Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-03-02
2002-10-29
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S382000, C315S371000, C313S002100, C313S463000
Reexamination Certificate
active
06472833
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on Russian Application No. 2000105121, filed Mar. 2, 2000, in the Russian Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic and quantum devices, and more particularly, to laser cathode-ray tubes, e.g., used in projection television systems for displaying images on large screens.
2. Description of the Related Art
Projection television equipment based on conventional cathode-ray tubes (CRT) having a luminescent screen is widely used for displaying images on projective screens having an area of up to several square meters. However, the size of an image on the projective screens of such equipment is limited because luminescent screens cannot form light flux of high intensity, thus making it difficult to form television images having required brightness and contrast.
An effective way to improve the parameters of projection television systems is connected with using laser CRTs (see, for example, U.S. Pat. No. 3,558,956).
As distinct from conventional CRTs, the source of radiation in the laser CRT is a laser target, not a luminescent layer, the laser target being a thin semiconductor mono-crystalline plate having both its parallel surfaces covered by light reflecting coatings. A fully reflecting mirror metal coating is usually applied to the surface on which the electron beam is incident, while the opposite side of the plate is covered with a semitransparent mirror coating.
The mirror surfaces constitute an optical resonator, while the semiconductor plate between them acts as an active medium of the laser with electron-beam excitation (pumping). The laser target is fixed to a substrate of a transparent dielectric material, the substrate serving as the optical output window of the laser CRT and also as a heat sink for the laser target. The substrate is usually made of sapphire having a high thermal conductivity. The laser target together with the transparent substrate constitute the screen of the laser CRT (laser screen).
The electron beam penetrates into the semiconductor plate through the metal coating and induces spontaneous light radiation. When the surface density of the current produced by the beam on the laser target exceeds a threshold value, the power of the induced light radiation will be greater than the losses in the optical resonator and the element of the target on which the electron beam is incident will generate laser radiation.
When the light passes repeatedly through the optical resonator, its spectrum narrows, with the result that the emitted light is substantially monochromatic. The laser light is radiated through the semitransparent mirror coating in essence perpendicularly to the surface of the semiconductor plate and leaves the CRT through the sapphire output window.
Known is a laser CRT (U.S. Pat. No. 5,280,360) including a cathode, a modulator having an orifice for forming a beam from the electrons emitted by the cathode, and means for directing the beam formed by the orifice of the modulator to the laser screen of the CRT. During the operation of this laser CRT, an electron beam is formed by the modulator from the electrons emitted by the cathode, and it is directed to the laser screen for excitation of laser radiation.
The resolution of a laser CRT is determined by the diameter of the electron beam in the plane of the laser screen. The influence of an aberration of the focusing magnetic or electrostatic lens and other known factors, including mutual repulsion of the electrons constituting the beam, make it impossible to focus the electron beam absolutely precisely in an indefinitely small point on the surface of the screen.
With the above-mentioned disturbing factors taken into account, a sharper focusing of the beam may be provided by reducing the original cross-section of the electron beam, said cross-section being determined by the diameter of the modulator orifice. Generally, the smallest possible diameter of the light spot formed on the laser screen by a focused electron beam is approximately proportional to the diameter of the orifice of the modulator. To increase the resolution of a laser CRT, the diameter of the modulator orifice should be made as small as possible.
At the same time, with the value of the cathode current density being constant, the current of the electron beam is proportional to the area of the modulator orifice. Therefore, if the diameter of the modulator orifice is made smaller, the current density of the cathode must be raised to maintain the required operating beam current, ensuring the required intensity of the laser radiation provided by the CRT.
However, the maximum current density that can be provided by modern cathodes is about 10 A/cm
2
. That is, given the operating beam current equal to, e.g., 1 mA, the diameter of the modulator orifice cannot be made less than 0.11 mm.
With the diameter of the CRT screen of 60 mm and with the effects of spherical aberration taken into account, a modulator having an orifice diameter of 0.11 mm makes possible formation of a spot having a diameter of about 25 microns on the laser screen. In some instances such resolution is not sufficient.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a laser CRT and a method of its operation which make reducing the diameter of the modulator orifice possible, thereby increasing the resolution of the laser CRT, while maintaining the required intensity of the laser radiation provided by the laser CRT.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to achieve the above and other objects, the laser CRT includes a cathode emitting electrons, a modulator having an orifice for forming a beam from the electrons emitted by the cathode, and a beam directing unit for directing the beam formed by the orifice of the modulator to a laser screen, wherein the modulator includes at least one further modulator having an orifice for forming a further beam from the electrons, wherein the beam directing unit is adapted for directing the further beam formed by the at least one further modulator to the laser screen.
The employment of additional modulators makes it possible to form additional light spots on the laser screen, and thus the required intensity of the laser radiation is still provided when smaller diameters of the orifices of the modulators are used. The reduction in the diameters of the orifices results in reduction in the diameters of the electron beams formed by the modulators, whereby the resolution of the laser CRT is improved.
The beam directing unit which directs the electron beam preferably comprises a common focusing system focusing the beams formed by the modulator orifices on the laser screen of the CRT, and a common deflection system deflecting the beams formed by the modulator orifices.
The diameters of the orifices of all the modulators are preferably selected to be approximately equal. The equal diameter of the orifices ensures the highest resolution of the laser CRT, because the resolution is determined by the maximum diameter of a light spot on the laser screen.
REFERENCES:
patent: 3558956 (1971-01-01), Basov et al.
patent: 5170181 (1992-12-01), Tamada
patent: 5280360 (1994-01-01), Derdyra et al.
patent: 5374870 (1994-12-01), Akhekyan et al.
patent: 5687185 (1997-11-01), Kozlovsky et al.
patent: 6329966 (2001-12-01), Someya et al.
patent: 6331749 (2001-12-01), Makienko et al.
Choi Jong-Sik
Makienko Oleg Mikhailovich
Petrushenko Yury Vladimirivigh
Rumyantzen Nikolai Grigoryevich
Petrushenko Yury Vladimirivigh
Samsung SDI & Co., Ltd.
Staas & Halsey , LLP
Vo Tuyet T.
Wong Don
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