Fluorescence Quenching Technique for Scanning Visual Systems

The present invention relates to the field of visual displays. More specifically, the present invention pertains to laser scan systems designed for visual display of scenes photographed or generated, up to and including real-time systems.

The lasers' high intensity, coherence and bandwidth make possible many new applications of laser light. When used in a scanning system for visual display of a scene, the laser has been precluded by inherent characteristics of the display system from providing a visual presentation that is of sufficient brightness to rival that of a cathode ray tube. Where a cathode ray tube has phosphores that contribute the persistence so well adapted for a scanning system, the display systems used with the laser scanning technique do not. This inability to rely on phosphorescence to extend the time an image exists with laser displays is a serious disadvantage to screen brightness. Coupled with the inefficiency of lasers, the lack of persistence causes laser displays to be very inefficient in energy terms, especially for large laser displays such as are found in simulator devices.

The result is that present laser scanning display systems are not fully acceptable or satisfactory for application where a bright image is required or desired. The present invention overcomes the deficiency by adapting the laser scanning display system to provide a bright screen for the image(s).

The present invention is a means and method to increase the brightness of a scanning system display. The system includes means to adapt the screen of such a display with a material that will fluoresce when illuminated by ultra-violet light, and means to illuminate the screen with ultra-violet light. Also included are means to adapt the scanning system to scan a negative of the desired image with infrared light. Inasmuch as infrared light quenches fluorescence generated by ultraviolet light, the resultant display is a positive image.

Brightness is enhanced by employing the natural glow of fluorescence as a substitute for increased laser intensity. The portions that are permitted to remain fluorescent form the positive image. They are brighter and therefore more acceptable and satisfactory as a display, particularly where large scale display systems are used or needed. Advantages include increased efficiency, especially with respect to the use of energy. And, where laser scanning is employed, the present invention eliminates the laser speckle problem that has been debilitating to visual lasers, and provides a viable alternative to the highly inefficient red and blue components in a color system.

The FIGURE is a pictorial view of a laser scanning display system showing a preferred embodiment of the present invention in a 360.degree. display system, with two alternative placements of the ultra-violet illumination means also shown.

The present invention adapts scanning visual systems to enhance the intensity of the displayed image in order to provide a brighter and therefore more usable display system, and to provide other advantages expressed herein. The present invention has broad application and may be adapted to all scanning display systems of the projection type, such as laser visual systems. The advantages afforded by the present invention are most noteworthy when the means and method disclosed herein are applied to large scale visual systems, such as are utilized in military and commercial simulator training devices.

The FIGURE shows an embodiment of the present invention in the 360.degree. Non-Programmed Visual System of U.S. Pat. No. 4,100,571 by Wiley V. Dykes et al and assigned to the United States of America as represented by the Secretary of the Navy.

Laser scanning system 10 is substantially as disclosed in the patent identified immediately above, but for modification to modulators 12 and, if necessary, modification to lasers 14. Likewise, display screen 16 is substantially as disclosed in the patent but for modification that will be described below. The pictorial representation, or image, 18 will remain a positive image for observer 20 in accordance with the present invention. The difference that is easily identifiable by observer 20 between the patented system, and the patented system as adapted by the present invention, is that image 18 provided by the latter is substantially brighter.

The adaptation to which the present invention is directed employs three parts. The first is an adaptation of screen 16 to render surface 22 responsive to ultra-violet illumination. The desired response is for surface 22 to fluoresce when illuminated by ultra-violet light. This response may be achieved by coating the inner surface of screen 16 with a fluorescent paint, by treating surface 22 with a whitener commonly used in laundry products, or by otherwise impregnating screen 16 by treatment with a fluorescent material during or after manufacture of screen 16.

The second part of the adaptation pertains to illuminating screen 16, so as to cause surface 22 to fluoresce. Provided for the purpose is source 24 that is included in the present invention to illuminate surface 22 with ultra-violet light. Any of the available ultra-violet sources may be employed that provide or can be made to provide wide-angle illumination 26 that is substantially uniform throughout the vertical angle that corresponds to illuminating surface 22 over all of the 360.degree. of the viewing screen. The placement shown in the FIGURE of source 24 would require a self-contained power source, or power leads on or within dome 28. Such leads would appear as stationary shadows in the display on screen 16. To do away with the shadows, the leads may be eliminated by placing source 24 in the alternative positions shown in the FIGURE. Placement 30 may be used for source 24 above dome 28, or, if a one-way mirror is suitable for use as mirror 32, source 24 may be positioned at placement 34. In either case, source 24 should be annular and be made to evenly radiate ultra-violet illumination to surface 22.

As another alternative to the placement of source 24, a user should consider positioning source 24 outside the visual system shown. For that arrangement, screen 16 would need to be transparent or translucent to ultra-violet light. Source 24 in the form of a plurality of radiating sources would be arranged to backlight screen 16 from outside the viewing arena occupied by observer 20. Observer 20 would still experience the fluorescent advantages of the present invention.

The third part of the adaptation pertains to scanning beam 36, and relates to lasers 14 and modulator 12. Infrared light will quench the fluorescence generated by ultra-violet source 24. By scanning a negative image of pictorial representation 18 with an infrared laser, a positive image of pictorial representation 18 formed by fluorescent portions will be visible to observer 20. Accordingly, scanning system 10 is adapted to provide a negative scanned image of infrared light by substituting an infrared laser for lasers 14, and by reversing modulators 12 to provide a negative scan of the image to be viewed. Infared lasers that may be adopted for the present invention are commercially available. Any of such lasers may be substituted for the laser otherwise used. If the original laser is an infrared laser or the system can be modified to provide infrared light from the original laser, substitution will not be necessary. Modification of modulators 12 is intended to be performed in accordance with presently available techniques to achieve the intended result. Obvious alternatives are, of course, permissible to provide the desired negative scan.

While the present invention has been described in terms of a specific laser scanning system, it is to be understood that the present invention has application to other laser scanning systems, and to other scanning systems such as television projection scanners.

In operation of the embodiment specifically described herein, image information is coupled to system 10 for viewing by observer 20 on screen 16. Laser light is provided by laser 14 and modulated by adapted modulator 12 to provide a negative scan of the image in beam 36 from optics 38. Beam 36 is of infrared light. Screen 16 is illuminated by ultraviolet source 24 and includes surface 22 which is adapted to fluoresce in ultra-violet light. The fluorescent glow of surface 22 is selectively quenched by beam 36 scanning in a negative mode to formpositive pictorial representation 18 of the image. The result is, observer 20 views an image enhanced by the fluorescent characteristics associated with the present invention.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.