Patent ID: 8116347

Claim:
A two-stage laser system, comprising an oscillation-stage excimer laser and an amplification-stage excimer laser, wherein: laser light output from said oscillation-stage excimer laser is injected into said amplification-stage excimer laser and is amplified therein, said amplified laser light is output from said amplification-stage excimer laser, said oscillation-stage excimer laser and said amplification-stage excimer laser each comprise a chamber filled with a laser gas, said oscillation-stage excimer laser oscillates laser light having divergence, and said amplification-stage excimer laser comprises a Fabry-Perot etalon type resonator, said resonator including an input side mirror and an output side mirror, and being configured as a stable resonator, a reflectivity range for the input side mirror ranges from about 65% to about 97%, a length of the resonator in the amplification-stage excimer laser is set longer than half of a time-based coherent length corresponding to a spectral line width of the oscillation-stage excimer laser, said length of said resonator being a distance between said input side mirror and said output side mirror, and said time-based coherent length corresponding to a spectral line width of the oscillation, stage excimer laser is λ 2 /Δλ when a wavelength of the laser light is λ and the spectral line width is Δλ.