Patent ID: 7822092

Claim:
A laser apparatus comprising: a seed laser oscillator producing an output comprising a laser output light beam of pulses, the seed laser oscillator comprising: a first gas discharge excimer or molecular fluorine laser chamber; a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, the laser amplification stage comprising: a ring power amplification stage comprising: a beam expander; and a partially reflecting optical element through which the seed laser oscillator output light beam is injected into the ring power amplification stage; and a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising an optical delay path having a delay length longer than the coherence length of a pulse in the seed laser oscillator laser output light beam of pulses; wherein the beam expander is configured to de-magnify the laser beam as the laser beam travels from the partially reflecting optical element toward the amplifying gain medium and to expand the laser beam as the laser beam travels from the amplifying gain medium toward the partially reflecting optical element.