nos 09 432 348 and 09 390 146 each of which is assigned to the same assignee as the present application and is hereby incorporated by reference into the present application the resonator includes optics for line selection and also preferably for narrowing the selected line see u s patent application ser nos 09 317 695 09 317 527 09 657 396 60 212 183 09 599 130 60 170 342 60 166 967 60 170 919 09 584 420 60 212 257 60 212 301 60 215 933 09 130 277 09 244 554 60 124 241 60 140 532 60 140 531 60 147 219 and 09 073 070 each of which is assigned to the same assignee as the present application and u s pat no 5 761 236 and 5 946 337 each of which is assigned to the same assignee as the present application and u s pat no 5 095 492 5 684 822 5 835 520 5 852 627 5 856 991 5 898 725 5 901 163 5 917 849 5 970 082 5 404 366 4 975 919 5 142 543 5 596 596 5 802 094 4 856 018 and 4 829 536 all of which are hereby incorporated by reference some of the line selection and or line narrowing techniques set forth in these patents and patent applications may be used in combination with or alternative to any of the embodiments set forth herein also and particularly for the f 2 and arf laser systems an enclosure not shown may seal the beam path of the beam 20 such as to keep the beam path free of photoabsorbing species smaller enclosures may.