mite States Patent
`
`Pinnow et a1.
`
`-
`
`3,691,482
`[151
`[451 Sept. 12, 1972
`
`[54] DISPLAY SYSTEM
`[72] Inventors: Douglas Arthur Pinnow, Berkeley
`Heights; Le Grand Gerard Van
`Uitert, Morris Township, Morris
`County, both of NJ.
`[73] Assignee: Bell Telephone Laboratories, Incor
`porated,
`Murray Hill, Berkeley
`Heights, NJ.
`Jan. 19, 1970
`[22] Filed:
`[21] Appl. No.: 3,636
`
`[52] U.S. Cl. ............... ..332/7.51, 250/199, 330/108,
`.
`330/334
`[51] lint. Cl .................................. ........... ..H01s 3/10
`[58] Field of Search ....... ..302/7.51; 250/71, 80, 199;
`330/334, 108-,252/3014; 331/945
`
`[56]
`
`References Cited
`
`3,524,011
`3,322,682
`3,488,503
`3,572,941
`3,495,034
`
`UNITED STATES PATENTS
`8/1970
`Korpel ...................... ..178/5.4
`5/1967 Thompson ............ ..252/301.4
`1/1970
`Reich et a1 ............... ..250/199
`3/1971
`Kiss ......................... ..350/150
`2/1970
`Arend et a1 ........... ..350/160 P
`
`3,541,542 11/1970 Dugway et al. .......... ..340/3 24
`3 ,453,604
`7/1969
`Geusic et al. ............. ..3 30/ 4.3
`
`FOREIGN PATENTS OR APPLICATIONS
`1,564,271
`4/1969
`France .................. ..252/301.4
`OTHER PUBLICATIONS
`C. E. Baker, Laser Display Technology, 12/68, pp.
`39- 50, IEEE Spactrum.
`Oliver, “ Sparkling Spots and Random Diffraction,"
`Proc. IEEE, Vol. 51, pp. 220- 221, 1/63
`Carsidive, “ Effects of Coherence or Imaging
`Systems” J. Opt. Soc. Am. Vol. 56, pp. l00l— 1009,
`8/66
`
`Primary Examiner-Benjamin A. Borchelt
`Assistant Examiner-N. Moskowitz
`Attorney-R. J. Guenther and Edwin B. Cave
`
`ABSTRACT
`[57]
`A single color display is produced by projection using
`a scanning laser beam operating in the visible or ul
`traviolet and a photoluminescent screen which emits
`in the visible. Combinations of phosphors may be em
`ployed to simulate white or desired colors.
`9 Claims, 3 Drawing Figures
`
`LASER IO
`
`MODULATOR
`
`I2
`
`\
`\\\ \_
`~
`.
`
`132’
`DEFLECTOR
`
`CERIUM DOPED
`GARNET PHOSPHOR
`SCREEN l5
`
`TCL 1022, Page 1
`
`

`

`PATENTEDSEP 12 1972
`
`3.691.482
`
`SHEET 1 UFZ
`
`
`
`
`
`RELATIVE EMISSION INTENSITY
`
`0
`5000
`
`5500
`
`I
`6000
`‘WAVELENGTH (A)
`
`l
`6500
`
`LASER l0
`H
`
`F76 3
`
`‘\
`MODULATOR
`I2
`
`'
`
`\I
`137
`
`DE FLECTOR
`l4
`
`CERIUM DOPED
`GARNET PHOSPHOR
`SCREEN I5
`
`D. A. P/NNOW
`INVENTORSI
`LG. VAN U/TERT
`
`ATTORNEY
`
`TCL 1022, Page 2
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`

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`PATENTEIISEP 12 I972
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`3,691,482
`
`SHEET 2 [IF 2
`
`FIG. 2
`
`I
`I
`I
`I
`I
`'I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`
`_
`
`0
`
`“ILLUMINANT C
`
`TCL 1022, Page 3
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`

`

`1
`DISPLAY SYSTEM
`
`3,691,482
`
`5
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`'
`The invention is concerned with projection display
`systems and is primarily concerned with those produc
`ing black and white images by coherent lighting.
`2. Description of the Prior Art
`Interest in laser display systems is based on the
`premise of screens of essentially unlimited size. Many 10
`of the elements necessary for such systems are
`presently available. High intensity lasers operating at a
`variety of frequencies within the visible spectrum have
`been demonstrated as have modulation and scanning
`techniques of sufficient capacity for most projection
`applications.
`One popular approach, production of images by
`direct re?ection of visible laser emission, is subject to
`two drawbacks. First, images are monochromatic of a
`particular well-de?ned wavelength so that images
`produced by use of an argon-ion laser, for example,
`may be blue and black; and, second, re?ection of
`coherent laser output produces a speckled image due
`to periodic reinforcement of the scattered beam. See
`Volume 46, Bell System Technical Journal, page 1479,
`September 1967.
`In copending U. S. Pat. application Ser. No. 827,644,
`filed May 26, 1969, there is described a laser display
`system which produces images essentially free from
`speckle problems. That system relies on a phosphor
`screen, the functional portion of which is cerium doped
`YAG (yttrium aluminum garnet). The phosphor, when
`excited by a laser beam of appropriate wavelength,
`emits a broad band of yellowish coloration which, in a
`preferred embodiment, combines with re?ected laser
`light to produce an apparent black and white image.
`This system has been demonstrated and appears ap
`propriate for commercial exploitation.
`
`15
`
`20
`
`25
`
`35
`
`SUMMARY OF THE INVENTION
`It has now been determined that a practical single
`color laser display system alternative to that described
`above may utilize a range of phosphor compositions
`which are, at least in part, organic. As in the copending
`application, the system depends upon use of laser ener
`gy at one or more wavelengths, at least one of which
`emits in the visible or ultraviolet spectra at a somewhat
`shorter wavelength than a major portion of the
`phosphor emission.
`Due to the large variation of organic phosphor
`materials which are suitable for use, few limitations are
`placed on the nature of the energizing laser. Suitable
`lasers include argon-ion emitting at 4,880 A. and cad
`mium-ion emitting at 4,416 A. The range of suitable ex
`citing wavelengths for useable monochromatic displays
`is from about 2,500 A. to about 5,500 A.
`Speci?c wavelengths within this broad range are
`chosen in accordance with the phosphor charac
`teristics. Suitable phosphors are discussed at some
`length in the Detailed Description. Generally speaking,
`suitable materials are organic dyes or pigments many of
`which are commercially available and in widespread
`use.
`In this description, use will be made of the term “
`colorant” or “organic colorant.“ It is to be understood
`that this term includes photoluminescent organic dyes
`
`45
`
`50
`
`60
`
`65
`
`2
`and pigments. Pigments are particularly useful and may
`be formed by dissolving a dye in anorganic resin solu
`tion which is subsequently condensed. It is known that
`luminescent ef?ciency in certain cases may be
`enhanced if the dye is absorbed on a colloid which may
`take the form of gell ?bers or particles of high molecu
`lar weight polymers.
`As in the YAG-cerium phosphor display, absorptions
`in the phosphor are generally broadband and the emis
`sion peak is relatively insensitive to a shift in energizing
`wavelength. This phenomenon is quite useful since it
`may permit substitution of laser sources without
`marked change in apparent emission color.
`The invention is broadly premised on the use of such
`organic colorants. Monochromatic displays result from
`use of homogeneous phosphor screens. These may be
`present as self-supporting members or as coatings, and
`they may be made up on one or any combination of
`colorants required to produce the desired balance.
`Similarly, the amount of re?ected laser radiation may
`be varied by deliberate inclusion of “inert” ingredients
`in the phosphor. So, for example, a ?ller such as talc
`results in an increase in ratio of re?ected to converted
`energy.
`
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1, on coordinates of intensity in arbitrary units
`and wavelengths in angstroms, is a plot of the emission
`for illustrative colorants under 4,880 A. excitation;
`FIG. 2 is a chromaticity diagram showing the coor
`dinates of several particularly useful phosphor emis
`sions; and
`FIG. 3 is a perspective view of a system in ac
`cordance with the invention.
`
`DETAILED DESCRIPTION
`1. Drawing
`Referring again to FIG. 1, the data presented are the
`emission spectra for two organic phosphors and their
`50-50 blend. The types are 4-amino, 1,8-napthal p
`xenylimide (peaking at 5,300 A.) (curve A) and
`Rhodamine (peaking at 6,050 A.) (curve B). Both
`?uoresce with high efficiencies (greater than 50 per
`cent ) under 4,880 A. excitation. The broken line
`represents a particulate 50-50 mixture of these two
`phosphors. The individual phosphors ?uoresce yellow
`green and red. Their combined output is orange. The
`blue content of radiation from the screen can also be
`enhanced by addition of re?ective matter to increase
`the fraction of 4,880 A. laser radiation re?ected when
`this argon-ion laser radiation is use, for example.
`Hence, the overall effect is to produce a whiter ap
`pearance to the eye.
`FIG. 2 is the internationally accepted CIE chro
`maticity diagram (see Applied Optics: A Guide to
`Modern Optical System Design (J. Wiley & Sons 1968)
`Ch. 1 by L. Levi) which can be used as a guide in as
`sessing the color quality of a display system. In this dia
`gram, the saturated (monochromatic) colors are
`located on the perimeter of the horseshoe'shaped plot,
`while colors of decreasing saturation approach illumi
`nant C which is a white color equivalent to average
`daylight illumination. Every real color, regardless of its
`spectral complexity, can be represented by a single
`point on or within this plot. A straight line connecting
`
`TCL 1022, Page 4
`
`

`

`3,691,482
`3
`any two points (primaries) represents the locus of
`possible colors that can be achieved by blending them
`in varying proportions. Similarly, the gamut of colors
`possible by the combination of more than two prima
`ries are those which fall within the polygon determined
`by straight lines which connect adjacent primaries. As
`an example, the dotted triangle in FIG. 1 encloses the
`color gamut of a shadow mask color CRT. For com
`parison, there is also shown the major cadmium and
`argon laser lines at 4,416 A., 4,880 A., and 5,145 A. as
`well as the emissions of the YAGzCe phosphor and of
`the three organic dyes (related to 4-amino, 1,8-napthal
`p-xenylimide); and phosphors (3485, 3483 and 3484
`which are Rhodomine based pigments). The arrow on
`the 3485 dye emission shows the effect of adding
`phthalocyanine toner, which selectively absorbs the
`longer wavelength yellow and red portion of the emis
`sion to produce a more vivid green. It can be seen that
`the combination of light from either of these blue laser
`sources and emission from the 3,483 A. and 3,485 A.
`phosphors results in a color gamut similar to that of the
`color cathode ray tube.
`A black and white display can be achieved by
`scanning a monochromatic laser beam on a viewing
`screen that is coated with an appropriate blend of
`phosphors and direct scattering materials such as pow
`dered MgO or talc. For example, a combination of scat
`tered light from a blue argon-ion laser beam (4,880 A.)
`and blue-to-red converted light from either of the
`Rhodamine dye phosphors can produce a white ap
`pearance since a straight line connecting these prima
`ries on the chromaticity diagram passes very near to il
`luminant C.
`A combination of more than two primaries can also
`be used to produce white. As an example, a Cd-He
`laser beam which illuminates a correctly proportioned
`mixture of MgO and dye phosphors 3,484 A. and 3,485
`A. can be used to achieve a white appearance. Al
`ternately, MgO may be replaced by pyrelene-contain
`ing materials or 7-diethyl amino, 4-methyl coumarin
`containing materials (blue-to-blue and ultraviolet-to
`blue converting phosphor, respectively, to completely
`eliminate speckle).
`Regardless of how many phosphors are used, it is ap
`parent from the chromaticity diagram that a necessary
`condition for achieving a true white is that the illu
`minating laser beam have a wavelength of approxi
`mately 4,950 A. or shorter. Otherwise, it is impossible
`to include illuminant C within a polygon whose prima
`ries are the source and any combination of longer
`wavelengths that can be achieved by down-conversion
`of frequency. Fortunately, the argon-ion laser satis?es
`this necessary condition.
`
`20
`
`25
`
`35
`
`45
`
`4
`FIG. 3 is a perspective view ofa simple system in ac
`cordance with the invention. Energizing light is
`produced by laser 10 which may, for example, be an
`argon-ion laser or a cadmium-ion laser. The emerging
`beam 11 ?rst enters modulator 12 which is provided
`with a modulating signal by means, not shown, for am
`plitude modulating the beam. Modulation may be ac
`complished, for example, by electro-optic, acousto-op
`tic, or magneto-optic techniques.
`A description of suitable acousto-optic devices is
`contained in V0]. 46, Bell System Technical Journal, p. _
`367, February 1967. A description of suitable electro- '
`optic devices is described in Vol. 38, Journal of Applied
`Physics, pp. l6l 1-1617, March 1967. In any event,
`modulation may be accomplished by altering the total
`amount of light of a particular polarization sense which
`is passed by an analyzer incorporated in the modulator,
`or alternatively by controlling the amount of light
`which is de?ected acoustooptically.
`Upon emerging from modulator 12, the beam, now
`denoted l3, enters de?ector 14 which produces the ap
`propriate horizontal and vertical de?ection so as to fill
`screen 15. Deflector 14 may advantageously operate
`on an acousto-optic principle, see, for example, Vol.
`57, Proceedings of the IEEE, p. 160, February 1969.
`The de?ector 14 may also perform the modulation
`function eliminating the need for a separate modulator
`l2. Earlier de?ector systems utilize mechanical, some‘
`times motor driven, scanners.
`Inventive novelty is premised largely on the nature of
`phosphor screen 15 as incorporated in the overall
`system. Laser display systems of the general nature of
`that of FIG. 2 are described in some detail in the exist
`ing scientific literature. See, for example, IEEE Spec
`trum for December 1968, at page 39, et seq.
`The chemical nature of this screen is described in
`, some detail in the section which follows.
`2. Composition
`40
`The inventive system depends upon a phosphor
`screen containing at least one ?uorescent organic dye
`or pigment. Representative materials and the color
`which they ?uoresce include pyrelene (blue);
`?uorescein
`(yellow-green);
`eosin
`(yellow);
`Rhodamine-B (red); Rhodamine-6G (yellow); acridine
`(blue); acri?avin (yellow-green); napthalene red (red);
`auromine-O (yellow-green); 4-amino, 1,8-napthal p
`xenylimide (yellow-green) and 7-diethylamino, 4
`methyl coumarin (blue). Other dyes are xanthene,
`azine, oxazine, thiazine, acridine, ?avin, napthalimide
`and coumarin derivatives. Data on absorption and
`emission of selected dyes is given in Table I. Such data
`may be used to optimize screen composition for a give
`laser source.
`
`55
`
`TABLE I.—ABSORPTION AND FLUORESCENCE BANDS OF DYES IN
`AQUEOUS OR ALCOHOLIC SOLUTIONS
`(Approximate limits of bands in A.; peaks of bands in parentheses)
`
`Compounds
`
`I. Xanthene:
`
`First absorp
`tion band
`
`Fluorescence
`Band Color
`
`Fluoran __________________ _ .
`
`a .
`
`Fluoresceln (dihydroxy
`Egslilgruetrabromo?uores-
`Ercseitillli'osin (tetraiodo?uo-
`Ram...
`tetrachloro?uorescein).
`
`U.V. 2' 90%;:1'288? }Violet, strong.
`4, 50045:
`5, 206%}
`11
`4, 6005?: égg) 5, 1895222) }ieuowy Stroll?‘
`£21.22; Home} 8
`'
`'
`{ ’
`(6,1300) }0fang8, Very Weak
`
`TCL 1022, Page 5
`
`

`

`5
`TABLE I.—-ABSORPTION AND FLUORESCENCE BANDS OF DYES IN
`AQUEOUS OR ALCOHOLIC SOLUTIONS~Cominued
`(Approximate limits of bands in A.; peaks of bands in parentheses)
`
`3,691,482
`
`Compounds
`
`_
`First absorp
`tion band
`
`Fluorescence
`Band Color
`
`4' 80022’
`4' 800'5'
`4, 550-6’, 000
`5, 400—5, 900
`
`5' mtg/h2g9 }Red, strong.
`5'
`Yellow, strong.
`5, 60043, 800 Orange medium.
`6, 600-6, 500
`Do.
`-
`4, 0004, s00 Blue-violet, medium
`3, 000-4, 500
`4, 750-6, 400 Green.
`U.V.—5, 200
`U.V.—5,400 5’ 052?’ 700 Greonish yellow, medium.
`U.V.—5, 100
`4. roo-é. 50o Grew, Weak
`U.V.-5, 000
`4, 850-6, 600 Yellowish-green, strong.
`4' ooozgrgg) 5' mtglbggg) }Red, strong.
`(5:390) _______ ,:_____ Yellow-rod.
`
`--
`
`20
`
`25
`
`Rhodamine B extra _______ _ _
`Rhodamine 6 G __________ __
`Acridine red ____________ __
`Pyronme B _______________ __
`II. Acridine"
`Aoridino __________________ __
`Aendme yollow.__.
`Euchrysine ______ ._
`Rheonine A ______________ __
`Acrl?avine (trypalievine—~_.
`III. Azine:
`Magdela red. _____________ __{
`Safram'ne _________________ __
`IV. Thiazine:
`Thionine _________________ __
`4' 80022’
`’"}Orango, medium.
`Methylene blue
`_
`5, GOO-7,1000
`_- RBd, medlllllw
`A napthalimide dye; 4-amino, 1,8-napthal p-xenyli
`mide (yellow~green) and two Rhodamine dyes (orange
`and red) are exemplary. Their emission spectra for
`4,880 A. excitation exhibit peaks at 5,300 A. (yellow
`green), 6,050 A. (orange-red) and 6,200 A (red),
`respectively. It has been determined that their lifetimes
`are all considerably less than 1 microsecond and their
`absorption cross sections are so large that the entire
`laser beam is absorbed within the thin ?lms which are
`approximately 0.1 mm thick. Their absorption bands
`are quite broad, including essentially all of the violet
`and blue and a portion of the green. It has been esti
`mated that their quantum ef?ciencies are above 50 per
`cent. Thus, these materials are well suited for laser dis
`play systems.
`The colors of these ?uorescing dyes may be modi?ed
`35
`somewhat by varying the type of carrier which is used
`to form pigments, and to a lesser extent by varying the
`type of vehicle, or binder, into which the pigment is in
`corporated. It is also possible to modify colors by com
`bining ?uorescent dyes with non?uorescent dyes that
`selectively absorb a portion of the emission spectrum.
`For example, the emission spectrum of the naphthali
`mide dye (type 3485) shown in FIG. 1 peaks at 5,300
`A. in the green. Normally this ?uorescence appears to
`have a yellowish-green cast due to the broad tail of the
`45
`emission spectrum which extends into the yellow and
`red. However, this tail can be substantially reduced by
`the addition of a non?uorescing green toner such as
`phthalocyanine which absorbs in the yellow and red.
`The result then is a tradeoff of brightness for the ability
`to limit the spectral content.
`In contrast to the many yellow and red emitting dyes,
`blue emitting dyes are less common. However, ex
`amination of pyrelene in dilute alcoholic solutions in
`dicates that it is blue-?uorescing when excited by short
`55
`wavelength blue light such as the 4,579 A. emission of
`an argon laser or the 4,416 A. emission of a cadmium
`laser, while it becomes green ?uorescing under longer
`wavelength blue excitation such as the 4,880 A. line of
`an argon laser. In addition, pigments of coumarin
`which ?uoresce blue under near ultraviolet excitation
`are commercially available.
`3. Design Criteria
`While occasions may arise in which it is desired to
`produce colored or off-white images, the more signifi
`cant aspect of the invention is concerned with white or
`near~white images. In the system using an argon or cad
`mium laser, white images may result by adjustment of
`the screen composition to a yellow cast so that
`re?ected blue adds in to give a whiter image.
`
`However, suitable choices of phosphors can readily
`be made so that no compensation is needed. This may
`be accomplished, for example, by blending particulate
`mixtures of blue, yellow and red emitting phosphors.
`Under such circumstances, the phosphor layer is
`designed so as to result in little or no re?ection. This
`may be accomplished by providing for essentially
`°°i?l’§"駧£%§fi ‘ZR ilh‘i?dé‘él‘g‘?léige? ‘83mm screen
`depends upon power levels, laser wavelength, phosphor
`absorption level, and emission wavelength. Re?ection
`of unconverted laser emission may be enhanced by
`using thin coatings, by re?ective backings (although
`this also results in additional secondary emission during
`retraversal) and by incorporation of “inert” re?ective
`material such astalc.
`In the main, inventive novelty is premised on
`phosphor composition and the chromaticity balance
`achieved between the laser wavelength and the emis
`sion wavelength. Display systems have been discussed
`in terms of one exemplary arrangement. Variations
`may utilize a laser source which is behind rather than in
`front of a screen and a variety of other arrangements
`for folding beams, for modulation, for de?ection, etc.
`What is claimed is:
`1. Visual display apparatus comprising a laser for
`emitting at a wavelength in the visible spectrum, first
`means for amplitude modulating the output of such
`laser, second means for de?ecting said beam, and a
`screen, characterized in that said screen comprises a
`layer of a phosphorescent composition consisting es
`sentially of at least one organic colorant, in which ap
`paratus the said laser emits at a wavelength between
`0.3 and 0.53;.t and the said phosphorescent composi
`tion appears to the eye to ?uoresce essentially white, it
`being a characteristic of such apparatus that a visual
`display resulting from use is essentially free from
`speckle.
`2. Apparatus of clam l in which the said
`phosphorescent composition and screen design are
`such that a portion of the laser emission is unconverted
`so that the combination of re?ected laser emission and
`the phosphor emission from the screen appears approx
`imately white.
`3. Apparatus of claim 1 in which the laser is an
`argon-ion laser.
`4. Apparatus of claim 1 in which the laser is a cadmi
`um-ion laser.
`5. Apparatus of claim 1 in which the phosphor com
`position contains at least one ?uorescent organic com
`ponent selected from the group consisting of coumarin,
`
`40
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`101053
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`095 l
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`TCL 1022, Page 6
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`3 ,691 ,482
`
`7
`xanthene, acridine, Rhodamine naphthalimide, azinc,
`thiazine, type compounds.
`6. Apparatus of claim 5 in which the said component
`is selected from the group consisting of pyrelene, 7
`diethylamino 4-methyl coumarin, Rhodamine B,
`Rhodamine 6G, acridine, 4-amino l,8-naphthal p
`xenylimide.
`7. Apparatus of claim 1 in which the said ?rst means
`
`8
`is an electro-optic modulator and in which the said
`second means is an acousto-optic deflector.
`8. Apparatus of claim I in which the said ?rst and
`second means depend upon an acousto-optic interac
`tion.
`9. Apparatus of claim 7 in which the said first and
`second means constitute a single unit.
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`10
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`TCL 1022, Page 7
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