Laser output light pulse stretcher

摘要

An apparatus and method for providing a high peak power short pulse duration gas discharge laser output pulse is disclosed which may comprise a pulse stretcher which may comprise a laser output pulse optical delay initiating optic diverting a portion of the output laser pulse into an optical delay having an optical delay path and comprising; a plurality of confocal resonators in series aligned to deliver an output of the optical delay to the laser output pulse optical delay initiating optic. The plurality of confocal resonators comprises four confocal resonators comprising a twelve pass four mirror arrangement. Each of the plurality of confocal resonators may comprise a first concave spherical mirror having a radius of curvature and a second concave spherical mirror having the same radius of curvature and separated by the radius of curvature. The pulse stretcher may comprise a first confocal resonator cell which may comprise: a first concave spherical mirror having a radius of curvature receiving an input beam from the laser output pulse optical delay initiating optic comprising the portion of the output laser pulse at a first point on a face of the first concave spherical mirror and generating a first reflected beam; a second concave spherical mirror having the same radius of curvature and separated from the first concave spherical mirror by the radius of curvature and receiving the first reflected beam at a first point on a face of the second concave spherical mirror and generating a second reflected beam incident on a second point on the face of the first concave spherical mirror, the second reflected beam being reflected by the first concave spherical mirror from the second point on the first mirror to form an output beam from the first confocal resonator cell; and, a second confocal resonator cell receiving the output beam of the first confocal resonator cell as an input beam of the second confocal resonator cell. The apparatus and method may form part of a beam delivery unit and may be part of an integrated circuit lithography lights source or an integrated circuit lithography tool. The apparatus and method may comprise a plurality, e.g., two pulse stretchers in series and may include spatial coherency metrology.