I CLAIM

1. An electron beam addressed liquid crys-tal light valve for modulating transmitted light in an image projection system, comprising:
(a) a liquid crystal cell having a transpar-ent faceplate including a transparent electrode disposed on one surface there-of, a transparent target plate disposed on the same side of said faceplate as said transparent electrode and substan-tially parallel to and at a predeter-mined distance from said transparent electrode, said target plate having a target surface on the size thereof oppo-site said transparent electrode, liquid crystal material disposed between said target plate and said transparent elec-trode, and sealing means for containing said liquid crystal material between said target plate and said transparent electrode, a portion of said cell defin-ing a window through said faceplate, transparent electrode and target plate;
(b) writing gun means for altering the elec-tric 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 elec-tric potential of said target surface to predetermined value by directing a cloud of electrons toward said target surface; and (d) collector means disposed adjacent the periphery of said target plate 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 anisotropy, 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 polar-izer means for polarizing light prior to passing through said window of said cell and analyzer means for receiving light which has passed through said win-dow and transmitting said light with an intensity de-pendent 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 com-prising a first alignment film disposed on said trans-parent 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 align-ment 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 trans-mitting 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.