Abstract:
A method of forming a hermetically sealed electrodless lamp envelope includes: (1) forming an envelope blank; (2) depositing a gas and light generating expedient material in an interior of the envelope blank; (3) arranging a window on an open end of the envelope blank; and (4) using an ultra-short pulse laser system to locally heat the axial end of the envelope blank and the window to seal the window on the envelope blank without degrading the contents deposited in an interior of the envelope or damaging or cracking the envelope blank and/or window.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/988,431, filed on May 5, 2014, currently pending, the disclosure of which is incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    This disclosure is directed to an electrodeless lamp envelope although it could be applied to other lamp and ampule configurations. In an electrodeless lamp system, the power required to generate the light from the electrodeless lamp envelope is transferred from outside the lamp envelope to the gas inside the lamp envelope via an electric or magnetic field. An interior of the envelope may be filled with a gas capable of producing a desired emission of light energy, such as neon, xenon, or argon. There may also be trace materials added to the interior of the envelope such as mercury or metal halides to help ignite the gas of the lamp and create a desired emission of light energy. In particular, the disclosure is related to methods of hermetically sealing the envelope. In one aspect, the disclosure is related to methods of hermetically sealing an envelope formed from sapphire. This disclosure is also related to deposition of dielectric coatings on surfaces of the envelope and forming desired geometric surfaces on portions of the exterior of the envelope for focusing the light energy emitted from the lamp and/or to generate other desired optics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIGS. 1A-1E  show a process of forming an envelope blank. 
           [0004]      FIG. 2  shows the process of arranging the envelope blank into fixturing to allow processing of the envelope blank into a hermetically sealed envelope. 
           [0005]      FIGS. 3-8  detail the process of finishing the envelope blank to form a hermetically sealed envelope using the fixturing of  FIG. 2 . 
           [0006]      FIGS. 9-14  show exemplary envelopes with illustrative lenses that may be applied to the lamp envelope. 
           [0007]      FIG. 15  is an exemplary envelope with a dielectric coating deposited on an axial end and outer surface of the envelope. 
           [0008]      FIG. 16  is an alternate embodiment of an envelope with a dielectric coating deposited on a lens of the envelope and a parabolic outer surface of the envelope. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0009]    Although the terms “top,” “bottom,” “base,” “cylinder,” and “end” are used in the discussion that follows, the use is not intended to be limiting in any sense. Rather, the use is merely for illustrative purposes in describing certain embodiments as they appear in the drawings. The embodiments may have other orientations and shapes. 
         [0010]      FIGS. 1A-1E  show the process of forming an envelope blank. The envelope blank  20  comprises a lamp tube  22  and a base end window  24 . The base end window  24  and lamp tube  22  may be any size and shape. The base end window  24  and lamp tube  22  may be formed from a sapphire material. The base end window  24  may be fitted at an axial end of the lamp tube  22 . Preferably, the lamp tube  22  and the base end window  24  have their crystal orientation matched to provide a strong seal for the base end window on the axial end of the lamp tube. The preferred orientation for aligning the base end window with the lamp tube may be along the axis  26  as shown in  FIG. 1 . The mating faces of the base end window  24  and the axial end of the lamp tube  22  may be both perpendicular to the axis  26 . The base end window and axial end of the lamp tube may be polished flat. The base end window may be placed on the axial end of the lamp tube allowing the mating surfaces of the base end window and the tube to be in contact ( FIG. 1B ). Using localized heating  28  from an ultra-short pulse laser system, which is capable of heating on a microscopic level, as described below, the axial end area of the tube and base end window may be heated, sealing the tube and base end window together to form an envelope blank  20  ( FIG. 1C ). The mating surfaces of the lamp tube and the base end window may be fused together with the localized heating to form a monolithic structure between the base end window and the tube, thereby forming the envelope blank for later processing as described below. The method has been proven effective for a base end window and lamp tube made from sapphire. Materials other than sapphire may also be sealed. After the envelope blank  20  is formed, the envelope blank may be finished into a desired form to allow it to be further processed as will be described below in greater detail. As shown in  FIGS. 1D-1E , excess end material may trimmed and removed from the base end window  24  to allow the end of the envelope blank  20  to have a slim profile which will allow the envelope blank to be received in fixturing for further processing as will be described below. While  FIGS. 1A-1  E show a generally cylindrically shaped envelop blank, the envelope blank may be other shapes, for instance, parabolic as shown in  FIGS. 13 and 16 . 
         [0011]    The ultra-short pulse laser system may be a picosecond pulse laser system, for instance, one developed by Primoceler. The laser may be of the type disclosed in U.S. Pat. App. Pub. No. 2012/0067858 and U.S. Pat. App. Pub. No. 2013/0070428, the disclosures both of which are incorporated herein by reference. The laser may also be a femtosecond pulse laser system or an attosecond pulse laser system. The laser is capable of heating the materials on a microscopic level in selected localized areas and thus not heating other areas of the envelope or its contents. The laser, and the lamp tube and bottom end window, may also be configured as disclosed in US Pat. App. Pub. No. 2013/0112650, the disclosure of which is incorporated by reference. A thin heat absorbing material may be applied on one of the sealing faces as disclosed in U.S. Pat. App. Pub. No. US 2013/0112650 to enhance the localized heating and thus the sealing process to form the envelope blank. 
         [0012]    In the alternative, depending upon the application, the envelope blank may be formed by conventional heating means. For instance, the base end window and lamp tube may be placed in contact and heated in a high temperature furnace to form the envelope blank. Such a process is disclosed by example in U.S. Pat. No. 5,621,275, the disclosure of which is incorporated herein by reference. This method may be used when the base end window does not contain a lens or coating prior to sealing with the lamp tube, and general heating may be acceptable when forming the envelope blank. 
         [0013]      FIGS. 2 through 8  show an exemplary process and tooling that may be used for finishing the envelope blank  20  to a hermetically sealed envelope. The tooling comprises a high purity pressure chamber  30 . The pressure chamber  30  comprises a fixture body  32  with a base  34  and a hollow interior  36  that closely matches the exterior shape of the lamp tube, for instance, a cylindrical shape with a hollow interior diameter of generally corresponding to the outer diameter of the envelope blank. The fixture body base  34  is disposed at an axial end of the cylindrical interior with an opening  38  into the hollow interior  36  opposite the base. The opening  38  provides access to the hollow interior  36  of the fixture body  32 . The fixture body  32  may have a port  40  that connects to a three-way valve  42 . The three-way valve  42  may be configured to align to a gas source  44  to pressurize the pressure chamber, or a vacuum  46  to evacuate the pressure chamber, as will be described below in greater detail. The open axial end  38  of the fixture body  32  may have annular seals  48  (e.g., o-ring type gaskets). An outer surface  50  of the fixture body  32  adjacent to the open axial end  38  may be threaded. The fixture body base  34  may have a plunger  52  extending therethrough into the hollow interior  36  of the fixture body  32 . A shaft of the plunger  52  may be configured for sliding motion with the fixture body base  34  through a vacuum tight seal  54 . A coil spring  56  may be disposed on the plunger end in the hollow interior of the fixture body. 
         [0014]    The pressure chamber  30  may comprise a compression seal cap  60  that is configured to fit over the open axial end  38  of the fixture body  32 . The compression seal cap  60  may have an inner cylindrical wall  62  with internal threads that match the threading on the outer diameter surface  50  of the fixture body  32 , allowing the cap to be threaded around the fixture body to seal the pressure chamber. Other means may be provided to releasably connect the seal cap to the fixture body, i.e., mechanical fasteners, clamps, quick release connectors. The seal cap  60  may have an internal shoulder with annular seals  64  (e.g., o-ring type gaskets) and an access opening  66  on an axial end of the seal cap. The pressure chamber  30  may be portable to allow it to be inserted into and removed from an atmosphere controlled glove box. 
         [0015]    As shown in  FIG. 2 , the pressure chamber  30 , and a polished and clean top end window  70 , and the clean envelope blank  20  may be introduced into the atmosphere controlled glove box. The top end window  70  and envelope blank  20  may be arranged with the matching crystal axis  26  with the mating faces of the top end window and the axial end of the envelope blank both perpendicular to the axis  26 . The envelope blank  20  may be loaded with halides, mercury, and/or any other light emission expedient materials  72  that are desired to be enclosed in the envelope. 
         [0016]    As shown in  FIG. 3 , the envelope blank  20  may be placed in the hollow interior  36  of the fixture body  32 , and the top end window may be placed adjacent to the axial end of the envelope blank. The top end window  70  may rest on the fixture body axial end seals  48 . As the seal cap  60  is secured onto the fixture body  32 , the top end window  70  may be fixed in place between the seals  64  of the seal cap  60  and the axial end seals  48  of the fixture body. When the pressure chamber  30  is sealed, the plunger  54  may be moved downward in the fixture body hollow interior  36  to a first, lowered position. Under gravity, the envelope blank  20  may move vertically downward in the fixture body hollow interior  36  thereby allowing a gap  72  to form between the top end window  70  and the open axial end of the envelope blank  20 . Once the gap  72  is formed between the top end window  70  and the open axial end of the envelope blank  20 , the pressure chamber  30  may be evacuated through the three way valve  42  to the vacuum source  46 . Drawing a vacuum in the pressure chamber  30  removes any impurities from the pressure chamber prior to hermetically sealing the envelope blank. 
         [0017]    Once the vacuum is drawn in the pressure chamber  30  and any impurities are removed, the three-way valve  42  may be switched to direct fill gas from the gas source  44  into the pressure chamber  32  as shown in  FIG. 4 . The three-way valve  42  may be actuated to direct gas through the three-way valve and through the port  40  into the pressure chamber  30 . The gas may flow into the hollow interior of the envelope blank  20 . The gas may be neon, xenon, argon, or any other selected gas to create a desired emission of light energy. The plunger  52  is maintained in the first, lowered position during filling to maintain the gap between the axial end of the envelope blank and the top end window to allow the gas to flow into the interior of the envelope. In addition, or in the alternative, to drawing a vacuum and filling operation, the pressure chamber may be purged with the fill gas. 
         [0018]    Once the envelope blank is filled with the gas, the plunger  52  may be moved to a raised, second position such that the coil spring biases  54  the envelope blank  20  against the top end window  70 . The valve  42  may be closed, as shown in  FIG. 5 . The pressure chamber  30  may then be removed from the glove box prior to the commencement of the final sealing operations. 
         [0019]    With the top end window  70  and axial end of the envelope blank  20  in mating contact, localized heating  28  with an ultra-short pulse laser system may commence to hermetically seal the envelope blank. The envelope blank  20  may be filled at close to room temperature or cooled lower than room temperature to protect the solids, such as, mercury and halides, which may be sealed into the envelope blank.  FIG. 6  shows further detail of the top of the threaded compression seal cap  60 . As described above, the seal cap  60  has an access opening  66  that has a diameter larger than the outer diameter of the envelope blank. The access opening  66  in the seal cap  60  accommodates the needed travel of the beam of the ultra-short pulse laser system laser so that the beam may be directed to the axial ends of the envelope blank to seal the top end window and with axial ends of the envelope blank  20  to form the completed hermetically sealed envelope. As shown in  FIG. 7 , the beam  28  may travel in a circular path corresponding to the axial end of the envelope blank  20 . The mating surfaces of the envelope blank and the top end window may be fused together with the localized heating  28  to form a monolithic structure, hermetically sealing the envelope. Because of the localized (microscopic level) heating from the ultra-short pulse laser system to seal the envelope, the gas, and radiation emission expedients, disposed in the interior of the envelope are not degraded from excess heat, nor is the window or envelope damaged or cracked by excessive heat. A laser absorbing layer may be applied to the top end window  70  and/or the open axial end of the envelope blank  20  to improve the localized heating and overall sealing process. 
         [0020]      FIG. 8  shows an alternate embodiment of the pressure chamber  130  wherein the envelope blank is hermetically sealed by subjecting the pressure chamber to a cooling fluid  132  such as a cryogenic solution (i.e., liquid nitrogen). The cooling fluid allows the gas in the envelope blank to condense to a liquid, which creates a partial vacuum in the hollow interior of the envelope blank prior to sealing. This may improve laser sealing using the methods described above. For instance, if the gas pressure is in excess of one atmosphere (1 ATM), cooling fluid  132  may be directed into a jacket surrounding the fixture body  32  to cool the hollow interior of the fixture body and the envelope, and thereby turning the gas to a liquid and creating a partial vacuum in the envelope blank interior. Once the laser operations are complete, the hermetically sealed envelope may be removed from the pressure chamber for use. 
         [0021]      FIGS. 9-14  provide examples of precision optics that may be applied to the envelope  20 . Because the laser sealing operations do not heat the top and/or base end window(s)  24 , 70 , precision lenses  140  may be formed on any surfaces of the top and base end window(s)  24 , 70  without distortion of the optics. The lenses  140  may be provided on one or both ends of the envelope blank  20 . Using the methods described previously, the base end window  24  may have a lens formed thereon prior to laser sealing to the lamp tube to form the envelope blank  20 . Thus, the envelope blank may have a lens  140  formed on its axial end adjacent the spring and plunger shown in the fixturing of  FIGS. 2-8 . As shown in  FIGS. 9-14 , the lenses  140  applied to the surfaces of the top and base end window(s) may be concave or convex, thereby providing the end window with a parabolic and/or mushroom shape, as may be desired by the application of the lamp envelope. 
         [0022]      FIGS. 15 and 16  provide examples of envelopes  20  with dielectric coatings applied to lenses  140  and an exterior of the lamp envelope. The dielectric coatings may be deposited on the top and/or base end window(s)  24 , 70  of the envelope  20  and to the interior and/or exterior of the lamp tube  22  prior to laser sealing operations. Dielectric coatings may be arranged on the top and/or base end windows  24 , 70 , and/or the lamp envelope exterior/interior to reflect and transmit specific, selected wavelengths of light from the envelope. This allows the lamp envelope to be configured for specific applications as desired, for instance, for UV lithography, ellipsometry, transmission of infrared radiation, or transmission of visible light. Because the laser sealing operations do not raise the temperature of the top and/or base end window(s) or the lamp envelope, the laser sealing operations do not detrimentally degrade the dielectric coating applied to the top and/or base end window(s), and/or exterior surfaces of the lamp envelope. Lenses and/or lamp envelopes with dielectric coatings allow the selection of wavelengths to be reflected, filtered, and transmitted depending upon a particular application. Certain wavelengths that the lamp does not need to transmit may be reflected back into the lamp envelope thereby increasing lamp efficiency and power output by further heating of the plasma. Selected areas on the exterior of the lamp envelope may be coated with the dielectric to further enhance the performance of the lamp. Because the dielectric coatings are nonconductive, the coating will not be affected by or impact the magnetic or electric fields used to power the lamp. The coatings may be deposited on any surface of the envelope blank that is not used for sealing. The sealing surfaces of the blank envelope and the window may be masked prior to coating with the dielectric to keep the areas to be sealed free of any coating. This allows a coated end window and envelope blank to be sealed together without contaminating the sealing surfaces with the coating and thus reducing sealing reliability. 
         [0023]      FIG. 15  shows a lamp envelop  20  with a dielectric coating  146  comprising a broad band UV transmissive coating that transmits only desired wavelengths of ultraviolet light disposed over the lens  140  formed on the top end window  70 . The lens  140  of the top end window of the envelope focuses the UV emission to the target. Desired ultraviolet radiation is focused out of the lamp envelope by the lens shape. The exterior of the lamp envelop  20  is coated with a broad band UV reflector coating  148  that reflects radiation back into the lamp. The other wavelengths are reflected back into the lamp to further heat the plasma and make the lamp more efficient.  FIG. 16  provides another example of a lamp envelope configuration where the envelope  20  is a generally parabolic tube. The dielectric coating  150  deposited on the top end window  70  allows emission of white light from the lamp. Infrared and ultraviolet emissions are reflected back into the lamp to further heat the plasma of the lamp and make the lamp more efficient. The dielectric coating  152  deposited on the tube exterior comprises a broad band reflector that reflects all radiation back into the lamp. The visible or white light is focused out of the lamp by the parabolic shape of the envelope and the dielectric coating  152  on the envelope. 
         [0024]    The methods described herein may be used to fabricate lamp envelopes from other materials in addition to sapphire. Lamps envelopes may be formed from diamond, crystalline quartz, ruby, magnesium fluoride, spinel, silicon, YAG, and salts. Because the methods do not heat the lamp envelope, the methods described herein may be used to fabricate lamps made of more traditional glass materials, such as fused quartz, borosilicate, alumino silicate, etc., where a precision glass lens or coated glass lens may be sealed onto an envelope blank to form the sealed lamp envelope. An additional advantage of the methods disclosed herein involves pure material to material sealing with no foreign sealing materials involved. For instance, no brazes, frits, etc. are used. This reduces weaknesses and contaminants that would otherwise come from foreign sealing material. 
         [0025]    In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.