Pulse Stretcher with Reduced Energy Density on Optical Components

A lithography apparatus comprising a beam delivery system having a pulse stretcher for increasing a pulse length of a pulsed laser beam, the pulse stretcher 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, 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
• one or more optical elements in an optical path of the input light beam prior to the beam splitter such that an intermediate focal point of the first beam is formed at a distance away from the fold mirror reducing energy density-related damage to the fold mirror.

A method of increasing a pulse length of a pulsed laser beam, the method comprising:

• diverging or converging an input light beam into an altered light beam;
• splitting the altered light beam into a first beam and a second beam such that the first beam is directed to travel through a pulse stretching device having a plurality of optical elements, wherein the divergence or convergence of the input light beam shifts an intermediate focal point of the first beam away from any of the plurality of optical elements;
• and
• recombining at least a portion of the first beam with the second beam into a recombined beam.