Patent ID: 7227881

Claim:
An excimer or molecular fluorine laser system comprising: a master oscillator including therein a first discharge chamber filled with a first gas mixture, the first discharge chamber containing a plurality of electrodes connected to a discharge circuit for energizing the first gas mixture and generating a pulsed laser beam; a power amplifier including therein a second discharge chamber filled with a second gas mixture, the second discharge chamber containing a plurality of electrodes connected to a discharge circuit for energizing the second gas mixture to define a gain region for amplifying the pulsed laser beam, said power amplifier having an entrance end and an exit end; and a set of reflective optics positioned about the power amplifier so that at least a portion of the pulse exiting the exit end of the power amplifier after a first pass therethrough is directed around the outside of the power amplifier and then redirected back into the entrance end thereby making a second pass through the power amplifier wherein the reflective optics includes a first reflector for intercepting the pulse exiting the power amplifier and a second reflector for redirecting the pulse back through the power amplifier, said first and second reflectors being configured and positioned so that the pulsed laser beam exiting the master oscillator bypasses the second reflector prior to entering the power amplifier for the first pass and bypasses the first reflector after making the second pass through the power amplifier, wherein the first pass propagates through a first portion of the gain region of the power amplifier and the second pass propagates through a second portion of the gain region of the power amplifier, said first and second portions being substantially different.