CA1221725A - Cathode ray tube - Google Patents
Cathode ray tubeInfo
- Publication number
- CA1221725A CA1221725A CA000470630A CA470630A CA1221725A CA 1221725 A CA1221725 A CA 1221725A CA 000470630 A CA000470630 A CA 000470630A CA 470630 A CA470630 A CA 470630A CA 1221725 A CA1221725 A CA 1221725A
- Authority
- CA
- Canada
- Prior art keywords
- faceplate
- screen
- thin film
- cathode ray
- ray tube
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/86—Vessels; Containers; Vacuum locks
- H01J29/89—Optical or photographic arrangements structurally combined or co-operating with the vessel
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
- H01J29/18—Luminescent screens
- H01J29/185—Luminescent screens measures against halo-phenomena
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/89—Optical components associated with the vessel
- H01J2229/8907—Image projection devices
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/89—Optical components associated with the vessel
- H01J2229/8913—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices
- H01J2229/8916—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices inside the vessel
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/89—Optical components associated with the vessel
- H01J2229/8913—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices
- H01J2229/8918—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices by using interference effects
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/89—Optical components associated with the vessel
- H01J2229/893—Optical components associated with the vessel using lenses
Landscapes
- Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
- Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
- Transforming Electric Information Into Light Information (AREA)
Abstract
ABSTRACT:
Cathode ray tube.
A cathode ray tube faceplate arrangement including a halo suppression layer disposed between a faceplate and a thin film luminescent screen having a light scattering surface. The halo suppression layer has a refractive index which is smaller than that of the faceplate and the screen and which reflects toward the scattering surface part of the rays of luminescent radiation which would otherwise contribute to halo.
Cathode ray tube.
A cathode ray tube faceplate arrangement including a halo suppression layer disposed between a faceplate and a thin film luminescent screen having a light scattering surface. The halo suppression layer has a refractive index which is smaller than that of the faceplate and the screen and which reflects toward the scattering surface part of the rays of luminescent radiation which would otherwise contribute to halo.
Description
I
PHI 21200 1 16.6.1984 Cathode far tube, The invention relates to a cathode I tube having a faceplate arrangement for suppressing halo, said arrangement comprising a faceplate consisting essentially of a transparent material and an internally disposed thin 5 film luminescent screen having an index of refraction ?
larger than that of the faceplate and having opposing surfaces, one of said surfaces being a light scattering surface disposed further from the faceplate than the other lo Cathode ray tubes can be operated at higher electron beam currents, and thus it higher brightness levels if the conventional powdered layer luminescent screen is replaced with a thin film luminescent screen capable ox operating at higher temperatures. This improve-mint in brightness is offset, however, by the adverse effects of multiple reflections within the thin film screen, Thin film screen cathode ray tubes are especially useful in projection systems because of the high bright-news required in these systems.
I Such a cathode ray tube with a thin film screen is known from Patent 20 00 173 and also from GB-patent 20 24 842.
US. Patent 4,310~783 discloses a cathode ray tube faceplate construction including a multi layer absorb bring filter disposed between a faceplate and a lupines-cent screen for reducing halo by attenuating light rays multiply-reflected within the jilter, which would other-wise contribute to halo. This absorbing filter not only reduces halo, but also usable light. In an alternative embodiment disclosed in the patent, the absorption filter is combined with a multi layer layer halo suppressing inference filter disclosed in US. Patent 4,310,784~ This interference filter is angle sensitive to provide low ~.,,,~
v I I
PHI. 21.200 2 observer side reflectance and high screen side reflect-awns Such a combination of a multi layer interference filter on a multi layer absorption filter is overly come placated.
It is an object of the invention to provide a simple cathode ray tube faceplate arrangement which effect lively suppresses halo.
It is another object of the invention to provide swish faceplate arrangement which suppresses halo without substantially reducing luminescent light which does not contribute to halo.
According to the invention the cathode ray tube comprises an intermediate thin film layer disposed between the screen and the faceplate, said intermediate layer having a refractive index smaller than that of the faceplate.
Said faceplate arrangement may include according to the invention multi layer interference filter disposed between the sereen.and the faceplate, the layers of said interference filter having alternating lower and higher refractive indices, one of said layers being said inter-mediate thin film layer.
The present invention will now be described by way of example with reference to the:aecompanying drawings, in which:
Figure 1 issue sectional view of one end of a cathode ray tube faeeplate:and.a lens in a projection system employing a prior art cathode ray tube;
Figure 2 is a schematic diagram showing the 30 angular distribution of light rays emitted from the cathode ray tube screen in the system of Figure l;
Figure 3 is:a:seetional view of one end of a cathode ray tube faceplate.and.a lens Inca projection system employing first embodiment of a cathode ray tube in:aeeordanee with the invention; and Figure 4 issue sectional view of one end of a cathode ray tube faceplate and a lens in a projection system employing a second embodiment of a cathode ray I
PHI. 21.200 3 tube in accordance with the invention.
The objects of the invention are accomplished by providing a faceplate arrangement which not only sub Stan-tidally prevents -transmission of light rays that would ordinarily contribute to halo, but which also partially converts these rays to usable light which does not contra-byte to halo, thereby increasing image brightness and improving contrast. The manner in which this is accom-polished can be best understood by referring to Figure 2 which graphically depicts as a function of emission angle the distribution of light rays emitted from any excited point on the luminescent screen. This figure illustrates only the principal sources of light transmitted through the faceplate-air interface Andy ignores the relatively weak rays IIH which are derived from light rays that have been largely transmitted through interface 23. Further, the rays I'M do not derive from rays originally emitted at any particular band of: angles, but from rays duster-butted over the entire range of angles outside eCFA -ecpF
Andre thus dispersed over a larger of the face-plate arrangement thereby preventing their collective contribution Tony localized halo effect. This is not true of the rays IT, however, which are high intensity rays deriving from fully reflected rays emitted in the screen:at.angles within the well defined band of angles ecFA -ecpF. In accordance with the invention, the light rays emitted from the screen within this band of angles ware largely converted to rays IT which are reflected back toward the scattering surface, which redirects part of the rays toward the interface at angles within the useful band of angles Ox - Cole This conversion is effected by disposing between the faceplate and -the screen thin film intermediate layer of a material ha~i.ng:an index of refraction which is sufficiently smaller than that of the faceplate to decrease the angle ecpF toga value near that I 9CFAI thereby causing reflection of rays within band of angles which would otherwise haze contributed to halo. The refractive I
PHI. 21~200 4 index of the intermediate layer should be smaller than that of the screen material.
The intermediate layer may be provided as the sole layer between the faceplate and the screen or in combination with other layers disposed between the face-plate and the screen. In one embodiment the intermediate layer is incorporated as one of the layers of an inter-furriness filter, which further improves performance of the faceplate arrangement for a narrow band of wavelengths near the primary emission wavelength of the luminescent screen, by converting a large part of both the rays IT and IT to rays IT which are reflected toward the scattering surface. This arrangement has the advantage that it can be designed to convert spurious rays having wavelengths outside the narrow band to rays IT which totally miss the lens in a projection system, thereby reducing chromatic aberration.
The multiple reflections are illustrated in Figure 1, which depicts part of a cathode ray tube project lion system including the right end of a cathode ray tube faceplate arrangement 10 spaced from a focusing lens 12, both shown in cross-section. The lens 12 magnifies an image formed by light rays received from the faceplate arrangement lo and projects the image onto a relatively large reflective or transmissive screen (not shown). The arrangement 10 includes a faceplate 14 made of a material having goon thermal conductivity, such as sapphire, and a thin film luminescent screen 16 deposited onto the face-plate. Typical thicknesses for the faceplate and the screen, which are not drawn to scale, are 2 5 millimeters and 1-3 microns, respectively.
Although Figure 1 is not drawn to scale, it demonstrates conceptually the effects of multiple reflect lions within the thin film luminescent screen. Because the refractive indices of luminescent screen materials are higher than -those of conventionally used faceplate mater-tats, a very small percentage of light emitted by the excited screen succeeds in reaching the lens 12. For LIZ
PEA 21200 5 1~6.1984 example in a projection cathode ray tube having a sapphire faceplate 14 with a refractive index no = 1.8 and a thin film luminescent screen 16 with a refractive index no = 2.3, the amount of emitted light actually lea-vying the faceplate was determined to be less than 5/0. This amount can be doubled by covering the inner surface of the screen with a highly reflective layer 18 of a material such as aluminum, thereby reflecting light directed toward the vacuum of the tube back toward the faceplate. A further lo increase in the amount of light reaching the lens can be achieved by roughening the inner surface of the screen 16, such as by chemically etching this surface before applying the reflective layer 18. The roughened surface 20 serves to scatter light emitted within the screen and reflected from a 15 faceplate-screen interface 21 such that some of this light is redirected toward the interface at angles for which there is less reflection and more light directed toward the lens.
The reflective layer 18 and the scattering 20 surface 20 not only increase the amount of useful light reaching the lens 12, however, they also increase light contributing to halo surrounding the image of the electron beam spot focused by the lens.
The manner in which light rays emitted by the 25 luminescent screen are transmitted through the faceplate arrangement 10 can be best understood by referring to Fig-no 1 which shows a plurality of light rays emitted at different angles from a point 22 in a spot excited by an electron beam 24. All angles are measured relative to a 30 line 26 originating at point 22 and passing perpendicularly through the faceplate-screen interface 21 and a faceplate-air interface 28. All light rays emitted toward the inter-face 21 are at least partly reflected back toward the scattering surface 20 as rays IBM where they are scattered 35 and redirected toward the interface. Light rays emitted at angles equal to or greater than the critical angle OCPF for total internal reflection prom the interface 21 are totally Jo PEA 21200 6 16.6.1984 reflected to the scattering surface 20. Part of this light is redirected toward the interface 21 at an angle less than ecpF and passes through the interface The lateral shift between point 22 and the point at which the reflected rays impinge on the scattering surface 20 are typically on the order of the sickness of the thin film screen 16 (erg. I microns) and -thus does not substantially increase the diameter of the luminescent electron beam spot, which is typically about 100 microns.
lo The light rays emitted from point 22 which pass s through the faceplate-screen interface 21 reach the face-plate-air interface 28. Portions IL of these rays, emitted from point 22 at angles between 0 and equal pass through interface 28 and are collected by lens 12. Portions IT
5 emitted from point 22 at angles between Cool and ~CFA (the critical angle for the face-plate-air interface) totally miss the lens and are lost within the system. A portion IT or IT of each ray reaching the interface 28 is reflect ted, passes through or is reflected by interface Al and 20 eventually returns to and passes through interface 28. The lateral shifts between the point 22 and the points at which the rays IT and IT eventually pass through the interface 21 are on the order of the faceplate thickness (e.g. 2-5 millimeters). These laterally-shifted rays form a number 25 of concentric ring-shaped halos around the image of the electron beam spot, causing a decrease in image contrast Figure 3 illustrates a first embodiment of a cathode ray tube faceplate arrangement including a thin film halo suppression yen in accordance with the invent 30 Sheehan The face plate arrangement 30 includes the same face-plate 14, thin film screen 169 reflective layer 18 and scattering surface 20 as the arrangement in Figure 1, but further includes a thin film layer 32 disposed between the faceplate and the screen. The layer 32 consists essentially 35 of MgF2 having a refractive index no = 1~38, which substantially decreases the angle OCPF from that of the prior art Figure 1 embodiment. This is demonstrated by L72~
PHI 21200 7 16.6.1984 Table 1 which lists the angles ~CFA and ecpF for the Figure 1 and Figure 3 embodiments, The smaller band of angles lying between ~CPF and ~CFA is also apparent from the rays shown in Figure 3.
TABLE
Fig. 1 (prior art) Fig, 3.
lo ~CFA Sweeney no = 26 sin 1 = 26 ~CPF Sweeney F _ 52 sin no 37 lo The thickness of -the intermediate layer 32 is not critical, but should be greater than one-half the wave-length of the light emitted by the screen to prevent interference effects and should be substantially smaller than the diameter of the luminescent spot produced by the electron beam For an intermediate layer thickness of 0.8 microns it has been determined that the exemplary arrangement shown in Figure 3 will reduce halo intensity by a factor of three and increase image rightness by a factor of two.
Figure 4 illustrates a second embodiment of a cathode ray tube faceplate arrangement in which a thin film halo suppression layer in accordance with the invention is incorporated into an interference filter. The faceplate arrangement 40 includes the same faceplate 14, thin film screen 16, reflective layer 18 and scattering surface 20 as the arrangement in Figure 3, but the halo suppression layer 42 also serves as a low refractive index layer in the multi layer interference filter 44 which has alternating low and high retractive indices. The halo suppression layer 42 need not be disposed on the thin film screen 16 itself as is shown, jut may serve as any one of the low refractive index layers in the filter 44.
~22~72~ii PHI 21200 8 1606~198~
A ray diagram is not presented in Figure 4 because of the difficulty in illustrating the operation of the inter-furriness filter, but the angles illustrated in Figure 3 would be identical in the I use 4 embodiment.
Roth the thickness and the refractive index of the halo suppression layer 42 will be determined by the same criteria as for the Figure 3 embodiment. The refractive indices of the remaining layers in the interference filter 44 are not critical, but the differ lo fence between the refractive indices of any two adjacent layers should be as large as possible to maximize the reflection of rays originating from point 22 at angles between COLE and OF The thicknesses of the layers in the filter 44 are very important and are determined by use of conventional techniques such as those described in Born and Wolf Principles of Optics Pergaman Press, Thea edition, 1980. The thicknesses of the layers are selected to provide a pass band centered around the primary wave-length of luminescent light emitted by the screen 16.
An exemplary 8 layer interference filter has been designed for use in a face plate arrangement, such as that of Figure 4, having a primary emission wavelength of 5440~ and refractive indices and thickness as listed in Table I The layers are listed in order of successive distance from the screen 16, with layer A corresponding to the halo suppression layer lo The materials used for this filter are MgF2( = 1.38) and Ins (no = 2.3).
Layer A B C D E F G H
Refractive 1~382.3 1~382.3 1.382.3 1.38 2.3 Index Thickness .62 .39~62 .39.62 .79~62 .79 (microns) _. .
~22~%5 PHI 21200 9 16,6.1984 It has been determined that in comparison with the prior art faceplate arrangement of figure 1, the above described filter will reduce halo by a factor of I increase image brightness by a factor of 5, increase image brightness by a factor of 3, and reduce spurious wavelength emissions by a factor of 3.
PHI 21200 1 16.6.1984 Cathode far tube, The invention relates to a cathode I tube having a faceplate arrangement for suppressing halo, said arrangement comprising a faceplate consisting essentially of a transparent material and an internally disposed thin 5 film luminescent screen having an index of refraction ?
larger than that of the faceplate and having opposing surfaces, one of said surfaces being a light scattering surface disposed further from the faceplate than the other lo Cathode ray tubes can be operated at higher electron beam currents, and thus it higher brightness levels if the conventional powdered layer luminescent screen is replaced with a thin film luminescent screen capable ox operating at higher temperatures. This improve-mint in brightness is offset, however, by the adverse effects of multiple reflections within the thin film screen, Thin film screen cathode ray tubes are especially useful in projection systems because of the high bright-news required in these systems.
I Such a cathode ray tube with a thin film screen is known from Patent 20 00 173 and also from GB-patent 20 24 842.
US. Patent 4,310~783 discloses a cathode ray tube faceplate construction including a multi layer absorb bring filter disposed between a faceplate and a lupines-cent screen for reducing halo by attenuating light rays multiply-reflected within the jilter, which would other-wise contribute to halo. This absorbing filter not only reduces halo, but also usable light. In an alternative embodiment disclosed in the patent, the absorption filter is combined with a multi layer layer halo suppressing inference filter disclosed in US. Patent 4,310,784~ This interference filter is angle sensitive to provide low ~.,,,~
v I I
PHI. 21.200 2 observer side reflectance and high screen side reflect-awns Such a combination of a multi layer interference filter on a multi layer absorption filter is overly come placated.
It is an object of the invention to provide a simple cathode ray tube faceplate arrangement which effect lively suppresses halo.
It is another object of the invention to provide swish faceplate arrangement which suppresses halo without substantially reducing luminescent light which does not contribute to halo.
According to the invention the cathode ray tube comprises an intermediate thin film layer disposed between the screen and the faceplate, said intermediate layer having a refractive index smaller than that of the faceplate.
Said faceplate arrangement may include according to the invention multi layer interference filter disposed between the sereen.and the faceplate, the layers of said interference filter having alternating lower and higher refractive indices, one of said layers being said inter-mediate thin film layer.
The present invention will now be described by way of example with reference to the:aecompanying drawings, in which:
Figure 1 issue sectional view of one end of a cathode ray tube faeeplate:and.a lens in a projection system employing a prior art cathode ray tube;
Figure 2 is a schematic diagram showing the 30 angular distribution of light rays emitted from the cathode ray tube screen in the system of Figure l;
Figure 3 is:a:seetional view of one end of a cathode ray tube faceplate.and.a lens Inca projection system employing first embodiment of a cathode ray tube in:aeeordanee with the invention; and Figure 4 issue sectional view of one end of a cathode ray tube faceplate and a lens in a projection system employing a second embodiment of a cathode ray I
PHI. 21.200 3 tube in accordance with the invention.
The objects of the invention are accomplished by providing a faceplate arrangement which not only sub Stan-tidally prevents -transmission of light rays that would ordinarily contribute to halo, but which also partially converts these rays to usable light which does not contra-byte to halo, thereby increasing image brightness and improving contrast. The manner in which this is accom-polished can be best understood by referring to Figure 2 which graphically depicts as a function of emission angle the distribution of light rays emitted from any excited point on the luminescent screen. This figure illustrates only the principal sources of light transmitted through the faceplate-air interface Andy ignores the relatively weak rays IIH which are derived from light rays that have been largely transmitted through interface 23. Further, the rays I'M do not derive from rays originally emitted at any particular band of: angles, but from rays duster-butted over the entire range of angles outside eCFA -ecpF
Andre thus dispersed over a larger of the face-plate arrangement thereby preventing their collective contribution Tony localized halo effect. This is not true of the rays IT, however, which are high intensity rays deriving from fully reflected rays emitted in the screen:at.angles within the well defined band of angles ecFA -ecpF. In accordance with the invention, the light rays emitted from the screen within this band of angles ware largely converted to rays IT which are reflected back toward the scattering surface, which redirects part of the rays toward the interface at angles within the useful band of angles Ox - Cole This conversion is effected by disposing between the faceplate and -the screen thin film intermediate layer of a material ha~i.ng:an index of refraction which is sufficiently smaller than that of the faceplate to decrease the angle ecpF toga value near that I 9CFAI thereby causing reflection of rays within band of angles which would otherwise haze contributed to halo. The refractive I
PHI. 21~200 4 index of the intermediate layer should be smaller than that of the screen material.
The intermediate layer may be provided as the sole layer between the faceplate and the screen or in combination with other layers disposed between the face-plate and the screen. In one embodiment the intermediate layer is incorporated as one of the layers of an inter-furriness filter, which further improves performance of the faceplate arrangement for a narrow band of wavelengths near the primary emission wavelength of the luminescent screen, by converting a large part of both the rays IT and IT to rays IT which are reflected toward the scattering surface. This arrangement has the advantage that it can be designed to convert spurious rays having wavelengths outside the narrow band to rays IT which totally miss the lens in a projection system, thereby reducing chromatic aberration.
The multiple reflections are illustrated in Figure 1, which depicts part of a cathode ray tube project lion system including the right end of a cathode ray tube faceplate arrangement 10 spaced from a focusing lens 12, both shown in cross-section. The lens 12 magnifies an image formed by light rays received from the faceplate arrangement lo and projects the image onto a relatively large reflective or transmissive screen (not shown). The arrangement 10 includes a faceplate 14 made of a material having goon thermal conductivity, such as sapphire, and a thin film luminescent screen 16 deposited onto the face-plate. Typical thicknesses for the faceplate and the screen, which are not drawn to scale, are 2 5 millimeters and 1-3 microns, respectively.
Although Figure 1 is not drawn to scale, it demonstrates conceptually the effects of multiple reflect lions within the thin film luminescent screen. Because the refractive indices of luminescent screen materials are higher than -those of conventionally used faceplate mater-tats, a very small percentage of light emitted by the excited screen succeeds in reaching the lens 12. For LIZ
PEA 21200 5 1~6.1984 example in a projection cathode ray tube having a sapphire faceplate 14 with a refractive index no = 1.8 and a thin film luminescent screen 16 with a refractive index no = 2.3, the amount of emitted light actually lea-vying the faceplate was determined to be less than 5/0. This amount can be doubled by covering the inner surface of the screen with a highly reflective layer 18 of a material such as aluminum, thereby reflecting light directed toward the vacuum of the tube back toward the faceplate. A further lo increase in the amount of light reaching the lens can be achieved by roughening the inner surface of the screen 16, such as by chemically etching this surface before applying the reflective layer 18. The roughened surface 20 serves to scatter light emitted within the screen and reflected from a 15 faceplate-screen interface 21 such that some of this light is redirected toward the interface at angles for which there is less reflection and more light directed toward the lens.
The reflective layer 18 and the scattering 20 surface 20 not only increase the amount of useful light reaching the lens 12, however, they also increase light contributing to halo surrounding the image of the electron beam spot focused by the lens.
The manner in which light rays emitted by the 25 luminescent screen are transmitted through the faceplate arrangement 10 can be best understood by referring to Fig-no 1 which shows a plurality of light rays emitted at different angles from a point 22 in a spot excited by an electron beam 24. All angles are measured relative to a 30 line 26 originating at point 22 and passing perpendicularly through the faceplate-screen interface 21 and a faceplate-air interface 28. All light rays emitted toward the inter-face 21 are at least partly reflected back toward the scattering surface 20 as rays IBM where they are scattered 35 and redirected toward the interface. Light rays emitted at angles equal to or greater than the critical angle OCPF for total internal reflection prom the interface 21 are totally Jo PEA 21200 6 16.6.1984 reflected to the scattering surface 20. Part of this light is redirected toward the interface 21 at an angle less than ecpF and passes through the interface The lateral shift between point 22 and the point at which the reflected rays impinge on the scattering surface 20 are typically on the order of the sickness of the thin film screen 16 (erg. I microns) and -thus does not substantially increase the diameter of the luminescent electron beam spot, which is typically about 100 microns.
lo The light rays emitted from point 22 which pass s through the faceplate-screen interface 21 reach the face-plate-air interface 28. Portions IL of these rays, emitted from point 22 at angles between 0 and equal pass through interface 28 and are collected by lens 12. Portions IT
5 emitted from point 22 at angles between Cool and ~CFA (the critical angle for the face-plate-air interface) totally miss the lens and are lost within the system. A portion IT or IT of each ray reaching the interface 28 is reflect ted, passes through or is reflected by interface Al and 20 eventually returns to and passes through interface 28. The lateral shifts between the point 22 and the points at which the rays IT and IT eventually pass through the interface 21 are on the order of the faceplate thickness (e.g. 2-5 millimeters). These laterally-shifted rays form a number 25 of concentric ring-shaped halos around the image of the electron beam spot, causing a decrease in image contrast Figure 3 illustrates a first embodiment of a cathode ray tube faceplate arrangement including a thin film halo suppression yen in accordance with the invent 30 Sheehan The face plate arrangement 30 includes the same face-plate 14, thin film screen 169 reflective layer 18 and scattering surface 20 as the arrangement in Figure 1, but further includes a thin film layer 32 disposed between the faceplate and the screen. The layer 32 consists essentially 35 of MgF2 having a refractive index no = 1~38, which substantially decreases the angle OCPF from that of the prior art Figure 1 embodiment. This is demonstrated by L72~
PHI 21200 7 16.6.1984 Table 1 which lists the angles ~CFA and ecpF for the Figure 1 and Figure 3 embodiments, The smaller band of angles lying between ~CPF and ~CFA is also apparent from the rays shown in Figure 3.
TABLE
Fig. 1 (prior art) Fig, 3.
lo ~CFA Sweeney no = 26 sin 1 = 26 ~CPF Sweeney F _ 52 sin no 37 lo The thickness of -the intermediate layer 32 is not critical, but should be greater than one-half the wave-length of the light emitted by the screen to prevent interference effects and should be substantially smaller than the diameter of the luminescent spot produced by the electron beam For an intermediate layer thickness of 0.8 microns it has been determined that the exemplary arrangement shown in Figure 3 will reduce halo intensity by a factor of three and increase image rightness by a factor of two.
Figure 4 illustrates a second embodiment of a cathode ray tube faceplate arrangement in which a thin film halo suppression layer in accordance with the invention is incorporated into an interference filter. The faceplate arrangement 40 includes the same faceplate 14, thin film screen 16, reflective layer 18 and scattering surface 20 as the arrangement in Figure 3, but the halo suppression layer 42 also serves as a low refractive index layer in the multi layer interference filter 44 which has alternating low and high retractive indices. The halo suppression layer 42 need not be disposed on the thin film screen 16 itself as is shown, jut may serve as any one of the low refractive index layers in the filter 44.
~22~72~ii PHI 21200 8 1606~198~
A ray diagram is not presented in Figure 4 because of the difficulty in illustrating the operation of the inter-furriness filter, but the angles illustrated in Figure 3 would be identical in the I use 4 embodiment.
Roth the thickness and the refractive index of the halo suppression layer 42 will be determined by the same criteria as for the Figure 3 embodiment. The refractive indices of the remaining layers in the interference filter 44 are not critical, but the differ lo fence between the refractive indices of any two adjacent layers should be as large as possible to maximize the reflection of rays originating from point 22 at angles between COLE and OF The thicknesses of the layers in the filter 44 are very important and are determined by use of conventional techniques such as those described in Born and Wolf Principles of Optics Pergaman Press, Thea edition, 1980. The thicknesses of the layers are selected to provide a pass band centered around the primary wave-length of luminescent light emitted by the screen 16.
An exemplary 8 layer interference filter has been designed for use in a face plate arrangement, such as that of Figure 4, having a primary emission wavelength of 5440~ and refractive indices and thickness as listed in Table I The layers are listed in order of successive distance from the screen 16, with layer A corresponding to the halo suppression layer lo The materials used for this filter are MgF2( = 1.38) and Ins (no = 2.3).
Layer A B C D E F G H
Refractive 1~382.3 1~382.3 1.382.3 1.38 2.3 Index Thickness .62 .39~62 .39.62 .79~62 .79 (microns) _. .
~22~%5 PHI 21200 9 16,6.1984 It has been determined that in comparison with the prior art faceplate arrangement of figure 1, the above described filter will reduce halo by a factor of I increase image brightness by a factor of 5, increase image brightness by a factor of 3, and reduce spurious wavelength emissions by a factor of 3.
Claims (4)
1. A cathode ray tube having a faceplate arrange-ment for suppressing halo, said arrangement comprising a faceplate consisting essentially of a transparent material and an internally disposed thin film luminescent screen having an index of refraction larger than that of the face-plate and having opposing surfaces, one of said surfaces being a light scattering surface disposed further from the faceplate than the other, characterized in that an inter-mediate thin film layer is disposed between the screen and the faceplate, said intermediate layer having a refractive index smaller than that of the faceplate.
2. Cathode ray tube according to Claim 1, charac-terized in that said faceplate arrangement includes a multilayer interference filter disposed between the screen and the faceplate, the layers of said interference filter having alternating lower and higher refractive indices, one of said layers being said intermediate thin film layer.
3. A cathode ray tube as in Claim 1 where the refractive index of the intermediate thin film layer is sufficiently small with respect to the faceplate to minimize the difference between sin-1 nA/np and sin nM/np, where nA, np and nm are the refractive indices of air, the thin film luminescent screen and the intermediate thin film layer, respectively.
4. A cathode ray tube as in Claim 3 where said faceplate arrangement includes a multilayer interference filter disposed between the screen and the faceplate, the layers of said interference filter having alternating lower and higher refractive indices, one of said layers being said intermediate thin film layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56568383A | 1983-12-27 | 1983-12-27 | |
| US565,683 | 1983-12-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1221725A true CA1221725A (en) | 1987-05-12 |
Family
ID=24259674
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000470630A Expired CA1221725A (en) | 1983-12-27 | 1984-12-20 | Cathode ray tube |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0148530B1 (en) |
| JP (1) | JPS60157143A (en) |
| KR (1) | KR850004342A (en) |
| CA (1) | CA1221725A (en) |
| DE (1) | DE3469639D1 (en) |
| ES (1) | ES539027A0 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4132919A (en) * | 1977-12-12 | 1979-01-02 | Lockheed Missiles & Space Company, Inc. | Absorbing inhomogeneous film for high contrast display devices |
| US4263061A (en) * | 1978-03-27 | 1981-04-21 | Minnesota Mining And Manufacturing Company | Process for forming a high resolution X-ray intensifying screen with antireflecting substrate |
-
1984
- 1984-12-18 DE DE8484201897T patent/DE3469639D1/en not_active Expired
- 1984-12-18 EP EP84201897A patent/EP0148530B1/en not_active Expired
- 1984-12-20 CA CA000470630A patent/CA1221725A/en not_active Expired
- 1984-12-24 KR KR1019840008312A patent/KR850004342A/en not_active Application Discontinuation
- 1984-12-24 ES ES539027A patent/ES539027A0/en active Granted
- 1984-12-24 JP JP59272734A patent/JPS60157143A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE3469639D1 (en) | 1988-04-07 |
| ES8602298A1 (en) | 1985-11-16 |
| EP0148530A1 (en) | 1985-07-17 |
| KR850004342A (en) | 1985-07-11 |
| EP0148530B1 (en) | 1988-03-02 |
| JPS60157143A (en) | 1985-08-17 |
| ES539027A0 (en) | 1985-11-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |