Patent Publication Number: US-2006001346-A1

Title: System and method for design of projector lamp

Description:
BACKGROUND  
      The invention relates generally to the field of lighting systems and, more particularly, to high-intensity discharge (HID) lamps. Specifically, embodiments of the present technique include a hermetically sealed lamp having improved dosing, sealing, and electrode mounting features.  
      High-intensity discharge lamps are often formed from a ceramic tubular body or arc tube that is sealed to one or more end structures. The end structures are often sealed to this ceramic tubular body using a seal glass, which has physical and mechanical properties matching those of the ceramic components and the end structures. Sealing usually involves heating the assembly of the ceramic tubular body, the end structures and the seal glass, to induce melting of the seal glass and a reaction with the ceramic bodies to form a strong chemical and physical bond. The ceramic tubular body and the end structures are often made of the same material, such as polycrystalline alumina (PCA). However, certain applications may require the use of different materials for the ceramic tubular body and the end structures. In either case, various stresses may arise due to the sealing process, the interface between the joined components, and the materials used for the different components. For example, the component materials may have different mechanical and physical properties, such as different coefficients of thermal expansion (CTE), which can lead to residual stresses and sealing cracks. These potential stresses and sealing cracks are particularly problematic for high-pressure lamps.  
      Additionally, the geometry of the interface between the ceramic tubular body and the end structures also may contribute to the foregoing stresses. For example, the end structures are often shaped as a plug or a pocket, which interfaces both the flat and cylindrical surfaces of the ceramic tubular body. If the components have different coefficients of thermal expansion and elastic properties, then residual stresses arise because of the different strains that prevent relaxation of the materials to stress-free states. For example in the case of the plug type end structure, if the plug has a lower coefficient of thermal expansion than the ceramic tubular body and seal glass, then compressive stresses arise in the ceramic-seal glass region while tensile stresses arise in the plug region.  
      Other components of the lamp further complicate the assembly of the lamp, and can further degrade the sealing and structural characteristics of the lamp. For example, existing lamps generally have a technique for injecting a dosing material, such as mercury or any rare gas or a halide, such as bromine, or a rare-earth metal halide. Unfortunately, this complicates the sealing process for the lamp. In other words, the lamp is typically heated to a temperature that melts a seal material, e.g., seal glass, but this heating process needs to maintain a temperature of the lamp that is not too hot to evaporate the dose (e.g., mercury and halide).  
      In addition, existing lamps generally have an arc electrode, which is mounted to the end structure. In operation, the mounted position of the arc electrode can affect the creation and characteristics of an arc within the lamp. Unfortunately, it is relatively difficult to mount the arc electrode at the desired location on the end structure. Moreover, existing mounting techniques may involve the application of heat, which can cause stress cracks in the lamp and can embrittle the arc electrode.  
      Accordingly, a technique is needed to provide a lighting system with improved dosing, sealing, and electrode mounting features.  
     BRIEF DESCRIPTION  
      In accordance with certain embodiments of the present technique, a system and method for hermetically sealing a lamp is disclosed. Certain embodiments of the lamp have an arc envelope and, also, an end structure bonded to the arc envelope at an open end. The end structure also has a dosing passageway extending into the arc envelope. In other embodiments, a lighting device is provided with an end structure adapted to close an open end of an arc envelope, and a dosing tube diffusion bonded to the end structure. Another embodiment of the lighting device has an arc envelope and an end structure diffusion bonded to an open end of the arc envelope. In another embodiment, the present technique includes means for mounting the arc electrode to the end structure and sealing the end structure with the open end of the arc envelope. In a further embodiment, the present technique includes a means for doing the arc envelope through the end structure sealed to the arc envelope and means for mounting the arc envelope. 
    
    
     DRAWINGS  
      These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:  
       FIG. 1  is a perspective view of an exemplary lamp having opposite end structures in accordance with embodiments of the present technique;  
       FIG. 2  is an exploded cross-sectional side view of an end structure, an arc electrode exploded from a receptacle in the end structure, and a plug member exploded from a dosing passage through the end structure in accordance with embodiments of the present technique;  
       FIG. 3  is a cross-sectional view of the end structure of  FIG. 2  illustrating the arc electrode shrunk-fit into the receptacle and the dosing passageway in accordance with embodiments of the present technique;  
       FIG. 4  is a flow chart illustrating a process of manufacturing the lamp of  FIG. 1  in accordance with embodiments of the present technique;  
       FIG. 5  is a flow chart illustrating another process of manufacturing the lamp of  FIG. 1  in accordance with embodiments of the present technique;  
       FIG. 6  is a cross-sectional view of the lamp of  FIG. 1  having an arc envelope, end structures plugged into opposite ends of the arc envelope, an arc electrode shrunk-fit into each of the end structures, and a plug member exploded from a dosing passageway in one of the end structures in accordance with embodiments of the present technique;  
       FIG. 7  is a cross-sectional view of an alternative lamp the having an arc envelope, end structures butt-sealed to opposite ends of the arc envelope, an arc electrode shrunk-fit into each of the end structures, and a plug member exploded from a dosing passageway in one of the end structures in accordance with embodiments of the present technique;  
       FIG. 8  is a diagrammatical view of a dosing system for the lamp of  FIG. 6  in accordance with embodiments of the present technique;  
       FIG. 9  is a cross-sectional view of the lamp of  FIG. 6  having a dosing material disposed within the arc envelope and the plug member disposed within the dosing passageway in accordance with embodiments of the present technique;  
       FIG. 10  is a cross-sectional view of an alternative end structure having a dosing passageway, a dosing tube exploded from the dosing passageway, a coil exploded from the dosing tube, and an arc electrode exploded from the coil in accordance with embodiments of the present technique;  
       FIG. 11  is a cross-sectional view of the end structure of  FIG. 10  having the dosing tube hermetically sealed within the dosing passageway and a protective layer disposed over an interior surface of the end structure in accordance with embodiments of the present technique;  
       FIG. 12  is a cross-sectional view of a lamp having an arc envelope, end structures plugged into opposite ends of the arc envelope, an arc electrode shrunk-fit into one of the end structures, a dosing tube hermetically sealed within a dosing passageway of another one of the end structures as illustrated in  FIG. 11 , and a dosing system coupled to the dosing tube in accordance with embodiments of the present technique;  
       FIG. 13  is a cross-sectional view of the lamp of  FIG. 12  having a coil disposed within the dosing tube, an arc electrode disposed within the coil, and a sealed portion extending across the dosing tube in accordance with embodiments of the present technique;  
       FIG. 14  is a cross-sectional view of a lamp having an arc envelope, end structures butt-sealed to opposite ends of the arc envelope, an arc electrode shrunk-fit into one of the end structures, and a dosing tube, coil, and arc electrode hermetically sealed to a dosing passageway of another one of the end structures in accordance with embodiments of the present technique; and  
       FIG. 15  is a flow chart illustrating an exemplary process of manufacturing the lamp of  FIGS. 13 and 14  in accordance with embodiments of the present technique. 
    
    
     DETAILED DESCRIPTION  
      Turning now to the drawings,  FIG. 1  is a perspective view of an exemplary lamp  10  in accordance with certain embodiments of the present technique. As illustrated, the lamp  10  comprises a hermetically sealed assembly of a hollow body or arc envelope  12  and end structures  14  and  16  coupled to opposite ends  18  and  20  of the arc envelope  12 . These and other components of the lamp  10  are formed from a variety of materials, which are either identical or different from one another. For example, different embodiments of the arc envelope  12  are formed from a variety of transparent ceramics and other materials, such as yttrium-aluminum-garnet, ytterbium-aluminum-garnet, microgram polycrystalline alumina (μPCA), alumina or single crystal sapphire, yttria, spinel, and ytterbia. Other embodiments of the arc envelope  12  are formed from conventional lamp materials, such as polycrystalline alumina (PCA). Turning to the end structures  14  and  16  of the lamp  10 , these components are formed from a variety of ceramics and other suitable materials, such as niobium, niobium coated with a corrosion resistant material (e.g., a halide resistant material), a cermet (e.g., a zirconia-stabilized cermet, an alumina-tungsten, etc.), and other conductive or non-conductive materials depending on the particular embodiment described in detail below.  
      Regarding the geometry and sealing characteristics of the lamp  10 , certain embodiments of the arc envelope  12  comprise a hollow cylinder, a hollow oval shape, a hollow sphere, a bulb shape, a rectangular shaped tube, or another suitable hollow transparent body. Moreover, the end structures  14  and  16  may have a variety of geometries, such as a plug-shaped geometry that at least partially extends into the arc envelope  12 . Alternatively, some embodiments of the end structures  14  and  16  have a substantially flat mating surface, which seals against the opposite ends  18  and  20  without extending into the arc envelope  12 . In other words, the ends structures  14  and  16  butt-seal against the opposite ends  18  and  20 . In addition to these structural geometries, some embodiments of the lamp  10  have a seal material applied between the end structures  14  and  16  and opposite ends  18  and  20  of the arc envelope  12 . These seal materials can include a sealing glass, such as calcium aluminate, dysprosia-alumina-silica, magnesia-alumina-silica, and yttria-calcia-alumina. Other potential non-glass seal materials include niobium-based brazes. In other embodiments, the end structures  14  and  16  are diffusion bonded to opposite ends  18  and  20  of the arc envelope  12  via material diffusion without using any seal material. For example, localized heating (e.g., a laser) may be applied to the interface between the end structures  14  and  16  and the opposite ends  18  and  20  to bond the materials together, thereby forming a hermetical seal. In certain embodiments, the end structures  14  and  16  comprise ceramic parts, such that the end structures  14  and  16  and the arc envelope  12  can be co-sintered together.  
      The illustrated lamp  10  also includes a plug member  22  disposed in a dosing passageway  24  extending through the end structure  14 . As discussed in further detail below, the lamp  10  is filled with a dosing material through the dosing passageway  24 . For example, certain embodiments of the dosing material comprise a rare gas and mercury. Other embodiments of the dosing material further comprise a halide, such as bromine, or a rare-earth metal halide. The dosing passageway  24  is subsequently sealed by the plug member  22 . For example, the plug member  22  can be sealed by a seal material, diffusion bonding (e.g., using localized heating), or other suitable sealing techniques. In the illustrated embodiment, the plug member  22  comprises a material, such as a cermet, having a coefficient of thermal expansion substantially similar or identical to that of the end structure  14 .  
      The illustrated lamp  10  also includes arc electrodes  26  and  28  having arc tips  30  and  32 , respectively. These arc electrodes  26  and  28  are mounted at the interior of the end structures  14  and  16 , respectively. At the exterior, the lamp also includes lead wires  31  and  33 , which are mounted to the end structures  14  and  16 , respectively. In certain embodiment, the arc electrodes  26  and  28  comprise tungsten or Molybdenum. However, other materials are within the scope of the present technique. The arc electrodes  26  and  28  are mounted to the end structures  14  and  16 , such that the arc tips  30  and  32  are separated by a gap  34  to create an arc  36  during operation of the lamp  10 . For example, as discussed in detail below, the arc electrodes  26  and  28  can be shrink-fit into receptacles in the end structures  14  and  16 , respectively. In the illustrated embodiment, the arc tips  30  and  32  are oriented along the centerline  38  of the arc envelope  12 . However, alternative embodiments of the arc electrodes  26  and  28  position the arc tips  30  and  32  offset from the centerline  38 , such that the arc  36  is substantially centered within the arc envelope  12 . For example, alternative arc electrodes  26  and  28  may be angled outwardly from the centerline  38  and/or mounted to the end structures  14  and  16  at positions offset from the centerline  38 .  
      Turning now to the next drawing,  FIG. 2  illustrates a cross-sectional side view of the end structure  14  of  FIG. 1  having the plug member  22  exploded from the dosing passageway  24 , the arc electrode  26  exploded from an electrode receptacle  40 , and the lead wire  33  exploded from a lead receptacle  41  in accordance with embodiments of the present technique. The illustrated end structure  14  comprises an outer seal structure  42  and an inner seal structure  44 . As discussed below with reference to  FIG. 5 , the outer seal structure  42  of the end structure  14  abuts and seals against the opposite end  18  of the arc envelope  12 . The inner seal structure  44  plugs into the opposite end  18  and seals with an inner surface of the arc envelope  12  adjacent the opposite end  18 . Referring back to  FIG. 2 , the end structure  14  comprises a porous form or uncondensed material, such as a pressed powder material (e.g., a cermet). After inserting the arc electrode  26  into the electrode receptacle  40  and inserting the lead wire  31  into the lead receptacle  41 , the end structure  14  is further compacted or condensed to shrink the electrode receptacle  40  about the arc electrode  26  and to shrink the lead receptacle  41  about the lead wire  31  as illustrated in  FIG. 3 . In certain embodiments, the end structure  14  is formed by pressing a powder material to a first compaction percentage, sintering the pressed powder material to condense the end structure  14  to a second compaction percentage, drilling the end structure  14  to form the electrode receptacle  40  and the dosing passageway  24 , inserting the arc electrode  26  into the electrode receptacle  40 , and further sintering the end structure  14  to condense the end structure  14  to a third compaction percentage at which the electrode receptacle  40  is shrunk about the arc electrode  26  as illustrated in  FIG. 3 . As illustrated in  FIG. 3 , the latter sintering process facilitates sinter bonding between the arc electrode  26  and the end structure  14 , as indicated by numeral  46 . Similarly, this sintering process creates a sinter bond between the lead wire  31  and the lead receptacle  41 , as indicated by numeral  47 .  
      Turning now to  FIGS. 4 and 5 , exemplary processes are illustrated for manufacturing the end structures  14  and  16  described above with reference to  FIGS. 1-3 .  FIG. 4  is a flow chart illustrating a process  50  for manufacturing the lamp  10  in accordance with embodiments of the present technique. As illustrated, the process  50  comprises providing an end structure for an arc envelope (block  52 ). For example, as described in detail below, the end structure comprises a porous form or partially compacted structure of a particulate material, such as a cermet powder. At block  54 , the process  50  comprises inserting an arc electrode into a receptacle in the end structure. The process  50  then proceeds to condense the end structure to shrink-fit the arc electrode within the receptacle (block  56 ).  
       FIG. 5  illustrates another process  60  for manufacturing the lamp  10  in accordance with embodiment of the present technique. As illustrated, the process  60  begins by pressing a particulate material to form an end structure having a first compaction percentage (block  62 ). For example, a particulate material, such as a powder cermet, may be pressed approximately 45 to 65 percent, e.g., 55 percent, to form the end structures  14  and  16 . At block  64 , the process  60  proceeds to sinter the end structure to a second compaction percentage, which is greater than the first compaction percentage but not entirely condensed. In certain embodiments, the end structures  14  and  16  are sintered to partially condense the compacted particulate material, e.g., pressed powder cermet, thereby reducing the void space between particles of the compacted particulate material. For example, the sintering may heat the end structures  14  and  16  to approximately 1150 to 1350 degrees Celsius, e.g., 1250 degrees Celsius, to condense or conglomerate the particulate material by about an additional 10 to 20 percent, e.g., 16 percent. At block  66 , the process  60  proceeds to machine and/or drill the end structure to form various features, including an electrode receptacle and/or a dosing passageway. At block  68 , the process  60  then proceeds to insert an arc electrode into the electrode receptacle in the end structure. At block  70 , the process  60  further sinters the end structure to a third compaction percentage, thereby shrink-fitting the electrode receptacle about the arc electrode. In certain embodiments, the sintering block  70  involves heating the end structure  14  to approximately 1700 to 2000 degrees Celsius, e.g., 1880 degrees Celsius. However, the specific temperatures and percentages described in the process  60  above may vary depending on the materials, pressures of pressing, durations of sintering, and other factors.  
       FIG. 6  is a cross-sectional view of the lamp of  FIG. 1  having the arc envelope  12 , end structures  14  and  16  plugged into opposite ends  18  and  20  of the arc envelope  12 , the arc electrodes  26  and  28  shrunk-fit into each of the end structures  14  and  16 , the lead wires  31  and  33  shrunk-fit into each of the end structures  14  and  16 , and the plug member  22  exploded from the dosing passageway  28  in the end structure  14  in accordance with embodiments of the present technique. As illustrated, the end structure  14  is hermetically sealed with the arc envelope  12  by a seal material  80 , which is disposed between the outer seal structure  42  and the arc envelope end  18  and between the inner seal structure  44  and an interior surface  82  of the arc envelope  12 . Similarly, the end structure  16  is hermetically sealed with the arc envelope  12  by a seal material  84 , which is disposed between an outer seal structure  86  of the end structure  16  and the arc envelope end  20  and between an inner seal structure  88  of the end structure  16  and an interior surface  90  of the arc envelope  12 . Moreover, similar to the shrink-fit mounting of the arc electrode  26  into the electrode receptacle  40  the end structure  14 , the arc electrode  28  is shrunk-fit into an electrode receptacle  92  within the end structure  16 . In both of these end structures  14  and  16 , elements  46  and  94  illustrate a sinter bond between the arc electrodes  26  and  28  and the electrode receptacles  40  and  92 , respectively. In addition, the lead wires  31  and  33  are shrunk-fit into lead receptacles  41  and  93 , such that the lead wires  31  and  33  are sinter bonded  47  and  95  into the end structures  14  and  16 , respectively.  
      The seal materials  80  and  84  used for the foregoing bonds have characteristics at least partially attributed to the type of materials used for the various lamp components, e.g., the arc envelope  12  and end structures  14  and  16 . For example, some embodiments of the lamp  10  are formed from a sapphire tubular arc envelope  12  bonded with polycrystalline alumina (PCA) end structures  14  and  16 . By further example, some embodiments of the lamp  10  are formed from a YAG tubular arc envelope  12  bonded with cermet end structures  14  and  16 , which have a similar coefficient of thermal expansion (CTE) as alumina (PCA). The seal materials  80  and  84  generally have a coefficient of thermal expansion (CTE) to control stresses at each interface between the arc envelope  12  and the end structures  14  and  16 , e.g., each PCA/sapphire seal interface. For example, the seal materials  80  and  84  may comprise a niobium braze or a seal glass that minimizes tensile stresses developed upon cooling, e.g., a seal glass with a CTE value that is the average value of PCA and the a-axis or radial value of edge-defined-grown sapphire. In certain embodiments, localized heating is applied to the seal materials  80  and  84  to control the local microstructural development of the seal material, e.g., the seal glass.  
       FIG. 7  is a cross-sectional view of a lamp  100  having an arc envelope  102 , end structures  104  and  106  butt-sealed to opposite ends  108  and  110  of the arc envelope  102 , arc electrodes  112  and  114  shrunk-fit into electrode receptacles  116  and  118  in each of the end structures  104  and  106 , lead wires  111  and  113  shrunk-fit into lead receptacles  115  and  117  in each of the end structures  104  and  106 , and a plug member  120  exploded from a dosing passageway  122  in the end structure  104  in accordance with embodiments of the present technique. As illustrated, the lamp  100  has end-to-end or butt-seals  124  and  126  between the arc envelope  102  and the end structures  104  and  106 , respectively. As illustrated, the end structures  104  and  106  are hermetically sealed with the arc envelope  102  by diffusion bonding of the materials at the interface between the end structures  104  and  106  and the arc envelope  102 . In certain embodiment, localized heating, such as a laser, may be applied to this interface to facilitate diffusion bonding to form these butt-seals  124  and  126 . Alternatively, the illustrated butt-seals  124  and  126  can include a seal material  841 , such as described in detail above. In both of the end structures  104  and  106 , elements  128  and  130  illustrate a sinter bond between the arc electrodes  112  and  114  and the electrode receptacles  116  and  118 , respectively. Similarly, elements  129  and  131  illustrate a sinter bond between the lead wires  111  and  113  and the lead receptacles  115  and  117 , respectively.  
       FIG. 8  is a diagrammatical view of a system  140  for dosing the lamp  10  of  FIG. 6  in accordance with embodiments of the present technique. As illustrated in  FIG. 8 , the lamp  10  of  FIG. 6  is coupled to a processing system  142  having a dosing process  144 , which facilitates dosing the lamp  10  prior to sealing the plug member  22  into the dosing passageway  24 . At block  146 , the process  144  begins by connecting the processing system  142  with the dosing passageway  24  of the lamp  10 . For example, tubing  148  can be connected between the processing system  142  and the dosing passageway  24 . At block  150 , the process  144  evacuates material  152  from the lamp  10 . At block  154 , the process  144  injects a dosing material  156  into the lamp  10 . At block  158 , the process  144  proceeds to disconnect the processing system  142  from the dosing passageway  24  of the lamp  10 . The process  144  also seals the dosing passageway  24  with the plug member  22  at block  160 .  FIG. 9  is a cross-sectional view of the lamp  10  of  FIG. 6  having the dosing material  156  disposed within the arc envelope  12  and the plug member  22  disposed within the dosing passageway  24  in accordance with embodiments of the present technique.  
       FIG. 10  is a cross-sectional view of an alternative end structure  170  having a dosing passageway  172 , a dosing tube  174  exploded from the dosing passageway  172 , a support structure (e.g., tube or coil)  176  exploded from the dosing tube  174 , and an arc electrode  178  exploded from the coil  176  in accordance with embodiments of the present technique. As illustrated, the end structure  170  comprises an outer seal structure  180  and an inner seal structure  182 . As discussed above with reference to the end structure  14  of  FIGS. 1 and 2 , the outer seal structure  180  is adapted to seal against an end of an arc envelope, whereas the inner seal structure  182  is adapted to plug into and seal against an inner surface of the arc envelope. Although a variety of materials combinations are within the scope of the present technique, the illustrated embodiment has a metal, niobium, molybdenum coated niobium, or cermet end structure  170 , a molybdenum or molybdenum-rhenium dosing tube  174 , a molybdenum coil  176 , and a tungsten arc electrode  178 .  
      Turning now to  FIG. 11 , the end structure  170  is illustrated partially assembled with the dosing tube  174  hermetically sealed within the dosing passageway  172  and a protective layer  184  disposed over an interior surface  186  of the end structure  170  in accordance with embodiments of the present technique. More specifically, the dosing tube  174  is inserted within the dosing passageway  172  and subsequently bonded to the end structure  170  at the interior surface  186 . In this exemplary embodiment, a laser beam is applied about the periphery of the dosing tube  174  at the interior surface  186 , such that a laser welded seal  188  is formed between the dosing tube  174  and the end structure  170 . The protective layer  184 , such as a molybdenum coating, is then applied over the interior surface  186  to protect the end structure  170  from corrosive materials disposed within the lamp, e.g., halide dose. As further illustrated in  FIG. 11 , the arc electrode  178  is inserted within the coil  176 , which is later mounted in the dosing tube  174  as described in detail below. In addition, a seal material may be used to hermetically join the dosing tube  174  to the end structure  170 .  
      Turning to  FIG. 12 , a system  190  having a processing system  192  is illustrated for dosing a lamp  194  in accordance with embodiments of the present technique. As illustrated in  FIG. 12 , the lamp  194  includes an arc envelope  196 , the end structure  16  of  FIG. 6  coupled to an end  198  of the arc envelope  196 , and the end structure  170  of  FIG. 11  coupled to an end  200  of the arc envelope  196 . In the illustrated embodiment, the end structures  170  and  16  are hermetically sealed to the arc envelope  196  via seal materials  202  and  204 , which are disposed between the interface of the end structures  170  and  16  and the arc envelope  196 . Alternatively, other embodiments hermetically seal the end structures  170  and  16  to the arc envelope  196  via diffusion bonding, as described in detail above. Similar to the protective layer  184  disposed on the interior surface  186  of the end structure  170 , the illustrated end structure  16  includes a protective layer  206 , such as a molybdenum coating, to protect the end structure  16  from corrosive materials disposed within the lamp  194 .  
      As further illustrated in  FIG. 12 , the lamp  194  is coupled to the processing system  192 , which includes a dosing process  208  to dose the lamp  10  prior to sealing the dosing tube  174 . At block  210 , the process  208  begins by connecting the processing system  192  with the dosing tube  174  of the lamp  194 . For example, tubing  212  can be connected between the processing system  192  and the dosing tube  174 . At block  214 , the process  208  evacuates material  216  from the lamp  194 . At block  218 , the process  208  injects a dosing material  220  into the lamp  194 . At block  222 , the process  208  proceeds to disconnect the processing system  192  from the dosing tube  174  of the lamp  194 . With reference to  FIGS. 11 and 13 , the process  208  of  FIG. 12  also inserts the assembly of the coil  176  and the arc electrode  178  into the dosing tube  174  of the lamp  194  (block  224 ). At block  226 , the process  208  seals the dosing tube  174  about the coil  176  and the arc electrode  178 , as illustrated in  FIG. 13 .  
      As discussed above with reference to  FIG. 12 , the hermetically sealed assembly of the lamp  194  is illustrated in  FIG. 13 . In the illustrated embodiment, the coil  176  and the arc electrode  178  are inserted one within the other inside the dosing tube  174 , which is hermetically closed at a bond or seal  230 . The coil  174  supports the arc electrode  178  within the dosing tube  174 , while also permitting some freedom of movement and stress relaxation of the respective components. Regarding the seal  230 , certain embodiments form the seal  230  by applying localized heat, such as a laser beam, onto the dosing tube  174 , the coil one under  176 , and the arc electrode  178 . Alternatively, the dosing tube  174  may be formed of a ductile material, such as a niobium or molybdenum-rhenium alloy, which can be mechanically compressed by a crimping tool or other mechanical deformation tool to form the seal  230 . In addition, localized heating can be applied to the seal  230  during or after the crimping process to improve the seal  230 .  
       FIG. 14  is a cross-sectional view of an alternative lamp  240  having an arc envelope  242 , end structures  244  and  246  butt-sealed to opposite ends  248  and  250  of the arc envelope  242 , an arc electrode  252  shrunk-fit into the end structure  246 , a lead wire  253  shrunk-fit into the end structure  246 , a coil  256 , and an arc electrode  258  hermetically sealed to a dosing passageway  260  of the end structure  244  in accordance with embodiments of the present technique. As illustrated, the lamp  240  has end-to-end or butt-seals  262  and  264  between the arc envelope  242  and the end structures  244  and  246 , respectively. As illustrated, the end structures  244  and  246  are hermetically sealed with the arc envelope  242  by diffusion bonding of the materials at the interface between the end structures  244  and  246  and the arc envelope  242 . In certain embodiments, localized heating, such as a laser, may be applied to this interface to facilitate diffusion bonding to form these butt-seals  262  and  264 . Alternatively, the illustrated butt-seals  262  and  264  can include a seal material, such as described in detail above. In the illustrated embodiment, the end structure  246  is sintered to shrink-fit the arc electrode  252  and the lead wire  253  within an electrode receptacle  266  and a lead receptacle  267 , respectively. Thus, this sintering process creates a sinter bond  268  between the arc electrode  252  and the electrode receptacle  266  and, also, a sinter bond  269  between the lead wire  253  and the lead receptacle  267 . On the end structure  244 , the dosing tube  254  can be used as a lead for the arc electrode  258 . As discussed above with reference to  FIGS. 11-13 , the dosing tube  254  is hermetically sealed to the end structure  244  via localized heating (e.g., a laser weld) to form a bond  270 . Moreover, the dosing tube  254  is hermetically closed about the coil  256  and the arc electrode  258  by a bond or seal  272 , such as a crimped and/or locally heated bond.  
       FIG. 15  is a flow chart illustrating an exemplary process  280  of manufacturing a lamp in accordance with embodiments of the present technique. With reference to the lamps described above with reference to  FIGS. 10-14 , the process  280  begins by providing an arc envelope having a hermetically sealed end structure with a dosing passageway (block  282 ). At block  284 , the process  280  doses the arc envelope with a dosing material through the dosing passageway. At block  286 , the process  280  positions a coil about an arc electrode within the doing passageway of the end structure. At block  288 , the process  280  seals the dosing passageway about the coil and the arc electrode.  
      While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.