Patent GB-1306614-A (GB)
Title: Visual display apparatus
IPC: H04N9/31
Filed: 1970-07-07
Abstract: 1306614 Uses of luminescence WESTERN ELECTRIC CO Inc 7 July 1970 32807/70 Heading C4S [Also in Divisions H1 and H4] In a television-type display in which a laser beam comprising blue and/or green emission wavelength is scanned over a screen, a red component is produced by secondary emission from a phosphor material disposed on the screen.  The laser comprises an argon laser having a totally reflecting flat mirror 1, Fig. 1, and a partially transmitting curved mirror 2, emission lines at 4880 Š (blue) and 5145 Š (green) of variable amplitude being obtained by selective Q-switching with an acoustic-optic Bragg deflector element 4 provided with separate piezo-  electric or magnetostrictive transducers 5 and 6. The element 4 may comprise alpha-iodic acid or lead molybdate. Separate deflectors may be used or the deflector may also serve as mirror 1. In a first embodiment, Fig. 2, the polarized output of'the above argon laser (polarization resulting from the presence of Brewster's faces within the laser cavity) is modulated 14 (e.g. by LiTaO 3  or Ba 2 NaNb 5 O 15  electro-optic modulators), split into two beams by calcite prism 15, and raster scanned by deflection system 18 (e.g. two orthogonal acoustically driven Bragg diffraction elements or by rotating mirrors) over a screen 10 with beam 17 directly reflected therefrom to produce the blue and/or green contribution to the image and with beam 16 absorbed by horizontal phosphor strips so as to result in secondary red emission (for example the phosphor strips may be energized by 4880 Š light but not by the 5145 Š light). A second embodiment, Fig. 3, which does not require the critical alignment of the screen relative to the rest of the system as in Fig. 2, includes a screen 26 entirely coated with a phosphor 27 for effecting red emission, separation of that portion of the light to be reflected and that portion to be converted being accomplished by a polarizing element 28 such as a cholesteric liquid crystal layer. In this embodiment the laser output is split into its 4880 Š portion 21 and its 5145 Š portion 22 which are passed via a modulator 24, deflector 25 and a quarter wave plate 29 which converts vertically polarized light into left circularly polarized light and horizontally polarized light into right circularly polarized light. The liquid crystal scatters left or right circularly polarized light. As indicated in Fig. 3 the blue beam 21 is-reflected into blue beam 21A and transmitted to phosphor layer 27 resulting in a red beam 21B. The green beam 22 is also reflected from and transmitted through layer 28 does not excite the phosphor layer 27 (e.g. Tb sensitized-Eu activated phosphors) and thus both portions make a green contribution.  In a third embodiment, Fig. 5 two argon (blue-green) lasers are scanned across a corrugated screen, beam 36 being directly scattered and beam 37 (also blue-green but modulated with red information) being incident on the phosphor regions 38 and converted into red light.  In a fourth embodiment, Fig. 6, a blue output laser beam 40, such as the 4416 A line of a cadmium laser, is modulated, scanned 41 and split into three beams 44, 45 and 46 which are modulated by green, red and blue information respectively and directed via cylindrical lenses 49 on to blue-to-green converting phosphor strips 51, blue-to-red converting phosphor strips 52, and bands 53 which directly scatters the blue beam respectively. Alternatively strips 53 may be a phosphor which converts the coherent blue beam into an incoherent blue colour which eliminates speckle associated with direct scattering. Critical alignment in this embodiment is not necessary. A black and white display may be achieved by scanning a monochromatic laser beam over a viewing screen coated with an appropriate blend of phosphors and directly scattering materials such as powdered MgO or talc. For example, a combination of scattered light from a blue argon-ion laser beam (4880 Š) and blue to red converted light from either Rhodamine dye phosphors 3483 or 3484 produces a white appearance. Phosphor compositions suitable for carrying out the above embodiments are given in the Specification, e.g. an organic colourant containing coumarin, xanthene, acridene, Rhodamine, napthalimide, azine, a thiazine, preferably pyrelene, 7 - diethylamino, 4 - methyl coumarin, Rhodamine B or 6G, acridine, 4-amino 1,8.- naphthal p - xenylimide; Zn 0À6 Cd 0À4 S: Cu; NaTb 0À8 Eu 0À2 W 2 O 8  : Tb, Eu while Eu<SP>+2</SP>- Eu<SP>3+</SP> transfer may also be used; YAG : Ce; phosphors activated by Eu<SP>3+</SP>, Sm<SP>3+</SP>, Er<SP>3+</SP> or Pr<SP>3+</SP>; (Zn, Cd, Sr) (S, Se) : (Cu, Ag, Mn) and Mg 2 TiO 4  : Mn systems; Tb<SP>3+</SP> sensitized-Eu<SP>3+</SP> activated tungstates and molybdates and similar phosphates, borates, aluminates, gallates, indates, silicates, germanates, halides, chalcogenides, and many other specific phosphors are disclosed with specific concentration ranges.