Patent ID: 7792176

Claim:
A narrow-band laser device for exposure apparatus being an injection-locked discharge excited laser device comprising a narrow-band oscillation stage laser (MO) and an amplification stage laser (PO) arranged with a ring-type resonator including a plurality of optical elements, the ring-type resonator not expanding a laser beam, wherein the ring-type resonator comprises a first optical element and a second optical element opposing each other and disposed on opposite sides of discharge electrodes, each of the first optical element and the second optical element including two nonparallel mirror surfaces, the first optical element and the second optical element being arranged such that an MO laser light injected from the narrow band oscillation stage laser (MO) into the ring-type resonator makes a round trip within the ring-type resonator via optical paths which are parallel to an optical axis direction of the ring-type resonator, the plurality of the optical elements are arranged such that a first axis and a second axis are offset to each other with respect to a plane parallel to a discharge direction and parallel to the optical axis direction of the ring-type resonator, the first axis passing through an intersection line of two planes including the two mirror surfaces of the first optical element and being parallel to the optical axis direction of the ring-type resonator, the second axis passing through an intersection line of two planes including the two mirror surfaces of the second optical element and being parallel to the optical axis direction of the ring-type resonator, whereby a n+1th round trip optical path of the MO laser light injected into the ring-type resonator travels parallel and spaced with respect to a n th round trip optical path, within a plane perpendicular to the discharge direction.