Patent ID: 8610874

Claim:
An apparatus for increasing a pulse length of a pulsed laser beam, comprising: a beam splitter configured to split an input light beam into a first beam and a second beam; a con-focal resonator including a first con-focal mirror and a second con-focal mirror; a fold mirror in an optical path between the first and second con-focal mirrors, the fold mirror being configured to redirect the first beam or at least a portion of the first beam between the first and second con-focal mirrors, wherein the beam splitter, the con-focal resonator, and the fold mirror are in an optical arrangement such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement; and an optical element in an optical path of the input light beam prior to the beam splitter, wherein the optical element is configured to form an intermediate focal point of the first beam at a distance away from the fold mirror, in order to reduce energy density-related damage to the fold mirror.