Patent Publication Number: US-2004057250-A1

Title: Xenon short-arc lamp with fiberoptic filters

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates generally to xenon short-arc lamps, e.g., so-called ceramic arc lamps, and more specifically to lamps and assemblies that incorporate infrared filters to control melting of the input ends of fiberoptic bundles used to pipe the light output.  
       [0003] 2. Description of the Prior Art  
       [0004] Xenon short-arc lamps provide intense point sources of light that collect their light in reflectors for applications in medical endoscopes, instrumentation, video projection, and industrial endoscopes, for example in the inspection of jet engine interiors. More recent applications have been in color television receiver projection systems and dental curing markets.  
       [0005] A typical short-arc lamp comprises an anode electrode and a sharp-tipped cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains xenon gas pressurized to several atmospheres. U.S. Pat. No. 5,721,465, issued Feb. 24, 1998, to Roy D. Roberts, describes such a typical short-arc lamp. These are marketed under the brand name CERMAX xenon illuminators by ILC Technology (Sunnyvale, Calif.), now a part of Perkin-Elmer Optoelectronics, Inc.  
       [0006] The natural spectral power output distribution of xenon short-arc lamps spans the ultraviolet (UV) wavelengths of 200-400 nanometers (nm), the visible light wavelengths of 400-680 nm, and the infrared (IR) wavelengths of 680-5000 nm. A large portion of the total power output is in the IR band. The powerful UV and IR radiation from such lamps can cause skin burns and eye damage. UV radiation can also generate ozone. So depending on the final application of use, these extreme wavelengths are often filtered out by combinations of color filters that absorb a selected energy, and hot/cold mirrors that reflect a chosen energy.  
       [0007] In dental curing applications, the raw light output of the lamp must be filtered to cut off both the UV and IR wavelengths and some of the visible. Typically the 420-500 nm band is preferred. Flexible light pipes of fiberoptic bundles are typically used to channel the lamp output to the point of application. If the IR wavelengths from the lamp entering the fiberoptic bundle are too intense, the input end is subject to melting because too much IR heat is absorbed.  
       SUMMARY OF THE PRESENT INVENTION  
       [0008] It is therefore an object of the present invention to manage the IR radiation produced by ceramic arc lamps to prevent overheating and burning of fiberoptic bundles that conduct the useful light away to a point of application.  
       [0009] It is another object of the present invention to provide a ceramic arc lamp for fiberoptic uses that is simple and compact.  
       [0010] Briefly, a fiberoptic-driving ceramic arc lamp system embodiment of the present invention comprises a ceramic arc lamp fitted with as many as three filters attached to the lamp unit and its heat sinks. A heat-collecting ring is nested into matching groves in the front of the lamp unit and is thermally connected to the lamp&#39;s heatsinks and cooling system. A hot mirror is disposed in the heat-collecting ring nearest the lamp unit&#39;s window. Such mirror is coated on its near side with IR reflecting materials and is coated on its distal side with UV reflecting materials. A heat-absorbing glass is also disposed in the heat-collecting ring after the hot mirror. It collects more of the longer-wavelength IR that was missed by the hot mirror and disperses it as heat through the cooling system. The remaining light can then be focused onto the input end of a fiberoptic bundle without danger of overheating and melting the fiberoptic materials.  
       [0011] An advantage of the present invention is that an illumination system is provided that prevents destruction of its own fiberoptic bundles.  
       [0012] Another advantage of the present invention is that an illumination system is provided for dental blue curing applications.  
       [0013] These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawing figures.  
     
    
    
     IN THE DRAWINGS  
     [0014]FIG. 1 is cross sectional view of a fiberoptic and xenon short-arc lamp system embodiment of the present invention; and  
     [0015]FIG. 2 is cross sectional view of an arc lamp and filter holder/cooling-ring assembly similar to that of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0016]FIG. 1 illustrates a fiberoptic and xenon short-arc lamp system embodiment of the present invention, and is referred to herein by the general reference numeral  100 . The system  100  comprises a ceramic arc lamp  102  that focuses a beam of light  104  into the input end of a fiberoptic bundle  106 . The constituent wavelengths of light included in the beam of light  104  are controlled by a hot mirror/filter assembly  108  to limit dangerous, destructive, and harmful infrared (IR) and ultraviolet (UV) radiation that reach the fiberoptic bundle  106 . In particular, the high power output of lamp  102  in the IR band is enough to melt or deteriorate the fiberoptic bundle  106  if left unchecked. A cathode heatsink  110  and an anode heatsink  112  are used to cool a ceramic lamp body  114  and the hot mirror/filter assembly  108 .  
     [0017]FIG. 2 shows a lamp and filter assembly  200  that is similar to ceramic arc lamp  102  and hot mirror/filter assembly  108 . A hot mirror/filter assembly  202  is shown detached from a ceramic arc lamp  204 . A filter holder and cooling ring  206  carries a hot mirror  208  and a heat-absorbing filter  210 . A split-ring spacer  209  is typically used to separate hot mirror  208  and heat-absorbing filter  210  and keep them in position. Another split-ring spacer  211  retains the heat-absorbing filter  210  in the cooling ring  206 . The glass optics in lamp and filter assembly  200  preferably are comprised of glass, fused-silica, quartz, and/or synthetic sapphire.  
     [0018] The side of hot mirror  208  nearest lamp  204  is preferably coated with a material that will reflect IR radiation and pass through visible and UV radiation. For example, wavelengths longer than about 680 nm are reflected. In alternative embodiments of the present invention, side of hot mirror  208  toward filter  210  is coated with a material that will reflect UV radiation and pass through visible and IR radiation. In this case, wavelengths shorter than 400 nm are reflected back toward lamp  204 . The heat-absorbing filter  210  blocks passage of IR radiation with wavelengths longer than about 1200 nm. The energy is absorbed and carried away as heat by filter holder and cooling ring  206  and any cathode heatsink, e.g., cathode heatsink  110  in FIG. 1.  
     [0019] Commercially available filters that pass wavelengths 420-500 nm allow for IR blocking as well. For example, products like the HEATBUSTER model DS-3600, dental blue curing filters marketed by Deposition Sciences Incorporated (Santa Rosa, Calif.) can be used for hot mirror  208 .  
     [0020] The longer IR wavelengths would be felt as heat in sensitive tissues by a dental patient if passed on by the lighting system. The dental blue curing filters can be applied directly to the lamp cover window surfaces, as well as the glass optics connecting the fiberoptics to the light source.  
     [0021] The heat-absorbing filter  210  preferably absorbs IR wavelengths longer than 1200 nm. For example, such filter can be implemented with a Melles Griot (Irvine, Calif.) KG4 Schott glass type heat absorbing filter, e.g., part number 03-FCG-569.  
     [0022] Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.