Abstract:
A gas discharge laser includes a laser chamber containing a halogen laser gas, two electrode elements defining a cathode and an anode, each having a discharge receiving region defining two longitudinal edges and having a region width defining a width of an electric discharge between the electrode elements in the laser gas. The anode comprising a first anode portion comprising a first anode material defining a first anode material erosion rate, located entirely within the discharge receiving region, a pair of second anode portions comprising a second anode material defining a second anode material erosion rate, respectively located on each side of the first anode portion and at least partially within the discharge receiving region; an electrode center base portion integral with the first anode portion; and wherein each of the respective pair of second anode portions is mechanically bonded to the center base portion.

Description:
RELATED APPLICATIONS 
   The present application is a continuation-in-part of U.S. patent application Ser. No. 10/629,364, entitled HIGH REP-RATE LASER WITH IMPROVED ELECTRODES, filed on Jul. 29, 2003, which is a Divisional of U.S. patent application Ser. No. 10/104,502, entitled HIGH REP-RATE LASER WITH IMPROVED ELECTRODES, filed on Mar. 22, 2002, (now U.S. Pat. No. 6,690,706, issued on Feb. 10, 2004, and a continuation-in-part of U.S. patent application Ser. No. 10/638,247, entitled HIGH REP-RATE LASER WITH IMPROVED ELECTRODES, filed on Aug. 7, 2003 as a continuation of the &#39;502 application, each of which is assigned to applicants&#39; common assignee, and the disclosures of each of which is hereby incorporated by reference. The present application is also a continuation-in-part of U.S. patent applications Ser. Nos. 10/672,722, entitled ANODES FOR FLUORINE GAS DISCHARGE LASERS, filed on Sep. 26, 2003, Ser. No. 10/672,181, entitled CATHODES FOR FLUORINE GAS DISCHARGE LASERS, filed on Sep. 26, 2003, and 10/672,182, entitled ELECTRODES FOR FLOUORINE GAS DISCHARGE LASERS, filed on Sep. 26, 2003, each of which is assigned to applicant&#39; common assignee, and the disclosures of each of which are hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to high repetition rate, high power, gas discharge laser light source electrodes. 
   BACKGROUND OF THE INVENTION 
   Electrodes of the type discussed in the above referenced patent and patent applications are well known for use in the art of providing light at small wavelengths, e.g., UV and DUV, i.e., below about 500 nm, using halogen based gas discharge media within an enclosed chamber and providing the gas discharge between a pair of electrodes at very high voltages, e.g., tens of thousands of volts and high amperage, e.g., hundreds of amps, in very short duration electrical discharges in the medium, e.g., tens of nanoseconds. This pulsed laser light is used for a variety of industrial purposes, e.g., in integrated circuit photolithography to expose photoresist on wafers by passing the light through a mask (reticle) to accomplish the desired exposure. The stability of various parameters of the light delivered to the wafer as provided by the laser light source is critical to proper performance of the manufacturing process, e.g., the proper exposure of the photoresist to define microscopic patterns on the wafer for manufacturing integrated circuits with critical dimensions measured in under 0.1 microns. 
   One aspect of this criticality of the maintenance of the stability of the light delivered is the maintenance of the stability, pulse-to-pulse and over long periods of operation, measured in tens of billions of pulses, of the electrodes. The above referenced patent and patent applications discuss various aspects of the geometries, materials and the like utilized for such electrodes. Applicants have developed aspects of electrode materials and geometries and structures aimed at increasing the discharge stability pulse to pulse and over life and at increasing useful life during which such stable pulses can continue to be provided in order to improve the efficiency and economic of operating such laser light source systems as will be explained in more detail below. 
   Applicants have noticed an end wear region of the discharge receiving region of electrodes generally just beyond where the electrodes being used by applicant&#39; assignee in laser systems begin a roll-off toward an end portion of the electrodes, wherein, e.g., the erosion causes the discharge to widen somewhat at the end which hastens end of life for the electrode. Applicants herein propose certain aspects of embodiments of the present invention that will alleviate this end of life syndrome for electrodes. 
   SUMMARY OF THE INVENTION 
   A method and apparatus for operating a gas discharge laser is disclosed which may comprise a laser chamber containing a laser gas, the laser gas comprising a halogen, two elongated electrode elements defining a cathode and an anode, each of the cathode and anode having an elongated discharge receiving region having a discharge receiving region width defining a width of an electric discharge between the electrode elements in the laser gas, the discharge receiving region defining two longitudinal edges, and the anode comprising: a first elongated anode portion comprising a first anode material defining a first anode material erosion rate, located entirely within the discharge receiving region of the anode, a pair of second elongated anode portions comprising a second anode material defining a second anode material erosion rate, respectively located on each side of the first anode portion and at least partially within the discharge receiving region; an elongated electrode center base portion integral with the first elongated anode portion; and wherein each of the respective pair of second elongated anode portions is mechanically bonded to the center base portion. The electrode element may comprise a cathode. The first and second materials may be different materials such as different brass alloys with different erosion rates in the halogen gas. The first elongated cathode portion may comprise a first cathode material, located entirely within the discharge receiving region comprising a first portion of an ellipse intersecting elongated side walls, with a bottom wall opposite the portion of the ellipse; and a pair of second elongated cathode side portions comprising a second cathode material with the intersection of each respective second cathode portion and the portion of the ellipse forming the discharge receiving region of the first cathode portion, forming respective ellipsoidal extensions of the first portion. The members may be mechanically bonded to the center base portion. Some may be diffusion bonded to the center base portion and/or each other. The electrode assembly may have a hooded discharge receiving region extension at respective ends of the electrode and the electrode portion may be formed with or bonded to the center base portion and may have slanted side walls. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Turning now to  FIG. 1  there is shown a top plan partially cut-away view of an electrode assembly  20  according to an aspect of an embodiment of the present invention; 
       FIG. 2  shows a cross-sectional view of the embodiment of  FIG. 1  taken along the cross-sectional lines  2 — 2  in  FIG. 1 ; 
       FIG. 2A  shows a detail of  FIG. 1  contained in the circle shown in  FIG. 1 . 
       FIG. 3  shows a cross-sectional view of the embodiment of  FIG. 1  along the cross-sectional lines  3 — 3  of  FIG. 1 ; 
       FIG. 4  shows a cross-sectional view of the embodiment of  FIG. 1  along the cross-sectional lines  4 — 4  in  FIG. 1 ; 
       FIG. 5  shows a perspective view of one end of a central base portion of an electrode assembly according to aspects of an embodiment of the present invention shown in  FIG. 1 ; 
       FIG. 6  shows a perspective view of an end of an electrode assembly according to aspects of an embodiment of the invention shown in  FIG. 1 ; 
       FIG. 7  shows a partially cut-away plan view of the bottom on an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 8  shows a perspective view of an electrode assembly according to the embodiment of  FIG. 1  viewed from the bottom; 
       FIG. 9  shows a cross-sectional view of a center base portion taken along cross-sectional lines  9 — 9  in  FIG. 3   
       FIG. 10  illustrates aspects of an assembly and manufacturing process for an electrode assembly according to aspects of embodiments of the present invention; 
       FIG. 11  illustrates aspects of an assembly and manufacturing process for an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 12  illustrates aspects of an assembly and manufacturing process according to aspects of an embodiment of the present invention; 
       FIG. 13  illustrates a perspective side view of an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 14  shows an isometric perspective view of an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 15  shown a cross sectional view of an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 16  shows a perspective view with cross-section of an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 17  shows a cross sectional view of a portion of an electrode assembly according to aspects of an embodiment of the present invention; 
       FIG. 18  shows a cross sectional view of a portion of a laser chamber showing an anode and a cathode; 
       FIGS. 19 and 19A  show a cross-sectional and plan view respectively of a partly schematic view of aspects of an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a top plan partially cut-away view of an electrode assembly  20  according to an aspect of an embodiment of the present invention. The electrode assembly  20  may have an elongated center base portion  22  made of a first material, e.g., a relatively low erosion rate brass alloy as discussed in the above referenced 706 patent, such as, e.g., C26000 brass, and a first elongated side portion  24  and a second opposing elongated side portion  26  each made of a second material, e.g., an alloy of relatively higher erosion rate, such as, e.g., a C36000 brass. It will be understood that erosion rate is meant to mean that erosion which is caused due to the environment within the medium, e.g., the presence of highly ionized fluorine atoms during and after the electric discharge between the electrodes of a gas discharge laser, and the position of the electrode as an anode or cathode, and other such factors, e.g., the time during the discharge and the direction of flow of current through the medium between the electrodes, the voltage extant at any given time, etc. The erosion rate for a given material being an average erosion rate over a life time for an electrode or pair of electrodes due to continuous exposure to the just mentioned environmental factors. It being understood that over time a given material may erode faster on an electrode than on a cathode, i.e., the anode, where, e.g., the center base portion  22  may be made of C36000 and the side portions of C26000. 
   Turning now to  FIG. 2  there is shown a cross-sectional view of the embodiment of FIG. I taken along the cross-sectional lines  2 — 2  in  FIG. 1 . As shown in  FIG. 2 , the electrode assembly  20  may include a center base portion lower portion  30 , forming a pair of shelves  31 , a center base portion intermediate portion  32  forming a pair of shelves  33  and a center base portion upper portion  34  which may have a pair of opposing side walls  36 . It will be understood that the center base portion may extend essentially for the entire longitudinal length of the electrode assembly  20  and may look as shown in perspective view in  FIG. 5 , prior to some finishing processing steps, e.g., a machining process. Also as shown in  FIG. 2  the first and second side portions  24 ,  26  may be configured to abut the shelves  31  of the lower center base portion  30 , and  33  of the intermediate center base portion  32  and the side walls  36  of the upper center base portion  34 . 
   Turning now to  FIG. 2A , there is shown a detail from  FIG. 1  contained within the circle shown in  FIG. 1 .  FIG. 2A  shows that the facing portion of the electrode assembly  20 , which faces an opposing electrode may comprise a discharge receiving region  40 , which extends longitudinally along the electrode assembly  20 . The facing portion  62  of the upper center base portion  34  of the electrode assembly  20  may comprise a portion of an ellipse  60 , e.g., a portion of one half of the ellipse  60 . In addition as shown in  FIG. 2A  according to an aspect of an embodiment of the present invention, the upper facing surfaces of the respective opposing side portions  24 ,  26  on either side of the upper center base portion  34  may contain respective ellipsoidal portions that essentially form an extension of the portion of the ellipse  60  forming the facing portion  62  of the upper portion  34  of the center base portion  22  extending on either side of the facing portion  62  ellipsoidal surface. It will be understood that according to aspects of an embodiment of the present invention the discharge receiving region  40  of the electrode assembly  20  may be essentially coextensive with the ellipsoidal surface formed by both the facing portion  62  of the upper portion  34  of the center base portion  22  and the ellipsoidal extensions formed in the respective opposing portions of the side portions  24 ,  26 . Thus according to an aspect of an embodiment of the present invention an elongated discharge receiving region  40  extends substantially the length of the electrode assembly  20  formed by the ellipsoidal surface formed by the facing portion  62  of the upper portion  34  f the center base portion and the adjoining ellipsoidal surfaces of the opposing side portions  24 ,  26  along the respective edges of the facing portion  62  of the upper portion  34 . It will also be understood as is also shown in  FIG. 2A , that the discharge receiving region  40  is not completely the top half of an ellipse  60 , either because the discharge, according to one aspect of an embodiment of the present invention, extends partly into the generally flat upper surfaces  64 , 66  of the respective side portions  24 ,  26 , or according to another aspect of an embodiment of the present invention, remains on the combined ellipsoidal surface, but, as shown, that ellipsoidal surface is not the complete half of the ellipse  60 . 
   Turning now to  FIG. 3  there is shown a cross-sectional view of the embodiment of  FIG. 1  along the cross-sectional lines  3 — 3  of  FIG. 1 . As shown in  FIG. 3 , the electrode assembly  20  center base portion  22 , according to aspects of an embodiment of the present invention in longitudinal cross section may have a generally flat elongated portion  48  that may be rounded toward the end of the electrode assembly  20 , e.g., in the shape of a portion of an ellipse  42 . Turning now to  FIG. 4  there is shown a cross-sectional view of the embodiment of  FIG. 1  along the cross-sectional lines  4 — 4  in  FIG. 1 .  FIG. 4  shown that the lower portion  30  of the center base portion  22  of the electrode assembly may be formed into an upper curved skirt portion  45  at the end of the electrode assembly and a lower curved skirt portion  44  also at the end of the electrode assembly. Also shown is that the respective side portions  24 ,  26  (only  26  being shown in  FIG. 4 ) may be formed to smoothly follow the contour of the upper skirt portion  45  and vice-versa. 
   Turning now to  FIG. 5  there is shown a perspective view of one end of the center base portion  22  of an electrode assembly  20  according to aspects of an embodiment of the present invention shown in  FIG. 1 .  FIG. 5  shown that in the first shelf  31  of the lower portion  30  and corresponding vertical side walls of the intermediate portion  32  may be formed nooks  56 , which may also contain an opening  57 , e.g., for a bolt  80  (shown in  FIG. 10  or an alignment dowel  96  (also shown in FIG.  10 )., which may be formed, e.g., intermediate high voltage connecting rod opening  50  (shown, e.g., in  FIGS. 3 ,  8  and  9 ) formed in the bottom portion  30  and intermediate portion  32  of the center base portion  22 . 
   Turning now to  FIG. 6  there is shown a perspective view of an end of an electrode assembly  20 according to aspects of an embodiment of the invention shown in  FIG. 1 . As shown in  FIG. 6  the side members  24  and  26  and the center base portion  22  may be machined, e.g., from a starting center base portion as illustrated in  FIG. 5  and starting side portions as illustrated by the starting blocks  90 ,  92  shown in  FIGS. 10 and 11 , to form the end portion of an electrode assembly  20 . also shown in  FIG. 6  is a gradual roll-off of the electrode assembly facing surfaces on the upper base portion  34  and side portions  24 ,  26  with the end of the actual discharge receiving region of the electrode assembly  20  ending shortly, e.g., about one eighth of an inch from the beginning of the roll-off at the end portions of the electrode assembly  20 . This is about where towards end of life for such electrode assemblies, whether multimember or machined, from a single piece of metal or diffusion bonded piece of metal as discussed in the above referenced co-pending applications and patent, the erosion toward the longitudinal ends of the discharge receiving region causes the discharge to widen at the ends with undesirable effects on the laser output beam parameters necessitating electrode replacement. 
   Turning Now to  FIG. 7  shows a partially cut-away plan view of the bottom on an electrode assembly according to aspects of an embodiment of the present invention. As shown in  FIG. 7  the bottom  72  of the lower center portion  30  has a generally flat bottom surface  80  with a number of high voltage feed through rod well  50  machined into it as are also shown in  FIGS. 3 ,  8  and  9 . Also shown in  FIG. 7  is the plurality of high voltage feed through well ledges  82  surrounding the respective wells  50  and intermediate the well  50  and vacuum seal grooves  52 , also illustrated in  FIG. 3 ,  8 ,  9  and  16 . Also illustrated in  FIGS. 7 and 8  are a plurality of bolt holes  57 , which may be recessed. As is also shown in  FIGS. 7 and 8  grooves  84  and  86  formed in the bottom  72  allow for the assurance that when the chamber is pumped down to a vacuum to, e.g., remove contaminants from the chamber there is not a slow pressure release after the chamber is sealed from the seal groves  52  of the recesses of the bolt holes  57 . 
   Turning now to  FIG. 8  there is shown a perspective view of an electrode assembly according to the embodiment of  FIG. 1  viewed from the bottom, and as has been discussed above, shown in some more detail in  FIG. 8  are the preionizing tube shim holding openings  58  which allow electrical contact with high voltage for the shim (not shown) that forms one plate of a capacitive corona discharge preionizer tube as is known in the art. 
   Turning now to  FIG. 9  there is shown a cross-sectional view of a center base portion taken along cross-sectional lines  9 — 9  in  FIG. 3  and as has been discussed above. 
   Turning now to  FIG. 10  there is illustrated aspects of an assembly and manufacturing process for an electrode assembly according to aspects of embodiments of the present invention. As can be seen from  FIG. 10 , the blanks  90 ,  92  for side portions  24 ,  26  may be mechanically bonded to the center base portion by, e.g., inserting bolts  80  through the bolt holes  57  in the lower center base portion  30  and into bolt sleeves  94  formed in the side walls of the blanks  90 ,  92  adjoining the side walls of the intermediate portions  32  of the center base portion  30 , which are aligned with the bolt nooks  56 . also shown in  FIG. 10  are a plurality of alignment dowels  95  inserted into alignment dowel holes in the center base portion  22  and fit into corresponding sleeves on the blanks  90 ,  92 , for alignment of the blanks  90 ,  92  with the center base portion  22 . 
   Turning now to  FIG. 11  there is illustrated aspects of an assembly and manufacturing process for an electrode assembly  20  according to aspects of an embodiment of the present invention as discussed also in regard to  FIG. 10  with the blanks  90  and  92  in place prior to machining the final shape of the electrode formed by the electrode assembly  20 . 
   Turning now to  FIG. 12  there is illustrated aspects of an assembly and manufacturing process according to aspects of an embodiment of the present invention.  FIG. 12  shows the placement of the alignment dowels  96 . 
   Turning now to  FIG. 13  there is illustrated a perspective side view of an electrode assembly according to aspects of an embodiment of the present invention. In the embodiment of  FIG. 13 , also shown in  FIG. 14 , the center base portion  22  upper portion  34 , intermediate portion  32  and lower portion  30  and the side portions  24 ,  26  may be machined somewhat differently to form a hood  100  by rolling off the side portions  24 ,  26 , and the intermediate portion  32  and lower portion  30  of the center base portion  22 , but leaving the upper portion  34  of the center base portion  22  substantially intact and machine side walls for the upper base portion  34  into the intermediate portion  32  and lower portion  30  toward the very end of the electrode assembly  20 ′ to form a substantially sharper roll off beginning at about location  106  to a substantially vertical end wall section  104 . In this embodiment, the discharge widening at the longitudinal end of the discharge on the electrode  20 ′ cannot occur because of the sharp drop off of the side walls at the end of the discharge, e.g., in about region  106 . It will be understood that the embodiment of  FIGS. 13 and 14  may be machined from a single piece of material or a single piece of diffusion bonded material of a plurality of different bonded materials.  FIG. 14  shows an isometric perspective view of the electrode  20 ′ according to aspects of an embodiment of the present invention just described. 
   Turning now to  FIG. 15  there is shown a cross sectional view of an electrode assembly  20 ″ according to aspects of an embodiment of the present invention as also illustrated in  FIG. 16 , which shows a perspective view with cross-section of an electrode assembly  20 ″ according to aspects of an embodiment of the present invention. As is shown in  FIGS. 15 and 16 , the center base portion  22  may have a lower portion  30  and an intermediate portion  32  only. The upper portion may be replaced, e.g., with a mechanically bonded electrode  70 , with the center base portion acting as a support bar. Thus the overall assembly  20 ″ for an electrode used as a cathode is much like existing anode assemblies with a blade electrode mechanically mounted or mechanically bonded to an anode support bar as is known in the art. In this embodiment, the side portions  24 ,  26  may be made, e.g., of a suitable dielectric, e.g., ceramic. In this embodiment, and particularly when machined, e.g., according to the embodiments illustrated in  FIG. 15 , the facing surface  62  may be broadened to substantially include all of the width of the discharge receiving region  40 , such that the hood region  100  as illustrated in  FIGS. 13 and 14 , will be wide enough to extend the longitudinal extent of the discharge along the hood region sufficiently far to avoid electrode discharge region widening at the end of the discharge which was believed by applicants to be at least a part of the cause of end of life for prior art gas discharge laser light source electrodes. 
   Turning now to  FIG. 17 , a further embodiment of the present invention is shown, schematically and not necessarily to proper scale, in which the electrode  70  is not formed to relatively smoothly join with the upper surfaces of the side portion  24 ,  26 , whether they be formed of conductive metal or insulator, e.g., ceramic, such that the electrode  70  and its discharge receiving region  40  coextensive with its facing accurate surface (ellipsoidal, oval, circular arc, etc.)  62  extends above the elevation of the surfaces of the side portions  24 ,  26  and protrudes above the elevation of the surfaces of the side portions  24 ,  26 . The electrode  70 , so mounted on an electrode support bar, similarly to electrode support bar  201  as shown in  FIG. 18 , can be separately replaced and the remaining portions of the assembly utilized again after end of electrode life. 
   In operation, therefore, according to various aspects of embodiments of the present invention the embodiments involving multiple pieces will serve to provide several advantages over prior art electrodes for gas discharge laser light source laser systems for carrying the electrical discharges in the lasing gas medium. The mechanically bonded electrode is cheaper to initially manufacture, involving initially, e.g., no diffusion bonding to obtain, e.g., the differential erosion discussed in above referenced applications and patents. In addition, the embodiments with the electrode mechanically bonded to an electrode center base portion involve cost savings at end of life, as noted, with the need to dispose only of the electrode portion, e.g.,  70  as shown in  FIGS. 15 and 17 . This same version of an electrode, e.g., with ceramic fairings as the side members and a protruding electrode, e.g.,  70 , can be sustained in operation for many billions of pulses of laser operation above and beyond the electrodes, e.g., cathodes, of the prior art. Similarly the hooded versions discussed above also can serve to increase the electrode life for many billions of pulses due to elimination of end-wear end of life syndrome discussed above and when combined with the aspects just described for the lifetime advantages of the protruding electrode and the mechanical bonding of the electrode to the central base portion have the combined beneficial effects of longer life and lower cost. 
   Turning now to FIGS.  18  and  19 – 19 A there is shown a cross-sectional view of a portion of the interior of a fluorine gas discharge laser chamber containing an anode  200  mounted on an anode mounting bar  201 . The anode  200  comprises an anode blade  202 , which forms the electrically conductive portion (electrode) of the anode  200 . The anode blade  202  is abutted on the upstream side (in relation to gas flow from left to right as shown in  FIG. 18  over the anode  200 ) by an upstream fairing  204  and on the downstream side by a downstream fairing  206 . The upstream fairing  204  and the downstream fairing  206  may be constructed of insulating material, e.g., ceramic insulating material. 
   As can be seen in more detail in  FIGS. 19 and 19   a , the surfaces of the upstream fairing  204  and the downstream fairing  206  may be essentially covered by a plurality of indentations, e.g., dimples  210 . The dimples  210  may be arranged in a number of ways, either uniformly over the entire upper surface  214  of the upstream fairing  204  and/or the upper surface  216  of the downstream fairing  206 . The dimples  210  may be uniform in depth or have randomly selected depths. The dimples  210  may be non-uniform in distribution, but uniform in clusters, e.g., with randomly distributed clusters. They may be generally abutting, e.g., in the nature of the cover of a golf ball or be separated by (surrounded by) non-dimpled regions. The dimples  210  may be of uniform shape, e.g., circular, polygonal of the same number of sides, etc., or may be randomly shaped and may be in either event of the same general size or randomly sized. 
   The dimples  210  serve, e.g., to remove, e.g., wavefront uniformities in, e.g., acoustic/shock waves, e.g., created by the periodic discharging of the laser gas between the gas discharge electrodes within the chamber in an effort to mitigate against BW resonances and center wavelength resonances over the range of operating gas discharge pulse repetition rates. The dimples will serve to break up the reflection of the acoustic/shock waves initially upon striking the respective upstream fairing upper surface  214  and downstream fairing upper surface  216 , and subsequent reverberations will similarly tend to be broken up when reflecting off of the surfaces  214 ,  216 , adding to BW resonance and center wavelength resonance mitigation efforts. The dimples  210  may also serve as a drag reducing instrument to trip the boundary layer to turbulence, thereby delaying the separation across the surface of the anode and reducing the drag downstream of the anode surface, e.g., in the pressure recovery area, much the same way that dimples on a golf ball improve the way that the golf ball moves through a fluid, the air around it. In this case, however, the anode and fairings  214 ,  216  and dimples  210  are stationary and the fluid, the laser gas, is flowing past the dimples  210 . Such dimples may also be placed in the chamber in other locations, e.g., on the chamber walls. main insulator or anode support bar. 
   The various embodiments of the present invention disclosed in the present applications according to aspects of those embodiments comprise elongated discharge regions extending essentially along the longitudinal centerline axis of the electrode, whether that be a mechanically bonded version with metallic side portions, i.e., having an arcuate facing region, e.g., an essentially elliptical facing discharge receiving region extending also into the side portions adjoining the center electrode portion or only the curvilinear facing portion of the electrode with adjoining ceramic side portions, which may extend above the adjoining ceramic side portions as opposed to relatively smoothly blending into the surface contour of the respective side portions. Some part or all of the facing region, depending on aspects of the embodiments of the present invention disclosed in the present application may coincide with the discharge receiving region, with the discharge receiving region generally defining the transverse extent of the discharge between the electrodes in the lasing medium between the electrodes, as is understood in the art. This discharge receiving region may also extend longitudinally along the respective facing surface of the electrode, but not necessarily aligned with or coextensive with the longitudinal centerline axis of the electrode and/or electrode assembly, i.e., simply defining a raised facing region of the electrode coinciding with the discharge formed between the electrodes. Discharge receiving region as used in the application should be interpreted to include such aspects of embodiments of the present invention disclosed in the present application. 
   Applicants have discovered that an essentially bandwidth resonance-free laser performance can be attained by canting the elongated gas discharge cathode and the elongated gas discharge anode (at least with respect to acoustically generated resonances at particular repetition rates. By this is meant, e.g., for a standard ArF elongated gas discharge electrode, serving e.g., as the elongated gas discharge cathode, having, e.g., its gas discharge receiving region, which forms a somewhat pointed area and is contained within the discharge receiving region for the elongated gas discharge cathode, machined at an angle relative to the longitudinal axis of the elongated gas discharge cathode and, e.g., the longitudinal centerline axis of a main insulator. This angle is such that the gas discharge crown, longitudinally centered along the discharge receiving region intersects the gas discharge electrode longitudinal center axis of the elongated gas discharge electrode generally on the longitudinal centerline axis of the elongated gas discharge electrode. The ends of the gas discharge crown at the respective rounded ends of the electrode assembly are approximately 2 mm displaced from the longitudinal centerline axis, which has been selected based upon the width of one half of the gas discharge region, but could, as noted below, be selected otherwise within the scope of the present invention. The elongated gas discharge anode may also be machined in the same fashion as the elongated gas discharge electrode′, however, in the mirror image so both crowns align with each other when installed. Alternatively the elongated gas discharge anode may simply be pivoted about its center to rotate the gas discharge crown (centered on the longitudinal gas discharge receiving region, of the elongated gas discharge anode to align the discharge receiving region of the elongated gas discharge anode with that of the canted gas discharge crown  74  machined on the elongated cathode. In such an embodiment, e.g., the anode fairings on either side of the anode blade discharge receiving region of a blade anode or hour-glass anode) may also be so rotated. Similarly, the chamber could be modified to receive the entire cathode and main insulator structure and also the anode mount structure canted to, e.g., the centerline axis of the chamber, i.e., for a rectangular chamber, which would then cant the discharge region also to the centerline axis of the chamber. In this manner the gas discharge region is canted or tilted to the normal longitudinal and optical axis of the previously constructed gas discharge laser chambers resulting in the substantial reduction in, e.g., BW resonance peaks up to and beyond 6000 Hz and specifically between about 3500 HZ and 6000 Hz. 
   It will also be understood that according to aspects of an embodiment of the present invention, in operation the two elongated electrode elements defining a cathode and an anode may each have an elongated discharge receiving region having a discharge receiving region width defining a width and length, with the length ordinarily extending to approximately where the roll off of the electrode assembly occurs as shown in, e.g.,  FIGS. 3 ,  4 ,  6  and  8 . This length may be extended, as noted above avoiding electrode end-wear life-shortening erosion, e.g., as is shown in  FIGS. 13 and 14 , e.g., by the discharge receiving length in at least one of the electrode elements extending beyond a point of roll-off of the respective electrode element facing region by forming a hooded extension of the respective discharge receiving region above the roll-off portion of the electrode assembly. This may comprise the extension as well as the corresponding center portion of the electrode forming both the facing region and the discharge receiving region for the electrode assembly so that, e.g., the discharge receiving region extends out along the hooded region to substantially the end of the electrode assembly where the hooded region falls off relatively precipitously and there is no facing portion of the electrode assembly on either side of the discharge receiving region into which the discharge can transversely migrate at end of life, thereby undesirably widening the discharge receiving region at the respective electrode end due to the height of the hooded portion of the electrode assembly at the end of the hooded portion. 
   It will be understood by those skilled in the art that many changes and modifications may be made to the aspects of the embodiments of the invention as disclosed above without changing the spirit and scope of the appended claims and that the claims should not be limited to the aspects of the embodiments disclosed in the present application. For example, other smoothed curvilinear surfaces than ellipses may be employed, e.g., ovals and circular arcs, to define, e.g., the facing surfaces and/or discharge receiving regions noted above. Mechanical bonding can include a variety of detachable joinder mechanism such as bolts, screws, made of metal or ceramic or other insulating material, dovetail, mortice and tenon and the like joints, etc. In addition the detachable cathode having slanted side walls can simply be inserted into the slot formed by the adjoining metallic or insulative side portions as shown, e.g., in  FIG. 16  and, e.g., held in place by set screws within the slot longitudinally, e.g., at both ends of the cathode member, and mechanically bonded as used in this application should be considered to cover all of such mechanical bonding and joining embodiments and equivalents. In addition brass alloys may be substituted for by nickel or nickel alloys. 
   The claims of the above application, therefore, should not be considered to be limited to aspects of preferred embodiments disclosed in this application but should be interpreted solely based upon the appended claims.