United States Patent
`Pinnow et al.
`
`3,699,4 78
`[IS]
`!451 Oct. 17, 1972
`
`[541 DISPLAY SYSTEM
`Inventors: Douglas A. Pinnow, Berkeley
`(72]
`Heights; Le Grand G. Van Ultert,
`Morris Township, Morris County,
`both of N .J.
`[73) Assignee: BeD Telephone Laboratories, Incor(cid:173)
`porated, Murray Hill, N.J.
`May 26, 1969
`[22) Filed:
`[21) Appl. No.: 827,644
`
`[52] U.S.CI •................... 332/7.51,250/ 199, 178/6.8
`Int. CI... .............................................. HOls 3/00
`[51)
`[58) Field of Search ......... 332/7.51; 250/71,80, 199;
`330/334, I 08; 252/30 1.4; 340/324, 173;
`178/6.8
`
`[56]
`
`References Cited
`
`3,541,542
`3,495,034
`3,341,825
`
`UNITED STATES PATENTS
`11/1970
`Duguay et al... ........... 340/324
`2/1970
`A reno et al... ............. 350/160
`9/ 1967
`Schrieffer .................. 340/173
`
`3,453,604
`3,322,682
`3,374,381
`3,474,248
`3,488,503
`3,513,346
`3,524,011
`
`7/1969 Geusic et al .........•...... 330/4.3
`5/ 1967 Thompson .............. 252/301.4
`3/1968 Albinaketal ............. 313/108
`10/1969 Brown et al . ................ 250/71
`1/ 1970 Reich et a1... .............. 250/ 199
`5/1970 Awazuetal ............... 313/ 108
`8/ 1970 Korpe1. ...................... 250/199
`
`FOREIGN PATENTS OR APPLICATIONS
`1,564,271
`· 3/ 1969
`France .................... 252/30 1.4
`
`Primary Examiner-Benjamin A. Borchelt
`Assistant Examiner-N. Moskowitz
`Attorney-R. J. Guenther and Edwin B. Cave
`
`[57)
`
`ABSTRACT
`A black and white display is produced by projection
`using a scanning argon laser beam operating at 4,880
`A and a phosphorescent screen of cerium-doped yttri·
`urn aluminum garnet which emits a broad range of
`frequencies centering about 5,500 A. The yellowish. ·. :
`cast of the phosphor output is compensated by a small
`amount of reflected blue argon light.
`
`.
`
`8 Claims, 2 Drawing Figures
`
`LASER 10
`
`/1 I MODULATOR 12
`
`CERIUM DOPED
`
`·.~{d,f~~R-~-4--~~~~~~~0SA-IOR
`
`~---' \.
`
`TCL 1012, Page 1
`
`

`

`PATENTEDDCT 171972
`
`3.699.478
`
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`
`FIG./
`
`EXCITATION
`SPECTRUM
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`r-EMISSION
`\ SPECTRUM
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`
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`
`.4416)-l
`(CADMIUM ION
`LASER LINE)
`
`.5.).£
`
`.6)J
`
`.488)1
`(ARGON ION)
`LASER LINE
`
`LASER 10
`
`FIG. 2
`II MODULATOR 12
`/
`CERIUM DOPED
`-t.._,___ /
`GARNET PHOSPHOR
`-~uFL£~0-~~REEN 15
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`D. A. PINNOW
`INVENTORS L. G. VAN UITERT
`
`8V /.~ ~ ATTORNEV
`
`TCL 1012, Page 2
`
`

`

`DETAILED DESCRIPTION
`
`30
`
`1
`DISPLAY SYSTEM
`
`3,699,478
`
`2
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1, on coordinates of relative intensity based on
`a maximum scale value of 100, and wavelength in
`microns, is a plot of the emission and associated excita(cid:173)
`tion spectra for unmodified cerium-doped Y AG; and
`FlO. 2 is a perspective view of a system in ac(cid:173)
`cordance with the invention.
`
`BACKGROUND OF THE INVENTION
`I. Field of the Invention
`The invention is concerned with projection display S
`systems and is primarily concerned with those produc(cid:173)
`ing black and white images.
`2. Description of the Prior Art
`Interest in laser display systems is based on the
`premise of screens of essentially unlimited size. Many 10
`I. Drawing
`of the elements necessary for such systems are
`Referring again to FIG. 1, the data presented are the
`presently available. High intensity lasers operating at a
`emission and related excitation spectra for cerium-
`variety of frequencies within the visible spectrum have
`doped Y AO. The emission spectrum is in broken out-
`been demonstrated as having modulation and scanning
`techniques of sufficient capacity for most projected 1 S line with the broad peak of concern having its max-
`uses.
`imum value at a wavelength of about 0.55 micron. The
`One popular approach, production of images by
`associated excitation spectrum shown in solid outline is
`direct reflection of visible emission is subject to two
`a measure of the intensity of the emission noted for
`drawbacks. First, images are monochromatic of a par-
`various pump frequencies. The most pronounced ex-
`ticular well-defined wavelength
`so
`that
`images 20 citation peak coincides with a pump wavelength of
`produced by use of an argon-ion laser, for example,
`about 0 .46 micron. The emission wavelengths for two
`may be blue and black; and, second, reflection of
`prominent laser lines are also indicated. The first, for
`coherent laser output produces a speckled image due
`the argon-ion laser, is at 0.488 micron. The second, for
`to periodic reinforcement of the scattered beam. See
`the cadmium-ion laser, is at 0.4416 micron. The laser
`Vol. 46, Bell System Technical Journal, p. 1,479, Sept. 25 lines are shown as solid vertical lines.
`196 7.
`FIG. 2 is a perspective view of a simple system in ac-
`So far as is known, there is no demonstrated or
`cordance with
`the
`invention. Energizing light
`is
`proposed laser visual display system producing black
`produced by laser 10 which may, for example, be an
`and white images free from speckle problems.
`argon-ion laser or a cadmium-ion laser. The emerging
`beam 11 first enters modulator 12 which is provided
`SUMMARY OF THE INVENTION
`with a modulating signal by means, not shown, for am-
`plitude modulating the beam. Modulation may be ac-
`A laser display system results in a black and white
`complished, for example, by electro-optic, acousto-op-
`image with a minimum of speckling. The system de-
`pends ~pon the use of a p~ospborescent scr~e~ o~ ceri- 35 tic, or magneto-optic techniques.
`A description of suitable acousto-optic devices is
`um-act.Jvated garnet energized by a laser em1ttmg m the
`contained in Vol. 46, BSTJ, p. 367, February, 1967. A
`visible at~ s_omewhat shorter wavelength than the bulk
`of the emJ~SJOn fro~ the screen. In a pr~f~rred ar!ang~-
`description of suitable electro-optic devices
`is
`ment yttnum alum•.n~m garnet c?ntainmg cenum .•s
`described in Vol. 38, Journal of Applied Physics, pp.
`u_sed. The c~aractenstJcally yellow1sh cas~ of t~e emas- 4o 1,611- 1,617, March, 1967. In any event, modulation
`s1on from th1s phosphor .as seen b~ the eye IS adj~sted to
`may be accomplished by altering the total amount of
`app~ar more nearly w~Jt~ by dehberate reflection of a
`light of a particular polarization sense which is passed
`portion of the laser e.~•ssJon.
`.
`.
`by an analyzer incorporated in the modulator, or alter-
`F~om the composJU<!nal s~~dpomt, a preferred e!"-
`natively by controlling the amount of light which is
`bo~1ment of the m~ent.Jon u!1hzes a screen coated wath 45 deflected acousto-optically.
`c~num-doped yttn~m alummum garnet (VAG) e~er-
`Upon emerging from modulator 12. the beam, now
`gazed by an argon-Jon laser arranged so as to emit at
`denoted 13 enters deflector 14 which produces the ap-
`4,880 A. The cerium-activated p~osphor emits over a
`propriate h~rizontal and vertical deflection so as to fill
`broad range of wavelengths centenng about S ,500 A.
`v · f
`h
`d
`· 1 d
`th 1
`screen 15. Deflector 14 may advantageously operate
`. an_a •o,ns me uh.ehomer amse'rtsotu4rc4est6' suAc aass aecllaas- so on an acousto-optic principle, see, for example, Vol. 57
`maum-aon aser w 1c
`ay e 1 a
`, w
`.
`f
`.
`,
`the IEEE, P8· 160, Feb.,_ 1969. ~he
`Proceedmgs 0
`variations in the phosphor composition. All such com-
`d~fl~cto~ 14 may also perform the modulataon functao~
`positions are cerium-activated and utilize a host of the
`ehmanatmg the need for a_s~parate mo~ulator 12. ~arb-
`garnet structure (i.e. the structure of Y 3Ala01S) since
`er defle~tor systems ut1hze mechamcal, sometimes
`this is the only known combination to produce reemis-
`sion· of appropriate color and brightness. The absorp- 55 motor d~ven, scann~rs.
`.
`Inventive novelty 1s pre~nsed largely o~ the nature of
`tion peak for the phosphor may, however, be shifted to
`more closely match a particular energizing source; and
`phosphor scree_n 15 as mcorporated m the overall
`system. Laser diSplay s~stem.s of the gen~r~l nature. of
`to this end, aluminum may be partially replaced by gal-
`Jium to shift the absorption to shorter wavelength, or 60 !hat o~ Fl? . 2 ~re descnbed m some detail In the elust-
`yttrium may be replaced, in whole or in part, by
`mg sctentJfic literature. See, for example, IEEE Spec-
`trum for December 1948 at page 49, et seq.
`gadolinium
`to shift
`the absorption
`to
`longer
`wavelength. Since a shift in absorption generally
`The chemical nature of this screen is described in
`produces a corresponding shift in emission in the same
`some detail in the section which follows.
`direction, color adjustment (for example, to produce a 65
`2. Co~posi~ion
`white image) by reflection of a portion of the laser
`The mventtve system depends upon a phosphor
`beam continues to be feasible. Other variants are
`screen containing trivalent cerium in an appropriate
`host. Emission of Cea+ is generally in the near ul-
`discussed.
`
`TCL 1012, Page 3
`
`

`

`3,699,478
`
`4
`minimum concentration required for a reem1ssJon
`image discernible in ordinary room lighting, and the
`upper lim it is occasioned by the fact that further in(cid:173)
`crease results in little improvement. Its preference is
`based largely on economics (as compared with the
`broad maximum above).
`In view of the above considerations, the overall
`phosphor limits may be set forth as:
`
`3
`traviolet. However, it is known, probably due to the
`large crystal field splittings in garnet such as Y AG, that
`emission may be shifted to the visible. As seen from
`FIG. 1, the emission for Y AG:Ce3+ is quite broad with a
`peak at about 0.55 micron (yellowish white). The peak 5
`absorption in that lattice centers about 0.46 micron
`and this absorption spectrum is s uitable for use either
`with the argon (0.4884#4) or cadmium (0.4416#4) laser.
`As discussed in a subsequent section, there may be no
`particular advantage gained by shifting the absorption 10
`in which
`to exactly coincide with the laser emission.
`xis from 0.001 to 0.15 or in the preferred range, is
`While reference has been made to "absorption spec-
`from 0.005 to 0.0 l ,
`trum ," only the absorbed energy which is converted to
`Y is from 0 to 2. 999 and
`visible emission as discussed, is of consequence for the
`purposes of the invention. Absorbed energy usefully 15
`z is from 0 to 3.0.
`Certain other substitutions are possible. So, for ex-
`converted in this fashion may be represented in terms
`ample, lutecium or lanthanum may be substituted for
`of an ''excitation" spectrum, and it is in these terms
`that the data of FIG. 1 is represented.
`yttrium, and indium or scandium may replace alu-
`The excitation spectrum in the cerium-doped garnet 20 minum in part. However, since suitable excitation and
`may be shifted to accommodate the lasers discussed or
`emission spectra may be obtained in the more common
`to more effectively utilize other laser sources. To this
`and more economical Y AG or substituted Y AG
`end, the prototypical composition, Y 3A1~012, may be
`system, it is not expected that further modifications will
`modified by partial or total substitution of gallium for
`go into commercial use.
`aluminum and/or gadolinium for yttrium. The former 25
`3. Design criteria
`has the effect of moving the excitation peak to shorter
`While occasions may arise in which it is desired to
`wavelength while the latter has the opposite effect. The
`produce colored or off-white images, the more sign ifi-
`peak of the excitation spectrum may be tailored in this
`cant aspect of the invention is concerned with white or
`manner within the range of from about 0.33 micron to
`near-white images. In the unmodified Y AG:Ce system
`about 0.48 micron; however, useful excitation may be 30 using an argon or cadmium laser, white images may
`accomplished over the broader range of about 0.30
`result by compensation of the secondary yellow cast
`micron to 0.53 micron.
`emission by some reflection of the shorter wavelength
`laser emission. Under these circumstances it is desired
`A shift in the excitation spectrum produces an ac-
`companying shift in the emission spectrum with the
`to design layer thicknesses and compositions or provide
`range of emission peaks being from about 0.51 micron 35 for some reflection such that total absorption does not
`to about 0.61 microns. For the preferred embodiment
`result.
`designed to produce a white or near-white image, the
`Modification of the YAG:Ce system within the com-
`emission peak should not be at wavelengths less than
`positional range described may shift the emission so
`about 0.52 micron (corresponding with an excitation
`that it needs no compensation. This may be accom(cid:173)
`0
`peak of about 0.43 micron which results in a Y AG 4 plished, for example, by partial substitution of gallium
`aluminum in the 20 to 60 percent range per formula
`composition modified by substitution of about 45 atom
`percent gallium for aluminum ). From the same stand-
`unit. Under such circumstances, the phosphor layer is
`point for this preferred embodiment, the phosphor
`designed so as to result in little or no reflection. This
`should not be modified so as to result in an excitation 45 may be accomplished by providing for essentially
`complete absorption and minimal reflection.
`peak at wavelengths greater than about 0.58J.t (or,
`more properly energization should not exceed this
`In one experimental arrangement, apparently white
`limit) since even ineffective conversion will result in
`images resulted from use of the composition Y u 8Ce 0 •01
`addition of some longer wavelength light and, there-
`Al5012· It was found that approximately 50 percent of
`fore, will impart a yellowish tinge to the reflected emis- 50 the energy of a one watt 0.488J.L argon beam was ab-
`sorbed in a layer thickness of about 0.4 millimeters.
`sion. Y AG in which 70 atom percent yttrium is
`replaced by gadolinium corresponds with this condition
`The image could be further intensified by providing a
`and, therefore , this represents the maximum uncom-
`mirror backing thereby resulting in total absorption
`pensated partial substitution of gadolinium for the
`(within the excitation band) of about 75 percent of the
`55 laser energy. The approximate 25 percent of the con-
`preferred embodiment.
`Phosphor compositions suitable for use in ac-
`verter laser energy suffices to compensate for the yel-
`cordance with the invention invariably depend upon
`lowish cast of the reemission.
`It is apparent that final design of a phosphor screen
`cerium activation. A suitable cerium range is from
`about 0.00 1 to about 0.15 atom per form ula unit of gar-
`depends upon power levels, laser wavelength , phosphor
`net (based on the stoichiometry Y3AI50 12 ) . (CeH sub- 60 absorption level and emission wavelength. Reflection
`stitutes for yttrium and therefore reduces the amount
`of unconverted laser emission may be enhanced by
`of this action by an equal amount). The lower limit on
`using thinner coatings, by reflective backings (although
`cerium content represents the minimum concentration
`this also results in additional secondary emission during
`resulting in a readily discernible reemission image, 65 retraversal) and by incorporation of "inert" material
`such as talc.
`while the maximum approximately coincides with the
`In
`the main, inventive novelty is premised on
`solubility limit in the garnet. A preferred cerium range
`is from 0.005 to 0.1 0. The lower limit is based on
`phosphor composition and the chromaticity balance
`
`(I)
`
`TCL 1012, Page 4
`
`

`

`3,699,478
`
`s
`6
`2. Apparatus of claim 1 in which
`the said
`achieved between the laser wavelength and the emis-
`phosphorescent composition and screen design are
`sion wavelength. Display systems have been discussed
`such that a portion of the laser emission is unconverted
`in terms of one exemplary arrangement. Variations
`may utilize a laser source which is behind rather than in
`so that the combination of reflected laser emission and
`front of a screen and a variety of other arrangements 5 the_p. emission from the screen appears approxfmately
`for folding beams, for modulation, for deflection, etc.
`white.
`3. Apparatus of claim 1 in which the laser is an
`What is claimed is:
`1. Visual display apparatus comprising a laser for
`argon-ion laser.
`emitting at a wavelength in the visible spectrum, first
`4. Apparatus of claim l in which the laser is a cadmi-
`means for amplitude modulating the output of such 10 urn-ion laser.
`s. Apparatus of claim l in which the phosphor com-
`laser, second means for deflecting said beam, and a
`screen, characterized in that said screen comprises a
`position consists essentially ofY ,_..,ce .. AI
`0
`•
`5
`12
`6. Apparatus of claim l in which the said first means
`layer of a phosphorescent composition consisting es-
`sentially of a material which may be represented by the
`is an electro-optic modulator and in which the said
`formula Y :~-.... ucezGd.,AilkGa,Ou in which x is from
`second means is an acousto-optic deflector.
`0.001 to 0.15, Y is from 0 to 2.999 and z is from 0 to
`7. Apparatus of claim 1 in which the said first and
`3.0, in which apparatus the said laser emits at a
`second means depend upon an acousto-optic interac-
`wavelength between 0.3 and 0.53p. and the said
`tion.
`phosphorescent composition appears to the eye to
`8. Apparatus of claim 7 in which said first and second
`fluoresce essentially white, it being a characteristic of 20
`means constitute a single unit.
`such apparatus that a visual display resulting from use
`* * • • •
`is essentially free from speckle.
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
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`55
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`60
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`65
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`TCL 1012, Page 5
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